Mercury Low in Women of Childbearing Age

But Mercury in Fish Can Potentially Harm Fetus, Women Need to Choose Fish Wisely

WebMD Health News

April 1, 2003 - As many as 8% of women of childbearing age in the U.S. have dangerously high levels of mercury in their blood that could pose a danger to a developing fetus. A new study suggests that women who are pregnant or intend to become pregnant should pay close attention to safety guidelines when it comes to selecting what kind and how much fish to eat.

Mercury is found throughout the environment, but eating fish is one of the most common means of exposure in humans. Methylmercury is the type of mercury found in fish and studies have shown that it can be harmful to the brain in large amounts.

Researchers say the developing fetus is most sensitive to these hazardous effects of methylmercury. Women have long been warned against eating mercury-rich fish during pregnancy for this reason, but researchers say little is known about the extent to which women of childbearing age are exposed to methylmercury in the U.S.

Although all fish and shellfish contain at least trace amounts of methylmercury, the levels vary widely. It is found in relatively small amounts in shellfish and other fish such as haddock, tilapia, salmon, cod, Pollock, and sole, but it accumulates through the food chain and concentrations are highest in large predatory fish like shark and swordfish. The EPA advises women who are pregnant or intend to become pregnant to avoid shark, swordfish, king mackerel, and tilefish.

The study, published in the April 2 issue of The Journal of the American Medical Association, compared blood mercury levels based on surveys on fish consumption and blood tests in a group of 1,709 women aged 16-49 years and 705 children aged 1 to 5 years from 1999-2000.

Researcher Susan E. Schober, PhD, and colleagues at the CDC, found that measures of mercury exposure in women of childbearing age and young children generally fell below levels of concern. But 8% of the women had concentrations that were higher than the U.S. Environmental Protection Agency's limits for minimizing the risk of adverse health effects.

Blood mercury levels were almost four times higher among women who ate three or more servings of fish in the past 30 days compared to women who ate no fish during that period. The average concentration of mercury was also three times higher among women compared to the children.

"The importance of careful choices in fish selected for consumption has been emphasized by recent advisories from the U.S. government as well as other countries," write the authors. "Because of wide variations in the concentrations of mercury in fish and shellfish, it is possible to have the nutritional benefits of moderate fish consumption and avoid fish high in mercury."

But the researchers say women who are pregnant or intend to become pregnant should follow federal and state advisories on consumption of certain types of fish.

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