Fish consumption during pregnancy helps fetal brain development

FoodConsumer.org, David Liu, Ph.D.
Published October 11, 2005

Many people know that eating fish during pregnancy boosts mental capacity of babies. A new Harvard study confirmed that fish consumption during the second trimester may aid fetal brain development. The new study, conducted by Emily Oken and colleagues at Harvard Medical School in Boston, involved 135 mothers and infants, who participated in Project Viva, a prospective cohort study of gestational diet and other exposures, pregnancy outcomes, and offspring health in eastern Massachusetts. For the study, researchers surveyed pregnant women finding out their fish intake during the second trimester. Also women's mercury levels were measured from hair samples. In this study, a visual memory test was performed on six month old infants of participating mothers. Researchers showed babies a single picture a number of times and then showed them the picture along with another new picture. If familiar with a picture, babies would gaze on it for a longer time, indicating a good memory. Researchers found that eating fish during pregnancy was positively associated with enhanced fetal brain development. It was observed that the more fish the pregnant women ate during the second trimester, the better her six month old performed on a standard mental test. The test showed that mothers who ate fish raised the baby's score by four points for each weekly serving of fish. However, the boost of mental capacity did not happen to those mothers who ate the wrong fish. Fish containing high levels of mercury counteract the positive effect of fish and their babies tended to have relatively lower test scores. The scores for those babies whose mothers ate the mercy-loaded fish went down as the mercury level went up. An increase of one part per million in mercury was associated with a decrement in the mental score of 7.5 points. The mental scores were highest among infants of women who consumed more than two weekly fish servings but had mercury levels at less than 1.2 parts per million. Because of this, researchers cautioned that pregnant women should avoid mercury-loaded fish such as those large and long lived fish, which tend to accumulate high levels of mercury and other pollutants. Mercury in fish has long been a concern to many people. The U.S. government advises against child-bearing women or pregnant women to eat certain types of fish such as shark, swordfish, king mackerel and tilefish. States also periodically issue fish consumption advisories to alert residents on the risk of fish caught from local waters. The Environmental Working Group criticized that the FDA fish consumption advisory is too loose and some fish the FDA recommends for consumption are unfit either because they contain high levels of mercury or the number of servings are too many. Fish has been touted long for the health benefits of its omega-3 fatty acids. Previous studies proved that eating fish and omega-3 fatty acids can reduce cardiovascular disease, dementia, stroke and Alzheimer's disease. Nevertheless, many people are concerned about the safety of fish, particularly those farm-raised and caught from fresh waters, which tend to carry high levels of mercury and other pollutants such as PCBs and dioxins. Studies by the U.S. Environmental Protection Agency found that freshwater fish is one of major foods that are polluted with high levels of dioxins. The current study was reported in the October issue of Environmental Health Perspectives.