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Summary of Published Research on the Beneficial Effects of Fish Consumption and Omega-3 Fatty Acids for Certain Neurodevelopmental and Cardiovascular Endpoints: Section B - Neurodevelopmental

January 2009

This information is distributed solely for the purpose of pre-dissemination peer and public review under applicable information quality guidelines. It has not been formally disseminated by FDA. It does not represent and should not be construed to represent any agency determination or policy.

Introduction and Summary  |  Section A  |  Section B  |  References

Section B: Overview of Scientific Information on the Effect of Fish Consumption and Omega-3 Fatty Acids on Neurodevelopmental Health Benefits

(a) Introduction

There is a large volume of original scientific studies on the health benefits associated with consumption of fish. Overall, there is a body of data on the relationship between fish consumption and neurodevelopment. This section provides an overview of this body of data, and also identifies reports of quantitative dose-response relationships with potential for use in risk and benefit assessment modeling.

Fish is a source of easily digestible protein of high biological value, and provides micronutrients including vitamins A and D, the minerals iodine and selenium and the amino acids taurine, arginine and glutamine (EFSA 2005 p 30, He and Daviglus 2005). Additionally, many fish provide a unique food source of omega-3 (also called n-3) long-chain polyunsaturated fatty acids (LC PUFA), and a large body of scientific literature addresses the health benefits of these lipids.

The n-3 LC PUFA, docosahexaenoic acid (DHA) has been shown to be is essential for development of the central nervous system. Consequently, there is interest in knowing whether there is an association between fetal, infant, and child neurodevelopment and maternal intake of fish or n-3 LC PUFA during pregnancy and lactation (SACN 2004). A related research question is whether consumption of fish or n-3 LC PUFA by adults is associated with prevention of neuropsychiatric disorders including depressive symptoms, psychosis, aggression, suicide, mild cognitive decline with aging, or overt dementia (Schachter 2005).

The n-3 long chain polyunsaturated fatty acids found in fish and fish oil, EPA and DHA, are 20-carbon and 22-carbon fatty acids, respectively. Another n-3 fatty acid, found in plant foods and vegetable oil, is alpha-linolenic acid (ALA), an 18-carbon fatty acid. ALA cannot be synthesized by humans, but must be supplied by dietary means and is therefore considered an essential nutrient (IOM 2002). Additionally, humans can use ALA as a starting material to synthesize the n-3 long-chain fatty acids, EPA and DHA. Preterm and term infants are able to convert ALA to DHA, but it is not known whether this conversion can meet the needs of the developing brain for DHA (IOM 2002).

Studies of the neurodevelopmental health benefits of fish consumption include studies of the effects on fetal, infant and child development of maternal consumption of fish or supplemental DHA (such as from fish oil) during pregnancy or lactation. The major neurodevelopmental outcomes studied are visual development and cognitive development. Related studies looked at effects on fetal, infant and child neurodevelopment of varying levels of DHA in breast milk, reflecting the DHA in maternal diet. Additionally, there is a body of literature examining the effect on infant and child development of infant formula supplemented with DHA. Although supplementation of infant formula with DHA does not fall in the category of fish consumption, results of these studies may help to answer scientific questions regarding possible neurodevelopmental benefits of DHA during infancy.

The table below lists a number of recent reports and reviews on the neurodevelopmental health benefits of fish or n-3 LC PUFA consumption. These include reports and recommendations from national and international expert groups. Also listed are a number of review articles, including systematic reviews, meta-analyses and risk assessments. This report will summarize the purpose and conclusions of the reports and reviews listed in Table B-1, followed by an overview of selected key studies, and a brief synthesis and discussion.

Table B-1. Recent reports and reviews on the neurodevelopmental health benefits of fish or n-3 LC PUFA consumption


Recent Reports and Recommendations

  • WHO (World Health Organization), 1994
  • NIH/ISSFAL Workshop Statement on the Essentiality of and Recommended Dietary Intakes for Omega-6 and Omega-3 Fatty Acids, 2000
  • Child Health Foundation Report of Workshop. LC-PUFA and Perinatal Development, 2001
  • IOM (Institute of Medicine) Dietary Reference Intakes, 2002
  • SACN (Scientific Advisory Committee on Nutrition), United Kingdom, 2004
  • EFSA (European Food Safety Authority) 2005
  • AHRQ (Agency for Health Care Research and Quality), DHHS, Omega-3 Fatty Acids, Effects on Maternal and Child Health , 2005
  • IOM Seafood Choices, 2006
  • ISSFAL (International Society for the Study of Fatty Acids and Lipids), expected, 2008

Other Recent Systematic Reviews, Meta-Analyses and Risk Assessments

  • Willatts and Forsyth., Prostaglandins 2000, premature and term, cognitive
  • SanGiovanni et al., Early Human Development, 2000; premature infants, clinical trials, vision
  • SanGiovanni et al., Pediatrics, 2000; term infants, clinical trials, vision
  • Simmer, Cochrane Systematic Reviews, term infants, 2001
  • Lauritzen et al., Progress in Lipids Research, 2001; comprehensive review, 94 pages
  • Uauy et al., Journal of Pediatrics, 2003; term infants, clinical trials, vision
  • Simmer and Patole, Cochrane Systematic Reviews, preterm infants, 2004
  • Harvard Risk/Benefit Papers, American Journal of Preventive Medicine 2005
    • Cohen et al. (2005c) meta-analysis of n-3 fatty acid supplements and cognitive development in infants
    • Cohen et al. (2005a) assessment of risk and benefit of fish consumption
  • Fleith, 2005, narrative review
  • Mozaffarian and Rimm, JAMA, 2006; risk benefit assessment
  • Eilander et al., Prostaglandins 2007, narrative review
  • Smithers et al., American Journal of Clinical Nutrition 2008, preterm infants, cognitive
  • Simmer et al. (2008a). Cochrane Systematic Reviews, preterm infants
  • Simmer et al. (2008b). Cochrane Systematic Reviews, term infants

See reference list for full citations for Table B-1.

[Note regarding citations: Complete citations for selected references are found in the Reference Section. For the complete citation for the remaining references marked "#," please refer to the respective report or review.]

(b) Conclusions and Recommendations from Some Recent Reports

Food and Agriculture Organization/World Health Organization (FAO/WHO)

A Joint FAO/WHO Expert Consultation on Fats and Oils in Human Nutrition was published in 1994. The experts reviewed the roles of dietary fats and oils in human nutrition, the intakes and health effects of different types of fats and oils, and the technical factors associated with production and utilization of edible fats and oils. The consultation made recommendations about dietary fats and oils to assist policy makers, health-care specialists, the food industry and consumers.

Minimum desirable intakes of fats and oils:

The consultation concluded that the consumption of an adequate amount of essential fatty acids is important for normal growth and development, that AA and DHA are particularly important for brain development, and that breast milk is a good source of these acids. (The 20-carbon n-6 fatty acid, arachidonic acid, is abbreviated AA.) The experts noted potential problems for preterm infants who had an insufficient intra-uterine supply of AA and DHA and are born with low fat reserves. The consultation recommended that infants should be fed breast milk if at all possible, and that the fatty acid composition of infant formulas should correspond to that of breast milk. Young children from weaning to at least two years of age should consume 30 to 40 percent of energy from fat, and the fat composition should provide similar levels of essential fatty acids as are found in breast milk.

Essential fatty acids:

The consultation discussed the role of n-6 and n-3 fatty acids in membrane structures and as precursors of biologically active eicosanoid molecules. The experts noted that essential fatty acids are especially important for normal fetal and infant growth and development, especially for brain development and visual acuity. In well-nourished women, approximately 2.2 grams of essential fatty acids are deposited in maternal and fetal tissues each day during pregnancy. The consultation recommended that

  1. "Particular attention must be paid to promoting adequate maternal intakes of essential fatty acids throughout pregnancy and lactation to meet the requirement of fetal and infant development."

NIH/ISSFAL Workshop Statement on the Essentiality of, and Recommended Dietary Intakes for, Omega-6 and Omega-3 Fatty Acids

A workshop on omega-6 and omega-3 fatty acids was co-sponsored in 1999 by the National Institutes of Health (NIH), the International Society for the Study of Fatty Acids and Lipids (ISSFAL) and several industry groups. The workshop statement made recommendations for adequate intakes (AIs) for adults for various fatty acids (Simopolous et al., 2000). The Workshop AIs were given for a 2,000 calorie diet. The AI for ALA was 2.22 grams per day (one percent of energy), for DHA plus EPA the AI was 0.65 grams per day (0.3 percent of energy), with at least 0.22 grams per day (0.1 percent of energy) for DHA and the same for EPA. In addition, the workshop recommended that pregnant and lactating women should ensure a DHA intake of 300 milligrams per day (0.3 grams per day). The workshop statement also recommended AIs for infant formula as percent of fatty acids. The Workshop AI for ALA was 1.5 percent of fatty acids, and the AI for DHA was 0.35 percent of fatty acids. An upper limit for EPA in infant formula was given as 0.1 percent of fatty acids. The workshop statement noted that the views expressed in the statement were not an official position of the U.S. Department of Health and Human Services. (Note that the "AIs" from the NIH/ISSFAL Workshop are different recommendations from the AIs and other Dietary Reference Intakes from the Institute of Medicine, described below.)

Several individual reflections and commentaries were published together with the workshop statement. One commentary summarized the strengths of the statement and also noted some limitations (Cunnane 2000). The commentary by Cunnane observed that the workshop statement is too brief and is not referenced. The commentary also stated that, although in principle it seems reasonable to recommend a certain amount of DHA intake during pregnancy, there is little experimental or epidemiologic research to support the specific intake recommendation. Therefore, the commentary concluded that, although the Workshop recommendations for fatty acid intake deserve serious consideration, a clearer, referenced description of the rationale for the proposals is needed.

Child Health Foundation. Report of Workshop. LC-PUFA and Perinatal Development

A scientific workshop on the role of LC-PUFA in pregnancy, lactation and early life was organized and funded by the Child Health Foundation, Munich, Germany. Participants were the leading researchers who conducted randomized trials of LC-PUFA status and function in pregnancy and lactation and in preterm and term infants. The workshop, which was closed to the public, was held in Munich and resulted in a consensus statement (Koletzko et al., 2001). Only studies published in full or in abstract form were used to provide information for the consensus statement. The workshop statement briefly reviewed the scientific knowledge base regarding LC-PUFA and perinatal development, citing 48 references. The consensus statement recommended breastfeeding, which supplies preformed LC-PUFA, as the preferred feeding method for healthy infants. The statement recommended that formulas for term infants should contain at least 0.2 percent of total fatty acids as DHA and 0.35 percent as AA. These levels were stated to be prudent because they are at the lower end of the range of human milk DHA worldwide. Formulas for preterm infants were recommended to contain at least 0.35 percent of total fatty acids as DHA and 0.4 percent as AA. It was stated that higher levels of LC-PUFA might provide additional benefits, and further study was recommended in order to define optimal intakes for term and preterm infants.

The consensus statement found an absence of published studies showing direct functional benefits of supplementation of LC-PUFA for pregnant and lactating women, and therefore did not recommend supplementation. In the meantime, the statement recommended that

  1. "It seems prudent for pregnant and lactating women to include some food sources of DHA in their diet in view of the assumed increase in LC-PUFA demand in these physiological conditions and the relationship between maternal and foetal DHA status."

Institute of Medicine of the National Academies. Dietary Reference Intakes

The Institute of Medicine (IOM) considered recommendations for intake of n-3 fatty acids in its 2002 report on Dietary Reference Intakes, called the IOM Macronutrient Report (IOM 2002). The IOM Macronutrient Report covered first, the metabolic requirements for specific nutrients and second, quantitative guidance on proportions of energy sources (such as protein, carbohydrate and fat) to decrease chronic disease risk.

Metabolic Requirements for N-3 Fatty Acids:

The IOM reviewed scientific evidence showing that the n-3 PUFA, ALA, which is an 18-carbon fatty acid, is an essential nutrient. Specifically, ALA cannot be synthesized by humans, and must be supplied by dietary means. There was not sufficient data for the IOM Macronutrient Committee to determine an Estimated Average Requirement (EAR) or a Recommended Dietary Allowance (RDA) for ALA. Instead, the IOM set a level for Adequate Intake (AI) of ALA, based on median intake of the population. For adults age 19 and older, the AI for ALA was set at 1.6 g/d for men and 1.1 g/d for women.

Additionally, humans can use the 18-carbon n-3 fatty acid, ALA, as a starting material to synthesize the long chain n-3 fatty acids, EPA and DHA, which are 20-carbon and 22-carbon fatty acids, respectively. Thus, the IOM stated that small amounts of EPA and DHA can contribute towards reversing a deficiency of n-3 fatty acids. EPA and DHA contribute approximately10 percent of the total n-3 fatty acid requirement, and therefore this percent contributes toward the AI for ALA.

The IOM Macronutrient Report noted that the membrane lipids of brain gray matter and the retina contain very high concentrations of DHA. The developing brain accumulates DHA during prenatal and postnatal development, continuing through the first two years after birth. The essential role of ALA seems to be as a precursor for EPA and DHA, and the developing brain is more sensitive to n-3 fatty acid deficiency than the mature brain. Studies have confirmed that preterm and term infants are able to convert ALA to DHA, but the studies do not provide quantitative information on whether the conversion can meet the needs of the developing brain for DHA.

Adequate Intakes for Infants:

The IOM Macronutrient Report tabulated clinical trials comparing term infants fed formula with and without added DHA regarding growth and measures of visual, motor and mental development. Based on studies from 1995 through 2000, the Committee stated:

"In conclusion, randomized clinical studies on growth or neural development with term infants fed formulas currently yield conflicting results on the requirements for n-3 fatty acids in young infants, but do raise concern over supplementation with long-chain n-3 fatty acids without arachidonic acid. For these reasons, growth and neural development could not be used to set an EAR."

Therefore, the Committee based the AI for infants from birth through six months on the amount of n-3 fatty acids, total fat and energy provided by human milk from women in the U.S. and Canada. The AI for infants ages seven through 12 months was based on the average intake from human milk and complementary foods. For both age groups of infants, the AI for total n-3 polyunsaturated fatty acids is 0.50 grams per day. For birth through 6 months of age, this corresponds to approximately one percent of energy (calories). For ages seven through 12 months, this corresponds to approximately 0.67 percent of energy (calories).

Adequate Intakes for Pregnancy and Lactation:

The Committee noted that, during pregnancy, the demand for n-3 polyunsaturated fatty acids for incorporation into placental tissue and for the developing fetus must be met from maternal tissues or through dietary intake. The demand for n-3 fatty acids for secretion in milk during lactation must also be met from maternal tissues or diet. There is some data showing lower plasma and red blood cell DHA levels during pregnancy and lactation, compared with nonpregant, nonlactating women. However, the Committee stated that this may be a normal physiological change of pregnancy. Additionally, studies show that supplementation with fish oil during pregnancy increases DHA in the mother and newborn infant and that fish oil supplementation during lactation increases DHA in breast milk and in the infant's blood. However, the Committee concluded that: "Evidence is not available to show that increasing intakes of DHA in pregnant and lactating women consuming diets that meet requirements for n-6 and n-3 fatty acids have any physiologically significant benefit to the infant."

Therefore, the Committee set AIs for pregnant and lactating women based on the median intake of ALA in the United States, where a deficiency is basically nonexistent in noninstitutionalized populations. The AI for pregnant women for ALA is 1.4 grams per day, based on the median intake of 81 pregnant women studied in the 1994-1996 Continuing Survey of Food Intake of Individuals (CSFII). The AI for lactating women for ALA is 1.3 grams per day, based on the median intake of 44 lactating women in CSFII 1994-1996. The Committee stated that small amounts of DHA and EPA can contribute towards reversing an n-3 fatty acid deficiency and therefore contribute toward the AI for ALA.

Quantitative Guidance on Proportions of Energy Sources to Decrease Chronic Disease Risk:

The 2002 Macronutrient Report reviewed the scientific evidence on macronutrients and chronic disease, and described Acceptable Macronutrient Distribution Ranges (AMDRs). The AMDR represents intakes that are associated with reduced risk of chronic disease, intakes at which essential nutrients can be consumed at adequate levels and to maintain energy balance.

The IOM report discussed the scientific evidence regarding the association of n-3 fatty acid intake with decreased risk of heart disease and stroke. The committee concluded that EPA and DHA may provide beneficial health effects when consumed at moderate levels. The AMDR for ALA was estimated by using the AI for ALA as the lower end of the intake range. For adults, the ALA AI of 1.1 g/d for women and 1.6 g/d for men would correspond to about 0.6 percent of energy (calories). The highest intake of ALA from food in North America corresponds to around 1.2 percent of energy. This was set as the upper end of the AMDR intake range. Thus the AMDR for ALA was set at 0.6 to 1.2 percent of energy. The committee stated, "Approximately 10 percent of the AMDR for n-3 fatty acids (linolenic acid) can be consumed as EPA and/or DHA (0.06 to 0.12 percent of energy)."

Scientific Advisory Committee on Nutrition, United Kingdom

As described in Section A, the Food Standards Agency (FSA) of the United Kingdom requested advice on the benefits and risks of fish consumption, particularly oily fish, from the Scientific Advisory Committee on Nutrition (SACN) and the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT). A report, Advice on Fish Consumption: Benefits and Risks, was published in 2004 by the joint SACN/COT Subgroup (SACN 2004). The report had the purpose of combining the nutritional considerations of fish consumption from SACN and the toxicological considerations of contaminants in fish from COT; weighing the nutritional benefits against possible risks; and developing dietary advice for the public.

The SACN report reviewed two aspects of health benefits of fish consumption: the effects of LC PUFA on early human growth and cognitive function and the relationship of fish consumption and cardiovascular disease (discussed in Section A).

DHA Requirements in Pregnancy and Lactation:

A background paper in an Annex to the SACN report reviewed the knowledge base on DHA requirements in pregnancy and lactation. The Annex estimated that during pregnancy at least 10 grams of DHA must be accreted, including about six to seven grams accreted by fetal brain development over the last trimester. In addition, about 2 grams DHA would be deposited in fetal adipose tissue, and additional DHA would be deposited in the placenta. The deposition of 10 grams DHA in the last trimester would correspond to a need for about 100 mg DHA per day above nonpregnant DHA intake. During lactation, about 70 to 80 mg DHA per day would be needed for milk formation, with a total of about 12 grams DHA needed during six months of lactation. For a non-pregnant woman, a typical DHA intake would be about 100 mg per day, corresponding to a total intake of nine grams DHA in the last trimester and 18 grams DHA during six months of lactation. Thus, if a non-pregnant woman was in balance when consuming 100 mg DHA per day, she would need to double her DHA intake during the last trimester of pregnancy and increase DHA intake by about 70 percent during lactation. However, there is no evidence that such an increased intake occurs.

Thus, it seemed that many women would not meet the additional need for DHA for pregnancy and lactation from their typical daily intake. Additionally, there was little evidence that this need would be met by metabolic conservation of LC-PUFA, by mobilization of DHA from adipose tissue stores, or by increased maternal formation of DHA from the precursor ALA. The background paper concluded that there is some evidence that many women may have marginal status for n-3 LC-PUFA during pregnancy and lactation. However, the full SACN report noted that the data currently available from which to draw this conclusion are limited.

Studies of Maternal or Infant LC N-3 PUFA Intake and Infant Neurodevelopment and Growth:

The SACN report tabulated and summarized the results of available studies of maternal or infant intake of n-3 LC PUFA, grouping the studies in three general categories: observational studies of maternal n-3 LC PUFA intake and infant development; clinical trials of infant formula supplements; clinical trials of maternal n-3 LC PUFA supplements.

Observational Studies of Maternal N-3 LC PUFA Intake and Infant Development

Two of the observational studies considered visual development. (These two studies are discussed later in this section):

  • Williams et al. (2001) found better visual stereoacuity (depth perception) at age 3.5 years in children whose mothers ate oily fish during pregnancy, in a prospective cohort study of 435 children.
  • Jørgensen et al. (2001) found a positive association between visual acuity at four months of age and DHA level in mothers' milk in a cross-sectional study of 39 breastfed infants.

Two studies considered cognitive development. These prospective studies found no significant association between cord blood levels of DHA and cognitive function in 128 four year olds (Ghys et al., 2002) and 306 seven year olds (Bakker et al., 2003). One study suggested that higher DHA and EPA intake from fish among Faroe Islanders compared with Danes accounted for longer gestation time among Faroe Islanders (Olsen et al., 1995). Olsen and Secher (2002) found increased risk of preterm delivery and low birth weight in women with low fish consumption in a prospective study of 8,729 pregnant women.

Clinical Trials of Infant Formula Supplements:

The available clinical trials were for visual or cognitive function in preterm or term infants.

  • Visual function, preterm infants (SACN Table 2.1). Nine of the 10 tabulated studies, published from 1990 to 2002, showed improved visual function in experimental groups fed infant formula supplemented with sources of n-3 LC PUFA. The report stated that these trials support the efficacy of LC PUFA intake on early development of the visual system, consistent with a meta-analysis by San Giovanni et al. (2000) and with a Cochrane review (Simmer 2000#).
  • Visual function, term infants (SACN Table 2.2). Four of the nine tabulated studies, published from 1995 to 2003, showed improved visual function in groups supplemented with n-3 LC PUFA.
  • Visual function, breastfed infants weaned to supplemented formula (SACN Table 2.3). Two studies, published in 2002 and 2003, both showed improved visual function, measured by sweep visual evoked potential, in groups of infants weaned to formula supplemented with n-3 LC PUFA. Positive effects in one study were measured at four, six, and 12 months of age and in the other study at 12 months of age.
  • Behavioral development, preterm infants (SACN Table 2.4). Four studies, published in 2001 and 2002, showed little or no effect on behavioral development, measured by the Bayley Mental Development Index and other instruments, in groups supplemented with n-3 LC PUFA.
  • Behavioral development, term infants (SACN Table 2.5). Three of the ten studies, published from 1995 to 2003, showed some positive effect on behavioral development in groups supplemented with n-3 LC PUFA.

In summarizing the results, the report found that the clinical trials on visual function in preterm infants consistently demonstrate a short-term beneficial effect on visual evoked potential. The results in term infants were less consistent, with six of 10 trials shoeing a beneficial effect, especially measuring visual evoked potential, but others found no effect, including the largest trial. Eleven of the 14 trials of behavioral measures in both preterm and term infants found no effect.

Clinical Trials of Maternal N-3 LC PUFA Supplements:
  • Infant neurodevelopment. Two supplement trials of pregnant women considered neurodevelopmental function in their children. (These studies will be discussed further in a later section):
  • Helland et al (2003) found higher intelligence test scores at age four among 48 children whose mothers had received fish oil supplements during pregnancy compared with 36 children whose mothers received placebo. The supplemented women received fish oil containing two grams per day of n-3 LC PUFA from 18 weeks of pregnancy to three months postpartum. The SACN report noted that the children studied in this follow up were only a small subgroup of the 590 pregnant women in the original supplement trial.
  • Malcolm et al (2003a and b) found no effect on visual function shortly after birth or at 50 or 66 weeks corrected age among 28 children whose mothers received fish oil supplements during pregnancy compared with 27 control children. The supplemented women received fish oil containing 0.2 grams per day of n-3 LC PUFA from 15 weeks of pregnancy until delivery.
  • Birth weight and length of gestation (SACN Table 2.7). Three of five studies, published from 1992 to 2003, found a beneficial effect of n-3 LC PUFA supplements on gestational length (two studies) or recurrence of preterm delivery (one study).

Thus, the SACN report found that there is some evidence that increased n-3 LC PUFA was beneficial, especially in lower birth weight populations, and this may be more relevant in populations that tended to have a lower background intake of n-3 LC PUFA. There were no adverse effects, even at relatively high doses of n-3 LC PUFA. In the trials that found no effect of maternal n-3 LC PUFA supplements on birth weight or gestation length, the infants of nonsupplemented mothers had birth weights greater than 3,600 grams (about 7.9 pounds).

This finding was reflected in the overall SACN advice on fish consumption:

"In pregnancy and lactation there is a demand on the mother to supply the fetus and infant with LC n-3 PUFA, which are required for the development of the central nervous system. There is some evidence that increased maternal LC n-3 PUFA intake produces beneficial effects, especially in lower birth weight populations, and this may be more relevant in populations that tend to have a lower background intake of LC n-3 PUFA, i.e. where fish intake is low. No adverse effects of maternal LC n-3 PUFA supplementation have been observed, even at relatively high doses."
"The dose-response relationship is derived from the cardiovascular evidence, as the evidence for maternal intake and pregnancy outcome is insufficient for this."
"SACN, therefore, endorsed the population recommendation to eat at least two portions of fish per week, of which one should be oily, and agreed that this recommendation should also apply to pregnant women. Two portions of fish per week, one white and one oily, contain approximately 0.45g/d LC n-3 PUFA."
"An increase in population oily fish consumption to one portion a week, from the current levels of about a third of a portion a week, would confer significant public health benefits in terms of reduced risk of CVD. There is also evidence that increased fish consumption might have beneficial effects on fetal development."

The SACN emphasized that this was a minimal achievable objective, considering the low background fish consumption in the United Kingdom. Although the Committee found that it may be beneficial for individuals to consume more fish than this guideline, they were unable to identify a level for increased consumption. They stated it would be inappropriate to discourage fish consumption at higher levels than the recommendation, unless there was an upper limit beyond which people should not consume.

The SACN advice took into account the toxicological considerations related to methylmercury and dioxins and dioxin-like PCBs in fish.

Regarding methylmercury, the SACN advice stated:

"On the basis of the COT opinion, the FSA has advised that pregnant women, women intending to become pregnant and children under 16 should avoid eating shark, marlin and swordfish. One weekly portion of these fish would not be harmful for other adults. Pregnant women and women intending to become pregnant may eat to up to four medium-size cans or two tuna steaks a week. Children and other adults do not need to restrict the amount of tuna they eat."

Regarding dioxins and dioxin-like PCBs, the SACN advice stated:

"Women of reproductive age and girls should aim to consume within the range of one to two portions of oily fish a week, based on maintaining consumption of dioxins and dioxin-like PCBs below the TDI of 2 pg WHO-TEQ/kg body weight per day."
"Women past reproductive age, boys and men should aim to consume within the range of one to four portions of oily fish a week, based on maintaining consumption of dioxins and dioxin-like PCBs below the guideline value of 8 pg WHO-TEQ/kg bodyweight per day."

European Food Safety Authority

As described previously in Section A, the European Food Safety Authority (EFSA) formed an Interpanel working group to respond to a request from the European Parliament for a scientific assessment of the human health risks related to consumption of wild and farmed fish. In June, 2005, the EFSA published its report, "Opinion of the Scientific Panel on Contaminants in the Food Chain on a Request from the European Parliament Related to the Safety Assessment of Wild and Farmed Fish." The Summary of the report stated

"There is evidence that fish consumption, especially of fatty fish (one to two servings a week) benefits the cardiovascular system and is suitable for secondary prevention in manifest coronary heart disease. There may also be benefits in foetal development, but an optimal intake has not been established."
Metabolism, Function and Physiological Requirement for N-3 LC PUFA in Humans:

In an appendix, the EFSA report reviewed the metabolism and function and the physiological requirement for n-3 LC PUFA in humans (EFSA Annex 2). This review noted that there is a dietary requirement for n-3 ALA and stated that there is no consensus on the need for an intake of preformed DHA in adults, although data indicated that DHA is conditionally indispensable for preterm infants. The report noted that the Scientific Committee on Food (SCF) of the European Commission in 1993 set population reference intakes for total n-3 fatty acids at 0.5 percent of energy intake (calories) for adults and recommended that total n-3 fatty acid intake not exceed five percent of energy intake. Regarding the need for n-3 LC PUFA during pregnancy and lactation, the review summarized the accretion of n-3 LC PUFA in the fetus and placenta during pregnancy and the DHA secreted in breast milk during lactation. The EFSA report noted the estimate of the SACN report (2004) that women may need to increase DHA intake to about 0.2 grams per day during pregnancy and about 0.16 to 0.17 grams per day during lactation. This may be particularly important in successive pregnancies.

