Does omega-3 supplementation during pregnancy prevent postpartum depression? Improve baby's brain development?
Omega-3 fats are essential – we must take them in from our diets because our body cannot synthesize them. These fats are extremely important for many facets of our health, especially the health of the brain and cardiovascular system. Omega-3 fat is a major structural component of brain cell membranes and the retina – about 60% of the dry weight of the brain is made up of fat, and DHA is the most abundant fat in the brain. 
As such, DHA is an essential factor in early brain development, and maintaining adequate levels during pregnancy is believed to benefit the child’s cognitive development. The current consensus is that pregnant women should consume at least 200 mg DHA each day to promote normal fetal brain development. Pregnant women are also urged to limit fish consumption because of mercury contamination, which is harmful to the brain of the developing baby. Fish oil or vegan DHA supplements are therefore an attractive option for pregnant women.
In 2009, the results of three randomized controlled trials were pooled and showed that babies given supplemental DHA in formula scored higher on a problem solving test at 9 months of age than babies given control formula. However, there is some disagreement in the literature as to whether DHA supplementation during pregnancy and infancy actually improves cognitive development in the child.
A recently published study in the Journal of the American Medical Association reported an unexpected finding: Pregnant women who took fish oil capsules (800 mg DHA and 100 mg EPA per day) compared to vegetable oil placebo capsules did not have lower incidence of postpartum depression, and their children did not have improved cognitive development at 18 months of age.
Of course, this does not mean that pregnant women shouldn’t bother taking DHA. The developing baby’s only source of DHA for beginning to build its brain tissue is its mother’s dietary intake. DHA supplementation also reduces the risk of preterm birth – a factor known to be associated with compromised cognitive development in the infant and maternal depression.
In reference to the lack of effect on symptoms of depression, the therapeutic effects of omega-3 supplements on depression are due mostly to EPA rather than DHA, according to a recent meta-analysis.  I recommend omega-3 supplementation including 1,000 mg of EPA to treat depression – the relatively low dose of EPA used in this trial may therefore be responsible for the lack of effect on depression in this study.
An editorial published in response to the study stated potential reasons why this outcome occurred – these comments also shed light on why there seem to be discrepancies in the medical literature on this subject. One possibility is that the criteria used to measure infant brain development in this study were not sufficiently sensitive to detect small but important differences in cognition in 18-month olds. The criteria used were based on global measures of cognition, and are not designed to detect differences in specific processes such as memory, attention, and problem-solving. As mentioned above, previous studies have seen differences in problem solving in infants given supplemental DHA. Furthermore, there are several cognitive functions that cannot be accurately measured until children reach preschool and school age – the editorial cites a smaller study of fish oil supplementation during pregnancy that found enhanced IQ scores in 4 year olds. I agree that it isn’t possibly to reliably measure intelligence in an 18-month old, and that better results would come from studies that measure cognitive function once the children are in school.
DHA is a vital component of brain tissue, and pregnant women should take at least 200 mg each day to prevent preterm birth and support normal fetal brain development to assure maximum intelligence.
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