Three-year-olds whose mothers ate more fish while pregnant with them score better on several tests of cognitive function than their peers whose mothers avoided seafood, a new study shows.
However, the researchers also found that the amount of mercury in a woman's body rose with the amount of fish she had consumed - and that children exposed to more mercury performed worse on these tests. Based on the findings, they say, it's possible fish could have even greater brain benefits for babies if mothers-to-be consumed seafood with lower mercury levels.
"Recommendations for fish consumption during pregnancy should take into account the nutritional benefits of fish as well as the potential harms from mercury exposure," Dr. Emily Oken of Harvard Medical School in Boston and her colleagues write in the May 15 issue of the American Journal of Epidemiology.
Advisories on mercury contamination of certain types of large, long-lived fish - including tuna and swordfish - have raised concerns about seafood consumption during pregnancy, Oken and her team note. On the other hand, fish are also the chief dietary source of omega-3 fatty acids, substances key to early brain development, they add.
To better understand the risks and benefits of fish consumption, Oken and her team surveyed 341 mothers about their intake of fish during the second trimester of pregnancy, and then had their children complete a battery of tests of cognitive function at three years of age.
On average, women reported eating 1,5 servings of fish each week while they were pregnant. The amount of mercury the women had in their red blood cells was directly related to the amount of fish they ate.
Children's test scores rose with the amount of fish their mothers had consumed, but those whose mothers had more mercury in their bodies performed less well on the tests.
Accounting for the effects of mercury exposure strengthened the effect of fish intake, and vice versa, the researchers found. Benefits were strongest for children whose mothers ate more than two servings a week.
"Our finding that the benefit of fish intake is strengthened with adjustment for mercury levels suggests that if mercury contamination were not present, the cognitive benefits of fish would be greater," Oken and her team explain.
"Maternal consumption of fish lower in mercury and reduced environmental mercury contamination would allow for stronger benefits of fish intake."