The review noted the lack of association between blood levels of DHA at birth and later cognitive performance in two studies (Ghys et al, 2002; Bakker et al, 2003). However, DHA status at birth was significantly related to better movement quality and visual acuity and behavior at seven to eight years of age in another study (Hornstra 2005). The review stated that:

"This underlines the importance of an adequate maternal DHA intake during pregnancy as a condition for an ample supply of the fetus and its importance for cognitive, motor, visual and behavioural development of the infant and child. This adequate maternal intake during pregnancy and lactation can be reached by a higher intake of fatty fish (or of fish oil)."
Effect of Fish or LC N-3 PUFA in Pregnancy on Outcome

The EFSA report noted that, for pregnant and breastfeeding women, the DHA level in blood phospholipids and in breast milk is determined by maternal fish consumption or LC n-3 PUFA intake. The report summarized research studies of associations between maternal fish intake, LC n-3 PUFA intake, LC n-3 PUFA blood levels or LC n-3 PUFA breast milk levels and health outcomes in mothers or offspring.

  • Gestational length and birth weight. In an observational study in the Faroe Islands, higher fish consumption was associated with longer gestational duration. An observational study in Denmark showed no association between intake of LC n-3 PUFA and gestational length, birth weight or birth length, but fish intake was associated with lower risk of preterm delivery and of low birth weight. A randomized trial of cod liver oil supplementation in pregnant women showed no differences in gestational duration or birth weight between supplemented and placebo groups. However, among all neonates, there was a positive association between DHA levels in cord blood phospholipids and gestational duration. Another trial of DHA supplements in eggs during pregnancy showed a statistically significant increase of gestational duration by six days for the supplemented group compared with placebo.
  • Pregnancy-induced hypertension (PIH). Observational studies in Inuit women suggested an association between LC n-3 PUFA and decreased risk of PIH. However, a clinical trial of fish oil supplementation in high risk pregnant women showed no difference in PIH risk with supplementation compared with placebo.
  • Visual function and cognitive development.
    • A neurological exam of apparently healthy term infants at 10-14 days of age showed the neurologic optimality score was positively associated with indices of DHA level in umbilical artery and vein. Neurologically abnormal infants had lower DHA indices (Dijck-Brouwer 2005).
    • In the randomized trial of cod liver oil supplementation in pregnant women, there was no difference in electroencephalogram (EEG) scores at age two days and three months or novelty preference (Fagan test) at age six and nine months between supplemented and placebo groups. However, among all neonates, there was a positive association between DHA levels in cord blood phospholipids and maturity of EEG scores at age two days (Helland 2001). In a subset of children tested at four years of age, children of supplemented mothers scored higher on an intelligence test, the Kaufman Assessment Battery for Children (Helland 2003).
    • In a group of healthy breastfed infants, length of breastfeeding was positively associated with IQ at age 6 ½ years. Length of gestation, duration of breastfeeding and the ratio of DHA to AA in colostrum (early breast milk) explained 76 percent of the total variation in IQ (Gustafsson 2004).
    • Visual function development has been used as a marker for neurodevelopment. In some but not all studies, breastfed infants were shown to have better visual acuity, more advanced retinal development and more advance visual function up to 3 ½ years of age.
    • In a group of pregnant women and their infants in the U.S., higher maternal fish consumption was associated with higher infant scores for visual memory recognition at six months of age. In the same study, visual memory recognition scores were negatively associated with maternal hair mercury concentration (Oken et al., 2005).
    • In a prospective study, stereoacuity (depth perception) in children at age 3½ years was associated with breastfeeding and with maternal consumption of fatty fish during pregnancy (Williams et al., 2001).
    • In another randomized trial of fish oil supplements in pregnant women, there was no difference in visual evoked potential (VEP) shortly after birth between supplemented group and placebo. Neither was there an effect of supplementation on gestation length, birth weight or on DHA concentration in umbilical cord red blood cells. However, among all infants, there was a significant correlation between infant DHA blood levels and maturity of the retina as assessed by electroretinography within the first week of life and with the maturity of the pattern-reversal VEP at 50 and 66 weeks postconceptional age (Malcolm et al., 2003a,b).

The Summary and Conclusions of the report stated:

  1. "Fish is an important source of proteins of high biological value, LC n-3 PUFA, essential minerals, especially iodine, selenium and calcium, and vitamins, especially vitamins A and D and B12. LC n-3 PUFA are not essential in human nutrition beyond the foetal and neonatal period, but may be conditionally essential in immature and young infants."

  2. "There is an increased demand for LC n-3 PUFA of the foetus with advancing pregnancy. This has to be satisfied predominantly by the mother by enhanced synthesis from the precursor LNA, by mobilisation of tissue stores or by dietary intake. Fish consumption corresponding to at least 0.2 g DHA/day can satisfy both the demands of the foetus and maternal requirements. However, both the intake of high amounts of LC n-3 PUFA (> 2 g/day) and of LNA (> 3 g/day) can decrease the AA status of the infant, which is undesirable. Therefore, both the requirement of LC n-3 PUFA and the relationship between n-3 and n-6 fatty acids and AA content in the maternal diet are of concern and the optimal mixture needs to be identified. The Scientific Committee on Food (2003) considered the available evidence insufficient for setting a mandatory minimum content of LC PUFA for infant formula intended for healthy mature infants."

The EFSA report concluded that there is evidence that fish consumption or fish oil benefits the cardiovascular system and is suitable for secondary prevention in manifest coronary artery disease. The report further stated:

"Nevertheless, results from both epidemiologic and interventional studies suggest that health benefits are associated with the consumption of certain levels of EPA/DHA from fish and fish oils also in the healthy population. The expected benefits include a decrease in the risk of cardiovascular disease and stroke and improved neurodevelopmental and perinatal growth in infants."

U.S. Agency for Health Care Research and Quality. Effects of Omega-3 Fatty Acids on Maternal and Child Health.

In 2005, the U.S. Agency for Health Care Research and Quality (AHRQ) published the results of a systematic review of the scientific literature regarding the human evidence for the effects of omega-3 fatty acids on maternal and child health. The review was conducted by the Evidence Based Practice Center at the University of Ottawa, Canada (Lewin 2005).

Key Questions:

The AHRQ review addressed a range of key research questions, involving both maternal and child populations and several types of outcome data, both clinical pregnancy outcomes and clinical child development outcomes. As outlined in the Summary of the AHRQ review, the key questions included:

"Maternal population, pregnancy outcomes/biomarkers associations:

  • What is the evidence that intake of omega-3 fatty acids influences
    • duration of gestation?
    • incidence of births of human infants small for gestational age (SGA)?

"Child population, growth patterns, neurological, visual or cognitive developmental outcomes/biomarkers associations:

  • What is the evidence that maternal intake of omega-3 fatty acids
    • during pregnancy influences any of the clinical outcomes in term or preterm human infants?
    • within maternal breast milk, infant formula, both and/or other sources (i.e., diet) influences any of the clinical outcomes in term or preterm human infants?
  • What is the evidence that term or preterm human infants' clinical outcomes are associated with the omega-3 or omega-6/omega-3 fatty acids content of
    • maternal or fetal biomarkers during pregnancy?
    • child biomarkers?"
Systematic Review:

The systematic review identified 2,049 records for initial screening. Of the 191 reports reviewed, 117 reports, describing 89 unique studies, met the inclusion criteria. These included 63 randomized controlled trials and 26 observational studies. If at least two randomized controlled trials (RCTs) were identified for a population and outcome, no other types of design were considered. However, if there were too few RCTs available, then non-RCT clinical trials (such as trials without random allocation) and observational studies (such as cohort, case control or cross sectional studies) were included. Descriptive study designs were not included.

Meta-analyses:

The full AHRQ report considered the evidence for each key research question individually. Meta-analyses were conducted for many of the research questions regarding the effect of omega 3 fatty acid supplements on pregnancy outcomes and child growth and development, including neurological and cognitive development of term infants and visual function in both term and preterm infants. The results of specific AHRQ meta-analyses will be summarized in this section under Other Recent Systematic Reviews, Meta-Analyses and Risk Assessments.

Conclusions:

In its overall conclusion, the AHRQ report found an absence of reports of moderate to severe adverse events associated with omega-3 fatty acids in maternal and child health. Regarding beneficial maternal and child outcomes, the report found that:

"Pregnancy outcomes were either unaffected by omega-3 fatty acid supplementation, or the results were inconclusive…. regarding evaluations of the duration of gestation, some discrepancies were observed, although most of the studies failed to detect a statistically significant effect. Biomarker data failed to clarify patterns in pregnancy outcome data."
"Results concerning the impact of the intake of omega-3 fatty acids on the development of infants are primarily, although not uniformly, inconclusive. The inconsistencies in study results may be attributable to numerous factors."
"In addition, making clear sense of the absolute or relative effects of individual omega-3 fatty acids, or even omega-3 fatty acid combinations, on child outcomes is complicated or precluded by the following problem. Studies typically employed interventions that involved various cointerventional or background constituents (e.g., omega-6 fatty acids), yet whose metabolic interactions with the omega-3 fatty acid(s) were not taken into account in interpreting the results. The dynamic interplay among these fatty acid contents (e.g., competition for enzymes), and how this interplay may influence outcomes, may differ in important ways depending on whether DHA or olive oil is added to the combination of cointerventional or background constituents, particularly in the maternal population. This strategy prevented the isolation of the exact effects relating to the omega-3 fatty acid content. It is thus very difficult to reliably ascribe definite child outcome-related benefits, or the absence thereof, to specific omega-3 fatty acids. Biomarker data failed to clarify patterns in child outcome data."
"Future research should likely consider investigating the impact of specific omega-6/omega-3 fatty acid intake ratios, in no small part to control for the possible metabolic interactions involving these types of fatty acids. To produce results that are applicable to the North American population, populations consuming high omega-6/omega-3 fatty acid intake ratios should likely be randomized into trials also exhibiting better control of confounding variables than was observed, especially in the present collection of studies of child outcomes."

Institute of Medicine of the National Academies. "Seafood Choices. Balancing Benefits and Risks"

In 2006, the Institute of Medicine (IOM) of The National Academies released a report, titled "Seafood Choices. Balancing Benefits and Risks," which examined relationships between benefits and risks associated with seafood to help consumers make informed choices. The report used a qualitative approach to balancing benefits and risks of seafood intake by population groups.

As part of its task to analyze and balance the benefits and risks of seafood consumption, the IOM report reviewed and evaluated the scientific literature on the benefits associated with nutrients from seafood. In Section A we summarized the IOM's review and evaluation of the literature regarding CHD and stroke. Here we summarize the IOM's review and evaluation regarding neurodevelopmental health benefits.

In an appendix, the report tabulated the studies reviewed, noting the author, study type, subjects, exposure, exposure timing, exposure amount and results. The table also classified the conclusion of each study by designating the conclusion as: B, evidence of benefit; N, evidence of no association or no clear association; A, evidence of an adverse effect; and N/A, conclusion not available, data presented for background only.

Benefits to Women During and After Pregnancy:

Postpartum depression. The report tabulated nine studies that addressed the question of whether low DHA levels in the brain in late pregnancy and early postpartum period may contribute to the emergence of postpartum depression. The nine studies included one review, one randomized controlled trial, one open trial, five cohort studies and five cross cultural (ecologic) study. The ecologic study compared 41 population groups and found a positive association between seafood consumption and higher DHA levels in breast milk, and this was associated with lower prevalence of postpartum depression (Hibbeln 2002). However, a clinical trial of DHA supplements in lactating women found no difference between supplemented and control groups for measures of postpartum depression. The report noted that there are no randomized clinical trials of omega-3 fatty acids supplementation in pregnancy and risk of postpartum depression. The committee found that the existing evidence was insufficient to draw a conclusion about the possible association of EPA/DHA intake and postpartum depression.

Since the 2005 IOM report, a large epidemiological study and a randomized controlled trial have provided additional information regarding depression during pregnancy.

Epidemiological study (Golding et al., in press): This study used a net risk and benefits of fish consumption approach to assess relative risk of high levels of depressive symptoms among approximately 9,000 women in the third trimester of pregnancy in the ALSPAC cohort in the United Kingdom. Statistical analysis took social and lifestyle factors into account. Results: Unadjusted and adjusted analyses showed lower maternal intake of omega-3 from seafood was associated with high levels of depressive symptoms. Compared to women consuming >1.5g omega-3 from seafood per week, those consuming none were more likely to have of high levels of depressive symptoms at 32 weeks gestation (AOR 1.54, 95% CI 1.25, 1.89). The authors concluded that a woman needs to consume at least three portions of seafood per week to maintain her mental health during pregnancy. They reported that since the risk of depressive symptoms was lowest among those consuming >1.5g of omega-3 from seafood per week (three or more portions of seafood per week), it was likely that limiting intake below this amount would increase the risk of maternal depressive symptoms during pregnancy.

Randomized Controlled Trial (Su et al., 2008): This randomized controlled trial compared 3.5 g/d of n-LC PUFAs compared to placebo among n="33" pregnant women with major depressive disorder severe enough to meet ICD -9 criteria. Twenty four women completed the study. At six weeks the group randomized to omega-3's higher rates of clinical response (62%, n-3 LC PUFA to 27% Placebo, p<0.03). At eight weeks the n-3 LC PUFA group had significantly lower depressive symptoms on the EPSD and Beck depression inventory rating scales. The n-3 LC PUFAS were well tolerated with no adverse effects for mother or infant.

Benefits to Infants and Children Associated with Prenatal Omega-3 Fatty Acid Intake:

The report noted that the level of maternal DHA intake influences DHA levels in both maternal blood and milk. DHA is selectively transported across the placenta, therefore increased maternal blood DHA in pregnancy may enhance placental DHA transfer to the fetus. This could influence the DHA supply available to the fetal brain and to other organs and tissues. Brain DHA accumulates rapidly from about 22 weeks of gestation to at least 2 years of age.

Duration of gestation and birth weight. The report tabulated 16 studies of the association of fish oil supplementation, seafood intake or other food sources of DHA with duration of gestation and birth weight. There were 10 randomized controlled trials, five cohort studies and one case control study. The report found that "observational studies suggest and several of the experimental studies support that EPA/DHA supplementation or higher seafood intake is associated with an increased duration of gestation."

Development in infants and children. The report tabulated 34 studies addressing the association of infant and child development with maternal n-3 LC PUFA intake. There were four reviews, six randomized controlled trials, 15 cohort studies, two case control studies, three cross sectional studies and four animal studies.

Visual acuity. In a prospective observational study, stereoacuity (depth perception) at 3½ years of age was associated with breastfeeding, greater maternal age, and maternal consumption of fatty fish during pregnancy in the Avon Longitudinal Study of Parents and Children (ALSPAC Study) (Williams et al., 2001). In a prospective observational study of breastfed infants, breast milk DHA levels were positively associated with visual acuity and speech perception at two months of age (Innis 2001).

Cognitive development. In a randomized controlled trial of cod liver oil supplementation in pregnant women in Norway, children of supplemented mothers had higher Mental Processing Composite scores at four years of age (Helland 2001, 2003). A randomized controlled trial of DHA supplementation in lactating women found a higher Bayley Psychomotor Development Index (PDI) in children of supplemented mothers at 30 months of age (Jensen 2005). In this study, there were no effects of supplementation on visual acuity at four or eight months or on developmental indexes at 12 months. In a preliminary report, children of supplemented mothers also had longer sustained attention at five years of age (Jensen 2004). The committee noted that these two trials found benefits from maternal supplementation not in infancy but in early childhood and suggested that other trials that did not continue developmental follow-up after infancy may have missed benefits to children of improving maternal omega-3 fatty acid intake.

A prospective observational study found positive association of maternal seafood intake with visual memory recognition score at six months of age. The study also found an inverse association of infant visual memory recognition score at six months with level of mercury in maternal hair during pregnancy (Oken et al., 2005). A prospective observational study of children in the ALSPAC cohort found a positive association between maternal fish intake during pregnancy and scores on the Denver Developmental Screening Test and on the MacArthur Communicative Development Inventory (Daniels et al., 2004). Cord tissue mercury levels were not associated with developmental scores.

Overall, regarding maternal intake of seafood or n-3 LC PUFA, the report found that:

"The strongest evidence of benefit for higher maternal seafood or EPA/DHA intake is an increase in gestation duration, with anticipated benefits to the newborn. Populations or subgroups within populations who have the lowest baseline consumption of seafood may show the greatest benefit in duration of gestation with higher EPA/DHA intake. Observational and experimental studies offer evidence that maternal DHA intake can benefit development of the offspring; however, there are large gaps in knowledge that need to be filled by experimental studies."
"The average EPA/DHA intake among U.S. women is considerably below that of most other populations in the world and the majority of the data on benefits to infants and children from increased DHA levels come from populations outside the U.S. and/or from studies using supplementation rather than seafood consumption."
Benefits to Infants from Postnatal Supplementation through Formula:

The committee reviewed evidence related to DHA-supplemented infant formulas to consider whether these data support the findings on benefits associated with seafood consumption or fish oil supplementation in pregnant and lactating women.

Visual Acuity. The report tabulated 23 studies considering DHA supplementation of infants and visual acuity. There were four reviews (including one Cochrane review), two meta analyses, 12 randomized controlled trials, three cohort studies, one cross sectional study and one animal study. Overall, the report found that all but one of the randomized controlled trials of preterm infants and about half of the trials of term infants found higher visual acuity at some age in infants consuming DHA supplemented formula. A review by Uauy et al. (2001) and meta-analyses by SanGiovanni et al. (2000a, b) concluded that DHA supplementation resulted in improved visual acuity in both term and preterm infants. However, a Cochrane systematic review concluded that there was no association between DHA supplementation and increased visual acuity or general development in term infants (Simmer 2001).

Cognitive and Motor Development. The report tabulated 32 studies considering DHA supplementation of infants and cognitive and motor development. There were nine reviews (including two Cochrane reviews), 18 randomized controlled trials, two cohort studies, and five animal studies. The report summarized some of the inconsistent results regarding cognitive and motor development in DHA supplement trials of preterm and term infants. The committee noted that global tests such as the Bayley Scales of Infant Development and the Brunet-Lezine administered in infancy may be less related to performance on cognitive tests in childhood than more specific tests of attention and problem solving. There is limited evidence from global tests of infant development to support cognitive benefit of DHA supplementation of infants. For specific tests more strongly related to developmental parameters, the evidence is mixed. Overall, the report stated:

"At most, specific outcomes have been measured in only one or two individual trials and these have been measured at different ages. Even though numerous developmental outcomes have been identified that collectively suggest there are benefits associated with EPA/DHA supplementation, it is difficult to subject the studies in total to a systematic review, because of the differences in experimental design among the studies. The benefits of postnatal DHA supplementation for cognitive development need further study because of the heavy reliance on global assessments as outcomes and the limited employment of more specific developmental outcomes. Furthermore, the majority of trials stopped looking at development well before children reached school age, when more sophisticated measures of cognitive function may be employed."

Overall, regarding visual acuity and cognitive and motor development with supplemented infant formula, the report stated:

"The strongest evidence of benefit for postnatal DHA supplementation in formula-fed preterm and term infants is higher visual acuity, an outcome that has been measured repeatedly in clinical trials. In addition, some positive effects have been found on cognitive function in infancy and childhood in both experimental and observational studies and in relation to both pre- and postnatal DHA intake. Reviews that take into account all lines of evidence have concluded that omega-3 fatty acid can be beneficial to cognitive development (Cohen 2005c, McCann and Ames 2005), whereas reviews that rely strictly on published results from experimental trials limited to global assessments of cognitive development, e.g., the MDI [Bayley Mental Development Index], do not offer strong support (Simmer and Patole 2005, Simmer 2005)." [Note these citations correspond to Simmer and Patole (2004) and Simmer (2001).]
Primary Findings:

The Primary Findings of the report regarding health benefits of seafood in women, infants and young children were stated as:

  1. Seafood is a nutrient-rich food that makes a positive contribution to a healthful diet. It is a good source of protein, and relative to other protein foods, e.g. meat, poultry, and eggs is generally lower in saturated fatty acids and higher in the omega-3 fatty acids EPA and DHA and selenium;
  2. The evidence to support benefits to pregnancy outcome in females who consume seafood or fish oil supplements as part of their diet during pregnancy is derived largely from observational studies. Clinical trials and epidemiological studies have also shown an association between increased duration of gestation and intake of seafood or fish oil supplements. Evidence that the infants and children of mothers who consume seafood or EPA/DHA supplements during pregnancy and/or lactation may have improved developmental outcomes is also supported largely by observational studies;
  3. Increased EPA/DHA intake by pregnant and lactating women is associated with increased transfer to the fetus and breast-fed infant.
    1. A number of observational studies show a positive association between maternal blood or breast milk DHA levels and a range of developmental outcomes in infants and children.
    2. Two experimental studies of maternal EPA/DHA supplementation found cognitive benefits for the children when they were four or five years of age.
    3. Because these two studies differed dramatically in timing of EPA/DHA supplementation (pre- and postnatally or postnatally), source (cod-liver oil or algal DHA), and amount (2.0 grams or 0.20 grams EPA/DHA) and, likely in usual seafood intake (Norway or U.S. residents), insufficient data are available to define an ideal level of EPA/DHA intake from seafood in pregnant and lactating women.
  4. A large number of experimental trials have provided DHA directly to human infants through infant formula and have found benefits for infant and child neurological development. These trials offer the best evidence that infants/children would benefit from increased DHA in breast milk and increased maternal seafood intake.
    1. Visual acuity has been measured in the most trials and is increased by DHA supplementation, with preterm infants more likely to benefit than term infants.
    2. Cognitive benefits of postnatal DHA supplementation with formula have also been found in infancy and early childhood. However, the number of trials has been limited and the specific outcomes varied, precluding a systematic review.
  5. At present, there is no convincing evidence that ADHD [attention deficit hyperactivity disorder], other behavioral disorders, and asthma can be prevented or treated in children with seafood or EPA/DHA consumption.
Research Gaps and Recommendations:

The Committee made the following research recommendations related to its review of health benefits for women, infants and children:

Pregnant and Lactating Women

Recommendation 1:

Better data are needed to determine if outcomes of increasing consumption of seafood or increasing EPA/DHA intake levels in U.S. women would be comparable to outcomes of populations in other countries. Such studies should be encouraged to include populations of high fish-consumers outside the continental United States to determine if there are differences in risks for these populations compared to U.S. populations.

Recommendation 2:

Dose-response studies of EPA/DHA in pregnant and lactating women are needed. This information will help determine if higher intakes can further increase gestation duration, reduce premature births, and benefit infant development. Other studies should include assessing whether DHA alone can act independent of EPA to increase duration of gestation.

Infants and Toddlers

Recommendation 3:

Research is needed to determine if cognitive and developmental outcomes in infants are correlated with performance later in childhood. This should include:

  • Evaluating preschool and school-age children exposed to EPA/DHA in utero and postnatally, at ages beginning around four years when executive function is more developed and;
  • Evaluating development of school-age children exposed to variable EPA/DHA in utero and postnatally with measures of distractibility, disruptive behavior and oppositional defiant behavior, as well as more commonly assessed cognitive outcomes and more sophisticated tests of visual function.

Recommendation 4:

Additional data is needed to better define optimum intake levels of EPA/DHA for infants and toddlers.

Children

Recommendation 5:

Better-designed studies about EPA/DHA supplementation in children with behavioral disorders are needed.

Balancing Risks and Benefits:

Because of scientific uncertainties, the committee found that it was not feasible to quantify the health benefits of seafood consumption, the health risks of potential contaminants for all population subgroups, or the benefit-risk interactions. Therefore, rather than presenting a quantitative benefit-risk assessment and balancing, the committee used its expert judgment to develop a qualitative scientific benefit risk analysis and balancing of the benefits and risks of seafood consumption. Based on its analysis and balancing, the committee developed specific guidance for healthy consumption for population subgroups. The consumption guidance for women and children is:

  1. Females who are or may become pregnant or are breastfeeding:
    1. May benefit from consuming seafood, especially those with relatively higher concentrations of EPA and DHA;
    2. A reasonable intake would be two three-ounce (cooked) servings but can safely consume 12 ounces per week;
    3. Can consume up to six ounces of white (albacore) tuna per week;
    4. Should avoid large predatory fish such as shark, swordfish, tilefish, or king mackerel.
  2. Children up to age 12:
    1. May benefit from consuming seafood, especially those with relatively higher concentrations of EPA and DHA;
    2. A reasonable intake would be two three-ounce (cooked), or age-appropriate, servings but can safely consume 12 ounces per week;
    3. Can consume up to six ounces of white (albacore) tuna per week;
    4. Should avoid large predatory fish such as shark, swordfish, tilefish, or king mackerel.

(c) Other Recent Reviews, Meta-Analyses and Risk Assessments

Controlled Clinical Trials of Omega-3 Fatty Acid Supplementation of Infant Formula

A number of clinical trials of omega-3 fatty acid supplementation of infant formula have examined possible risks and benefits of formula supplements for infant development. As noted above, although supplementation of infant formula with DHA does not fall in the category of fish consumption, results of these studies may help to answer scientific questions regarding possible neurodevelopmental benefits of DHA during infancy. Table B-2 lists several reports and reviews of this body of literature. Three of the reports were summarized in the previous subsection: the IOM Macronutrient Report, the United Kingdom SACN report and the IOM Seafood Choices report. This subsection will summarize the remaining reviews in Table B-2, including specific meta-analyses from the AHRQ report that was summarized in general in the previous subsection (Lewin 2005).

Willatts and Forsyth (2000)

Willatts P, Forsyth JS. The role of long-chain polyunsaturated fatty acids in infant cognitive development. Prostaglandins Leukot Essent Fatty Acids. 2000 Jul-Aug;63(1-2):95-100.

Developmental Outcomes: cognitive development in premature and term infants (narrative review with tabulated studies).

The authors noted an inconsistent pattern of results of randomized studies of the effects of infant formula supplemented with n-3 LCPUFA on cognitive development in both preterm and term infants. The studies reviewed used various types of behavioral assessments: psychomotor development, visual attention, problem solving and language development. Criteria for study inclusion and exclusion were not stated for this narrative review. According to the reference citations several of the studies reviewed were reported in abstract form.

  • Psychomotor development. Two studies of preterm infants found significantly higher scores for infants fed supplemented formula using the Mental Development Index (MDI) of the Bayley Scales of Infant Development at corrected ages of six months and 12 months, respectively. A third study found no difference in MDI scores in supplemented and unsupplemented preterm infants at corrected age 12 months. For term infants, several studies showed no differences between formula groups on various global developmental tests. However, one study showed significantly higher Bayley MDI scores for supplemented infants at age 18 months, as well as a positive correlation between 18 month MDI scores and four month plasma and red blood cell DHA levels across study groups (Birch 2000).
  • Visual information processing. Two studies of preterm infants showed no differences between supplemented and unsupplemented infants in visual recognition memory, but supplemented infants showed shorter duration of looking at familiar versus novel test stimuli, indicating more efficient information processing compared with controls. One study of term infants found significantly higher visual recognition memory scores in supplemented infants at nine months of age and another study found shorter look duration in supplemented term infants at three months of age compared with controls.
  • Infant problem solving. In one study, supplemented term infants showed higher problem-solving scores on a three-step problem at 10 months of age compared with controls. The same clinical trial found higher problem solving scores on a two-step problem compared with controls at age nine months in a subgroup of supplemented infants who had lower birth weight and poorer attention control at three months.
  • Infant language development. In one study, term infants supplemented with DHA alone (without arachidonic acid, AA) had marginally lower scores at age 14 months for vocabulary production on the MacArthur Communicative Development Inventory, compared with control infants or infants supplemented with DHA plus AA. There were no differences among groups for the vocabulary comprehension or communicative gesture scores. Also, there was a negative correlation between red blood cell DHA at age four months and both vocabulary production and comprehension scores. In a follow up at age 39 months, there were no differences between groups in measures of IQ and vocabulary.

The authors noted that, despite the inconsistent results of the clinical trials, it would be premature to conclude that n-3 LC PUFA has no effect on cognitive development. Tests of psychomotor development have limitations in assessment of infant cognitive ability, and global tests such as the Bayley Scales may be relatively insensitive in detecting specific but subtle effects on cognition. The authors observed that studies of infant visual attention and problem solving were more consistent in showing effects of n-3 LC PUFA supplementation. These measures also correlate with cognitive scores in later childhood. The authors also noted that in the clinical trials reviewed there were no adverse effects of infant formulas supplemented with DHA plus AA. Only one study reported a negative effect of supplementation and this was for a supplement of DHA without AA.

SanGiovanni et al. (2000a)

SanGiovanni JP, Parra-Cabrera S, Colditz GA, Berkey CS, Dwyer JT. Meta-analysis of dietary essential fatty acids and long-chain polyunsaturated fatty acids as they relate to visual resolution acuity in healthy preterm infants. Pediatrics. 2000 Jun;105(6):1292-8.

