Despite concerns that mercury in fish might endanger a developing fetus, the amount of fish a mother eats appears to pose no harm to the future mental health of her child, according to study findings released last week.
In a sample of almost 800 mothers and their children living in the Seychelles, where people eat fish an average of 12 times each week, the amount of mercury present in a mother's body at childbirth appeared to have no effect on the child's mental abilities at age 9.
In the U.S., the Food and Drug Administration advises pregnant women to avoid eating shark, swordfish, king mackerel and tilefish because they may contain high levels of mercury, which can potentially harm the developing fetal nervous system.
Mercury occurs naturally in the environment and as a byproduct of industrial pollution; it can accumulate in certain long-lived fish that consume other fish. Women in the Seychelles ate a diet with a rich variety of fish, some of which contained high levels of mercury.
During the current study, researches from New York measured mercury levels in hair samples taken from 779 women who had just given birth. Nine years later, the researchers performed tests of mental functioning in their children, and compared the two results.
Overall, how well children performed on the tests showed no relationship to the amount of mercury present in their mothers' bodies during pregnancy, with few exceptions. Children whose mothers had more mercury tended to perform more poorly on a particular motor skills test, a finding the researchers say may be due to chance.
Although previous laboratory experiments have indeed shown that high levels of mercury can harm the brain, the researchers explained that these tests involved much larger doses of mercury.
In an accompanying editorial, Dr. Constantine G. Lyketsos of Johns Hopkins Hospital in Baltimore, Maryland writes that, "in most parts of the world," the amount of fish women eat during pregnancy likely poses no overall harm to the future mental health of their children. "For now, there is no reason for pregnant women to reduce fish consumption below current levels, which are probably safe," Lyketsos writes.
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