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April 7, 2004

Fish Consumption May Expose More Than 300,000 Newborns Per Year to Mercury
Study in Environmental Health Perspectives Finds Number of Newborns Affected May Be Higher than Previously Thought

[RESEARCH TRIANGLE PARK, NC] An analysis of the dietary habits and blood mercury levels in more than 1,700 women suggests that more than 300,000 newborns in the United States each year may have been exposed to unacceptable levels of mercury from their mother’s consumption of fish, according to a study published in the April issue of the peer-reviewed journal Environmental Health Perspectives (EHP). Mexican-Americans studied were the least likely to have high levels of blood mercury, while Asians, Native Americans, and Pacific Islanders were the most likely.

In this study, researchers evaluated the levels of blood organic mercury in 1,709 women who participated in the National Health and Nutrition Examination Survey in 1999 and 2000. They also analyzed dietary habits through 24-hour recall, a 30-day log of how frequently various foods were eaten, and average mercury levels in the fish and shellfish that the women reported consuming. Dietary habits were strong predictors of the level of mercury in the blood. Each gram of fish or shellfish consumed per kilogram of body weight was associated with an increase of 0.2 to 0.5 micrograms of mercury per liter of blood.

The level of mercury in fish and shellfish meals varies greatly depending on the type of fish consumed and the volume of fish in proportion to the rest of the meal. “Women who eat fish and/or shellfish at least twice a week have blood mercury concentrations seven times greater than women who reported no fish/shellfish consumption in the previous 30 days,” the study authors write.

The researchers also estimated, based on the number of U.S. births in 2000, how many newborns would have been exposed to dangerous amounts of mercury in utero. Their analysis assumed that mercury in maternal blood is passed to cord blood in a 1:1 ratio. Recent research suggests that is a conservative estimate, and that cord blood may actually receive mercury from maternal blood in a 1.7:1 ratio. If the latter figure proves accurate, even more newborns than thought are being exposed to high concentrations of mercury in utero. Mercury exposure during gestation can increase the risk of adverse neurodevelopmental effects.

“This study combines actual analysis of mercury in the blood with a conservative measure of how much of that mercury can be transferred to a fetus. Realistically, hundreds of thousands of children are being exposed to harmful levels of mercury in utero,” said Dr. Jim Burkhart, science editor for EHP.
The lead author of the study was Kathryn R. Mahaffey of the Office of Prevention, Pesticides, and Toxic Substances of the U.S. Environmental Protection Agency. Other authors were Robert P. Clickner and Catherine B. Joseph.

EHP is published by the National Institute of Environmental Health Sciences, part of the U.S. Department of Health and Human Services. More information, including the full report, is available online at http://www.ehponline.org/.

Editor’s note: Working media can register to receive press releases via e-mail by visiting http://www.ehponline.org/press/, calling 919-653-2582, or e-mailing media@ehp.niehs.nih.gov.