Developmental Outcomes: vision in premature infants (meta-analysis).

Study Characteristics: The authors conducted a systematic review of peer-reviewed and published reports of clinical trials of n-3 LC PUFA supplementation and visual acuity in healthy preterm infants from 1965 through July, 1999. Four clinical trials, published in 1992 through 1996, met the inclusion criteria for the meta-analysis (Carlson et al., 1993#; Carlson et al., 1996#; Birch et al., 1992#; Birch et al., 1993#). Other studies were excluded because they had no measure of visual resolution acuity, had no comparison group that received no DHA or had results published only in abstract form. Visual acuity testing was behaviorally based or electrophysiologically based. For the meta-analysis, results of visual acuity measurements were reported in cycles per degree (cy/deg) of visual angle and expressed on an octave scale, where a one-octave difference is a doubling or halving of the number of cy/deg resolved. The review tabulated the fatty acid composition of the test formulas and the design, analytic and experiment-based characteristics of the included studies. Comparison groups fed test formulas without DHA were compared with test groups fed DHA-supplemented formula (randomized comparison) or with a group of breast fed infants (nonrandomized comparison) or both. The two studies from Carlson et al. (1993#, 1996#) were randomized comparisons; Birch et al. (1993#) was a nonrandomized comparison; and Birch et al. (1992#) used both types of comparisons. In Carlson et al. (1996#), the DHA test formula was fed until two months corrected age and then changed to a formula without DHA but with a higher level of ALA. Notably, in these relatively early studies, none of the test or comparison formulas contained AA. The Carlson et al. (1993#, 1996#) trials used behaviorally based acuity testing at zero, two, four, six, nine and 12 months corrected ages. The Birch et al. (1992, 1993) trials used both behaviorally based and electrophysiologically based acuity testing at four months corrected age and Birch et al. (1992#) also used electrophysiologically based testing at zero months corrected age.

Study results:

  • Behaviorally based tests.
    • Randomized comparisons.
      • Two months corrected age. Results showed significantly better visual acuity for DHA test formulas (Carlson et al., 1993, 1996).
      • Four months corrected age. There was significantly better visual acuity for DHA test formulas than for the comparison formula in Carlson et al. (1993#) and than for the corn oil based comparison formula in Birch et al. (1992#). There was also better visual acuity for the DHA formula than for the soy oil based comparison formula in Birch et al. (1992#), but the difference was not statistically significant. (The soy oil formula was higher in ALA than the corn oil formula.) Visual acuity was slightly but not significantly lower for infants who received the DHA test formula until 2 months corrected age than for infants who received the comparison formula in Carlson et al. (1996#).
      • Zero, six, nine and 12 months corrected age. At these ages, there were no significant differences in visual acuity between DHA and comparison formulas (Carlson et al., 1993#, 1996#).
    • Nonrandomized comparisons.
      • Four months corrected age. Breastfed infants had better visual acuity than infants given the comparison formula without DHA in Birch et al. (1993#) and than infants given either the corn oil or soy oil comparison formula without DHA in Birch et al. (1992#), but for the soy oil comparison formula the difference was not statistically significant.
  • Electrophysiologically based tests.
    • Randomized comparisons.
      • Zero months corrected age. There was better visual acuity for DHA test formulas than for either the corn oil or soy oil comparison formula in Birch et al. (1992#), but for the soy oil comparison formula the difference was not statistically significant.
      • Four months corrected age. There was significantly better visual acuity for DHA test formulas than for either the corn oil based or soy oil based comparison formula in Birch et al. (1992#).
    • Nonrandomized comparisons.
      • Four months corrected age. Results were parallel to the results for behaviorally based tests. Breastfed infants had better visual acuity than infants given the comparison formula without DHA in Birch et al. (1993#) and than infants given either the corn oil or soy oil comparison formula without DHA in Birch et al. (1992#), but for the soy oil comparison formula the difference was not statistically significant.

Meta-analysis results

  • Behaviorally based tests.
    • Randomized comparisons.
      • Two months corrected age.
        • Better acuity for infants in the DHA test formula groups.
        • Combined estimated difference in visual resolution acuity:
          • 0.47 octaves of cy/deg (95 percent CI 0.21 to 0.74), p < 0.001
          • based on two studies, two comparisons above
          • 48 infants in DHA groups, 49 infants in DHA-free groups
      • Four months corrected age.
        • Better acuity for infants in the DHA test formula groups.
        • Combined estimated difference in visual resolution acuity:
          • 0.28 octaves of cy/deg (95 percent CI 0.14 to 0.43), p < 0.001
          • significant heterogeneity between studies
          • based on 3 studies, 4 comparisons above
          • 70 infants in DHA groups, 56 infants in DHA-free groups
      • Zero, six, nine and 12 months corrected age.
        • At these ages, there was no significant difference in visual acuity between test formula groups
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on two studies, two comparisons above
    • Randomized and nonrandomized comparisons.
      • Four months corrected age.
        • When the randomized and nonrandomized comparisons above were combined, there was better acuity for infants in the breastfed or DHA test formula groups rather than in the groups with comparison formulas without DHA
          • combined estimated difference in visual resolution acuity
            • 0.35 octaves of cy/deg (95% CI 0.21 to 0.49), p < 0.001
            • significant heterogeneity between studies
            • based on four studies, seven comparisons above
            • 80 infants in DHA groups, 87 infants in DHA-free groups
  • Electrophysiologically based tests.
    • Randomized comparisons.
      • Zero months corrected age.
        • combined estimated difference in visual resolution acuity not reported
      • Four months corrected age.
        • better acuity for infants in the DHA test formula group
        • combined estimated difference in visual resolution acuity
          • 0.83 octaves of cy/deg (Standard error of the mean (SEM), ± 0.08), p < 0.001
          • results of heterogeneity test not reported
          • based on one study, two comparisons above
          • 13 infants in DHA groups, 28 infants in DHA-free groups
    • Randomized and nonrandomized comparisons.
      • Four months corrected age.
        • When the randomized and nonrandomized comparisons above were combined, there was better acuity for infants in the breastfed or DHA test formula groups rather than in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.75 octaves of cy/deg (SEM, ± 0.12), p < 0.001
          • results of heterogeneity test not reported
          • based on two studies, five comparisons above
          • 37 infants in DHA groups, 43 infants in DHA-free groups

Sample size calculations: The authors used the combined estimates of visual resolution acuity differences and the number of infants in the combined study groups to generate sample size curves for randomized studies for two and four months corrected ages. The curves show that for two months corrected age, a sample size of 21 per group would be needed for 85 percent power to detect a significant difference in visual resolution acuity in a two-tailed test with p < 0.05. For four months corrected age, a sample size of 57 per group would be needed for the same comparison. This estimate assumes that visual resolution acuity has a standard deviation of 0.5 octaves.

SanGiovanni et al. (2000b)

SanGiovanni JP, Berkey CS, Dwyer JT, Colditz GA. Dietary essential fatty acids, long-chain polyunsaturated fatty acids, and visual resolution acuity in healthy full term infants: a systematic review. Early Hum Dev. 2000 Mar;57(3):165-88.

Developmental Outcomes: vision in term infants (meta-analysis)

Study characteristics. The authors conducted a systematic literature review and meta-analysis of clinical trials of n-3 LC PUFA supplementation and visual acuity in healthy term infants through June, 1999. The purpose of the review was to evaluate the nature of discordant results in clinical trials of n-3 LCPUFA intake and visual acuity in term infants in order to improve the planning and implementation of future studies. Twelve studies were identified and 11 studies published from 1992 through 1998 met the inclusion criteria for the meta-analysis. The citation for the excluded study and the reason for exclusion were not stated.

Visual acuity testing was behaviorally based or electrophysiologically based. For the meta-analysis, results of visual acuity measurements were reported in cycles per degree (cy/deg) of visual angle and expressed on an octave scale, where a one-octave difference is a doubling or halving of the number of cy/deg resolved. The review tabulated the experiment-based characteristics and the design and analytic characteristics of the 11 studies and the fatty acid composition of the test formulas used.

The tabulations of study characteristics showed that DHA supplementation in various studies was provided by egg yolk phospholipids, single cell oils or fish oil. In supplemented formulas, DHA level ranged from 0.12 to 0.53 percent of lipids and AA level ranged from practically absent (0.01 percent) to 0.60 percent. The test formulas (both DHA supplemented and DHA free) also differed in levels of ALA (from 0.8 to 4.8 percent) and EPA (from 0.05 to 0.58 percent) and in ratio of n-6 linoleic to n-3 ALA (7.13 to 36.75).

Comparison groups fed test formulas without DHA were compared with test groups fed DHA-supplemented formula (randomized comparison) or with a group of breast fed infants (nonrandomized comparison) or both. For behaviorally based tests, there were a total of two, nine, four, 11, nine, five and eight comparisons (both randomized and nonrandomized) for subjects at less than or equal to one, two, three, four, six, nine and 12 months of age, respectively. For electrophysiologically based tests, there were a total of six, 10, one, six, two, three and six comparisons for subjects at two, four, five, six, seven, nine and 12 months of age, respectively.

Study Results:

  • Behaviorally based tests.
    • Randomized comparisons.
      • Age two months. Five of five comparisons in three studies showed better visual acuity for DHA test formulas, one comparison was statistically significant.
      • Age four months. Five of five comparisons in three studies showed nonsignificantly poorer visual acuity for DHA test formulas
    • Nonrandomized comparisons.
      • Age one month or less. One of two comparisons in two studies showed significantly poorer visual acuity for breastfed infants than for infants given the comparison formula without DHA.
      • Age one month. Four of four comparisons in four studies showed better visual acuity for breastfed infants than for infants given the comparison formula without DHA, three comparisons were statistically significant.
      • Age four months. Breastfed infants had better visual acuity than infants given the comparison formula without DHA in three out of six comparisons in six studies, two comparisons were statistically significant.
  • Electrophysiologically based tests.
    • Randomized comparisons.
      • Birch et al., 1998. Two comparisons showed better visual acuity for DHA test formula at ages two, four and 12 months, five of the six comparisons were statistically significant. There was no difference in visual acuity at age six months.
      • Auestad et al., 1997. Two comparisons showed slightly poorer visual acuity for DHA test formula at ages two, four, six, nine and 12 months, none of the 10 comparisons were statistically significant.
      • Makrides et al., 1995#. One comparison showed significantly better visual acuity for DHA test formula at ages four and seven months.
    • Nonrandomized comparisons.
      • Birch et al., 1998. Breastfed infants showed better visual acuity compared with test formula without DHA at ages two, four, six and 12 months, the comparisons at two and 12 months were statistically significant.
      • Auestad et al., 1997. Breastfed infants showed slightly poorer visual acuity compared with test formula without DHA at ages two, four, six, nine and 12 months, the comparison at six months was statistically significant.
      • Makrides et al., 1995#. Breastfed infants showed significantly better visual acuity compared with test formula without DHA at ages four and seven months.
      • Birch et al., 1992#; Birch et al., 1993#; Makrides et al., 1993#. Breastfed infants showed significantly better visual acuity compared with test formula without DHA in two comparisons at age four months (Birch et al., 1992#, 1993#) and one comparison at seven months (Makrides et al., 1993#).

Meta-Analysis Results:

  • Behaviorally based tests.
    • Randomized comparisons.
      • Age two months.
        • better acuity for infants in the DHA test formula groups
        • combined estimated difference in visual resolution acuity
          • 0.32 octaves of cy/deg (SEM, ± 0.09), p < 0.0005
          • based on five comparisons
          • 114 infants in DHA groups, 87 infants in DHA-free groups
      • Age four, six, nine and 12 months.
        • At these ages, there was no significant difference in visual acuity between test formula groups
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on five, five, three, and five comparisons, respectively
    • Nonrandomized comparisons.
      • Age two months.
        • Breastfed infants had better acuity than infants in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.49 octaves of cy/deg (SEM, ± 0.09), p < 0.0005
          • based on four comparisons
          • 117 breastfed infants, 174 DHA-free infants
      • Age four months.
        • Breastfed infants had better acuity than infants in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.18 octaves of cy/deg (SEM, ± 0.08), p < 0.05
          • based on six comparisons
          • 148 breastfed infants, 113 DHA-free infants
        • Age zero, three, six, nine and 12 months.
          • At these ages, there was no significant difference in visual acuity between test formula groups
          • The combined estimated differences in visual resolution acuity were not significantly different from zero
        • based on two, four, four, two and three comparisons, respectively
    • Randomized and nonrandomized comparisons.
      • Age two months.
        • When the randomized and nonrandomized comparisons above were combined, there was better acuity for infants in the breastfed or DHA test formula groups rather than in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.40 octaves of cy/deg (SEM, ± 0.06), p < 0.0005
          • 219 breastfed or DHA infants, 86 DHA-free infants
          • based on nine comparisons
      • Age zero, three, four, six, nine and 12 months.
        • At these ages, there was no significant difference in visual acuity between breastfed or DHA test formula groups and groups with comparison formulas without DHA.
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on two, four, 11, nine, five and eight comparisons, respectively
  • Electrophysiologically based tests.
    • Randomized comparisons.
      • Age seven months.
        • better acuity for infants in the DHA test formula group
        • combined estimated difference in visual resolution acuity
          • 1.03 octaves of cy/deg (SEM, ± 0.42), p < 0.05
          • based on one study
      • Age two, four, six, nine and 12 months.
        • At these ages, there was no significant difference in visual acuity between test formula groups
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on four, five, four, two and four comparisons, respectively
    • Nonrandomized comparisons.
      • Age four months.
        • Breastfed infants had better acuity than infants in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.37 octaves of cy/deg (SEM, ± 0.16), p < 0.02
          • based on five comparisons
          • 146 breastfed infants, 108 DHA-free infants
      • Age five and seven months.
        • Breastfed infants had better acuity than infants in the group with comparison formula without DHA
        • combined estimated difference in visual resolution acuity
          • age five months, 1.06 octaves of cy/deg (SEM, ± 0.47), p < 0.05
          • age seven months, 1.16 octaves of cy/deg (SEM, ± 0.29), p < 0.05
          • based on one study
      • Age two, six, nine and 12 months.
        • At these ages, there was no significant difference in visual acuity between breastfed infants and infants in the group with comparison formula without DHA
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on two, two, one and two comparisons, respectively
    • Randomized and nonrandomized comparisons.
      • Age four months.
        • When the randomized and nonrandomized comparisons above were combined, there was better acuity for infants in the breastfed or DHA test formula groups rather than in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 0.26 octaves of cy/deg (SEM, ± 0.10), p < 0.02
          • based on 10 comparisons
          • 265 breastfed or DHA infants, 109 DHA-free infants
      • Age seven months.
        • When the randomized and nonrandomized comparisons above were combined, there was better acuity for infants in the breastfed or DHA test formula groups rather than in the groups with comparison formulas without DHA
        • combined estimated difference in visual resolution acuity
          • 1.11 octaves of cy/deg (SEM, ± 0.24), p < 0.05
          • based on 2 comparisons (in one study)
      • Age two, six, nine and 12 months.
        • At these ages, there was no significant difference in visual acuity between breastfed or DHA test formula groups and groups with comparison formulas without DHA.
        • The combined estimated differences in visual resolution acuity were not significantly different from zero
          • based on six, six, three and six comparisons, respectively

Sample size calculations

The authors used the combined estimates of visual resolution acuity differences and the number of infants in the combined study groups to generate sample size curves for randomized studies for two and four months corrected ages. Not stated in the text, but estimated from the curves, for two months corrected age, a sample size of about 29 per group would be needed for 85 percent power to detect a significant difference in visual resolution acuity in a two-tailed test with p < 0.05. For four months corrected age, a much higher sample size of about 550 per group would be needed for the same comparison. This estimate assumes that visual resolution acuity has a standard deviation of 0.5 octaves.

Discussion

The authors stated the results show that, if DHA intake during infancy influences visual development, the effect is small to moderate. They stated that the tabulation of study characteristics indicates a need for more rigorous designs and more detailed reporting practice. The authors noted that only one study provided DHA levels above 0.30 percent of lipids, compared with a WHO/FAO recommendation that formula for full term infants provide 3.5 percent fat, and DHA level of 0.38 percent of lipids (WHO/FAO, 1994). Additionally, in most of the studies that included a group of breastfed infants, the DHA level in breast milk was not reported. The authors stated that this would have provided useful information about dose-response relationships. Overall, the likelihood that the infant would receive some DHA outside the test formula was higher in all dietary groups as age increased and solid foods were introduced. This could explain, at least in part, a decrease in the magnitude of visual acuity differences for supplemented or breastfed infants compared with those on control formula in older infancy. The authors also suggested that quality of visual stimulation in early infancy may lead to permanent functional alterations of the visual system and that the quality of early visual information may also affect the later development of brain systems.

Lauritzen et al. (2001)

Lauritzen, L., Hansen, H.S., Jørgensen, M.H., Michaelsen, K.F. (2001, January-March). The essentiality of long chain n-3 fatty acids in relation to development and function of the brain and retina. Progress in Lipid Research, 40(1-2), 1-94

Developmental outcomes: Vision and cognitive in term and preterm infants (narrative review with tabulated studies)

Lauritzen and coworkers published a comprehensive review of the essentiality of the long chain n-3 fatty acids with respect to the development and function of the brain and retina.

  • Section One. Brief outline of the essentiality of n-6 and n-3 polyunsaturated fatty acids. The authors noted that the understanding of the essentiality of the n-3 fatty acids lags behind that of the n-6 essential fatty acids. EPA, the 20-carbon n-3 fatty acid, can serve as a precursor of the "n-3 eicosanoids" (local hormones that participate in a number of physiological as well as pathological conditions). However, these n-3 eicosanoids have much lower potency than do the eicosanoids derived from arachidonic acid, the 20-carbon n-6 fatty acid. Additionally, the n-3 eicosanoids are formed at fairly high dietary intakes of EPA and DHA. The main biological role of ALA, the 18-carbon n-3 fatty acid, aside from its role as a source of energy or calories, is as a precursor to the longer chain (22-carbon) n-3 fatty acid, DHA, in cell membranes. Thus, the authors state that it is now generally accepted that n-3 fatty acids are essential in their own right. However, it is currently debated whether the dietary ALA precursor can meet the need for n-3 fatty acids in cell membranes, or whether intake of preformed DHA is needed. This 94-page review covers the metabolism of n-3 fatty acids, regulation of the n-3 fatty acid content of neuronal membranes and possible mechanisms for how DHA can influence neuronal membrane function. The review also covers the functional effects of dietary n-3 LC PUFA in human infants and discusses these results in the context of n-3 fatty acid metabolism.
  • Sections Two, Three and Four. Essential fatty acid metabolism. The fatty acid composition of cell membranes. The incorporation of docosahexaenoic acid in the brain.
  • Section Five. Maternal support of the docosahexaenoic acid demands of the infant brain. The authors summarized this section of the review by noting that autopsy studies of human infants show that the brains of infants fed formulas (without DHA) have reduced DHA content compared with breastfed infants. This indicates that the metabolic capacity of human infants receiving ALA as one to two percent of total fatty acids, when the n-6/n-3 ratio is 10 to one, does not provide for normal accretion of DHA in the brain. This raises the question of whether this difference in brain DHA content is of any importance to brain function. The authors state that this has not yet been full elucidated and that they will address this in the remainder of the review.
  • Section Six. Membrane fatty acid composition and cellular function. The summary of this section states that research has clearly indicated that phospholipids enriched with DHA may exert effects on membrane protein function. Additionally, non-esterified DHA (that is, DHA as a free fatty acid rather than in a phospholipid) may affect ion channels in cell membranes as well as transcription factors regulating the synthesis of specific proteins and enzymes. However, the authors state that "it is still premature to conclude anything about how dietary modulations of the 22:6n-3 [DHA] content in brain membranes will affect cellular function."
  • Section Seven. Functional effects of docosahexaenoic acid status. The authors note that there are potentially two important experimental approaches to examine the functional importance of dietary n-3 fatty acids:
    • First, whether varying ALA (n-3 18-carbon) content of the diet (both absolute amount and relative to n-6 content) has any functional consequences on infant development, and to determine the optimal ALA content of an infant diet.
    • Second, whether preformed dietary DHA (n-3 22-carbon) could lead to further improvements of infant development.

      Most studies have looked for n-3 effects on visual function, cognitive development, psychomotor development, and possible adverse effects. However, only a few of the studies have used the first approach above, looking at the effect of varying the ALA content of formula. Rather, most of the studies have addressed the second question, comparing the development of infants on formulas with and without DHA. The authors state that "This makes interpretation of the results difficult, because one cannot distinguish whether the infants have a requirement for 22:6n-3 [DHA] from whether they need a larger supply of n-3 fatty acids in general." The authors also note that, because of potential confounding factors in breastfed infants, "solid proof of effects of dietary 22:6n-3 [DHA] can only be obtained through controlled intervention studies…."

    • Section 7.1. Dietary n-3 fatty acids and visual function. 

      Animal studies. The authors briefly summarize the research on effects of n-3 fatty acids on visual function in animal studies in rodents, cats and monkeys. They state that the studies of n-3 fatty acid deficiency in animals do show that DHA plays a role in retinal function. However, in the animal models, the n-3 fatty acid deficiency is severe and the animals have often been depleted for more than one generation. Because a severe depletion is not a practical concern in humans, caution is needed in extrapolating to humans from the animal studies.

      Preterm infants. The authors cited five review articles published from 1997 to 1999 which concluded that the scientific evidence supports the addition of DHA (and AA) to preterm infant formula. According to Lauritzen and coauthors, such recommendations were based on four randomized clinical trials of adding DHA to infant formula for healthy preterm infants born at 28 to 31 weeks gestational age. This review tabulated the published results of these four clinical trials on visual and cognitive abilities of the infants, and also tabulated the test methods, sample sizes, gestational ages, and characteristics of the fatty acid composition of the test formulas. The three studies that examined visual acuity all found better acuity in preterm infants with DHA supplemented formula compared with infants with unsupplemented formula. All three studies found better visual acuity using Teller acuity cards, and the Uauy and Birch group (Birch et al., 1992#) also found better acuity using transient VEP. The study from the Uauy and Birch group found better acuity at six and 17 weeks corrected age. In the studies from the Carlson group, the effect was transient: better acuity at nine and 17 weeks, but not at 26, 39 or 52 weeks corrected age (Carlson et al., 1993#) or better acuity at nine weeks but not at 17, 26, 39 or 52 weeks corrected age (Carlson et al., 1996#). The tabulation showed that the two studies from the Carlson group were relatively high in 18-carbon ALA and moderate in DHA, while the Birch et al. (1992) study formula was low in ALA and higher in DHA.

      The study from the Uauy and Birch group (Birch et al., 1992#) also found lower rod thresholds in electroretinograms (ERG) (Uauy et al., 1990#), and the fourth study (Faldella et al., 1996#) found shorter VEP latencies at 52 weeks corrected age. Thus, Lauritzen et al. (2001) concluded that four randomized studies showed positive effects of dietary DHA on preterm infant visual development. Study results indicated that DHA could affect visual development through photoreceptor function and perhaps also through nerve impulse transmission.

      Term infants. The authors state that the results regarding term infants are less conclusive than the studies in preterm infants. They cite six reviews published in 1998 and 1999 that conclude that study results are inconsistent and that there is not sufficient evidence to recommend supplementation of term infant formulas with LC PUFA. These 1998-1999 reviews agreed that sample size was an important factor in the inconclusive results, and recommended further and larger randomized trials. Other factors cited in one or more of these reviews were infant age at testing, different methods to test functional outcomes and study duration. Two other reviews also discussed the ALA content of the test formulas and concluded that term infant formulas should contain ALA as two percent of fatty acids and the n-6 to n-3 ratio should be 10 or less.

      In order to elucidate the factors involved in the inconsistent results in studies of term infants, Lauritzen and coauthors presented three tables on infant visual acuity studies:

      • Observational studies in breastfed and formula fed term infants
      • Intervention studies in term infants with and without DHA in formulas
      • Intervention studies in term and preterm infants with high and low ALA in formulas

      Each table gave the infant age at testing, sample size per group, visual acuity testing method, fatty acid composition of formula or breast milk and relative visual acuity of the breastfed or supplemented formula group. If the infants were tested at more than one age, the tables showed the results for four months of age or the age nearest to four months of age. Relative visual acuity was calculated as the threshold visual acuity, in cycles per degree, for the experimental group divided by the control group. Each table was subdivided into the studies that found an effect of breastfeeding or supplemented formula and studies that found no effect. There were nine observational (breastfeeding) studies with no effect and seven with effect. There were four DHA supplementation studies with no effect and two with effect. The four ALA intervention studies showed no effect. To help identify possible systematic differences in study design between positive studies and those finding no effect, the tables gave "crude averages" for the tabulated numerical study parameters for the studies subdivided by effect. The authors caution that, "This crude approach should be distinguished from a formal meta-analysis, which we are not attempting." For the positive studies, on average, the breast fed infants had about 60 percent better visual acuity than the control infants and the DHA supplemented infants had about 40 percent better acuity. In the studies showing no effect, the average difference in visual acuity was about zero.

      The authors then reviewed the tabulated study parameters subdivided by study effect.

      • Sample size. It was previously suggested that, if the effect size for DHA effect in term infants is smaller than for preterm infants, a larger sample size may be needed to show an effect in term infants. However, in these tables, the studies showing no effect were, on average, larger than the studies finding an effect. (Average infants per group were 39 versus 17 in observational studies and 27 versus 20 in DHA supplement studies.) The largest intervention trial, with 49 per group, found no effect (Auestad et al., 1997), although other sources of variation in that trial were previously suggested.
      • Infant age at testing and possible transient effect. The tables were focused on results at four months of age, or as near as possible to four months of age, and did not address this factor directly. The authors noted that, similar to the preterm studies, the study of Carlson et al. (1996#) found an effect at two months of age but no effect at four months and older, for both breastfed and DHA supplemented term infants. In the two positive studies of DHA supplementation, the supplemented and breastfed infants had better visual acuity than control infants at four months of age, but there was no effect at seven months (Birch et al., 1998) or 12 months (Makrides et al., 1995#). These results suggest that for the older control infants, the production of DHA from dietary ALA eventually led to brain levels of DHA that supported optimal visual function. This might explain the lack of effect of breastfeeding on visual acuity in two observational studies that tested only age seven or nine months of age. The authors note that possible long-term effects of a slow visual development are hard to predict.
      • Methods of visual acuity assessment. The tabulation suggests that this factor is important for the results. Of the positive studies, six of the seven observational studies and both DHA supplementation studies used transient or sweep VEP methods. In comparison, of the studies finding no effect, only three of the nine observational studies and three of the four DHA supplementation studies used VEP methods. The Teller acuity card method (also called forced choice preferential looking) is a behavioral method and is more subjective and perhaps not as sensitive as electrophysiological methods such as VEP. In one study that used both methods, a significant difference between experimental and control groups was found using sweep VEP but not using Teller acuity cards (Birch 1998).
      • Infant age at start and duration of supplementation period. The available evidence did not seem to support importance of these factors regarding the inconclusiveness of the studies. In observational studies, the duration of breastfeeding in the control formula group was 0.7 weeks in four no-effect studies, very similar to 0.6 weeks in three positive studies. The remaining observational studies did not provide this information. In the intervention studies, the test formulas were initiated in the first week of life except for one no-effect study in which the intervention began at 24 days of life (Jørgensen et al., 1998#). In two of the four no-effect intervention trials, the test formulas were given for a full year (although not exclusively), but in one of the two positive trials the test formulas were given for only the first 17 weeks of life.
      • Differences in n-3 fatty acid dose. The authors stated that there would likely be a dose-response relationship in any effect of n-3 fatty acid intake on visual function in human infants. Thus, a larger effect would be observed for a greater difference in n-3 intake between the experimental and control groups. However, in general this had not been addressed in the available reviews.
        • Observational studies. In the observational studies, the no-effect studies had a higher level of ALA in the control formulas (average, 2.3 percent of fatty acids) than did the studies that found better visual acuity for breastfed infants (1.4 percent ALA in control formulas). The ratio of n-6 to n-3 fatty acids was fairly similar in the no effect and positive studies. In the observational studies that reported the breast milk composition, there was a tendency for higher DHA breast milk content in the positive studies (average, 0.31 percent of fatty acids) compared with the no effect studies (0.21 percent of fatty acids).
        • ALA intervention studies. Three term infant intervention studies found no effect on visual function when comparing formulas with low versus high ALA levels.
        • DHA intervention studies. In the intervention studies, the ALA content of control formulas was fairly similar in both positive and no effect studies. However, the two positive studies had slightly higher DHA content of test formulas (average, 0.35 percent of fatty acids) compared with the four no-effect studies (average, 0.25 percent). In order to account for both the ALA and DHA content of the control and test formulas, the authors developed a DHA Equivalent Intake, based on the DHA content plus the ALA content divided by a bioequivalence factor:

          DHA Equivalent Intake: A bioequivalence factor of 10 was assumed for the incorporation of dietary ALA into DHA in the brain. This was based on studies in primates that suggested a factor of 15 and studies in adult humans that indicated a factor of seven. Using an intermediate value between these two estimates, the authors assumed that each gram of dietary ALA provides for the accumulation of one tenth of a gram of DHA in the brain. The DHA equivalent intake, in percent of fatty acids in the formula, was converted to milligrams per day of DHA equivalent by assuming that human milk or formula contains 40 grams of fat per liter, that 92.5 percent of the fat is fatty acids, and that the infant consumes about 750 milliliters of milk per day. The DHA equivalent intake was tabulated for each experimental and control group, together with the difference between the two groups.

