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What's Fishy About Fish Oil Pills in Pregnancy?

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Like many other women wanting the most for their baby, I dutifully downed fish oil pills throughout my pregnancy. I had heard all about the brain-building 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. They 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.

My effort was largely inspired by a study that took place several years ago, in 2007, by the National Institute of Health. Nearly 12,000 expectant women who participated in the study were asked to record how much whole fish they ate. Researchers 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 -- for breakfast, lunch, and dinner.

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.

Naturally, this study -- and smaller studies like it involving whole-fish consumption -- inspired millions of pregnant women to focus on the fatty oils in fish. Problem is, not many of us want to or can afford to eat fish so often. 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 DHA and other omega-3s, 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:

• 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. For language development at 12 to 24 months and at five years in child attention, only weak evidence was found (one study) favoring the supplementation.

In 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 capsules during pregnancy did not result in improved cognitive and language development in their offspring during early childhood.

Worse, some fish oil supplement studies found 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 higher the early intake, the lower the child, at age seven, 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.

Looking at the recent studies, the ones that show support for a brain boost involve only eating fish (not fish oil pills):

  • In a study that took place the Arctic, 11-year-old Inuit children who had higher-than-average DHA at birth achieved significantly higher scores on tests related to recognition memory processing. The source of DHA in their mothers' diets was fish and marine mammals, not pills.
  • 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 in late pregnancy had a verbal IQ that was 7.55 points higher than those whose mothers did not eat fish.
  • A study at the Norwegian Institute of Public Health 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?

This is what I'd love to see next: large studies that compare fish-eaters versus pill-poppers during pregnancy and lactation. 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.

The researchers that found negative results of supplementation on nursing infants speculated on what goes wrong.

Here's one theory about what went wrong: If a woman takes fish oil pills for a few months during pregnancy, and stops taking them after the birth (or a baby is exposed to high quantities of DHA after birth but not before), there is a "environmental mismatch'' between prenatal and postnatal life. In other words, the fetus is "programmed" in the womb to have certain nutritional expectations, and is thrown off when conditions change. This is not as farfetched as it sounds. Fetuses learn in the womb what life will be like after birth, and "program" themselves accordingly. When these predictions turn out to be wrong (e.g. during a food shortage or a period of maternal anxiety that reverses after the birth, babies surprisingly, seem to fare worse than if the conditions had remained constant.)

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 one more 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 pharmacy can't compensate for a bad diet.

In the U.S., 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 check out my new book, Do Chocolate Lovers Have Sweeter Babies?: The Surprising Science of Pregnancy.