Since the current guidelines on fish consumption were issued, Dr. Emily Oken, a physician and assistant professor at Harvard Medical School, has led studies to examine the sum effect of eating fish.
One of those was published in May in the American Journal of Epidemiology. Researchers asked 341 pregnant women in Massachusetts about their diet and tested their blood mercury levels during the second trimester. Then, when their children were 3, they were tested in a range of thinking and movement tasks.
Children of mothers who ate more than two servings of fish per week had higher scores than kids of non-fish-eating moms, even when other influences of early childhood development, such as birth weight and breast-feeding duration, were factored out. No measurable benefit was seen in kids born to women who ate fewer than two servings of fish per week, which corresponds to the current FDA/EPA advice.
The improvements in kids were even more striking in kids of moms with lower mercury levels, suggesting that choosing low-mercury fish is key. Researchers did ask about broad categories of fish, but, Oken says, it's a big uncertainty in this kind of research. "We don't really know a lot of detail about the kind of fish that women are eating."