          The tables show that the positive observational studies had higher DHA equivalent intake in the test groups (average, 115 mg/d versus 82 mg/d) and lower DHA equivalent intake in the control groups (average, 37 mg/d versus 64 mg/d) than did the no-effect studies. Thus, the average DHA equivalent difference between test and control groups was 77 mg/d in the positive studies and only 16 mg/d in the no-effect studies. The tables also show that the 2 positive intervention studies had similar DHA equivalent intake in the control groups (average, 43 mg/d versus 49 mg/d) but higher DHA equivalent intake in the test groups (average, 141 mg/d versus 113 mg/d) than did the four no-effect studies. Thus, the average DHA equivalent difference between test and control groups was 99 mg/d in the positive studies (98 and 99, respectively) and only 64 mg/d in the no effect studies (22, 56, 89 and 88, respectively). The authors concluded that the greater DHA equivalent differences in the positive than in the no effect studies "could be important explanatory factors for the inconsistency of the results of the term infant studies."

      Variations in n-3 fatty acid intake and visual function within breastfed term infants. The authors summarized four studies that looked at visual function in relation to breast milk DHA level among breastfed infants.

      • In one study of breastfed infants, red blood cell DHA levels at two months of age were positively associated with visual acuity using Teller acuity cards at 12 months but not at two, four and six months (Innis et al., 2000#)
      • In a study by the authors' group, the sweep VEP visual acuity of breast fed infants was positively associated with the DHA content of breast milk at four months of age (Jorgenson et al., 2001).
      • In a supplementation study of lactating women, there was no effect of DHA supplement level on VEP visual acuity in small groups of infants at three to four months of age (Gibson et al., 1997). However, this study found a significant effect on cognitive development at 12 months.
      • In another supplementation study of lactating women, there was no effect of DHA from marine oil supplements on Teller card or sweep VEP acuity (Jensen et al., 1999#).

      Conclusions on the effect of dietary n-3 fatty acids on infant vision.

      • Animal studies. "…retinal function is affected in mammals deprived of n-3 fatty acids."
      • Preterm infants. Retinal function is also affected in preterm infants, "who do not receive a dietary supply of 22:6n-3 [DHA] to support the rapid accretion in the brain and retina."
      • Term infants. The authors suggested that the inconsistencies among the studies of term infants may be due to differences in study design, particularly methods of visual assessment and differences in n-3 fatty acid intake between experimental and control groups of infants. For example, in one of the positive intervention studies, the ALA level in test and control formulas was 1.5 to 1.6 percent of fatty acids and the n-6 to n-3 ratios were about 10 to one (Makrides et al., 1995#). The test formula also contained DHA at 0.36 percent and the DHA equivalent difference between the formulas was 98 mg/d. At 16 weeks of age, the transient VEP of the eight DHA supplemented infants was significantly greater than that of the 18 control infants with a relative visual acuity of 1.6. Lauritzen and coauthors recommend that, rather than simply recommending more and larger trials, the design of future studies should follow the example of existing positive studies, to see whether this leads to consistent results. Additionally, the authors note that, currently, the results of positive studies do not show whether infants need preformed DHA, or whether the ALA level, such as 1.5 percent in the above example, might not be sufficient for optimal visual development. Future studies should be designed to include a group with a higher ALA level (and no DHA), to examine this question in terms of DHA equivalent intake. Lastly, the authors stated that no conclusions could be drawn at present from the few studies of variation of DHA levels in human milk and infant visual acuity.
    • Section 7.2. Dietary n-3 fatty acids and mental development.

      Animal studies. The authors briefly summarized research on animal studies of effects of n-3 fatty acids on learning and cognition in animal models. The studies, mainly in rats, show that both n-3 fatty acid intake (such as ALA) and possibly also DHA intake have an effect on behavior. Similar to the situation with visual development, discussed above, the levels of n-3 fatty acid intake in the animal studies make it difficult to extrapolate the findings to infants.

      Cognitive development in infants and children.

      • Observational studies. The authors noted that non-randomized, or observational, studies of breastfeeding and cognitive development include three general study types: observational studies of breastfed infants compared with formula fed infants; studies that included a breastfed comparison group in a randomized trial of infant formula with and without DHA supplementation; and studies of mental development and DHA blood levels. Numerous studies have examined the association between breastfeeding and cognitive development in infants. A meta-analysis (Anderson et al., 1999) of 20 studies found that, after adjusting for confounding variables, the IQ of breast fed children was about 3.16 points higher than control children, corresponding to about 0.25 standard deviations. This IQ difference was stable across age of testing in childhood and adolescence. It is possible that this IQ difference is due to DHA in breast milk, but it could also be due to residual confounding. Lauritzen and coauthors tabulated nine observational studies of cognitive development and breastfeeding in term infants up to two years of age, including four studies from the Anderson et al meta-analysis. Seven of the nine studies showed positive effects of breastfeeding, consistent with the meta-analysis. In other types of studies, duration of breastfeeding in term infants was positively associated with scores on Bayley's Mental Development Index (MDI) at 12 months of age, and serum DHA level was positively associated with MDI score of preterm infants at 12 months corrected age.
      • Intervention studies. The authors tabulated six intervention studies of DHA supplementation and infant cognitive development in term infants. There were three no effect studies, all using Bayley's MDI. Of the three positive studies, two used the MDI or another global test and one used more specific tests--Fagan's look duration and Willatts' problem solving. Additionally, in two cognitive studies in preterm infants (tabulated with the preterm studies on visual acuity), Carlson's group found shorter look duration in DHA supplemented infants. In other types of studies, a supplementation study of lactating women found no effect of DHA supplement level on Bayley's MDI in small groups of infants at 12 months of age (Gibson et al., 1997). However, the MDI score was positively associated with DHA content of breast milk and infant plasma and red blood cells at three months of age. In a randomized study of preterm, tube fed infants, the infants fed banked human milk had higher MDI scores at 18 months compared with the formula fed group.
      • Influence of study design on results.

        Infant age. Six of the eight comparisons that tested infants younger than 12 month of age found a positive effect of DHA supplementation. In infants tested at 12 months of age, two comparisons found a positive effect and two found no effect. In older infants, one comparison found a positive effect at 18 months of age and three comparisons found no effect at 18 to 24 months of age. Some data suggested that differences in cognitive function might be transient, a possibility noted also for effects on visual function. This is in contrast to results in the meta-analysis of the association of cognitive function and breastfeeding, which found the effect to be stable through adolescence.

        Method of testing. The authors suggested that global tests such as the Griffith, Bayley or Brunet-Lezine scales might be too broad, including functions that are not sensitive to DHA status. Additionally, these global tests are designed to identify abnormalities rather than differences among normal infants. Specific tests such as Willatts' problem solving or Fagan's visual memory recognition may be attributable to more specific developmental domains and therefore may be more sensitive. The intervention studies using specific tests within the first year of life showed positive effects of DHA supplementation. Of the studies using global scales, three found a positive effect and three found no effect.

        Differences in n-3 fatty acid intake. On average, the three positive studies in term infants had somewhat lower ALA content in the control and test formulas than the no effect studies (1.0 versus 1.6 percent of fatty acids), while the average DHA in the test formulas and the average difference in DHA equivalents were similar in both groups of studies. In particular, in two of the positive studies the ALA level was only 0.7 percent of fatty acids, providing a marginal supply of n-3 fatty acids for the control infants.

      • Summary of studies of n-3 fatty acids and human cognitive development. The authors stated that three lines of evidence suggest an effect of early n-3 fatty acid intake on cognitive development. There is observational evidence that shows breastfeeding associated with better IQ during later childhood, but it has not been proven whether this association is caused by n-3 fatty acid content of human milk. A positive effect of breastfeeding was also found in a majority of intervention studies that included a comparison group of breastfed infants. Again, this observational evidence does not prove that the effect is caused by n-3 fatty acid intake. Finally, there is evidence from three randomized intervention studies in term infants that showed a significant positive effect of DHA supplemented formula. However, the evidence is not consistent because three other intervention studies found no effect.
    •  Section 7.4. Adverse effects of increased dietary n-3 fatty acid intake. The authors concluded that, for lactating women, observed changes in fatty acid composition of breast milk do not raise concern about increased intake of fish or fish oil, even if EPA intake is high. Based on the intervention trials, the authors conclude that it should be safe to add DHA or increase the level of ALA in infant formulas. In studies of term infants given formulas supplemented with DHA, there were no adverse effects on infant growth or morbidity, especially if the formulas were also supplemented with n-6 arachidonic acid (AA).
  • Section 8. Cellular mechanisms and functional effects in infants. In commenting on long-term versus transient functional effects of n-3 fatty acids in infants, the authors noted that two observational studies of three or 3.5 year old children found better stereoacuity (depth perception) in breastfed compared with formula fed infants. In one of these studies, the breastfed children also had better letter-matching ability (Birch et al., 1993) and in the other study maternal fish consumption during pregnancy was independently associated with the children's stereoacuity (Williams et al., 2001).
  • Section 9. Infant requirements and sensitivity to a deficient n-3 fatty acid supply.
    • Section 9.1. Critical periods of development (preterm or term infants). The authors state that the scientific evidence does not support the conclusion that preterm infants are more immature than term infants in their ability to convert the precursor ALA to DHA. However, the authors estimate that the preterm infant born at an average of 10 weeks before term would have missed the opportunity for 10 weeks of DHA brain accretion in utero, corresponding to DHA content of about two months of breast milk consumption, sufficient to meet the need for brain DHA consumption during the first 12 months of life. Thus, the preterm infant would be theoretically more susceptible to suboptimum supply of dietary DHA. Additionally, several of the preterm infant trials were early studies using test formulas based on corn oil and were low in n-3 ALA. Thus the positive result may have been due to the low n-3 content of the control formula rather than to specificity of the visual acuity effect on preterm rather than term infants. Also, in the preterm infant intervention studies, the average difference in DHA equivalent intake between control and supplemented infants was higher than the average difference in the term infant studies. The authors concluded that the evidence does not support that a DHA effect on visual acuity is specific for preterm infants. Rather, term infants have greater DHA stores at birth and demonstration of a DHA effect would require greater, not less, difference in DHA equivalent intake between control and supplemented infants.
    • Section 9.2. The n-3 fatty acid requirement of infants. The authors plotted the increase in functional outcomes for DHA supplemented infants relative to control infants in various randomized trials, versus the DHA equivalent intake in the respective control group. Trials were grouped according to the dose increase for supplemented compared with control DHA equivalent intake (from 1.5 fold through greater than 3.7 fold increase). Regression lines were plotted for each group of trials. The regression lines crossed the "no effect" threshold in the range of DHA equivalent intake between 70 and 110 mg DHA equivalent intake per day. The authors stated that this plateau for dose-response, 70 to 110 mg/day in DHA equivalents, approximates the n-3 fatty acid needs of infants. Assuming that human milk has an ALA content of one percent of fatty acids, a human milk content of 0.33 percent of fatty acids as DHA would provide approximately 120 mg/day of DHA equivalents. The authors noted that if an infant formula contained no DHA, the formula would need to contain ALA at 4.3 percent of fatty acids in order to supply 120 mg/day of DHA equivalents. However, the authors stated that trials with suitable formula fatty acid composition to test the effects of varying ALA content on infant neurodevelopment, including in the absence of DHA, have not been conducted, and they recommended additional research.
  • Section 10. Summary. The authors concluded:
    "When the employed n-3 fatty acid dose is taken into account the evidence do not indicate that a visual effect of 22:6n-3 [DHA] supplementation is specific to formula-fed preterm infants, as opposed to term infants. Furthermore, our presentation of the results indicate that an increase in 18:3n-3 [ALA] intake also affects the functional development of infants, but that no trial yet has examined a large enough increase in the 18:3n-3 [ALA] fatty acid intake above 2 FA% in a large enough group of infants to prove this. Regression analysis indicate that differences in the n-3 fatty acid intake to some extent explain what have been regarded as inconclusive results in the term infant intervention trial that have investigated the functional effects of n-3 supplementation. Furthermore, many of the studies have not had sufficient power, and some of the studies have employed inappropriate methods to assess the visual acuity and cognitive abilities of infants."
  • Section 11. Future Research. The authors gave specific recommendations for a trial of test formula high in ALA compared with a DHA containing formula and a breast fed group with high maternal DHA intake, with neurodevelopment outcomes including visual acuity by sweep VEP at two, four, and six months of age plus specific cognitive tests. The authors stated that it would be also desirable to investigate possible functional differences later in life resulting from n-3 fatty acid status in infancy. Additionally, it would be interesting to compare the functional effects of dietary interventions during pregnancy and during later infancy with dietary interventions in the first months of infancy.
Simmer (2001)

Simmer, K. (2001). Long chain polyunsaturated fatty acid supplementation in infants born at term. Cochrane Database of Systematic Reviews, 4, CD000376.

Developmental outcomes: Vision and cognitive in term infants (systematic review and meta-analysis).

The Cochrane Collaborative published a systematic review and meta-analysis by Simmer (2001) in order to assess whether supplementation of infant formula with LC PUFA is beneficial and safe for term infants. The outcomes of interest were infant visual function, development and growth. The systematic review identified ten randomized studies of formula supplemented with LC PUFA and with clinical endpoints. One of the studies was excluded because supplementation did not begin until three weeks of age (Jørgensen et al., 1998#). The included trials had at least three months of follow-up. Eight of the nine included studies were considered of high quality based on completeness of follow-up, method of randomization and blinding of intervention and measurement. For the ninth study (Clausen et al., 1996#), insufficient information was available to assess quality. The authors noted that endpoints in the studies were variable, making combinations of studies of limited use. In several studies, there was more than one test group, with one test group receiving formula with DHA supplement only and one receiving formula with DHA + AA supplement, as well as a control group. For these studies, this review included only the comparison using the DHA + AA supplemented formula.

1) Visual acuity. For the purposes of the present report, it is useful to compare the studies included in the systematic review by Simmer (2001) and in the review by Lauritzen et al. (2001) discussed above. Lauritzen and coauthors tabulated six randomized studies of DHA supplemented formula and visual acuity in term infant, measured at around four months of age, classifying four of the studies as showing no effect of DHA supplementation and two as positive studies. Simmer (2001) excluded one of these no effect studies because the test formulas did not begin until three weeks of age (Jørgensen et al., 1998#) and included an additional no effect study that was reported in proceedings of a conference (Clausen et al., 1996#). Additionally, for the positive study of Birch and coauthors (1998), the visual acuity results were presented in figures and graphs rather than numerically. Simmer (2001) stated that she could not obtain the numerical results from the original authors and therefore did not include these positive visual acuity results in the systematic review results.

In this review, visual acuity was reported as log MAR (minimum angle of resolution) or as log cycles/degree. The author stated that the use of log values prevented the use of meta-analysis for the visual acuity outcomes. Results of the comparisons between supplemented and control infants were shown in separate figures for each age of testing and for each testing method: steady state VEP (in log MAR), sweep VEP (in log cycles/degree) and Teller acuity cards (in log cycles/degree). For steady state VEP, there were two studies at four months and at seven-eight months. For sweep VEP, there was one study at two, four, six and 12 months. For Teller acuity cards, there were two studies at two, four and six months and a different study at three months. One study showed a positive effect used steady-state VEP at four and seven months (Makrides et al., 1995#), and another study showed a positive effect using a behavioral method at two months of age. As mentioned above, meta-analyses were not performed because the data were in logarithmic form. The positive study of Birch et al. (1998) was not included in the results in the figures because of the lack of available numerical data, but the text noted the positive result of this study using sweep VEP at six weeks and at four and 12 months but not at six months.

2) Cognitive development. The review by Lauritzen et al. (2001), discussed above, tabulated six intervention studies of cognitive development in term infants and DHA supplemented formula (three no-effect studies and three positive studies). Simmer and coauthors included these six studies plus the study by Clausen et al., (1996#), reported in conference proceedings, which found a positive effect. As with visual acuity, results of the cognitive development comparisons between supplemented and control infants were shown in separate figures for each age of testing and for each testing method. For the Fagan test there was one study at nine months. For the Brunet-Lezine Development Quotient, there was one study at four, 12 and 24 months. For the Knobloch, Passamanick and Sherrards test, there was one study at nine months. For the Bayley score (both MDI and PDI presented separately) there were two studies at one year, two different studies at 18 months and one study at two years (a follow-up of one of the one-year tests). The positive results included the Fagan test at nine months (Clausen et al., 1996#), the Brunet-Lezine test at four months (Agostini et al., 1995#), and the Bayley MDI and PDI at 18 months (Birch et al., 1998). For the Bayley scores at 18 months, the meta-analysis combined the positive results of Birch et al. (1998) with the larger study of Lucas et al., (1999#). For the two studies, the weighted mean difference in MDI scores was 1.85 (95 percent confidence interval, -1.05 to 4.76) and in PDI scores was 1.59 (95 percent confidence interval, -0.27 to 3.44), and the positive effect was not statistically significant.

Discussed in the text but not in the figures, was a study finding no significant difference in language development using the Macarthur Communicative Development Inventory at 14 months for DHA + AA supplemented infants compared with controls (Scott et al., 1998), but a negative correlation between plasma and red blood cell DHA levels at four months and vocabulary production and comprehension at 14 months, for infants from two formula groups combined: control formula, DHA supplement alone and DHA + AA supplement. Also discussed in the text were the positive results of a means-end problem solving test at 10 months (Willatts et al., 1998a).

3) Growth. The review also compiles the results of weight, length and head circumference measurements from the included studies. Overall, there were no notable differences reported between control infants and those fed DHA supplemented formula.

4) Discussion and Conclusions. The authors discussed the factors in the included studies and their possible relationship to positive or no effect results. They noted that, although electrophysiological measurements have the potential for more discrimination of small effects on visual acuity, the two largest studies found no effect of DHA supplementation using VEP measurement (Makrides 1996#; Auestad 1997). Regarding cognitive development, positive effects were found at four months (Agostini et al., 1995#) and nine months (Clausen et al., 1996#), but follow-up measurements found no effect at 12 and 24 months (Agostini et al., 1997). The authors observed that the follow-up results indicate that the DHA supplement conferred no significant benefit. Considering the positive results with the Fagan test (Clausen et al., 1996#) and the problem solving test (Willatts et al., 1998a), the authors suggested that, although no effect of DHA supplementation on global development has been demonstrated, it remains possible that DHA may improve attention and information processing. The authors also noted the various levels of ALA and DHA provided in the test and control formulas in the various studies. Overall, they concluded:

Implications for practice

"Data from randomized trials do not support the need for routine supplementation of formula for term infants with LCPUFA."

Implications for research

"There is little consistency in methodology of fatty acid measurement and neurodevelopmental assessment in published randomized trials of LCPUFA supplementation of formula. The intervention (composition of LCPUFA supplement) has also varied from trial to trial, as has the composition of the control formula, particularly the ALA content. If a benefit exists with LCPUFA supplementation, it is likely to be small and may be only detected with assessment tools targeted at specific processes such as information processing. LCPUFA supplementation is becoming routine and is increasing the cost of formula. Longer, larger trials are still required to prove any benefit on VEP acuity and attention and information processing."

Uauy et al. (2003)

Uauy, R., Hoffman, D.R., Mena, P., Llanos, A., Birch, E.E. (2003, October). Term infant studies of DHA and ARA supplementation on neurodevelopment: results of randomized controlled trials. Journal of Pediatrics, 143(4 Suppl), S17-25.

Developmental outcomes: Neurodevelopment in term infants, especially the development of visual acuity (meta-regression of visual acuity).

The authors reviewed 14 controlled trials of DHA supplemented formula in term infants and functional assessment of visual and other measures of neurodevelopment. The authors also conducted a meta-regression analysis to estimate the possible dose-response relationship between DHA intake and visual acuity in four month old term infants. The review briefly summarized the 14 controlled trials and also tabulated the characteristics and results of these studies. Most of the trials had limited sample size, but two were considered large controlled studies. Of these, the study of Lucas et al. (1999#), with over 150 infants each in the test and control groups, found no effect of DHA supplementation on Bayley mental and psychomotor development at 18 months of age. Uauy and coauthors noted that this study also found no effect of breastfeeding on cognitive development and that the mean MDI scores for all groups were four to six points below the norm. Thus, the study infants may have represented a disadvantaged subgroup in which environmental factors limited infant neurodevelopment. The study of Auestad et al. (2001), with about 80 infants each in test and control groups, found no effect of DHA supplementation on Teller card visual acuity at two through 12 months or on Bayley mental and psychomotor scores at 12 months. This study also found no effect of breastfeeding on developmental outcomes.

The authors also summarized three studies involving DHA levels in breast milk. One study supplemented mothers with DHA and studied the relationships between maternal DHA intake, breast milk DHA and infant DHA blood levels. There was no association between breast milk DHA and transient VEP acuity. The Bayley MDI at 12 months of age was correlated to breast milk DHA (Gibson et al., 1997). Two observational studies found an association between breast milk DHA levels and visual acuity at two and 12 months of age (Innis et al., 2001) and at four months of age (Jørgensen et al., 2001).

Meta-regression. In the meta-regression, the authors included seven controlled trials of DHA supplementation and visual acuity in term infants at four months of age. These included the six controlled trials tabulated in the review by Lauritzen et al. (2001), plus the more recent trial by Auestad and coauthors (2001). Following the approach suggested by Lauritzen et al. (2001), the authors estimated the DHA equivalent intake of infants consuming the test and control formulas in each comparison in the seven trials. Three possible bioequivalence factors were used to estimate the contribution of ALA to DHA equivalents: a 10 percent conversion factor, as assumed by Lauritzen et al. (2001), and lower conversion factors of five percent and one percent. Additionally, for formulas that contained EPA, these authors used a conversion factor of 18 percent for EPA to provide DHA equivalents. The remaining assumptions for estimation of DHA equivalent intake, in mg per day, were the same as those used by Lauritzen et al. (2001): formula containing 40 grams of lipid per liter; lipid triglycerides containing 92.5 percent fatty acids; and infants consuming 0.75 liters of formula per day. In studies where there were two DHA test groups, with and without n-6 arachidonic acid (AA) added to the formula, both comparisons were retained separately for the meta-analysis. Thus there were 12 test groups from the seven studies for inclusion in the analysis. Visual acuity measurements from Teller acuity cards or VEP measurements were converted from original units (such as cycles per second or Snellen scores) to logMAR (MAR = minimum angle of resolution) if needed, and expressed as relative visual acuity, that is the ratio of the acuity of the test group to that of the control group. This allowed the inclusion of studies using either behavioral (Teller card) or electrophysiological (VEP) results in the analysis, even if the absolute visual acuity measurements were different using the two methods. When both measurements were reported, the VEP result was included in the analysis.

The review tabulated the data for the meta regression of the 12 comparisons from the seven studies: sample size, formula levels of fatty acids (DHA, EPA, n-6 linoleic acid, ALA), DHA equivalent intake using three possible conversion factors for ALA to DHA, visual acuity (in log MAR) for each group and relative visual acuity response for each comparison. Four scatter plots and linear regression lines for relative visual acuity and DHA intake (in percent of fatty acids) or DHA equivalent (in mg/day) using three conversion factors were shown in a figure. The slopes and intercepts for the equations for the linear regression lines and the r-squared and p values, as reported in the figure caption, are summarized in Table B-3 in this section. (For convenience, in Table B-3 the slope based on DHA intake alone is also converted from percent of fatty acids to mg/day, to permit comparison with the slopes based on DHA equivalents.) Note that a lower minimum angle of resolution indicates better visual acuity, therefore the negative slopes show better visual acuity with increased intake of DHA or DHA equivalents.

Table B-3 shows that the magnitude of the negative slope, or predicted change in relative visual acuity per mg/day of DHA or DHA equivalent, increased with greater conversion factor of ALA to DHA. The slope was -0.0024 per mg DHA/day and -0.0039 per mg DHA equivalent/day with 10 percent ALA to DHA conversion. The r squared also increased with greater conversion factor and the statistical significance increased, from 0.395 (p = 0.03), to 0.68 (p = 0.001). The standard deviations or confidence intervals and statistical significance of the slope or intercept parameters were not stated in the review. The regression equations were reported for the unweighted analysis. When the data in the analysis were weighted by sample size, the r squared values were slightly lower, and the statistical significance was slightly decreased. For the conversion factor of 10 percent ALA to DHA, the weighted r squared was 0.58 (p = 0.004), compared with 0.68 (0.001) for the unweighted analysis. The slope and intercepts for the weighted regression equations were not given. The authors noted that the results of the meta-regression suggest that about 39 percent to 68 percent of the variability in relative visual acuity among these comparisons was explained by the DHA or DHA equivalent intake of the test formula. The DHA or DHA equivalent intake in the regression analysis was the intake of the test formula for each comparison. The authors stated that the regression analysis was also conducted using the difference in DHA or DHA equivalent intake between the test and control group. The results were not shown, and the authors stated that the results of this analysis were less significant than for the reported analysis.

The authors summarized the results of their studies regarding possible continued benefit of DHA intake by infants who may be weaned from breastfeeding. In a study of breastfed infants weaned to formula at six weeks of age, the group receiving DHA supplemented formula had better VEP acuity than those weaned to control formula when tested at 17, 26 and 52 weeks of age and had better stereoacuity at 17 weeks of age (Birch et al., 2002). In another study, infants weaned at four months of age to DHA supplemented formula had better VEP acuity than those weaned to control formula when tested at six months of age. At 12 months of age, those weaned to DHA supplemented formula at four or six months of age had better VEP acuity than those weaned to control formula by about 0.1 log MAR, corresponding to about one line on an eye chart (Hoffman et al., 2003).

The authors concluded that the results of the meta regression show a significant relationship between DHA dose, expressed as DHA equivalents, and effect on visual acuity at four months of age. The authors also concluded that the weaning studies show a need for LCPUFA in the infant's diet until at least 12 months of age. Their recommendation for further research was for a large dose-response study of visual acuity in the first year of life and of long term effects on cognitive development. Additionally, they stated that the optimal DHA content of breast milk remains to be determined.

Simmer and Patole (2004)

Simmer, K. and Patole, S. (2004). Long chain polyunsaturated fatty acid supplementation in preterm infants. Cochrane Database of Systematic Reviews, 1, CD000375.

Update of:

Simmer, K. (2000#). Long chain polyunsaturated fatty acid supplementation in preterm infants. Cochrane Database of Systematic Reviews, 2, CD000375.

Developmental outcomes: Vision and cognitive in preterm infants (systematic review and meta-analysis).

The Cochrane Collaborative published a systematic review and meta-analysis by Simmer and Patole (2004) in order to assess whether supplementation of infant formula with LC PUFA is beneficial and safe for preterm infants. This was an update of a Cochrane review by Simmer, published in 2000. The outcomes of interest were infant visual function, development and growth. The systematic review identified 11 randomized studies of formula supplemented with LC PUFA and with clinical endpoints. Trials were included if they had at least six weeks follow-up and involved enterally fed (rather than tube fed) preterm infants (less than 37 weeks gestation). Nine of the 11 included studies were considered of high quality based on completeness of follow-up, method of randomization and blinding of intervention and measurement. Two of the studies were not considered of high quality because of problems with the assessment methodology (Carlson 1996#; Fadella 1996#).

