Feb. 15, 2007 -- Pregnant women who limit their fish consumption to recommended government levels may be doing their unborn babies more harm than good, according to a study from the National Institutes of Health.
Researchers found that women who ate less than 12 ounces of fish or other seafood a week while pregnant were more likely to have children with verbal and other developmental delays than women who ate more than 12 ounces each week.
The findings challenge guidelines from the FDA that advise pregnant women to limit their weekly seafood consumption to 12 ounces, or about two average meals.
The FDA advisory stemmed from concerns that eating more fish could impair brain development by exposing developing fetuses to dangerously high levels of mercury.
But seafood is also a major dietary source of omega-3 fatty acids, which are critical for brain development.
The new findings suggest that, for developing brains, the risks of limiting seafood consumption outweigh the benefits of such a limit, the NIH's Joseph R. Hibbeln, MD, tells WebMD.
"Regrettably, these data indicate that the [FDA-EPA] advisory apparently causes the harm that it was intended to prevent, especially with regard to verbal development," Hibbeln says.
Limiting Fish Not Beneficial
Hibbeln analyzed data collected on close to 12,000 pregnant women in Britain who participated in one of the largest and most comprehensive pregnancy outcome studies ever conducted.
When they were 32 weeks pregnant, the women were asked to fill out detailed questionnaires on the foods they ate during pregnancy.
The British researchers tracked the developmental progress of the children born to the women through age 8, using standardized IQ and other tests.
Twelve percent of the women in the study reported eating no seafood during pregnancy, while 65% reported eating up to 12 ounces of seafood a week, and 23% reported eating more than 12 ounces weekly.
After adjusting for 28 separate potential risk factors for delayed development, Hibbeln and colleagues concluded that children born to women who ate 12 ounces or less were at increased risk for low verbal IQ and other developmental problems, compared with those who ate more than 12 ounces a week.
They also concluded that eating more than 12 ounces of fish a week during pregnancy "benefited a child's neurodevelopment" -- or brain development.
"We did not find compliance with the advisory [to limit seafood consumption] to be of any benefit," Hibbeln says.
"In contrast, we found that compliance with the advisory was associated with harm, specifically with regard to verbal development," he says.
What Should Pregnant Women Do?
Hibbeln stopped short of saying that pregnant women should ignore the FDA-EPA guidelines, or that the federal agencies should change their recommendations.
"It is not the role of the NIH to advise anyone to revisit their recommendations," he says.
But, he adds, "There are many bright scientists and competent administrators within the FDA and EPA who may wish to evaluate these data."
While that may happen in the future, a spokesman for the FDA tells WebMD the agency has no plans to change the recommendations.
The FDA-EPA advisory warns pregnant women not to eat shark, swordfish, king mackerel, or tilefish. These are the fish more likely to have high mercury levels.
Commonly eaten fish low in mercury can be eaten up to 12 ounces a week and include shrimp, salmon, canned light tuna, and catfish. Albacore tuna consumption should be limited to no more than 6 ounces a week since it contains more mercury than canned light tuna.
In an editorial accompanying the study, Gary J. Myers, MD, suggests there is little science to back up the FDA's recommendation to limit seafood consumption while pregnant.
The University of Rochester professor of neurology tells WebMD policymakers should not narrowly focus on only one thing when they make health recommendations.
"You have to take a holistic approach when it comes to the health and development of children," he says. "That means considering the things that improve health as well as the things that might theoretically be detrimental.
"It is very clear that omega-3 fatty acids are very important for brain development," says Myers. "It is less clear that mercury at the levels you get from eating fish poses a risk."