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For the nine-plus months of pregnancy, I dutifully downed fish oil pills. I had heard all about the virtues of essential fatty acids (especially DHA, docosahexaenoic acid), known collectively as omega-3s, which are found in fish such as salmon and sardines. These fats are involved in the development of new neurons and help form the cell walls -- the structural support -- of nerve cells. If the healthy brain is like a sponge, then the brain deprived of omega-3 is like a puddle.
Several years ago, in 2007, an enormous study funded by the National Institute of Health looked at the link between children's scores on aptitude tests (at ages 6 months to 8 years) and their mother's prenatal consumption of fish. It turned out that the kids whose moms ate fish more than twice weekly during pregnancy were significantly less likely to have low scores on cognitive tests. Low maternal seafood intake (two or fewer servings weekly) was also associated with increased risk of suboptimum outcomes for prosocial behavior, fine motor, communication, and social development scores. This was a huge deal. The nearly 12,000 expectant women who participated in the study were asked to record how much whole fish they ate, not fish oil supplements.
Naturally, this study -- and smaller studies like it involving whole-fish consumption -- inspired millions of pregnant women to focus on fish oil.
Problem is, not many of us want to or can afford to eat fish every day. Fears of mercury and PCB contamination are valid (many varieties of fish, such as tuna, have high levels that are toxic to fetuses). It's not much of a stretch to say that fish oil pills are a better way to get your daily DHA.
But here's the interesting part. Everyone has assumed that when it comes to omega-3 fatty acids like DHA, the source -- whole fish or fish oil pills --shouldn't matter. Seems reasonable, but is it?
A few very recent fish oil studies cast doubt:
Results of fish oil pill supplementation range from neutral to negative...
• A review of six clinical trials (1280 women in total) involving fish oil pill supplementation during breastfeeding found no significant difference in children's neurodevelopment: language development (intelligence or problem-solving ability, psychomotor development, motor development. In child attention there was a significant difference. For child visual acuity there was no significant difference. For language development at 12 to 24 months and at five years in child attention, weak evidence was found (one study) favouring the supplementation.
• At the Women's and Children's Hospital in Adelaide, Australia, researchers tracked the children of 2400 women who took DHA-rich fish oil pills in the last trimester of pregnancy. The use of these fish oil capsules compared with vegetable oil cap- sules during pregnancy did not result in improved cognitive and language development in their offspring during early childhood.
Other fish oil pill studies found disturbingly negative results:
• At the Universities of Copenhagen and Chapel Hill, researchers followed 120 Danish women who nursed their babies for four months after birth and took fish oil supplements (or olive oil pills). The children were tested in intervals up to seven years. The higher the early intake, the lower the child scored in speed of information processing, inhibitory control, and working memory tests. Boys whose mothers consumed fish oil had lower prosocial scores relative to the olive oil group.
Meanwhile, these recent studies strengthened the evidence that eating fish is brain-boosting:
• In a study that took place the Arctic, 154 11-year-old Inuit children took standardized tests for memory and verbal learning. Their scores were compared with their levels of DHA present in their cord blood at birth. Children who had higher cord plasma concentrations of DHA at birth achieved significantly higher scores on tests related to recognition memory processing. The source of DH in their mothers' diets was fish and marine mammals. Intriguingly, the connection with higher test scores remained intact regardless of seafood-contaminant (PCB and mercury) amounts.
* A UK study of 217 nine-year-olds whose mothers had eaten oily fish in early pregnancy had a reduced risk of hyperactivity and children whose mothers had eaten fish (whether oily or non-oily) in late pregnancy had a verbal IQ that was 7.55 points higher than those whose mothers did not eat fish.
This is what I'd love to see: large studies that compare pregnant/nursing fish-eaters versus pill-poppers. Few researchers have tackled this, in part because we assume DHA works the same no matter how we get it, and because DHA from sources other than pills is difficult to measure or isolate. Interestingly, a study at the Norwegian Institute of Public Health compared height, weight and head circumference results of newborns whose mothers whose main source of DHA was fish versus pills. They found that fish-eaters generally gave birth to larger babies while fish-oil-pill-poppers had newborns with a smaller head circumference.
Is it possible that fish consumption boosts IQ, but fish oil pills do not?
It's dumbfounding, the difference in results between whole fish and fish oil. The researchers that found negative results of supplementation on nursing infants speculated on what goes wrong. It may be that early intervention with fish oil pills results in an "environmental mismatch'' between prenatal and postnatal life," (e.g. the fetus is "programmed" in the womb to live in an environment without abundant DHA and is thrown off when inundated with these fats later on).
Another theory is that the timing in these recent fish oil pill studies is off. The critical period in which fish oil may influence brain growth may be in the first trimester of pregnancy or toward the end of the first year of life -- not during the time periods in which women in these studies were taking fish oil pills. It may be that DHA has a "sweet spot" -- an optimum level below and above which may be detrimental to the developing brain. Indeed, when researchers look at fish oil pill supplementation and DHA-deficient premature infants, the results are much rosier.
There's another compelling explanation of why fish oil pills don't yield the desired results: DHA doesn't do its magic alone. Nutrients and proteins in fish and seafood, other than DHA, may be brain-boosters -- or at least help us (and our fetuses or babies) to absorb or metabolize DHA better. All the fish oil in the sea can't compensate for a bad diet.
In the US, a federal advisory recommends that pregnant women not eat more than two servings of fish weekly. This advice may be misguided given that fish such as salmon and sardines are high in DHA but low in mercury. Pop fish oil pills instead; they're just as good-- that's been the message. But these recent studies point to a different truth.
Thus the case for fish, the whole fish, and nothing but the fish.
Food for thought.
*If you like this blog, click here for previous posts and here to read a description of my most recent book, Do Gentlemen Really Prefer Blondes?, on the science behind love, sex, and attraction. If you wish, check out my forthcoming book, Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.