As in the Cochrane review of term infants discussed above (Simmer 2001), when studies included more than one test group (with one test group receiving formula with DHA supplement only and one receiving formula with DHA + AA supplement), this review included only the comparison using the DHA + AA supplemented formula. Additionally, if studies included more than one DHA + AA test formula, this review included the comparison using a fish/fungal fatty acid source rather than an egg triglyceride/fish oil source, because microbial (fungal) oils are more similar to human milk than is egg. If studies used more than one control group, this review included the comparison with the control formula having a ratio of linoleic acid (n-6) to ALA (n-3) most similar to human milk.

1) Visual acuity. In the review by Lauritzen et al. (2001), discussed above, the authors tabulated four randomized studies of DHA supplemented formula and visual acuity in preterm infants. This review added the studies of Hansen and coauthors (1997#), published in abstract form, and van Wezel et al. (2002#) and Innis et al. (2002#). Additionally, for the positive studies of Birch et al. (1992#) and Carlson et al. (1993#), the visual acuity results were presented in figures and graphs rather than numerically. Simmer and Patole stated that they could not obtain the numerical results from the original authors and therefore did not include these positive visual acuity results in their display of results, but they do mention them in the text. In this review, visual acuity was reported as log cycles/degree for behavioral methods of visual acuity (Teller cards). The author stated that the use of log values prevented the use of meta-analysis for the visual acuity outcomes.

Results of the comparisons between supplemented and control infants were shown in separate figures for each age of testing and for each testing method: For visual acuity using Teller cards, there were results from one study at term, three at adjusted age two months, three at adjusted age four months, two at adjusted age six months, one at adjusted age nine months and two at adjusted age 12 months. (Results were also shown for a group of infants with bronchopulmonary dysplaysia (Carlson et al., 1996#), which are beyond the scope of the current report, which deals with healthy infants.) One study (Carlson et al., 1996#) found a positive effect of DHA supplementation at two months adjusted age, but no difference at term or at four, six, nine or 12 months adjusted age for healthy infants. No effect was seen in any of the other studies shown. As noted above, the results of Birch et al. (1992#) and Carlson et al. (1993#) were not included in the display in the figures because the numerical results were not available. Simmer and Patole state in the text that there was better visual acuity at two and four months adjusted age but not at six, nine and 12 months adjusted age using Teller cards in Carlson et al. (1993#) and at four months adjusted age using both Teller cards and VEP in Birch et al. (1992#). Other results regarding visual development were better retinal function by electroretinogram with DHA supplementation at 36 weeks postconceptual age but no difference at four months adjusted age (post-term) (Uauy et al., 1990#) and no difference in electroretinogram amplitude with DHA supplementation at four months post term (Faldella et al., 1996#). However, Simmer and Patole note several methodological problems with the ERG method of Faldella et al. (1996#).

3) Cognitive development. In the review by Lauritzen et al. (2001), discussed above, the authors tabulated two intervention studies of DHA supplemented formula and cognitive development in preterm infants, both from the Carlson group. This review added the studies of O'Connor et al. (2001) and van Wezel et al. (2002#). Results of the comparisons between supplemented and control infants were shown in separate figures for each age of testing and for each testing method: The two Carlson studies used the Fagan test at 12 months adjusted age as did one Carlson study and the O'Connor et al study at nine months adjusted age. The Bayley Scales (MDI and PDI) at 12 months adjusted age were used by three studies: Carlson et al. (1994#), O'Connor et al. (2001) and van Wezel et al. (2002#). In the Fagan test at 12 months adjusted age, novelty preference was lower in the DHA supplemented groups, potentially indicating poorer cognitive development. However, in the supplemented groups the number of looks was higher and the duration of each look was shorter, which the Carlson group authors interpreted as indicating better cognition. No differences were found in the studies using the Fagan test at nine months adjusted age. Regarding the Bayley scores, there was a trend towards lower scores for the DHA supplemented groups in the two smaller studies, and a slight trend towards higher scores in the larger study of O'Connor and coauthors. The meta- analyses of the three studies showed a slightly lower score for the supplemented infants that was not statistically significant: the weighted mean difference for the Bayley MDI was -0.45 (95 percent confidence interval, -3.05 to 2.51) and for the Bayley PDI was -1.69 (95 percent confidence interval, -4.94 to 1.55).

4) Growth. The authors stated that LCPUFA supplementation does not appear to negatively affect growth of preterm infants. Among studies reviewed, supplemented infants grew less well in the studies of Carlson (1992#) and Carlson (1996#), but these trials supplemented with DHA without AA. Later studies that supplemented with DHA plus AA usually found no effect on growth. The meta-analysis of five studies showed supplemented infants had increased weight and length at two months adjusted age. An exception was the study of Fewtrell (2002#), which showed slightly lower weight and length in supplemented infants at 18 corrected age.

5) Discussion and Conclusions.

Implications for practice.

"The data available do not support the suggestion that supplementation of formula benefits the development of preterm infants. Providing an optimized ratio of linoleic to alpha linolenic acid [ALA] (the precursors of LCPUFA) and sufficient alpha linolenic acid for infants to synthesize their own docosahexaenoic acid (DHA), may be adequate. No harm has been demonstrated with respect to growth when formula is supplemented with LCPUFA (DHA and AA)."

Implications for research.

"The methodology as well as the composition of the LCPUFA supplemented and the control formulas have shown little consistency in the trials conducted so far. These data may be useful in deciding the best dose and source of LCPUFA supplement to use in future studies, preferably including more immature preterm infants who are at risk of developmental delay."

Lewin et al. (2005) (AHRQ)

Lewin GA, Schachter HM, Yuen D, Merchant P, Mamaladze V, Tsertsvadze A, et al. Effects of Omega-3 Fatty Acids on Child and Maternal Health. Evidence Report/Technology Assessment No. 118. (Prepared by the University of Ottawa Evidence-based Practice Center, under Contract No. 290-02-0021.) AHRQ Publication No. 05-E025-2. Rockville, MD: Agency for Healthcare Research and Quality. August 2005.

Developmental outcomes: Vision and cognitive in term and preterm infants (specific meta-analyses).

The previous section of this document, Recent Reports and Recommendations, summarizes the key research questions, systematic review methodology and general conclusions of the AHRQ review. As described previously, the AHRQ review sought RCTs, where available, to address the research questions regarding efficacy or effectiveness of n-3 fatty acids. Where possible, the AHRQ review also conducted meta-analyses of RCT evidence of efficacy/effectiveness. In conducting meta-analyses, preference was given to RCTs in which clinical outcomes were evaluated using validated, currently accepted measures (such as the Bayley's scales for development.) The authors stated,

"The inclusion criteria to conduct meta-analysis were:

  1. at least two RCTs;
  2. same population characteristics (mean age, health status, gender);
  3. same co-interventions;
  4. same intervention based on the type of omega-3 FA supplemented (DHA+AA vs. DHA vs. DHA+EPA, etc.) regardless of the daily dose in the child population;
  5. same comparator based on source of placebo (e.g., olive oil, unsupplemented formula);
  6. outcomes relevant to respond to the key-questions."

The authors also stated that insufficient numbers of studies with comparable characteristics (according to the above criteria) prevented the conduct of many planned meta-analyses, virtually all of the planned subgroup analyses, and planned sensitivity analyses of study quality and publication bias.

Table B-4 shows the numbers of unique studies identified by the AHRQ review that addressed each key research question involving neurodevelopmental outcomes in children: visual, neurological or cognitive. (Some studies addressed more than one key research question.) Where possible, the authors conducted meta-analyses of the RCTs of n-3 fatty acid supplemented infant formula in term or preterm infants. Results of the meta-analyses for visual outcomes are summarized in Tables B-5 and B-6, and for neurological and cognitive outcomes in Tables B-7 and B-8. As shown in the tables, the AHRQ review analyzes the trials testing DHA containing formulas compared with controls separately from the trials testing DHA plus AA in formulas against controls. Trials were also analyzed separately by the age of the infant. Additionally, trials using behavioral or electrophysiological measurements of visual acuity were analyzed separately from each other.

Among the nine studies of visual acuity in preterm infants, there were one, two or three studies available for possible meta-analysis at various combinations of infant age, visual acuity method and formula type (DHA or DHA plus AA) (Table B-5). The individual study or meta-analysis result for each set of conditions showed a positive effect of n-3 supplemented formula on visual acuity, but most were not statistically significant. However, single studies at corrected ages zero and six months for electrophysiological tests of DHA plus AA showed statistically significant positive effects on visual acuity. Among the 13 studies of visual acuity in term infants, the individual study or meta-analysis results for tests of DHA containing formula had mixed results, and none were statistically significant (Table B-5). For tests of DHA plus AA in term infants, most individual study or meta-analysis results were mixed and not statistically significant. However, meta-analyses for three sets of conditions showed statistically significant or near significant positive effects of DHA plus AA on visual acuity: behavioral measures at two months of age and electrophysiological measures at four months (near significant) and 12 months of age (Tables B-5 and B-6). Table B-6 shows the pooled differences in visual acuity and 95 percent confidence intervals for these three meta-analyses.

For neurological and cognitive outcomes, using Bayley's PDI and Bayley's MDI, respectively, in preterm infants, meta-analyses could not be conducted (Table B-7). Among the five available studies, more than one study was available only at corrected ages 12 and 18 months. But of the two studies available at corrected age 12 months, one fed the test formula until 6 months corrected age and the other until 12 months corrected age. Therefore, the AHRQ review authors did not combine the two studies for meta-analysis. Of the seven available studies for neurological and cognitive outcomes in term infants, there were three studies available at age 12 months and the meta-analyses were negative but not statistically significant (Tables B-7 and B-8).

(Notes on methods: In general, the behavioral visual acuity results in individual studies were reported in cycles per degree (cy/degree) of visual angle, where a cycle is the number of high contrast (dark/light) grating pattern repeats. The electrophysiologic visual acuity results in individual studies were reported as minimal angle of resolution (MAR), where lower MAR values indicate better visual acuity (the opposite of cycles per degree). Differences in visual acuity are often measured in octaves, where one octave is a two-fold change (doubling or halving) of the visual stimulus frequency (or a thinning of the width of the individual stimulus lines by one half). For the systematic review, study results were reported in cy/degree, MAR, log(cy/degree) or log MAR, and standard deviations were reported in the same units or in octaves. For the meta-analyses, Lewin and coauthors converted all data into octaves. For studies which reported a graph, and not the actual data, Lewin and coauthors extracted the data from the graph.

(The authors included in meta-analyses only randomized trials of supplemented formula compared with control formula. The report also showed the results of nonrandomized (human milk) comparisons for reference. Diagrams were included for each meta-analysis, plotting the summary measure and 95 percent CI for RCTs and for nonrandomized comparisons. However, Forest plots or tables containing point estimates and 95 percent CI for individual studies were not presented with the results of the meta-analyses. It was difficult to trace the individual study data scattered in the voluminous tables in the report.)

As noted in the previous section, the authors concluded that, "Results concerning the impact of the intake of omega-3 fatty acids on the development of infants are primarily, although not uniformly, inconclusive." The general conclusions of the AHRQ report are also summarized in the previous section, and encompass the other key research questions of the report, including neurodevelopmental outcomes and maternal or child biomarkers; child growth pattern outcomes and maternal pregnancy outcomes.

Cohen et al. (2005a and c) (Harvard Risk/Benefit Papers)

Cohen, J.T., Bellinger, D.C., Connor, W.E., Kris-Etherton, P.M., Lawrence, R.S., Savitz, D.A., Shaywitz, B.A., Teutsch, S.M., Gray, G.M. (2005, November). A Quantitative Risk-Benefit Analysis of Changes in Population Fish Consumption. American Journal of Preventive Medicine, 29(4), 325-334.

Cohen, J.T., Bellinger, D.C., Connor, W.E., Shaywitz, B.A. (2005, November). A Quantitative Analysis of Prenatal Intake of n-3 Polyunsaturated Fatty Acids and Cognitive Development. American Journal of Preventive Medicine, 29(4), 366-74.

Developmental outcomes: Cognitive in term infants (meta-regression and risk benefit assessment).

Several papers describing a quantitative risk-benefit analysis of fish consumption were published together in 2005 by a group led by Cohen and Gray at the Harvard Center for Risk Analysis. The coauthors were an interdisciplinary expert panel assembled by the lead authors. One paper reported quantitative dose-response relationships between children's cognitive development and maternal prenatal methylmercury exposure. Another paper reported a quantitative dose-response relationship between children's cognitive development and maternal prenatal intake of n-3 fatty acids (Cohen et al., 2005c). A third paper combined these results in a quantitative risk benefit analysis of health effects of hypothetical population changes in fish consumption (Cohen et al., 2005a).

The paper by Cohen et al. (2005c) stated that there was little direct information on the relationship between children's cognitive development and maternal n-3 fatty acid intake during pregnancy. Therefore, the paper focused on the literature on the cognitive effect of increasing n-3 fatty acid intake of infants by supplementing infant formula. The authors included randomized trials of n-3 fatty acid supplementation of term infants. Eligible studies were those identified in the systematic review by Simmer (2001), plus those published in 2000 and later and found in an October, 2003 Medline search. The study results were grouped in three developmental domains: general intelligence (including Bayley MDI), verbal ability (including MacArthur Communicative Development Index) and motor skills (including Bayley PDI). Within each domain, this analysis used a single set of available results for each treatment group in each unique study, choosing the results for the oldest age at testing. Included studies reported the numerical difference in test score between supplemented and control formula groups. Also included was a study in which maternal diet was supplemented with 10 ml cod liver oil per day from week 18 of pregnancy through three months postpartum, compared with control mothers who received 10 ml corn oil per day, and children were tested at four years of age (Helland et al., 2003).

Analysis methods. The test result differences at various ages were weighted in the analysis to increase linearly with age in months because published correlations between test results at younger ages with IQ in later life increase with children's age at testing. In the absence of published correlations of the domain scores with general intelligence, the domains were subjectively weighted in the analysis: general intelligence, 1.0/1.8; verbal ability, 0.6/1.8; motor skills, 0.2/1.8. Additionally, test results were weighted by statistical precision (inverse of normalized standard error squared). In order to combine results of different tests and domains, the test scores were normalized and expressed as a fraction of the test standard deviation (SD).

Results and dose-response. The analysis included nine unique studies, with results for 12 comparisons in the general intelligence domain, four comparisons in the verbal domain and nine comparisons in the motor domain (Table B-9). The analysis showed that the infants receiving n-3 supplemented formulas had higher weighted test scores in the three domains, compared with control infants: general intelligence, 0.09 SDs; verbal ability, 0.08 SDs; motor skills, 0.05 SDs. Weighting the score differences across the domains as noted above, the n-3 supplemented infants had higher scores by 0.08 SDs. This would correspond to 1.2 IQ points, where one SD equals 15 points on the IQ scale. The 12 infant formula supplement groups in the included studies had an average DHA formula concentration of 0.26 percent of phospholipids, with an SE of 0.03 percent. Therefore, the average dose-response for the weighted score difference was 1.2/0.26 = 4.6 IQ points for each one percent DHA in infant formula as a percent of phospholipids.

Dose-response conversion factors. Conversion of this average dose-response to IQ points per one gram per day increase in maternal DHA intake in pregnancy was described in a Technical Appendix to Cohen et al. (2005c). Data for increase in breast milk DHA and in infant DHA blood levels (in plasma and red blood cells) with increasing levels of maternal DHA supplement was available from a study by Gibson et al. (1997). From these data for maternal supplements of 0 to 1.3 g/d DHA during the first 12 weeks after birth, Cohen et al. (2005c) estimated that each one percent DHA in breast milk corresponds to an increase of 4.68 percent DHA in infant plasma and 4.52 percent DHA in infant red blood cells. Data for infant DHA blood levels at birth when mothers were supplemented during pregnancy were available from a study by Connor et al. (1996). (Connor was also a co-author of Cohen at al. 2005c.) The mothers in Connor et al. (1996) were supplemented with DHA from either sardines or fish oil capsules beginning at week 24 to 30 of pregnancy and continuing to week 34 of pregnancy. (Note that the Technical Appendix incorrectly states that mothers were supplemented until delivery.) Maternal DHA supplements averaged 1.1 g/day DHA during 56 days of supplementation. The Technical Appendix states that at birth, the infants of supplemented mothers had an increment of 0.88 percent DHA in plasma and 1.89 percent DHA in red blood cells, compared with control infants. This corresponded to an increment of 0.83 percent DHA in plasma and 1.78 percent DHA in red blood cells per one g/d maternal DHA supplement. Combining the results from the Gibson et al. (1997) and Connor et al. (1996) studies, each one g/d maternal DHA supplement was estimated to raise infant plasma DHA an amount corresponding to 0.83/4.68 = 0.18 percent DHA in breast milk or formula, and to raise infant red blood cell DHA an amount corresponding to 1.78/4.52 = 0.39 percent DHA in breast milk or formula.

Dose-response conversion. Applying these conversion factors to the dose-response, the weighted score difference for infants was expressed as a range of 0.18 x 4.6 = 0.82 IQ points (based on infant plasma DHA) to 0.39 x 4.6 = 1.81 IQ points (based on infant red cell DHA) for each 1 g/day DHA maternal intake (Table B-9). The dose-response based on the average of infant plasma and red blood cell DHA was 1.31 infant IQ points per one g/day maternal DHA intake.

Sensitivity analyses. Cohen et al. (2005c) conducted sensitivity analyses of several of the assumptions in the analysis. The authors showed that the results were only modestly sensitive to the weighting of score differences by infant age at testing. Omitting the age weighting changed the overall IQ point difference from 1.3 to approximately 1.4 for the combined cognitive domains. The results had some sensitivity to weighting across domains. As shown in Table B-9, the IQ point difference for the motor domain was 0.8 points, smaller than the 1.2 points for the verbal domain and 1.3 points for general intelligence. However, the motor domain had a lower weight (0.2/1.8), so the point difference for the weighted combination was 1.2 points. The authors noted that the IQ difference would be lower if the motor domain had a higher weight. However, they considered it implausible for the motor domain to contribute a great deal of information to estimation of IQ compared with the verbal and general intelligence domains. Lastly, the authors noted that the analysis allowed for uncertainty by presenting a range for dose-response based on changes in either infant plasma or red blood cell DHA with maternal supplementation. The authors did not present sensitivity analyses of the assumptions in the dose-response conversion factors described in the Technical Appendix, and did not present any validation of the dose-response conversions based on other external information. They also did not comment on the appropriateness of incorporating the Helland et al. (2003) study, which was based on maternal supplementation rather than infant supplementation.

The authors noted that a major assumption of their analysis is that prenatal and postnatal DHA intakes which have the same impact on a child's DHA lipid fraction (either plasma or red blood cell) also have the same impact on the child's IQ.

Quantitative risk-benefit analyses. The quantitative risk-benefit analysis of fish consumption used a probabilistic model to predict changes in cognitive development of offspring, expressed in IQ points, that would result from changes in maternal intake of DHA as well as of maternal exposure to methylmercury during pregnancy, with specific changes in fish intake (Cohen et al., 2005b). (The model also predicted changes in coronary heart disease mortality and stroke in the United States that would result from specific changes in fish intake, as described previously in Section A.) This section will discuss the cognitive development effects of changes in maternal intake of DHA based on the dose-response estimated by Cohen et al. (2005c). The risk assessment model used an FDA exposure model (Carrington and Bolger 2002; Carrington et al., 2004) to describe the population distribution of U.S. fish consumption and to estimate changes in fish consumption under specific scenarios. The analysis assumed no change in fish intake in the 15 percent of the population who consume no fish.

Quantitative "What if" scenarios. The risk assessment developed five "What if" scenarios to examine hypothetical population responses to the FDA-EPA joint fish consumption advisory (FDA/EPA 2004). One focus of the scenarios was the response of the target population for the advisory, pregnant women and women of childbearing age. The principal outcome for the target population was the predicted effect on cognitive development of the offspring. Predicted effects were expressed as total changes in IQ across the population. (Additionally, Scenarios Three, Four, and Five included changes in fish consumption by adult men and by women aged 45 and older with predicted changes in CHD mortality and stroke. The results of Scenarios Three, Four, and Five in the general adult population are summarized in Section B of this document, covering cardiovascular health benefits.)

  • In Scenario One, women of childbearing age were projected to maintain the same overall level of fish consumption, but replace types of fish medium or high in methylmercury with fish low in methylmercury. This was projected to increase the women's DHA intake by 0.01 grams per day (and decrease hair mercury by 0.17 micrograms per gram). The change in DHA intake would correspond to an increase of 39,000 total IQ points across annual births in the population, or an average of 0.009 IQ points per child born. (The authors projected that an additional gain of 380,000 IQ points across annual births would result from decreases in maternal hair mercury, based on their dose-response model for methylmercury exposure (Cohen et al., 2005b); but see the note, below.)
  • In Scenarios Two and Three, women of childbearing age were projected to decrease total fish consumption by 17 percent, or 3.2 grams per day based on average intake of 18.7 grams per day. This change in fish consumption was projected to decrease the women's DHA intake by 0.01 grams per day (and decrease hair mercury by 0.06 micrograms per gram). The change in DHA intake would correspond to a decrease of 48,000 total IQ points across annual births in the population, or an average of around 0.011 IQ points per child born. (The authors also projected a gain of 140,000 IQ points across annual births due to decreases in maternal hair mercury; but see the note below.)
  • In Scenario Five, women of childbearing age were projected to increase their overall fish consumption by 50 percent, or 9.3 grams per day based on average intake of 18.7 grams per day. This change in fish consumption was projected to increase the women's DHA intake by 0.03 grams per day (and increase hair mercury by 0.18 micrograms per gram). The change in DHA intake would correspond to an increase of 140,000 total IQ points across annual births in the population, or an average of around 0.033 IQ points per child born. (The authors also projected a loss of 410,000 IQ points across annual births due to increases in maternal hair mercury; but see note below.)

(Note: The above IQ point changes from changes in maternal methylmercury exposure are based on the Cohen et al. (2005b) estimated dose-response of 0.7 IQ points per one ppm maternal hair mercury. As discussed elsewhere in this document and in the draft FDA risk and benefit report, dose-response estimates of other authors and a secondary analysis of Cohen et al. (2005b) are lower, about 0.18 to 0.2 IQ points per one ppm hair mercury. Therefore, the overall projected IQ point changes from methylmercury exposure (Cohen et al., 2005b) may be an overestimate.)

Comments on Assumptions in the Analysis, Including Dose-response Conversions. A table in Cohen et al. (2005c) shows the incremental average point score for each individual study, for supplemented compared with control infants, both in original units and normalized by test SD. However, the table does not show the individual scores weighted by statistical precision and age at testing. Instead, the weighted pooled average changes in score for the three cognitive domains are stated in the text. Additionally, no confidence interval is given for the weighted average score changes, and the text does not address whether the result is statistically different from no effect.

Several quantitative or qualitative analyses suggested that the DHA level of the test formula may influence the neurodevelopmental effect of supplemented formula in randomized trials (Lauritzen et al., 2001; Uauy et al., 2003; Morale et al., 2005; Eilander et al., 2007). However, Cohen and coauthors did not analyze cognitive score results by test formula composition or DHA level. Instead, they used the average DHA formula level across the trials as a point estimate, and developed conversions to relate this single DHA intake from infant formula to a maternal DHA intake during pregnancy that would yield a comparable infant DHA blood level. Only a single article was used to relate infant intake to infant blood level (Gibson et al., 1997) and a second article related maternal intake during pregnancy to infant blood level (Connor et al., 1996). The reasonableness of the resulting conversion was not compared with other information in the literature. Additionally, in the study by Connor et al. (1996) women were supplemented with fish or fish oil from week 25 to 34 of pregnancy and infant blood levels were measured at birth. A figure and a table in Connor et al. (1996) show that the maternal DHA blood levels peaked at week 34, when supplementation ended, and declined at week 40, just before delivery (although it remained above the DHA level of control women). Therefore, it seems likely that the infants' blood levels at birth would have been higher if maternal supplementation had continued until delivery. Thus, the reported newborn infant blood level associated with maternal supplementation of 1.1 g DHA per day is probably an underestimate, because supplementation ended about eight weeks before birth in Connor et al. (1996).

Additionally, the Technical Appendix of Cohen et al. (1996) apparently used maternal DHA blood levels from a table in Connor et al. (1996) instead of the intended infant blood levels from a figure and text. Using the correct infant blood levels, the infants of supplemented mothers had an increment of 1.58 percent DHA in plasma and 2.06 percent DHA in red blood cells, compared with control infants. This would correspond to an increment of 1.49 percent DHA in plasma and 1.94 percent DHA in red blood cells per 1 g/d maternal DHA supplement. Therefore, each 1 g/d maternal DHA supplement would raise infant plasma DHA an amount corresponding to 1.49/4.68 = 0.32 percent DHA in breast milk or formula, and to raise infant red blood cell DHA an amount corresponding to 1.94/4.52 = 0.43 percent DHA in breast milk or formula. This would increase the IQ point relationship to 1.7 points per g/d of maternal DHA intake, with bounds (1.5 to 2.0 points), compared with 1.3 points with bounds (0.8 to 1.8 points) in Cohen et al. (2005a, c).

The Helland et al. (2003) trial, which was based on maternal supplementation, was not distinguished from the infant supplementation trials in the analysis. The incremental average point score from Helland et al apparently was weighted and pooled with results of the other trials, before calculating the dose-response conversions summarized above. This seems inappropriate because the Helland et al. (2003) results were already in the desired form, 4.1 incremental IQ points per 1.2 g/d maternal DHA intake. Applying conversion factors would underestimate the potential contribution of this trial to the quantitative dose-response.

In summary, concerns about the assumptions in Cohen et al. (2005a, c) include: absence of confidence intervals or other measures of uncertainty for the weighted pooled incremental scores, absence of sensitivity analysis for or validation of the assumptions in the dose-response conversion, apparent numerical errors in the dose-response conversion, and apparent incorporation of the Helland et al. (2003) maternal supplementation results before applying conversion factors from infant to maternal intake.

The What If scenarios (Cohen et al 2005a) then used hypothetical changes in maternal fish intake to project average population changes in children's IQ based on changes in both maternal DHA intake and maternal methylmercury intake. Although the quantitative association of children's IQ with maternal DHA intake was derived from studies on infant formula supplements using a series of assumptions, quantitative association of children's IQ and maternal methylmercury intake came from observational studies of actual maternal methylmercury exposure and children's IQ (Cohen et al., 2005b). Because of the series of assumptions outlined here, the estimated quantitative relationship of children's IQ with maternal DHA intake could potentially be underestimated compared with the true relationship by several fold or even by a factor of 10 or more. Therefore, caution should be exercised in comparing estimated IQ increments based on this derived value with results obtained through entirely different methods, based on direct observational studies of maternal methylmercury exposure (Cohen et al., 2005 a,b,c). (Discussion of the studies of maternal methylmercury exposure is beyond the scope of this document. However, information in Appendix A of the FDA risk and benefit report entitled "Report on Quantitative Risk and Benefit Assessment of Commercial Fish, Focusing on Fetal Neurodevelopment (Measured by Verbal Development in Children) and on Coronary Heart Disease and Stroke in the General Population," suggests that the dose response estimate of Cohen et al. (2005b) may be an overestimate.)

Fleith and Clandinin (2005)

Fleith, M. & Clandinin, M.T. (2005). Dietary PUFA for preterm and term infants: review of clinical studies. Critical Reviews in Food Science and Nutrition, 45(3), 205-29.

Developmental outcomes: Vision and cognitive in term and preterm infants (narrative review with tabulated studies).

In a narrative review in 2005, Fleith and Clandinin noted that the addition of LCPUFA, DHA and AA, to infant formulas was a recent occurrence in Canada and the United States. The purpose of their review was to summarize and discuss the clinical, biochemical and functional outcomes in infants fed formulas with LCPUFA, and to include the most recent studies. The authors discussed non-randomized studies of visual and cognitive function in breast fed infants compared with infants fed formula not supplemented with LCPUFA. Results indicated an association between breast feeding and better cognitive function. However, the comparison cannot be readily attributed to a single component such as LCPUFA. Therefore, randomized trials of LCPUFA supplementation of infant formula were needed to examine causality between LCPUFA intake and visual and cognitive function.

