Abstract
QUESTION Several pregnant patients have asked recently whether mediareports of children’s intelligence quotients’ increasing with increased intake of essential fatty acids are meaningful enough to be worth the effort of supplementation. What advice should they be given?
ANSWER Existing evidence from interventional studies is sparse and conflicting and should not lead to supplementation with polyunsaturated fatty acids.
Polyunsaturated fatty acids (PUFAs) of the ω-3 and ω-6 families are essential for a healthy diet. ω-3 PUFAs mainly include alpha-linolenic acid (ALA), which is derived from plants, and eicosapentenoic acid (EPA) and docosahexaenoic acid (DHA), which are found in fish oil. ω-6 PUFAs mainly include linoleic acid (LA) and arachidonic acid (AA), which are found in most vegetable oils, whole grain breads, eggs, and cereals. These fatty acids are essential components of the human brain and are required especially in the third trimester of pregnancy when brain growth is at its peak.1,2 As PUFAs from both families are metabolized by the same enzymes, the ratio between them is important.3,4 For example, increasing dietary intake of ω-3 fatty acids might reduce the levels of essential ω-6 products in fetuses.5,6 When ω-3 PUFAs without AA were given to preterm infants, slower growth was reported.7,8 One-year-old children given DHA alone had lower language scores than those given DHA with AA or than controls.9 Therefore, a primary concern of giving ω-3 supplements is the risk of reducing AA levels in growing fetuses and children. Yet ω-3 intake during pregnancy might still have benefits.
Possible benefits of ω-3 supplementation during pregnancy
Prenatal ω-3 intake and preeclampsia
A negative relationship between PUFAs and preeclamspia, or pregnancy-induced hypertension, has been suggested through observational studies,10 but not shown in interventional trials.10–12 Recently, ω-3 intake was even associated with hypertensive disorders during pregnancy.13
Prenatal ω-3 intake and length of gestation
Several studies have suggested that maternal supplementation with ω-3 PUFAs can increase pregnancy duration by 4 to 6 days,5,11,14 but other studies found no such effect.15,16 No decrease in the rate of preterm deliveries, a much more important end point, was found. Among women with previous preterm deliveries, however, a nearly 50% reduction in prematurity was found.17
Prenatal ω-3 intake and fetal size
While several studies have addressed the potential effects of ω-3 supplementation on birth size, most did not find any effect.18 One recent study on LA with ALA supplementation during pregnancy noted higher birth weights in offspring.5
Prenatal ω-3 intake and brain function of offspring
Both ω-3 and ω-6 PUFAs are essential to normal brain development and function.1,2 Yet trials of postnatal ω-3 supplementation have yielded conflicting results. Studies of prenatal supplementation and children’s cognitive function are few and are mostly observational. The only interventional study that assessed maternal ω-3 supplementation and intelligence showed that, at 4 years old, children whose mothers took ω-3 supplements during pregnancy and lactation had higher cognitive function.19 Maternal DHA intake (but not infant intake) positively correlated with children’s mental processing ability. Another study, on prenatal supplementation with fish oil and infants’ visual function found no effect.16 It should be noted that, although statistically significant differences existed in some studies, changes were small and probably of little clinical importance.
Conclusion
Supplementation with ω-3 for pregnant women might influence several obstetric and neonatal characteristics, but conflicting results from too few studies prevent us from drawing definitive conclusions. Much evidence is still missing, such as which types of ω-3 fatty acids are of benefit (ALA, EPA, or DHA) and at what dosage; whether AA should also be added and at what exact ω-6–to–ω-3 ratio; when supplements should be given; and what benefits to mothers, infants, or children should be expected. Until evidence accumulates, no recommendation should be made to encourage pregnant women to take ω-3 fatty acid supplements.
- Copyright© the College of Family Physicians of Canada
