Mercury levels in the blood of most women in the U.S. fall within safe limits, according to a new study. But about 6 percent of women of childbearing age have blood mercury levels at or above safe limits.

Researchers say the findings confirm previous reports that show blood mercury levels in young children and women of childbearing age are usually below levels of concern.

Exposure to high levels of mercury can cause brain and kidney disorders. Women of childbearing age are particularly at risk because mercury exposure during pregnancy can cause neurological birth defects.

Most human exposure to mercury comes from eating seafood. The higher the fish is in the food chain, such as shark, swordfish, or king mackerel, the more likely it may contain unsafe concentrations of mercury.

Most Mercury Levels Safe

In the study, which appears in the Nov. 5 issue of the Morbidity and Mortality Weekly Report, researchers analyzed information on blood mercury levels in women of childbearing age and young children, as collected by the CDC’s National Health and Nutrition Examination Survey from 1999-2002.

The study showed that blood mercury levels for most women and children in these groups were below the levels known to produce negative health effects. But about 6 percent of childbearing-age women had levels at or above the level the EPA considers safe.

Researchers say women who are pregnant or who intend to become pregnant should avoid eating shark, swordfish, king mackerel, and tilefish to reduce their risk of mercury exposure.

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Jones, R. Morbidity and Mortality Weekly Report, Nov. 5, 2004; vol 53: pp 1018-1020. News release, CDC. WebMD Medical News: “Mercury Low in Women of Childbearing Age.“