Preterm infants: Preterm infants are particularly disadvantaged regarding DHA and AA for brain development, because about 80 percent of prenatal DHA and AA accumulation occurs during the last three months of gestation. After birth, preterm infants have a high rate of growth and have not benefited fully from DHA and AA accumulation during late gestation. This review tabulated results of 11 unique studies, published from 1990 to 2001, with biochemical data for preterm infants fed formula supplemented with DHA. Eight of the studies had functional outcomes for visual or auditory function, cognitive function or both. The authors reviewed the biochemical studies and concluded that preterm infants fed formulas supplemented with DHA alone have plasma and red blood cell DHA comparable to breastfed infants, but AA status is compromised. Adding AA to the DHA-supplemented formula provides better AA status in infant plasma and red blood cells than for infants fed standard formula with no DHA or AA. Based on their review of studies of visual function in preterm infants, the authors concluded that n-3 fatty acid feeding has transient beneficial effects that are not detected after six months. It is not known whether this short term benefit has any long term effect on visual acuity later in life. Regarding cognitive function in preterm infants, the authors stated that studies do not provide a basis for clear conclusions. Two studies found better visual attention in infants receiving marine-oil-supplemented formula, suggesting a benefit of better visual function early in life. A recent study by O'Connor et al. (2001) found better development in infants receiving supplemented formula on several cognitive tests at six, 12 and 14 months corrected age , including better language development on the MacArthur Communicative Development Inventories at 14 months corrected age. Overall, the authors concluded that formula levels of DHA and AA have been determined that will results in infant plasma and red blood cell levels similar to breast fed infants. Feeding of such formulas may improve growth and developmental measures in preterm infants. The authors noted that even these DHA levels are at the lower range of breast fed infants world wide. However, the authors cautioned that further studies would be needed to evaluate the effect on growth of higher DHA levels in formula, and to study whether increased DHA levels had any further benefit.

Term infants: This review tabulated results of 13 unique studies, published from 1995 to 2002, with biochemical or functional data for term infants fed formula supplemented with DHA. One study had biochemical data only, two studies had functional data only and the remaining studies had both kinds of data. Based on the biochemical data, the authors concluded that term infants fed formulas supplemented with DHA have plasma and red blood cell DHA levels comparable to breast fed infants, but AA status is decreased. Inclusion of AA in the DHA-supplemented formula results in the same AA status as in breast fed infants. Regarding visual function, the authors noted three studies that found a transient effect of LCPUFA on visual acuity in term infants, including two studies that used physiologic measurements and found better visual acuity in supplemented infants up to 52 weeks of age. However, other studies did not find an effect of supplemented formula on visual acuity. The authors commented that results may vary with the age at testing, with an effect of LCPUFA supplementation seen at ages of rapid developmental change. Additionally, in some studies, the DHA level in formula was low. Regarding cognitive development, results were varied when formula was supplemented with DHA and AA, but less than half the studies showed enhanced cognitive development with supplemented formula. The authors found the inconsistencies difficult to interpret, given that the bioavailability of the supplement may not have been not known and the formula composition varied across studies. However, the authors noted that no adverse effects of DHA and AA supplementation have been reported, and beneficial effects on visual or cognitive function had been found in several studies, suggesting that the positive findings are not simply spurious observations.

Mozaffarian and Rimm (2006)

Mozaffarian, D. & Rimm, E.B. (2006, October 18). Fish intake, contaminants, and human health: evaluating the risks and the benefits. Journal of the American Medical Association, 296(15), 1885-99.

Developmental outcomes: Vision and cognitive in term infants (risk benefit assessment).

Mozaffarian and Rimm (2006) published a clinical review to address the seemingly conflicting reports on the risks and benefits of fish intake and the role of fish consumption in a healthy diet. The review considered the scientific evidence for adverse and beneficial health effects of fish consumption. Regarding the effects of fish oil on early neurodevelopment, the authors noted that DHA is preferentially incorporated into the developing brain both prenatally and during infancy. The effects of maternal DHA consumption have been reported in observational studies and randomized trials that varied widely in outcome assessed and according to whether mothers were supplemented during pregnancy or lactation. The authors cited the meta-analysis of Uauy et al. (2003), which found a dose-response relationship for a beneficial effect of DHA supplemented infant formula on visual acuity based on 14 randomized trials. Results for cognitive development are less consistent, but the authors cited the pooled analysis of eight trials by Cohen et al. (2005c), which estimated that increased maternal prenatal intake of 100 mg/day DHA would increase child IQ by 0.13 points. The authors noted that few trials have studied the effect of maternal DHA intake during pregnancy. However, Helland et al. (2003) increased DHA levels in cord blood by supplementing mothers with cod liver oil from week 13 of pregnancy until delivery (and continued through three months postpartum). Children of supplemented mothers had higher mental processing scores, a measure of intelligence, at four years of age. This is consistent with three observational studies finding positive associations between maternal prenatal DHA levels or fish intake and cognitive test results in infancy (Oken et al., 2005; Colombo et al., 2004#; Daniels et al., 2004).

The authors concluded that, while dose-responses and specific effects need additional investigation, current information indicates that maternal intake of DHA is beneficial for early neurodevelopment. The authors also reviewed the literature on maternal prenatal exposure to methylmercury and early neurodevelopment. Overall, they concluded:

"DHA appears important for early neurodevelopment. Women who are or may become pregnant and nursing mothers should avoid selected species (shark, swordfish, golden bass, and king mackerel; locally caught fish per local advisories) and limit intake of albacore tuna (6 oz/wk) to minimize methylmercury exposure.31,142 However, emphasis must also be placed on adequate consumption--12 oz/wk--of other fish and shellfish to provide reasonable amounts of DHA 31,142 and avoid further decreases in already low seafood intake among women (74% of women of childbearing age and 85% of pregnant women consume < 6 oz/wk).206,207"

"Potential risks of fish intake must be considered in the context of potential benefits. Based on strength of evidence and potential magnitudes of effect, the benefits of modest fish consumption (1-2 servings/wk) outweigh the risks among adults and, excepting a few selected fish species, among women of childbearing age. Avoidance of modest fish consumption due to confusion regarding risks and benefits could result in thousands of excess CHD deaths annually and suboptimal neurodevelopment in children."

Eilander et al. (2007)

Eilander, A., Hundscheid, D.C., Osendarp, S.J., Transler, C., Zock, P.L. (2007, April). Effects of n-3 long chain polyunsaturated fatty acid supplementation on visual and cognitive development throughout childhood: a review of human studies. Prostaglandins, Leukotrienes, and Essential Fatty Acids, 76(4), 189-203. Epub 2007 Mar 21.

Developmental outcomes: Vision and cognitive in term and preterm infants (narrative review with tabulated studies). Also maternal supplementation in pregnancy and lactation.

In a systematic, narrative review in 2007, Eilander and coauthors noted that, although DHA and AA are the major structural components of the central nervous system, there is no consensus about whether dietary supplementation of these fatty acids has benefits for infant development. The authors cited the Cochrane reviews of Simmer and Patole (2004) on preterm infants, and Simmer (2001) on term infants. For preterm infants, the Cochrane review concluded that, although there is evidence for a beneficial effect of LCPUFA supplementation on early visual development (before six months of age), there are no positive visual or cognitive effects at older ages. For term infants, the Cochrane review found little evidence of supplementation benefit for visual or general development. Additionally, a review by McCann and Ames (2005) found that the evidence from animal and human studies was inconsistent and did not support a conclusion that infant formula should be supplemented with DHA. The purpose of the review by Eilander et al. (2007) was to re-evaluate the currently available evidence on the effect of LCPUFA on visual and cognitive function during infancy and later childhood, taking into account newer clinical trials of infant formula supplementation. In addition, Eilander et al. (2007) summarized recent research on the effect of maternal supplementation during pregnancy and lactation on infant development. In a disclosure, the authors stated they are employees of a food manufacturer that produces some products enriched with omega-3 fatty acids.

The authors conducted a systematic review of the effects of n-3 fatty acid supplementation on infant and child visual and cognitive development in four topic areas: maternal supplementation in pregnancy and lactation; supplementation of preterm infants during the first two years of life; supplementation of term infants during the first two years of life; supplementation of children older than two years of age. Accepted studies were randomized controlled trials that supplemented subjects for at least four weeks and the LCPUFA supplement was the only variable in the intervention. Thus the review did not include non-randomized trials of breast fed infants. There were fewer than three randomized trials of supplementation of children older than two years of age, therefore, observational studies were included in the search on this topic. For the studies of infant supplementation, the review covered papers published since the reviews of Simmer and Patole (2004) and Simmer (2001).

Maternal supplementation in pregnancy and lactation: The authors identified two trials of maternal supplementation during pregnancy alone, one trial of supplementation during both pregnancy and lactation, and three trials of supplementation during lactation alone (Table B-10). In the study by Malcolm et al. (2003a,b), there was no effect of maternal fish oil supplementation on infant retinal and visual development, including no effect on visual acuity by sweep VEP at 10 and 26 weeks of age. In the Malcolm et al. study, the dose of fish oil was low, providing only 0.2 g DHA/d beginning at week 15 of pregnancy, and did not significantly increase the infant DHA blood levels. In this study, cross-sectional analysis showed that maturity of the retina at one week of age and visual acuity at 10 and 16 weeks of age were positively associated with infant DHA blood levels at birth. Eilander and coauthors stated that this demonstrated that the outcome measures in the study were sensitive enough to detect an association with DHA status. The study by Tofail et al. (2006) found no effect of maternal fish oil supplementation on Bayley's MDI or PDI at 10 months of age for children in Bangladesh. The fish oil dose was higher than in the Malcolm et al study, providing 1.2 g DHA/d beginning at week 25 of pregnancy. However, the effect on DHA status of the infants was not confirmed biochemically. Additionally, Eilander and coauthors noted that there was no cross-sectional analysis of association between infant DHA status at birth and the Bayley's MDI or PDI scores at 10 months of age, and therefore no confirmation that the outcome measures were sensitive enough to detect an association with DHA status. Overall, Eilander et al. concluded that because of limitations of these two studies, there is uncertainty regarding whether fish oil supplementation during pregnancy is beneficial for infant visual or cognitive development.

In the study by Helland et al. (2001, 2003) in Norway, supplementation with cod liver oil during pregnancy and lactation had no effect on infants' electroencephalogram maturity at two days or three months of age or on the Fagan test at 27 or 39 weeks of age. However, in a subset of the cohort, at four years of age, the children of supplemented mothers had a significantly higher score, by four IQ points, on the Mental Processing Composite of the K-ABC test. The maternal supplement provided 1.2 g DHA/d from week 17-19 of pregnancy through three months postpartum, and the maternal DHA dose increased the infants' DHA status. Additionally, the Mental Processing Composite score at four years of age was positively correlated with infants' DHA status at four weeks of age. Eilander et al. stated that it is unclear whether the effect on the IQ score was due to maternal. supplementation during pregnancy, lactation or both. Eilander and coauthors concluded that this study suggests that effects of maternal DHA supplementation may appear later in life, when cognitive function is more mature and cognitive psychometric tests have higher discriminative power.

The studies of maternal supplementation during lactation alone included five increasing doses of DHA (up to 1.3 g/d) from algae oil for 12 weeks after birth (Gibson et al., 1997), fish oil supplements providing 1.3 g/d of n-3 LCPUFA for 16 weeks after birth (Lauritzen et al., 2004#, 2005#) and algae oil supplements providing 200 mg DHA/d for four months after birth (Jensen et al., 2005). The small study of Gibson et al found no effect on visual acuity at 12 and 16 weeks of age or Bayley's MDI or PDI at one and two years of age. However, there was an association of MDI with breast milk DHA concentration at one year of age but not two years of age. Lauritzen et al., studying Danish mothers with low fish intake, also found no effect of supplementation on infant visual acuity at two or four months of age. However, there was a significant positive cross-sectional association between infant DHA status and visual acuity at four months but not at two months of age. Results of developmental tests were inconsistent between boys and girls. There was a significant positive effect of maternal supplementation on problem solving in girls at nine months of age and a significant negative effect on vocabulary comprehension and sentence complexity in boys at one year of age, but not at two years of age. Jensen et al found a significant positive effect of maternal supplementation on Bayley's PDI at 30 months of age. However, there was no effect of supplementation on visual acuity at four or eight months of age or on gross motor development, language development or visual-motor problem solving at 12 or 30 months of age or on Bayley's MDI at 30 months of age. Eilander and coauthors noted that these three studies demonstrated that the maternal supplementation increased the DHA content of breast milk and the infant DHA blood levels in a dose dependent way. However, supplementation had no positive effects on visual development. Eilander et al. suggested that perhaps either 1) supplementation during lactation alone may be insufficient to affect visual development and should be combined with supplementation during pregnancy or 2) supplementation during lactation is not relevant to visual development of breastfed infants. The authors noted that the positive cognitive effects of maternal supplementation were seen in the Jensen study at a later infant age, 30 months. The inconsistent results for language development between the Lauritzen and Jensen studies and between girls and boys in the Jensen study were difficult to interpret. Overall, Eilander et al. concluded that there is some evidence of beneficial effects of maternal supplementation during lactation on infant psychomotor and cognitive development. An important question to these authors is whether this would be sustained in older children.

(Table B-10 updates the information from Eilander et al to include the study of Dunstan et al (2008). In this study in Australia, 98 pregnant women were randomized to fish oil (2.2g/d DHA and 1.1 g/d EPA) or olive oil from 20 weeks gestation until delivery. At age 2 ½ years, children of mothers in the fish-oil group (n = 33) had significantly higher scores for hand and eye coordination on the Griffiths Mental Development Scales, compared with control children ( n = 39). There were no significant differences between groups on the Peabody Picture Vocabulary Test or the Child Behavior Checklist.)

Preterm infants: The authors tabulated two large randomized trials and one smaller trial of LCPUFA supplements in preterm infants, published in 2004 and 2005. These studies were in addition to the nine studies reviewed by Simmer and Patole (2004). In the study of Clandinin et al. (2005#), LCPUFA supplemented infants had significantly higher scores than control infants for Bayley's MDI and PDI at 18 months corrected age. In a pre-planned comparison, supplemented male infants in the study of Fewtrell et al. (2004#) had significantly higher scores than control infants for Bayley's MDI at 18 months corrected age (there were no significant differences in MDI for females or for the total group). The study of Fang et al. (2005#) also showed a positive result for MDI and PDI at corrected ages six and 12 months. However, Eilander et al. viewed the results of Fang et al. with caution because, compared with other studies, the infants were less premature, the dose of LCPUFA was low, the sample size was small, and a complete description of the formula was not reported. Eilander et al. noted that the review of Simmer and Patole (2004) had reported on relatively few studies giving cognitive outcomes for corrected age 12 months or older. The two studies in Simmer and Patole that reported on Bayley's MDI and PDI at corrected age 18 or 24 months found no significant effects of LCPUFA supplementation. However, one of the studies had supplemented the infants only until one month corrected age, and the other study supplemented until six months corrected age. This compared with supplementation until 12 months corrected age in Clandinin et al. (2005#) and nine months corrected age in Fewtrell et al. (2004#). Eilander et al. stated, "Taken together, there are indications for a beneficial effect of LCPUFA supplementation on cognitive development of preterm infants." The authors suggested that the effects of LCPUFA supplementation may be greater when supplementation is continued until 12 months corrected age or when cognitive outcome is measured at older ages, when cognitive tests are more sensitive and reliable.

Term infants: The authors tabulated nine randomized trials of LCPUFA supplements in term infants, published in 2001 through 2005. These studies were in addition to the nine studies reviewed by Simmer et al. (2001). Four studies among the newer, tabulated studies showed positive effects of LCPUFA supplementation on infant visual development (Birch et al., 2002, 2005; Hoffman et al., 2003, 2004) and two studies showed no effect (Auested et al., 2001, 2003). The studies by Auestad and coauthors used relatively low DHA doses (0.12 percent to 0.14 percent of fatty acids as DHA in formulas that also contained AA) and a behavioral test for visual acuity. Three of the positive studies used higher levels of DHA in formula (0.36 percent of fatty acids) and all four positive studies used more sensitive, electrophysiologic tests of visual acuity. (The fourth positive study (Hoffman et al., 2004) used DHA supplemented egg yolk as weaning food.) Eilander et al., noted that this was consistent with earlier results summarized by Simmer (2001). In the earlier studies, no major effects on visual acuity were found using behavioral tests. Using physiologic tests, two of the earlier studies found significant positive effects on visual acuity of formula supplemented with DHA as 0.36 percent of fatty acids, but another study found no effect with a formula containing DHA as 0.12 percent of fatty acids. Eilander and coauthors also noted the meta-regression of Uauy et al (2003), showing a significant dose-response relationship for intake of DHA or equivalents and visual acuity in term infants at four months of age (Table 3, discussed above). Additionally, Eilander et al noted an analysis by Morale et al. (2005) suggesting that greater improvement in visual acuity may be associated with longer duration of LCPUFA supplementation through 52 weeks of age (discussed later in this document). Eilander et al concluded that, "Taken together, above studies suggest that LCPUFA supplementation to formula in high dose of 0.36 percent DHA plus 0.75 percent AA and prolonged supplementation up to 12 months benefits visual development in infants." The authors stated these LCPUFA doses corresponded to daily intake of about 100 mg DHA plus 200 mg AA (based on 4 percent lipid content of formula, 92.5 percent fatty acids in milk lipids, and 750 ml formula consumed per day, as assumed by Uauy et al.).

Regarding cognitive development, Eilander and coauthors noted that the newer studies were consistent with the earlier summary of Simmer (2001) in finding no effect of LCPUFA supplementation. In particular, the studies of Auestad et al. (2001, 2003) used multiple measures of cognitive outcome, including Bayley's MDI and PDI. Possible explanations for lack of effect include that the Auestad et al studies used lower doses of DHA, that the effect of LCPUFA may not appear until older ages, or that LCPUFA supplementation does not materially affect cognitive development. Eilander et al. concluded that, "Future studies are needed to assess the effect of LCPUFA supplementation on cognitive development at high dose (100 mg DHA plus 200 mg AA) and prolonged duration (preferably 12 months); conditions under which significant effects on visual development were found."

Older Children: Eilander et al. found no clinical trial data and only one prospective observational study on the association of n-3 status and cognitive performance of children older than two years of age. The prospective study by Bakker et al. (2003) did not find a significant positive association between scores on the Kaufmann Assessment Battery for Children at seven years of age and blood levels of DHA and AA at birth or at age seven. A cross-sectional study by Zhang et al. (2005#) found that higher total n-3 and n-6 PUFA intake in U.S. children age six to 16 years was associated with better memory performance but not with performance on block design, arithmetic or reading comprehension tests. However, this study could not distinguish between n-3 and n-6 fatty acid intake. Eilander and coauthors concluded that, although evidence is lacking to show an effect of n-3 fatty acid supplementation on cognitive performance of children older than two years of age, "it remains conceivable that n-3 fatty acid supplementation could be beneficial in these children, in particular when intake of n-3 fatty acids is low and nutritional status is poor. This should be addressed in future randomized controlled trials."

Conclusions: Overall, Eilander et al. concluded that:

  • "for supplementing pregnant and/or lactating women with DHA, there is currently no supporting evidence for a beneficial effect on visual development, but there is suggestive evidence for a beneficial effect of supplementation during pregnancy and lactation or lactation only on mental development and on longer term cognition;
  • "for supplementing preterm infants with DHA and AA, evidence for benefits on visual development at <six months of age remains inconclusive, while there are indications from two studies for a beneficial effect of supplementation in early in life on cognitive development at >12 months of age;
  • "for supplementing term infants, with LCPUFA in high doses (100 mg DHA and 200 mg AA per day), there is consistent evidence for a beneficial effect on visual development during the first year of life, while there is hardly such evidence for beneficial effects on cognitive development;
  • "for supplementing healthy children older than two years of age with DHA, there is no evidence for beneficial effect on cognitive performance."
Smithers et al. (2008)

Smithers, L.G., Gibson, R.A., McPhee, A., Makrides, M. (2008, April). Effect of long-chain polyunsaturated fatty acid supplementation of preterm infants on disease risk and neurodevelopment: a systematic review of randomized controlled trials. American Journal of Clinical Nutrition, 87(4), 912-20.

Developmental outcomes: Cognitive in preterm infants (systematic review and meta-analysis).

The authors conducted a systematic review and meta-analysis of the effect of LCPUFA supplemented formula on neurodevelopment of preterm infants, as well as on the risk of certain adverse health outcomes (necrotizing enterocolitis, sepsis, retinopathy of prematurity, intraventricular hemorrhage, and bronchopulmonary dysplasia). Included articles were randomized controlled trials of infants born before 37 weeks gestation fed a standard preterm formula supplemented with n-3 LCPUFA for one month or longer, compared with infants not receiving n-3 LCPUFA supplemented formula. Included studies for neurodevelopment used age standardized, clinically relevant techniques. The search was updated through January 24, 2007. Study authors were contacted for missing information. Seven studies were identified that assessed neurodevelopment at 12 or 18 months corrected age. Five studies used the Bayley Scales of Infant Development, Version II and two studies used Version I. Because the test scores are age-standardized, the results were combined across ages 12 to 18 months. Four of the studies were published in 1992 through 2001 and were included in the Cochrane review by Simmer and Patole (2004). The remaining three studies, published in 2004 and 2005, were included in the review by Eilander et al. (2007).

Weighted mean differences in scores between supplemented and control infants on the Bayley Scales were shown on Forest plots for the seven studies together with the pooled results across studies. Across fives studies using the Bayley Scales Version II, the mean difference in Mental Development Index (MDI) scores favored the infants supplemented with LCPUFA compared with control infants by 3.44 points, a statistically significant difference, p < 0.02 (Table 11). For these five studies, the mean difference in Psychomotor Development Index (PDI) scores favored the supplemented infants by 2.87 points but this difference was not statistically significant, p = 0.14. For the two studies using the Bayley Scales Version I, the mean difference in scores favored the control infants on both tests: by 4.09 points on the MDI, not statistically significant, p = 0.16 and by 7.99 points on the PDI, statistically significant, p < 0.009. For all seven studies combined, the mean difference in scores favored the supplemented infants on both tests, but neither was statistically significant: 2.13 points on the MDI, p = 0.16 and 0.7 points on the PDI, p = 0.73.

The authors were surprised that the effect of n-3 LCPUFA supplementation was generally favorable using the Bayley Scales Version II but unfavorable using Version I. They suggested that modifications made in development of Version II may have introduced systematic differences in evaluation of the underlying cognitive domains. Regarding the Version I results, the authors stated that they had limited confidence in the meta analysis results because the data were from only two trials with small sample sizes. The Version II results showed a generally favorable effect of n-3 LCPUFA supplementation. However, the authors stated that the result seemed to be driven by two large trials with large effect sizes and also large confidence intervals. Overall, the authors concluded that the results did not support a robust benefit of LCPUFA supplementation on global assessment of mental development at 12 to 18 months corrected age. Regarding the risk of adverse health outcomes, the analysis found no effect of LCPUFA supplementation on the risk of necrotizing enterocolitis or sepsis, and too few data were available to analyze the risk of the other conditions.

The authors also noted that the mean scores of the preterm infants on the neurodevelopment tests in these analyses was about one standard deviation lower than the standardized norm. Therefore, they concluded that any benefit to neurodevelopment outcome could be important to this group of vulnerable infants and further research is needed.

Simmer et al. (2008a)

Simmer, K., Schulzke, S.M., Patole, S. (2008, January 23). Longchain polyunsaturated fatty acid supplementation in preterm infants. Cochrane Database of Systematic Reviews, (1), CD000375.

Update of:
Simmer, K., Patole, S. (2004). Longchain polyunsaturated fatty acid supplementation in preterm infants. Cochrane Database of Systematic Reviews, (1), CD000375.

Developmental outcomes: Vision and cognitive in preterm infants (systematic review and meta-analysis).

The Cochrane systematic review for preterm infants was updated by Simmer and coauthors (2008a). For visual acuity of preterm infants, there was one additional study, published in 2005, examining the effect of DHA-supplemented formula. The review stated that the new study found no effect of supplemented formula on visual acuity at four and six months corrected age. The review authors stated that they did not conduct meta-analysis for visual acuity outcomes because results were reported in log values and there were varied assessment methods. The Forest plots for visual acuity were not updated to include the 2005 study, perhaps because numerical data were not available. The review concluded that, with a few exceptions, most studies found no differences in visual assessment between supplemented and control infants.

For outcomes using the Bayley Scales of Infant Development, there were three new studies, the same studies noted above in the summary of the Smithers et al. (2008) review. One new study assessed the Bayley Scales at corrected age 12 months, giving a total of four studies at that age. Two new studies assessed the Bayley Scales at corrected age 18 months, giving a total of three studies at that age. The separate meta-analyses of the Bayley's MDI and PDI scores at the respective ages showed no significant effect of supplemented formula on infant development.

The authors concluded that pooling data from 15 controlled trials did not show a long term benefit of n-3 LCPUFA supplemented formula on visual development, neurodevelopment or growth of preterm infants. They noted that there were methodology differences among the studies, and differences in formula composition, as well as medical complications and treatments associated with premature birth. Most studies enrolled relatively healthy preterm infants.

Simmer et al. (2008b)

Simmer, K., Patole, S.K., Rao, S.C. (2008, January 23). Longchain polyunsaturated fatty acid supplementation in infants born at term. Cochrane Database of Systematic Reviews, (1), CD000376.

Update of:
Simmer, K. (2001). Longchain polyunsaturated fatty acid supplementation in infants born at term. Cochrane Database of Systematic Reviews, (4), CD000376.

Developmental outcomes: Vision and cognitive in term infants (systematic review and meta-analysis).

The Cochrane systematic review for term infants was updated by Simmer and coauthors (2008b). Term infants in included trials received study formula beginning at two weeks of age or earlier and received study formula exclusively until at least eight weeks of age. Included outcomes, measured after three months or more of follow up, were visual acuity, physical growth and cognitive neurodevelopment. The review identified 20 potential trials and 14 met eligibility criteria. These included eight trials covered in the earlier review by Simmer (2001) and six new trials. Results of distinct trials could be reported in more than one published article, and the review also included newly reported follow up results of trials reviewed previously. (One trial included in Simmer (2001) did not meet eligibility criteria for the 2008 review (Clausen et al 1996#).) Two of the new trials studied physical growth outcomes but not visual acuity or cognition.

The review by Simmer et al. (2008b) included five of the nine new randomized trial outcome reports identified in the review by Eilander et al. (2007). In three studies not included, the n-3 LCPUFA supplementation was begun at six weeks (Birch et al., 2002) or four to six months (Hoffman et al., 2003) of age or was provided as weaning food (Hoffman et al., 2004). In a fourth study not included, the outcome was auditory brainstem evoked potential, not covered by Simmer (2008b).

In contrast with the 2001 review, the authors successfully obtained numerical data for the positive studies of Birch et al for visual acuity, and these results were included in Forest plots and meta-analyses. However, for studies that reported sweep VEP, the authors did not convert all results to the same units, but rather presented some results in logMAR and other results separately in cycles/degree. Whereas the review of preterm infant studies by Simmer et al. (2008a) did not perform meta analysis of visual acuity results expressed in logMAR or log(cycles/degree), this review did perform meta analysis, separately, for visual acuity results in logMAR and in cycles/degree.

Visual acuity. The new study by Birch et al. (2005) as well as the earlier Birch et al. (1998) study showed statistically significant benefits of DHA plus AA supplemented formula at four and 12 months of age using sweep VEP. At four months of age, the meta-analysis of the two studies found a weighted mean difference of -0.07 logMAR (95 percent CI, -0.10 to -0.04), significant at p < 0.00005, with no heterogeneity. (Note that lower logMAR indicates better visual acuity, so negative weighted mean difference indicates better acuity for the supplemented group.) At 12 months of age, the weighted mean difference was -0.16 logMAR (95 percent CI, -0.19 to -0.12), significant at p < 0.00001, no heterogeneity. Sweep VEP results of the earlier study from Auestad and coauthors (1997), at four and 12 months of age, showed no statistically significant effect of DHA plus AA supplementation. The Auestad et al. (1997) results were reported in cycles/degree and were not included in the same meta-analysis with the results of Birch and coauthors. The new study by Auestad et al. (2001) used Teller cards and showed no significant effect of DHA plus AA on visual acuity at four, six, or 12 months of age. Results of Auestad et al. (2001) using Teller cards were combined with two earlier studies and the meta analysis showed no significant effect on visual acuity at four, six, or 12 months of age. Similarly, follow up of the Auestad et al. (1997) study showed no significant effect of supplementation on visual acuity at three years of age using Teller cards (Auestad et al., 2003).

Cognitive neurodevelopment. Several new trials reported no significant effect of DHA plus AA supplemented formula on Bayley scales of infant development at various ages from three months to one year. When combined with earlier results, the meta-analyses showed no significant effect of DHA plus AA supplemented formula on cognitive development measured by Bayley scales. The earlier study of Birch et al. (1998) showed a statistically significant positive effect of DHA plus AA supplemented formula on Bayley's MDI but not on the PDI at 18 months of age. However, when combined with two other studies, the meta-analysis showed no significant effect of supplemented formula on Bayley's MDI at 18 months of age. Additionally, the new follow up of the Auestad et al. (1997) study showed no significant effect of supplementation on Stanford Binet IQ scores at 39 months of age (Auestad et al., 2003).

The authors concluded that, "Data from randomized trials do not support the need for routine supplementation of formula for term infants with LCPUFA to improve visual acuity, neurodevelopment or physical growth." The authors suggested that additional research is needed from trials at relatively higher DHA and AA supplementation levels for longer duration, similar to the protocol of Birch et al. (2005), to learn whether the results can be replicated in other settings. The authors also recommended further follow up of study infants from the various trials through school age for visual, cognitive and physical development.

Recent controlled trials of omega-3 supplemented formula for term infants

As summarized above, the review by Eilander et al. (2007) found that four studies among the newer, tabulated studies of term infants showed positive effects of LCPUFA supplementation on infant visual development (Birch et al. 2002, 2005; Hoffman et al. 2003, 2004). Compared with the two negative studies, the positive studies used more sensitive, electrophysiologic tests of visual acuity and three of the positive studies used higher levels of DHA in formula (0.36 percent of fatty acids). (The fourth positive study used DHA supplemented egg yolk as weaning food.) One of the positive studies (Birch et al., 2005) provided LCPUFA-supplemented formula from birth to 12 months of age, and the study conditions and visual acuity outcome can be compared with the recommendations of Lauritzen et al. (2001). The review by Eilander et al. also noted an analysis by Morale et al. (2005) suggesting that greater improvement in visual acuity may be associated with longer duration of LCPUFA supplementation through 52 weeks of age. Additionally, follow up results for visual acuity and cognitive function at four years of age were recently published (Birch et al., 2007) for a positive study (Birch et al., 1998, 2000) previously included in the Simmer (2001) and Simmer et al. (2008b) reviews. This section will briefly summarize the recent clinical trial by Birch and coauthors (2005), the analysis by Morale and coauthors (2005) and the follow up study by Birch and coauthors (2007).

Birch et al. (2005)

This study was a randomized, controlled trial of the effect of LCPUFA supplemented formula in term infants on visual function. Infants were supplemented from birth to 12 months of life, and the study design was intended to carry out the recommendations of Lauritzen et al. (2001) regarding sample size (greater than 20 per group), DHA level in infant formula (greater than 0.35 percent of lipids), and use of electrophysiological testing methods for visual acuity. The supplemented formula contained 0.36 percent DHA and 0.76 percent AA, and both supplemented and control formulas contained 1.5 percent ALA. Infants were randomized in the first 5 days of life, 51 to supplemented formula and 52 to control formula. The total group had visual acuity testing by sweep VEP at 17, 39 and 52 weeks of age. At these respective ages, there were 46, 44 and 42 supplemented infants and 46, 46, and 44 control infants participating. Additionally, a subgroup of 33 supplemented infants and 32 control infants had sweep VEP measurements at six weeks of age. Visual acuity was reported graphically in logMAR for each age at testing. There were significant effects of age and test formula and an age by test formula interaction. The planned comparisons showed a significantly better visual acuity in LCPUFA supplemented infants compared with control infants at ages 17, 39 and 52 weeks (p < 0.001). Additionally, at six weeks, the subgroup showed significantly better acuity for supplemented infants than control infants, p = 0.01. The authors stated that the acuity of the control group was about 0.12 logMAR poorer than the supplemented group, which corresponds to a little more than a one-line difference on an eye chart. In addition to sweep VEP for visual acuity, the trial also measured stereoacuity (or depth perception) using a random dot method. Again, there were significant effects of age and test formula and an age by test formula interaction. The planned comparisons showed the LCPUFA supplemented group had significantly better stereoacuity than the control group at 17 weeks (p < 0.001), but not at 39 or 52 weeks of age (p = 0.37 and 0.06, respectively). Biochemically, DHA levels in red blood cell lipids for the supplemented infants were more than twice that of the control infants at 17 weeks, and more than three times that of the control infants at 39 weeks of age.

Morale et al. (2005)

This study combined the results, all from a single laboratory, of four randomized controlled trials of the effect of LCPUFA supplemented formula on visual acuity in term infants and two reference groups of breastfed term infants. The purpose was to analyze the visual acuity at age 12 months according to the duration of supply of LCPUFA from breastfeeding, supplemented formula or both. The randomized trials analyzed included the study of Birch and coworkers (2005) discussed above, and two other trials reviewed by Eilander et al. Birch et al. (2002) and Hoffman et al. (2003), as well as an earlier trial, Birch et al. (1998). Two of the trials randomized infants to supplemented or control formulas at birth, for four months (Birch et al., 1998) or 12 months duration (Birch et al., 2005). The other two trials weaned infants from breast milk at six weeks, four months or six months of age to receive test formulas until 52 weeks of age (Birch et al., 2002; Hoffman et al., 2003). At 52 weeks of age, visual acuity of all infants was tested using the same sweep VEP methodology. The same test formulas were used in all the trials: supplemented formula contained 0.36 percent DHA and 0.76 percent AA, and both supplemented and control formulas contained 1.5 percent ALA. A graph showed a linear relationship between mean visual acuity of test groups at age 12 months in logMAR with duration of LCPUFA supply (from breastfeeding and/or supplemented formula). Results of linear regression were reported in the article text and are summarized in Table 12. For all test groups combined (n = 296), there was a significant improvement in visual acuity, -0.003 logMAR, per week of LCPUFA supply from breast milk or formula. This corresponded to about one line on an eye chart for 36 weeks of LCPUFA and 1 ½ lines for 52 weeks of LCPUFA (Table B-12). The dose-response was similar when limited to test groups that received LCPUFA from test formula only or from human milk only. The authors noted the apparent equivalence of human milk and the test formula in these trials in their effect on visual acuity by sweep VEP at 52 weeks of age. They suggested that the data support a sweep VEP acuity level of 0.157 ± 0.81 logMAR (equivalent to 20/29 vision on a standard, or Snellen, eye chart) as a possible functional standard to judge sufficiency of LCPUFA supply during the first year of life. The authors also commented that infants showed a continued benefit from a supply of LCPUFA even up to 52 weeks of age, suggesting that the brain may not have sufficient stores of LCPUFA from an early postnatal supply to support the continued maturation of the visual cortex.

Birch et al. (2007)

This study reported follow up results for visual acuity and cognitive function at four years of age for infants randomized to test formulas at birth for a four-month feeding period (Birch et al., 1998, 2000). One test formula contained both DHA (0.36 percent of lipids) and AA (0.72 percent of lipids), and another test formula contained DHA (0.35 percent of lipids) but no AA. Both test formulas and the control formula contained 1.5 percent ALA. At the completion of four months feeding, there were 23 infants in the control group, 22 in the DHA group, 23 in the DHA plus AA group, plus a comparison group of 38 breastfed infants. For follow up testing, the hypothesis was that control formula lacking LCPUFA for the first four months of life would result in significantly poorer visual acuity and IQ at four years of age than would breastfeeding during that period. At four years of age, testing was completed for 19 infants in the control group, 16 in the DHA group, 17 in the DHA plus AA group and 32 in the breast fed group. Visual acuity by HOTV testing was measured in each eye using a published method, the Electronic Visual Acuity system. (HOTV testing uses a visual stimulus of individual letters, H, O, T, V framed with crowding bars.) For visual acuity in the right eye, in logMAR, there was a significant difference among the four test groups (DHA formula, DHA plus AA formula, control and breastfed), p < 0.03. Planned comparisons showed that the control group had significantly poorer right eye acuity compared with the DHA group (p < 0.004) and with the breastfed group (p < 0.03). The right eye acuity of the DHA plus AA group was better than that of the control group and poorer than that of the other two groups, but the differences were not significant. For visual acuity in the left eye, there was no significant difference among the four test groups (p = 0.17), so paired comparisons were not done.

The Wechsler Preschool and Primary Scale of Intelligence, Revised was used to assess intelligence at 4 years of age, reported as Performance IQ, Verbal IQ and Full Scale IQ. The mean Performance IQ for the control group was 104.2 (SE 2.7), about four points lower than the means for the other three test groups: DHA, 108.1 (SE 3.8); DHA plus AA, 108.6 (SE 3.3); breastfed, 108.4 (SE 2.5); but there was no significant difference among the groups (p = 0.70) and paired comparisons were not done. The mean Verbal IQ of the control group was 98.8 (SE 2.6), compared with 102.7 (SE 4.1) for the DHA group, 104.5 (SE 2.9) for the DHA plus AA group and 112.6 (SE 2.3) for the breastfed group, a significant difference among groups, p < 0.003. Planned comparison showed the Verbal IQ for the control and DHA groups were significantly lower than for the breastfed group, p < 0.0004 and p < 0.02, respectively. Although the DHA and DHA plus AA groups had mean Verbal IQ about four and six points higher, respectively, than the control group, these differences were not statistically significant. The mean Full Scale IQ of the control group was 101.0 (SE 2.6), compared with 105.9 (SE 3.9) for the DHA group, 107.5 (SE 3.1) for the DHA plus AA group and 111.2 (SE 2.3) for the breastfed group. This was near statistical significance, p = 0.06, but paired comparisons were not done because the difference among groups was not significant at the planned p value, < 0.05.

Previous reports on this randomized trial found that infants receiving LCPUFA supplemented formula had better sweep VEP visual acuity during the first year of life and better Bayley's MDI scores at 18 months of age, compared with control infants. The authors stated that the finding that only the LCPUFA supplemented children had visual acuity and IQ similar to that of breast fed infants at four years of age further supports the need to supplement formulas with LCPUFA. Birch and coauthors noted that their results differed from those of Auestad and coworkers, who found no difference in IQ between breastfed infants and those fed control or LCPUFA supplemented formula. The authors suggested this may be due to the lower DHA level in supplemented formulas in the Auestad et al. study.

(d) Key Observational Studies of Maternal Fish Consumption and Neurodevelopment

As noted above and reviewed by Eilander et al, 2007, evidence from the small number of randomized clinical trials of maternal fish or fish oil supplementation in pregnancy and/or lactation shows inconsistencies and study limitations, as well as possible beneficial effects on infant and child neurodevelopment. Compared with randomized clinical trials, in observational studies pregnant or lactating women consume their usual diets; dietary intake of seafood or fish oil supplements is not randomly assigned by the investigator. Therefore, an observational study cannot conclusively demonstrate a cause and effect relationship. Observed relationships between maternal seafood intake and infant and child neurodevelopment could be due to another, confounding variable of participant characteristics or lifestyle. However, possible confounding variables that are known and measured can be adjusted for in the statistical analysis. An advantage of prospective cohort studies is that they study outcomes related to participants' actual diets and larger study sizes can be feasible. Additionally, in evaluating risks and benefits from maternal fish consumption on fetal neurodevelopment, maternal fish consumption, rather than infant or maternal fish oil supplementation, is the actual exposure most relevant to assessing potential health benefits.

Systematic reviews focused specifically on observational studies of maternal seafood consumption and infant and child neurodevelopment are not available. Several reports and recommendations, summarized above, considered observational studies of maternal seafood consumption as part of the body of evidence regarding neurodevelopment. These included SACN (2004), EFSA (2005), IOM Seafood Choices (2006), Mozaffarian and Rimm (2006). The systematic review by AHRQ (Lewin et al, 2005) considered observational studies only when fewer than two randomized trials were available for a given key question.

(A number of supplementation trials also reported, as secondary analyses, observational associations of biomarkers, such as infant or child DHA blood levels, and neurodevelopmental outcomes. These are mentioned in several of the reports and reviews, and tabulated together with the study characteristics in Lewin et al (2005). However, these findings have also not been systematically summarized or reviewed. Additionally, an observational study found a positive association between DHA level in cord blood and infant neurologic status at birth (Dijck-Brouwer et al 2005), but other reports found no association between cord blood DHA level and cognitive development at 4 or 7 years of age (Ghys et al 2002, Bakker et al 2003). The remainder of this section will consider observational studies of maternal seafood intake or breast milk DHA level.)

In the absence of a systematic review, Table 13 summarizes several observational studies of maternal seafood intake or breast milk DHA level and infant or child neurodevelopment. In a small cross-sectional study, DHA level in breast milk was significantly positively associated with infant visual acuity and with maternal fish intake (Jørgensen et al 2001). In one small cohort study, infant DHA blood level at 2 months of age was positively associated with mothers' breast milk level and with infant visual acuity at 2 months and 12 months and speech perception at 9 months (Innis et al 2001). In another small cohort study, LC PUFA ratios in colostrum, but not in mature breast milk, were positively associated with IQ at age 6 ½ years (Gustafsson et al 2004). The remaining studies in Table 13 are from two established prospective cohorts of pregnant women and their children: the Avon Longitudinal Study of Parents and Children (ALSPAC) in Avon, England and Project Viva, in Boston, Massachusetts.

ALSPAC Cohort

Children in the ALSPAC cohort were born between April 1, 1991 and December 31, 1992. Williams et al (2001) used a random dot method to examine development of visual depth perception (stereoacuity) at age 3.5 years in a random subset of the children born in the last 6 months of the ALSPAC enrollment. Of the 435 children tested, 34.5 percent achieved high quality (foveal or adult) stereoacuity, 52.6 percent had moderate (macular) stereoacuity and 12.9 percent had poor (peripheral) stereoacuity. After adjustment for covariates, maternal consumption of oily fish during pregnancy was independently, positively associated with children's high-quality stereoacuity, OR = 1.57 (95 percent CI, 1.00 to 2.45). Stereoacuity was also independently, positively associated with children's having been breast fed. Odds ratios were similar for breastfeeding less than four months (OR = 2.92, 95 percent CI; 1.58 to 5.43) or for four months or longer (OR = 2.77; 95 percent IE, 1.54 to 4.97). In a smaller subgroup (n = 154) with available data, children's stereoacuity was significantly correlated with mothers' DHA blood levels during pregnancy and mothers' DHA blood levels were correlated with consumption of oily fish (p = 0.004). The authors noted that the results suggest for the first time an association between maternal diet during pregnancy and children's visual status at 3.5 years of age.

Daniels and coauthors (2004) analyzed data on cognitive development in 7,421 children using the MacArthur Communicative Development Inventory at 15 months of age and the Denver Developmental Screening Test at 18 months of age. After adjustment for covariates, mean scores on the MacArthur vocabulary comprehension and social activity scales and the Denver total and language scales were significantly positively associated with frequency category of maternal fish intake during pregnancy. (There was no association of maternal fish intake with mean score on the Denver social development scale.) Most mean scores were also significantly independently associated with child fish intake at six months and 12 months of age. (About 43 percent of children ate fish at least once per week at six months of age and 81 percent did so at 12 months of age.) Odds ratios for children's low test scores on several of the test scales were significantly inversely associated with frequency of maternal fish intake during pregnancy, and odds ratios for high scores on several test scales were positively associated with maternal fish intake.

Cord tissue mercury levels were available for a subset of 1,054 women. Mercury levels were positively associated with frequency of fish consumption but there was no association between mercury levels and the developmental test scores. The authors stated that mercury levels were low (median = 0.01 micrograms per gram cord tissue wet weight). They also stated that this was lower than estimates of cord tissue mercury levels reported for the Faroe Islands, when expressed as tissue wet weight. Additionally, although fish consumption in the United Kingdom is relatively high, population mercury exposure estimates based on fish intake and mercury levels in commercial fish did not exceed WHO recommended levels, as explained by Daniels et al. Further information on the mercury exposure in Daniels et al. is provided in the draft FDA risk and benefit assessment report, in an estimate indicating that mercury exposure in this population was similar to exposures in the United State s. Daniels et al. (2004) concluded that maternal and infant fish intake may subtly enhance the child's early development of language and communication skills.

Hibbeln and coauthors (2007a) analyzed data on neurodevelopment outcomes for 8,916 children from various early development tests at six, 18, 30 and 42 months of age, behavior tests at seven years of age (n = 6,586) and an IQ test at eight years of age (n = 5,449). Usual fish intake of mothers during pregnancy was categorized as: none, 11.9 percent; 1 to 340 g/wk, 64.7 percent; more than 340 g/wk, 23.4 percent. After adjustment for potential confounding variables, maternal fish intake less than 340 g/wk was significantly associated with increased risk of children in the lowest quartile for verbal IQ at age eight years. Low maternal fish consumption was also significantly associated with increased risk of suboptimum outcomes for proscocial behavior scores at age seven years and for fine motor (18 and 42 months), communication (six and 18 months) and social development (30 and 42 months) scores. Overall, low maternal fish intake during pregnancy was significantly associated with risk of suboptimum infant or child performance for nine of the 23 test outcomes. The authors suggested that advice to limit fish consumption by pregnant women to less than 340 g/wk (about 12 ounces/wk) might reduce the intake of nutrients necessary for optimum neurological development. They noted that, in their data, the risks from limiting the neurodevelopmental benefits of nutrients in fish appear to outweigh the risk of exposure to trace levels of contaminants in fish intake of 340 g/wk.

In a later analysis, the authors further adjusted the results for methylmercury intake, by estimating the methylmercury content of seafood intake (Hibbeln et al., 2007b). Further adjustment for methylmercury strengthened the association of low seafood consumption with risk of low verbal IQ. There was also a small independent risk of low verbal IQ from methylmercury intake. When expressed as verbal IQ points, the analysis with additional adjustment for methylmercury intake found that, compared with maternal seafood intake greater than 340 g/wk, having no seafood intake was associated with children's verbal IQ 2.15 points lower and having low seafood intake (one to 340 g/wk) was associated with verbal IQ 0.61 points lower, significant test for trend, p < 0.05 (Table 13 and 14) (Hibbeln 2007). There was a small independent linear dose-response for methylmercury intake, -0.14 (lower) verbal IQ points per microgram methylmercury intake. This would result in a loss of 0.32 verbal IQ points associated with maternal methylmercury intake for children of mothers consuming more than 340 g seafood per week, compared with no seafood intake (as well as an independent gain of 2.15 verbal IQ points associated with maternal seafood intake).

Project Viva

Pregnant women enrolled in Project Viva during 1999 to 2002 and 2,138 women delivered a live infant and were eligible for further prospective study. Oken and coworkers (2005) studied a subset of 135 mother infant pairs who had maternal hair mercury collected at delivery and infant neurodevelopment assessed at six months of age using a visual memory recognition (VRM) method. Average maternal seafood intake during the second trimester of pregnancy was 1.2 servings per week. In analysis adjusted for covariates, fish intake was significantly associated with higher infant VRM scores and maternal hair mercury was significantly independently associated with lower infant VRM scores. The authors stated that the results suggest that in a U.S. cohort with moderate fish intake, maternal seafood consumption during pregnancy may benefit offspring cognition in infancy, but exposure to higher levels of mercury has adverse effects. They stated that the results merit further investigation and verification in a larger study and in other populations.

Of the 1,579 mother infant pairs remaining in the cohort for the age-three-year visit, 896 had information on maternal fish intake during pregnancy, maternal blood samples for mercury testing, and cognitive test results. The study of Oken and coauthors included 341 of the eligible participants, limited by funding for blood mercury measurements (Oken et al., 2008). Average maternal seafood intake was 1.5 servings per week (S.D. 1.4), 12 percent of mothers consumed more than 2 servings per week and 14 percent did not consume seafood. After adjustment for covariates, drawing and total scores on the Wide Range Assessment of Visual Motor Abilities (WRAVMA) were significantly higher for children whose mothers consumed more than 2 servings of seafood per week, compared with children whose mothers ate no seafood (Table 13 and 14). Children of mothers who ate more than two servings/wk of seafood also had higher scores on the Peabody Picture Vocabulary Test (PPVT) and the WRAVMA pegboard and matching tests, but the results were not statistically significant at p < 0.05. Additional adjustment for maternal red blood cell mercury levels during pregnancy strengthened the positive associations of seafood intake with cognitive scores. With adjustment for covariates, test scores were negatively associated with maternal red blood cell mercury levels, and the association was statistically significant for WRAVMA matching. With additional adjustment for seafood intake, the negative associations of maternal blood mercury with cognitive tests were strengthened and the associations were also statistically significant for PPVT and for WRAVMA total.

When the data were grouped both by maternal fish intake category and maternal red blood cell mercury levels above or not above the 90th percentile, children in the group with maternal seafood intake greater than two servings per week and red blood cell mercury level not above the 90th percentile had WRAVMA scores 5.9 points higher than those in the group with no maternal seafood intake and mercury level not above 90th percentile (Table 14). Based on hair mercury levels in a subset of the full Project Viva cohort, the authors estimated that the 90th percentile of mercury intake in the cohort corresponded to a hair mercury level of greater than 1.2 ppm. The authors stated, "we observed no overall adverse effect upon child development with higher maternal fish intake. Rather, maternal fish intake more than twice a week was associated with improved performance on tests of language and visual motor skills." Additionally, they stated, "Recommendations for fish consumption during pregnancy should take into account the nutritional benefits of fish as well as the potential harms from mercury exposure."

Recent Results from Danish National Birth Cohort

In addition to the studies in Table B-13, results were recently published from an observational study in the Danish National Birth Cohort:

Oken et al., (Oken et al., 2008a) aimed to study associations of maternal prenatal fish intake and breastfeeding duration with child developmental milestones. The authors studied 25 446 children born to mothers participating in the Danish National Birth Cohort, a prospective population-based cohort study including pregnant women enrolled between 1997 and 2002. Mothers reported child development by a standardized interview, which were used to generate developmental scores at ages 6 and 18 mo. The authors used multivariate cumulative ordinal logistic regression to evaluate the odds of higher developmental scores associated with maternal fish intake and breastfeeding, after adjustment for child age, sex, and growth; maternal size and pregnancy characteristics; and parental education and social status. Maternal fish intake increased from a mean of 5.4 g/d in the lowest quintile of intake to 22.3 g/d in the middle quintile and 58.6 g/d in the highest quintile. On average, women in the lowest quintile consumed less than 1 fish serving/wk, those in the middle quintile consumed about 1.5 fish servings/wk, and those in the highest quintile consumed about 3.5 fish servings/wk.

Results included the finding that higher maternal fish intake and greater duration of breastfeeding were associated with higher child developmental scores at 18 mo [odds ratio: 1.29 (95% CI: 1.20, 1.38) for the highest versus the lowest quintile of fish intake, and 1.28 (1.18, 1.38) for breastfeeding for > or =10 mo compared with breastfeeding for < or =1 mo]. The adjusted odds ratios for the association of maternal prenatal fish intake (in quintiles) with attainment of a greater number of developmental milestones at age 18 mo were similar for the lowest and second quintile of maternal prenatal fish intake, and then increased across each of the 3 highest quintiles of intake, respectively. The authors concluded that maternal fish intake during pregnancy and the duration of breastfeeding are independently associated with better early child development. The authors stated that future research and consumption guidelines, incorporating nutritional benefits as well as contaminant risks, should consider the overall effect of prenatal fish consumption on child development.

Dose Response Characteristics in Large Observational Studies

In the study of Daniels et al. (2004) in the ALSPAC cohort, the authors noted that, for most of the outcomes, there was a threshold, or plateau, effect for the relation between fish and cognitive development, indicating benefit from eating fish at least once every two weeks (second quartile), but not incremental increase in benefit with more frequent fish consumption (two highest quartiles). In the study of Hibbeln et al. in the ALSPAC cohort, as noted above, low maternal fish intake during pregnancy was significantly associated with risk of suboptimum infant or child performance for nine of the 23 test outcomes. This result compared test outcomes for children of mothers with prenatal fish consumption in the highest tertile (greater than 340 g/wk) with children of mothers with little or no prenatal fish intake (lowest tertile). The authors also compared test results for children with mothers in the middle tertile of fish intake (1 to 340 g/wk) with results for the highest tertile. In general, adjusted odds ratios showed increased risk of suboptimum performance for children of mothers in the middle tertile compared with children of mothers in the highest tertile, but most results were not statistically significant. For verbal IQ at age 8 years, the adjusted odds ratio was 1.09, but was not significant (95%CI 0.92 to 1.29). For full scale IQ at age 8 years, the result was near significance, adjusted odds ratio 1.19 (95%CI 0.99 to 1.42) and for social development at age 42 months, the result was significant, adjusted odds ratio 1.17 (95% CI 1.01 to 1.35). As mentioned above, in a later analysis, Hibbeln and coauthors (2007b) further adjusted for methylmercury, strengthening the association of low fish consumption with risk of low verbal IQ at age 8 years. For no maternal fish consumption compared with the highest tertile of consumption, the odds ratio for the risks of low verbal IQ was 1·98 (95% CI 1·39–2·81), and for maternal consumption 1–340 g/week compared with >340 g/week the odds ratio was 1·34 (95% CI 1·05–1·72), both significant, test for trend p=0·0001. (There was also a small risk of low verbal IQ from methylmercury exposure (odds ratio for one SD increase 1·14, 95% CI 1·02–1·27, p=0·0229).

In the study of Oken et al. (2008) in the Project Viva cohort, the association of better child test performance was found for children of mothers who consumed more than 2 servings of fish per week (highest tertile) compared with children of mothers with no fish intake. Fish consumption of two servings/week or less (middle tertile) was not associated with a benefit. As mentioned above, in the study of Oken et al. (2008a) in the Danish National Birth Cohort, the adjusted odds ratios for the association of maternal prenatal fish intake (in quintiles) with attainment of a greater number of developmental milestones at age 18 months were similar for the lowest and second quintile of maternal prenatal fish intake, and then increased across each of the three highest quintiles of intake, respectively.

Although the results of Daniels et al. (2004) suggested a threshold effect for the relation between maternal fish intake and children’s cognitive development, this was not seen in the other large cohort studies. In general, the maternal fish intake in the cohort studies was grouped for analysis (by tertiles, quartiles or quintiles), and the analyses were limited in their capacity to identify the presence or absence of a threshold or describe the shape of a dose-response relationship. As discussed previously in this document, there is inherent error in measuring dietary intake of individuals, and this includes measuring intake of fish or n-3 LC PUFA in observational studies. In general, nondifferential error in exposure measurement attenuates the apparent magnitude of the association between exposure and health outcome. In particular, potential misclassification of dietary intake is a barrier to identifying statistically significant differences in outcome between adjacent intake categories (tertiles, quartiles, quintiles), making it is difficult to identify the presence or absence of a threshold effect.

Comparison with Cohen et al. Dose-response

The observational studies of Hibbeln et al. (2007) and Oken et al. (2008) provide quantitative estimates of the association of maternal seafood intake during pregnancy, in grams of seafood/wk or servings/wk, with children's scores on neurodevelopment tests at age eight and three years, in ALSPAC and Project Viva, respectively (14). These results can be can be expressed as maternal DHA intake, in grams of DHA, for comparison with the analysis of Cohen et al. (2005a, c), which was based on trials of supplemented formula in infants. Hibbeln et al. grouped the DHA content of maternal fish as white fish, 0.32 grams of DHA/serving; oily fish, 0.89 grams of DHA/serving; shellfish, 0.34 grams of DHA/serving. Three fish servings per week corresponded to approximately 340 grams of fish/wk. Results showed that, adjusted for covariates, maternal intake greater than 340 grams per wk was associated with children's verbal IQ 2.15 points higher (95 percent CI 0.04 to 4.33). To express the results in terms of maternal DHA intake, one can assume that a woman consuming more than 340 grams of fish a week consumes white fish, oily fish and shell fish in equal amounts, obtaining a total of 1.56 grams of DHA from the three servings in a week. This would correspond to 1.38 verbal IQ points per one gram of DHA/wk (2.15 IQ points/1.56 gram of DHA). Oken et al. (2008) directly estimated the association of maternal DHA + EPA intake with children's scores on the WRAVMA. They found children's WRAVMA scores were 1.1 points higher for each 0.1 g ram of DHA + EPA per day maternal intake (95 percent CI 0.1 to 2.0). If one assumes that DHA is half the total of DHA + EPA, this would correspond to 2.2 points per 0.1 gram of DHA/day or 3.1 IQ points per one gram of DHA/week.

The analysis of Cohen et al. (2005a, c), based on trials of infant formula supplements and a series of assumptions, estimated that children scored 1.3 IQ points higher for each one gram per day maternal DHA intake, or 0.19 IQ points for each one gram DHA/week. This is considerably lower in magnitude than estimates derived for one gram/week maternal DHA intake in observational studies, approximately 1.38 verbal IQ points in Hibbeln et al., and 3.1 WRAMVA points in Oken et al.

(e) Summary and Conclusions

This section has summarized recent reports and review articles and presented an overview of current scientific information on the association of maternal fish consumption with infants' and children's visual and cognitive neurodevelopment. To provide background for risk and benefit assessment, this section also identified reports of quantitative dose-response relationships with potential for consideration in risk and benefit assessment modeling.

Randomized trials of maternal supplementation in pregnancy and lactation: Among the few available studies of maternal supplementation, women in the Helland et al. (2003) study were supplemented with fish or fish oil providing 1.2 grams of DHA per day during pregnancy and lactation and increased infant DHA blood levels were demonstrated biochemically (Eilander et al. 2007). Limitations included uncertain effect of the corn oil control supplement, the small subset of the population that received follow up IQ testing at age four years, and uncertain differences in background n-3 LC PUFA intake between Norwegian and U.S. women. However, the 4.1 point higher average K-ABC Mental Processing IQ scores of the children of fish oil supplemented mothers supports the plausibility of measurable neurodevelopmental benefits of maternal seafood consumption and gives one example of magnitude of dose-response. Additional maternal supplementation trials would be helpful to replicate this result, and to add features such as detailed background n-3 LC PUFA status, supplementation in pregnancy alone or including lactation, various levels of fish oil supplement dose, and several years of complete, planned follow up testing.

Randomized trials of infant formula supplementation: The complexity and inconsistency of the literature on supplementation of infant formula with DHA is a barrier to demonstrating the plausibility of measurable neurodevelopmental benefits for infants and children. The potential for estimating a quantitative dose-response from these data is limited. Among the factors that differed across the randomized trials were: infant population (preterm or term birth), timing of supplementation (beginning at birth or after period of breastfeeding; duration of a few months to one year), test formula composition (presence of AA; levels of DHA, AA and ALA), additional breastfed comparison group, neurodevelopment outcome (vision, cognitive, general development, other), visual acuity testing (behavioral or electrophysiologic), neurodevelopment testing (global or targeted assessment), age at testing (early infancy to three years or older). Systematic reviews and meta-analyses evaluated the randomized trials in subgroups according to various study conditions, and generally found the evidence for neurodevelopmental benefit of DHA supplemented formula to be inconsistent and inconclusive (Simmer 2001; Simmer and Patole 2004; Lewin et al., 2005; Smithers et al., 2007; Simmer et al., 2008a, 2008b). Studies were grouped differently in different systematic reviews, and newer studies were available for more recent reviews, making comparisons difficult across reviews.

The analysis of Lauritzen et al. (2001) concentrated on a single age at testing (four months) and identified formula composition and visual acuity method as likely sources of heterogeneity among trials. These authors recommended that future trials use conditions from previous positive trials, including DHA as 0.36 percent of lipids in test formula and electrophysiologic method for visual acuity testing. The meta-regression of Uauy et al (2003) quantified the dose-response for DHA equivalents in 12 comparisons from seven controlled trials of term infant visual acuity at four months of age (Table 3). Morale et al. (2005) analyzed visual acuity at age 12 months in studies from a single laboratory and found a linear dose-response for duration of supply of LCPUFA from formula supplemented with DHA as 0.36 percent of lipids, breastfeeding, or both (Table 12). Birch et al. (2005) designed a trial to carry out the Lauritzen et al. recommendations regarding DHA level in test formula and electrophysiological visual acuity as well as adequate sample size (greater than 20 per group). Supplemented infants had significantly better visual acuity at six, 17, 39 and 52 weeks of age and better stereoacuity at 17 weeks.

Most studies showed little evidence of a positive effect of supplemented formula on infant neurodevelopment using global tests, such as the Bayley scales. A few studies reported positive effects using more specific, focused developmental assessments, but these assessment methods were not adopted by other research groups (Willatts et al., 1998). The study of Birch et al. (1998) did find a positive effect of supplemented formula for four months using Bayley's MDI at 18 months of age. In a follow up at four years of age, infants supplemented with DHA plus AA had mean Wechsler Performance, Verbal and Full Scale IQ scores that were 4.4, 5.7 and 6.5 points higher, respectively, than scores of control infants (Birch et al., 2007). However, the statistical significance of this comparison was not tested directly but in a research design including a breastfed group and a DHA (with no AA) supplemented group. A secondary analysis of the IQ comparison for DHA plus AA supplemented and control infants from Birch et al. (2007) would show whether the result is statistically significant and if not significant, what sample size would be needed to replicate the results with adequate power.

Cohen et al (2005a, c) pooled the results of nine unique trials of supplemented formula and neurodevelopmental outcomes. Based on the average DHA level in supplemented formulas, the authors estimated an effect size of 4.6 IQ points for each one percent DHA (as percent of lipids) in infant formula (Table 9). In the supplemented formula of Birch et al. (2007), the DHA level was 0.36 percent, giving a Full Scale IQ effect size of 18 points (6.5/0.36) per one percent DHA in formula, considerably larger than the 4.6 point effect size of Cohen et al. (2005a,c). Cohen and coauthors reported only a point estimate and did not state whether their result was significantly different from no effect.

Observational studies: Observational studies, such as prospective cohort studies, consider outcomes related to participants' actual diets. In a project on the Risks and Benefits of Seafood, maternal fish consumption, rather than infant or maternal fish oil supplementation, is the actual exposure most relevant to assessing potential health benefits for infant and child neurodevelopment. Although an observational study cannot conclusively demonstrate a cause and effect relationship, possible confounding variables that are known and measured can be adjusted for in the statistical analysis.

In two large cohort studies, children's visual function (Williams et al., 2001) and neurodevelopment (Daniels et al., 2004, Oken et al., 2005) were positively associated with mother's fish intake during pregnancy, with adjustment for covariates. The association with visual function is consistent with certain analyses of supplemented infant formula (Lauritzen et al., 2001, Uauy et al., 2003, Morale et al., 2005, Birch et al., 2005). Recent results estimated a positive, quantitative association between maternal fish consumption and children's developmental scores in Project Viva at three years of age (Oken et al., 2008) and in the ALSPAC cohort at eight years of age (Hibbeln et al., 2007a,b, Hibbeln 2007) (Table 14). As discussed above, the magnitude of the quantitative estimates from observational studies is considerably larger than estimates based on infant supplementation studies and a series of assumptions (Cohen et al., 2005a, c).

In both observational cohorts, the positive association of neurodevelopment with mothers' fish intake was stronger with additional adjustment for maternal mercury exposure. As summarized above, independent, negative associations of neurodevelopment with maternal mercury exposure were also observed, but these were smaller than the independent, positive associations with maternal fish intake (Hibbeln et al., 2007a, b, Hibbeln 2007, Oken et al., 2008). This was in contrast to the Cohen et al. (2005a) risk benefit assessment, which used different types of data and evidence for DHA benefits of fish intake (Cohen et al., 2005a) and for risks of mercury (Cohen et al., 2005b). As discussed elsewhere in this document and in the draft FDA risk and benefit assessment report, Cohen et al. (2005b may have overestimated the dose-response for the risks of maternal methylmercury exposure. However, a possible underestimate of the dose-response for the benefits of maternal DHA intake in Cohen et al. (2005b) should not be overlooked. The quantitative estimates of neurodevelopmental DHA benefits of Cohen et al (2005a, c) have been used in other analyses (Guevel et al., 2008), but should be viewed with caution because of their inconsistency with the cohort studies.

The identification of independent neurodevelopmental benefits of maternal seafood intake and risks of maternal mercury exposure in Project Viva and the ALSPAC cohort are consistent with recent data from established cohort studies of maternal mercury exposure and children's neurodevelopment. Structural equation modeling of neurodevelopmental test data at seven and 14 years of age from the Faroe Islands showed that, after mutual adjustment for both variables, there was an independent, positive association with maternal fish intake as well as a negative association with maternal mercury exposure (Budtz-Jorgenson et al., 2007). Preliminary results from the Seychelles nutrition cohort suggested that children's developmental tests were positively associated with maternal n-3 LCPUFA blood levels and negatively associated with maternal hair mercury (Myers et al., 2007). These associations were stronger when mutually adjusted for the other variable.

Commenting on the results of the Seychelles study and the preliminary results of the Seychelles nutrition cohort, Myers and coworkers (2007) stated, "Given the known importance of prenatal nutrition to optimal infant development and the limited data linking prenatal MeHg exposure to adverse subtle developmental outcomes at the levels of exposure achieved by fish consumption, caution in limiting fish consumption would appear to be indicated." Other researchers have expressed similar concern that limiting the quantity of maternal fish consumption (with the exception of certain high mercury fish) may limit the potential neurodevelopmental benefits (Mozaffarian and Rimm 2006, Hibbeln et al., 2007, Oken et al., 2008).

Table B-2: Controlled trials of omega-3 fatty acid supplementation of infant formula: reports, reviews and meta-analyses included in this in this inventory.
Section Study Date Type of Study Neurodevelopmental Outcome
Preterm Infants Term Infants
Vision General or Cognitive Vision General or Cognitive
Discussed in Section on Recent Reports and Recommendations IOM Macronutrient Report 2002 Report with tabulated studies - - YES YES
SACN - 2004 Report with tabulated studies YES YES YES YES
Lewin AHRQ 2005 Report with meta-analyses— General conclusions YES YES YES YES
IOM Seafood Choices 2006 Report with tabulated studies YES YES YES YES
Discussed in Section on Other Recent Systematic Reviews, Meta-Analyses and Risk Assessments Willatts - 2000 Narrative review with tabulated studies - YES - YES
SanGiovanni - 2000 Meta analysis YES - - -
SanGiovanni - 2000 Meta analysis - - YES -
Lauritzen - 2001 Narrative review with tabulated studies YES YES YES YES
Simmer Cochrane 2001 Meta analysis - - YES YES
Uauy - 2003 Meta analysis and meta regression - - YES YES
Simmer Cochrane 2004 Meta analysis YES YES - -
Lewin AHRQ 2005 Report with meta-analyses— Detailed results YES YES YES YES
Cohen Harvard Risk Benefit 2005 Meta regression - - - YES
Fleith - 2005 Narrative review with tabulated studies YES YES YES YES
Eilander - 2007 Narrative review with tabulated studies YES YES YES YES
Smithers - 2008 Meta-analysis - YES - -
Simmer Cochrane 2008 Meta-analysis YES YES - -
Simmer Cochrane 2008 Meta-analysis - - YES YES
Table B-3: Meta regression equations from Uauy et al for prediction of relative visual acuity in term infants at four months of age by intake of DHA or equivalents, at different bioequivalence factors.
Bioequivalence Factor
  ALA:DHA  
Visual acuity relative response
(logMAR test/logMAR control)
Unweighted Weighted by sample size
Unweighted Slope Slope Intercept r squared p r squared p
visual acuity relative response per DHA % of FA visual acuity relative response per DHA or equivalent (mg/day) visual acuity relative response
none -0.6776 -0.0024 1.1307 0.395 0.027 - -
100:1 - -0.0026 1.1620 0.5313 0.006 0.41 0.025
100:5 - -0.0031 1.2621 0.5989 0.003 0.48 0.013
100:10 - -0.0039 1.4255 0.6781 0.001 0.58 0.004
Data from Uauy et al., 2003.
MAR = Minimum angle of resolution
Note that a lower minimum angle of resolution indicates better visual acuity, therefore the negative slopes show better visual acuity with increased intake of DHA or DHA equivalents.
Table B-4. Studies included in Systematic Review by Lewin and coworkers 2005 (AHRQ Report) for infant/child outcomes.
Outcome Research question Number of studies Randomized controlled trials Observational studies Observational studies
Prospective Cross sectional
Visual Acuity Maternal intake and/or biomarkers 2 1 - 1
Breast milk content 4 2 2 -
Infant formula supplements, preterm 9 9 - -
Infant formula supplements, term 13 13 - -
Maternal biomarkers 1 - - 1
Child biomarkers 21 3 preterm infants
9 term infants
3 8
Neurological Maternal intake and/or biomarkers 1 1 - -
Breast milk content 2 1 1 -
Infant formula supplements, preterm 6 6 - -
Infant formula supplements, term 8 8 - -
Maternal biomarkers 1 - - 1
Child biomarkers 5 4 term infants 1 -
Table B-5. Summary of Lewin et al (AHRQ) meta analyses of randomized controlled trials for infant/child visual outcomes.
Type of Study Infant Formula Visual Test Number of studies Summary of meta-analyses
Preterm,
Nine studies
DHA Behavioral 2 For corrected ages 0 and 12 months, there was just one study, results were positive but not statistically significant.
For corrected ages 2, 4 and 6 months, the meta analyses of the 2 studies were positive but not statistically significant.
DHA + AA Behavioral 6 For corrected ages 0 and 3 months, there was one study each, results were positive but not statistically significant.
For corrected age 12 months, there were 2 studies and for corrected ages 2 and 4 months, there were 3 studies each. Results of the meta analyses were positive but not statistically significant
DHA + AA Electro-physiological 2 For corrected ages 0 and 6 months, there was one study each, results were positive and statistically significant.
For corrected age 4 months, meta analysis of the 2 studies was positive but not statistically significant.
Term,
13 studies
DHA Behavioral 2 For age 9 months, there was just one study, results were negative but not statistically significant.
For ages 2, 4, 6, and 12 months, meta analysis of the 2 studies was negative but not statistically significant. (At age 12 months, the negative result was near significance, p = 0.05.)
DHA Electro-physiological 3 For ages 8 and 9 months, there was one study each, results were negative but not statistically significant.
For ages 2 and 12 months, there were 2 studies and meta analysis was positive but not statistically significant.
For age 6 months, there were 2 studies and for age 4 months there were 3 studies, the meta analyses were near neutral.
DHA + AA Behavioral 3 For age 9 months, there was just one study, results were near neutral.
For ages 6 and 12 months, there were 2 studies and meta analysis was near neutral.
For age 4 months, there were 3 studies and meta analysis was negative but not statistically significant.
For age 2 months, meta analysis of the 3 studies was positive and statistically significant.
DHA + AA Electro-physiological 7 For age 9 months, there was just one study, results were negative but not statistically significant.
For age 8 months, there was just one study, results were near neutral.
For age 2 months, there were 2 studies and for age 6 months there were 3 studies, meta analyses were positive but not statistically significant.
For age 12 months, there were 4 studies, meta analysis was positive and statistically significant.
For age 4 months, there were 6 studies and meta analysis was positive and near statistical significance ( p = 0.07).

Table B-6. Quantitative results of selected Lewin et al (AHRQ) meta-analyses of randomized controlled trials for infant/child visual outcomes in term infants.
Infant Formula Visual Test Age Number of Studies Difference in visual acuity (octaves) 95% CI p value Hetero-geneity (p value)
DHA + AA Behavioral 2 months 3 * 0.37 0.15 to 0.6 <0.01 0.32
DHA + AA Electro-physiological 4 months 6 ** 0.17 -0.01 to 0.36 0.07 < 0.01
DHA + AA Electro-physiological 12 months 4 *** 0.32 0.09 to 0.56 0.01 < 0.01
* Auestad 1997, Carlson 1996, Birch 1998
** Birch 2002, Auestad 1997, Birch 1998, Makrides 1999, Makrides 1995, Jorgensen 1997
*** Birch 2002, Auestad 1997, Birch 1998, Hoffman 2003
Table B-7. Summary of Lewin et al (AHRQ) meta analyses of randomized controlled trials for infant/child neurological and cognitive outcomes.
Type of Study Outcome and Test Number of studies Summary of meta-analyses
Preterm
Neurological (Bayley's PDI) 6 The authors stated that meta analysis was not possible for this outcome. Five of the studies measured neurological outcome using Bayley's PDI, but results from more than one study were only available at 2 ages: corrected age 12 and 18 months.
Of the 2 studies with results at 12 months corrected age, one study fed supplemented formula until 6 months corrected age and in the other until 12 months corrected age. Therefore, data from the 2 studies was not combined.
Cognitive (Bayley's MDI) 6 The authors stated that meta analysis was not possible for this outcome. Five of the studies measured cognitive outcome using Bayley's MDI, but results from more than one study were only available at 2 ages: corrected age 12 and 18 months.
Of the 2 studies with results at 12 months corrected age, one study fed supplemented formula until 6 months corrected age and in the other until 12 months corrected age. Therefore, data from the 2 studies was not combined.
Term Neurological (Bayley's PDI) 8 Seven studies measured neurological outcome using Bayley's PDI.
For age 12 months, there were 3 studies, meta analysis was negative but not statistically significant.
(Test formula was supplemented with DHA + AA. Infants were exclusively formula fed until 4 months of age)
Cognitive (Bayley's MDI) 8 Seven studies measured cognitive outcome using Bayley's MDI.
For age 12 months, there were 3 studies, meta analysis was negative but not statistically significant.
(Test formula was supplemented with DHA + AA. Infants were exclusively formula fed until 4 months of age)
Table B-8. Quantitative results of selected Lewin et al (AHRQ) meta-analyses of randomized controlled trials for infant/child neurological and cognitive outcomes in term infants.
Formula Test Age Number of Studies Difference in Score 95% CI p value Hetero-geneity
(p value)
DHA + AA Neurological
(Bayley's PDI)
12 months 3 * -2.8 -7.43 to 1.82 0.24 0.21
DHA + AA Cognitive
(Bayley's MDI)
12 months 3 * -0.8 -3.24 to 1.63 0.52 0.92
* Auestad 1997, Auestad 2001, Makrides 1999
Table B-9. Meta-regression (dose-response) for DHA exposure and cognitive development based on randomized controlled trials of formula supplements.*
Cognitive domain Number of unique studies Number of comparisons Weighted Average Test Score Point Difference, Supplement Group Compared to Control Group ** Dose-response
(Standard Deviations) ("IQ points")*** (IQ points per 1% of formula phospholipids as DHA)## (IQ points per 1 gram per day increase in maternal DHA intake in pregnancy)###
Point estimate Range
General intelligence 8 12 0.09 1.3 - - -
Verbal 2 4 0.08 1.2 - - -
Motor 5 9 0.05 0.8 - - -
Weighted combination# 9 25 0.08 1.2 4.6 1.3 0.8 to 1.8
* Data from Cohen et al (2005c).
** Test result differences weighted by statistical precision (inverse of normalized standard error squared) and test result differences at various ages weighted to increase linearly with age in months at testing.
*** One Standard Deviation equals 15 points on the IQ scale.
# The domains were subjectively weighted in the analysis: general intelligence, 1.0/1.8; verbal ability, 0.6/1.8; motor skills, 0.2/1.8.
## Based on average DHA formula concentration of 0.26 percent of phospholipids (Standard Error, 0.03 percent).
### Based on Gibson et al (1997) each 1 percent DHA in breast milk corresponds to an increase of 4.68 percent DHA in infant plasma and 4.52 percent DHA in infant red blood cells. Based on Connor et al (1996) an increment of 0.83 percent DHA in plasma and 1.78 percent DHA in red blood cells corresponds to 1 g/day maternal DHA supplement. Therefore, each 1 g/d maternal DHA supplement was estimated to raise infant plasma DHA an amount corresponding to 0.83/4.68 = 0.18 percent DHA in breast milk or formula, and to raise infant red blood cell DHA an amount corresponding to 1.78/4.52 = 0.39 percent DHA in breast milk or formula. 1
Table B-10. Randomized controlled trials of maternal DHA supplementation on infant visual and cognitive development.
First author Year Number Pregnancy Lactation Visual Age Benefit Cognitive Age Benefit
Malcolm 2003a, b 63 YES - YES 0-5 d; 50, 66 wk none - - -
Tofail 2006 249 YES - - - - YES 10 mo none
Helland 2001 341 YES YES - - - YES 27, 39 wk none
Helland 2003 90 YES YES - - - YES 4 yr + 4.1 IQ pt
Gibson 1997 52 - YES YES 12, 16 wk none YES 1, 2 yr none
Lauritzen 2004, 2005 97 - YES YES 2, 4 mo negative YES 2, 4, 9, 12, 24 mo positive and negative
Jensen 2005 160 - YES YES 4, 8 mo negative YES 12, 30 mo positive
Dunstan 2008 98 YES - - - - YES 2½ yr positive
Based in part on Eilander et al. (2007). Updated to include Dunstan et al. (2008).
Table B-11. Meta-analysis of randomized controlled trials of n-3 long chain polyunsaturated fatty acid formula supplementation of preterm infants on neurodevelopment by Bayley Scales of Infant Development at 12 to 18 months corrected age.
Neurodevelopment test Number of Studies Pooled weighted
mean difference in test score
95% CI p value Heterogeneity (p value)
MDI - BSID II - Subtotal 5 3.44 (0.56, 6.31) 0.02 0.08
MDI - BSID I - Subtotal 2 -4.09 (-9.85, 1.67) 0.16 0.29
MDI - Total 7 2.13 (-0.87, 5.14) 0.16 0.02
PDI - BSID II - Subtotal 5 2.87 (-0.9, 6.65) 0.14 0.02
PDI - BSID I - Subtotal 2 -7.99 (-14, -1.99) 0.009 0.51
PDI - Total 7 0.70 (-3.26, 4.66) 0.73 0.002
Data from Smithers et al, 2008
MDI, Mental Development Index; PDI, Psychomotor Development Index; BSID, Bayley Scales of Infant Development
Table B-12. Difference in infant visual acuity at 52 weeks of age by duration in weeks of DHA consumption from human milk or formula
Data source Source of DHA N Dose-response slope Difference in visual acuity at age 52 weeks
Difference in visual acuity Some DHA consumption compared with no DHA
36 weeks DHA 52 weeks DHA
change in logMAR per week of DHA consumption) p (logMAR) Lines on eye chart (logMAR) Lines on eye chart
Group Human milk and/or formula 296 -0.003 <0.001 -0.1 1 -0.14 1 1/2
Group Formula only 80 -0.003 - - - - -
Group Human milk only 94 -0.002 - - - - -
Individual Human milk only 94 -0.002 <0.005 - - - -
Data from Morale et al (2005).
Supplemented formulas contained DHA as 0.36% of lipids and AA as 0.72% of lipids.
DHA, docosahexaenoic acid; AA, arachidonic acid; logMAR, log of minimum angle of resolution
Note that a lower minimum angle of resolution indicates better visual acuity, therefore the negative slopes show better visual acuity with greater duration of DHA consumption in weeks. 1
Table B-13: Observational studies of maternal fish or DHA intake in pregnancy or lactation and infant development.
Study and Location Cohort Number Outcome Result Other

Jørgensen et al., 2001

Denmark

Cross-sectional 39 Vision DHA level in breast milk was significantly positively associated with visual acuity of 4-month old term infants in multiple regression analysis. Frequency of maternal fish intake was positively associated with breast milk DHA level. Frequency of maternal fish intake together with maternal fish consumption the previous day explained 57% of the variation in breast milk DHA level.

Innis et al., 2001, 2002, 2003

Canada

- 83 Vision, speech perception, cognitive development Infants were fully breastfed for at least 3 months; infant DHA blood levels at age 2 months after adjusting for covariates were significantly related to: 1) visual acuity at 2 months and 12 months; 2) speech perception performance at 9 months; In follow-up studies, the infants' DHA blood levels at age 2 months were significantly related to language production and comprehension at 14 and 18 months and vocabulary comprehension and production at 18 months, from conference proceedings. Average DHA level in mothers' breast milk increased by tertile of infant DHA blood levels at 2 months. No association with visual acuity at 4 or 6 months or with cognitive development tests at 6, 9 or 12 months.

Williams et al., 2001

Avon, England

Avon Longitudinal Study of Parents and Children (ALSPAC) 435 Vision, stereoacuity Both breastfeeding and maternal oily fish consumption during pregnancy were independently positively associated with children's visual stereoacuity (depth perception) at age 3 ½ years;   Stereoacuity results have persisted in the children at age 7 years, unpublished data Maternal pregnancy red blood cell DHA in the full cohort was significantly higher in multiple regression analysis for women who reported consuming oily fish, N = 4,733

Daniels et al., 2004

Avon, England

Avon Longitudinal Study of Parents and Children (ALSPAC) 7,421 Cognitive Development Fish intake by the mother during pregnancy, and by the infant postnatally, was associated with higher mean developmental scores on adaptations of the MacArthur Communicative Development Inventory at 15 months and the Denver Developmental Screening test at 18 months No association of cord tissue mercury with these development tests N = 1,054

Gustafsson et al., 2004

Sweden

- 28 Cognitive development Ratio of DHA to AA level in breast milk (colostrum) was positively associated with IQ at age 6 ½ years, adjusted for covariates. Length of breastfeeding was also significant in the model. IQ was also significantly associated with colostrum ratio, (22:5n-6 + DHA)/(AA +EPA), step 4+5 of desaturation chain. No association of IQ with fatty acid or ratio levels in mature breast milk.

Oken et al., 2005

Boston, USA

Project Viva 135 Cognitive development After adjustment, maternal fish consumption in pregnancy positively associated with cognitive development by visual memory recognition (VMR) test at age 6 months. Maternal hair mercury at delivery negatively associated with VMR test.

Hibbeln et al., 2007a, 2007b

Avon, England

Avon Longitudinal Study of Parents and Children (ALSPAC) 8,916 Development-al, behavioral, cognitive After adjustment, maternal fish intake during pregnancy of less than 340 g/wk was associated with increased risk of children in lowest quartile for verbal IQ at age 8 years. Low maternal fish consumption was also associated with increased risk of suboptimum outcomes for prosocial behavior scores at age 7 years and for fine motor (18 and 42 months), communication (6 and 18 months) and social development (30 and 42 months) scores. Additional adjustment for estimated maternal methylmercury intake from fish increased the risk of low verbal IQ with low maternal fish consumption. There was also a small risk of low verbal IQ associated with estimated maternal methylmercury exposure.

Hibbeln, 2008

Avon, England

Avon Longitudinal Study of Parents and Children (ALSPAC) 11, 875 Development-al, behavioral, cognitive After additional adjustment for estimated maternal methylmercury intake, results were expressed as verbal IQ points. Having no maternal fish intake was associated with children's verbal IQ 2.15 lower (95% CI -4.33 to 0.04) and low maternal fish (1 to 340 g/wk) intake was associated with children's verbal IQ 0.61 points lower (95% CI -2.08 to +0.86) compared with maternal intake greater than 340 g/wk, significant test for trend p<0.05. The linear effect of estimated maternal methylmercury intake was verbal IQ 0.14 points lower per µg of intake (95% CI -0.82 to +0.54), with maternal fish intake greater than 340 g/wk had a loss of 0.32 verbal IQ points attributable to estimated maternal methylmercury intake (yet an overall gain of 2.15 verbal IQ points attributable to fish intake) compared with children with no maternal fish intake.

Oken et al, 2008

Boston, USA

Project Viva 341 Cognitive development After adjustment, maternal fish intake of more than 2 servings per week during pregnancy compared with no fish intake was associated with higher mean scores of 1.2 (95% CI -3.5 to 6.0) at age 3 years on Peabody Picture Vocabulary test and 5.3 (95% CI 0.9 to 9.6) on Wide Range Assessment of Visual Motor Abilities. Association strengthened after further adjustment for maternal red blood cell (RBC) mercury during pregnancy. Maternal RBC mercury was independently associated with lower scores on both tests.
Table B-14. Dose-response slopes for association of maternal seafood intake during pregnancy and children's scores on neurodevelopment tests in observational cohorts.
Cohort N Age Neurodevelopment test Maternal Fish Intake Comparison Dose Response Slope 95% Confidence Interval Dose Response Slope 95% Confidence Interval
Adjusted for covariates Additional adjustment for maternal mercury intake
ALSPAC Cohort 8916 8 Verbal IQ more than 340 g/wk compared with none - - 2.15 0.04 to 4.33
Project Viva 341 3 Peabody Picture Vocabulary Test more than 2 servings/wk compared with none 1.2 -3.5 to 6.0 2.2 -2.6 to 7.0
- 3 Wide Range Assessment of Visual Motor Abilities more than 2 servings/wk compared with none 5.3 0.9 to 9.6 6.4 2.0 to 10.8
- 3 Wide Range Assessment of Visual Motor Abilities more than 2 servings/wk compared with none, in women with blood mercury levels at or below 90th percentile - - 5.9 1.0 to 10.9
ALSPAC data from Hibbeln et al 2007a and b, Hibbeln 2007; Project Viva data from Oken et al 2008.
Verbal IQ from abbreviated Wechsler Intelligence Scale for Children, WISC-IIIUK