Fish and mercury

Among women of childbearing age in the U.S., fish consumption has increased in recent years while blood mercury concentrations have decreased, suggesting improved health for women and their babies, a new study shows.

The research at Oregon State University also indicates fish consumption advisories tailored to specific regions and ethnic groups would help women of childbearing age to eat in even more healthy ways, including better monitoring of mercury intake.

Food from the ocean has a unique and valuable nutritional profile. Among seafood’s many benefits are the omega-3 fatty acids that promote neurodevelopment, and the nutrients in seafood are especially important for pregnant women to pass on to developing fetuses.

But the main way people are exposed to toxic methylmercury – a mercury atom with a methyl group, CH3, attached to it – is through eating seafood. Thus the need for precise, nuanced fish consumption advisories, said Leanne Cusack of Oregon State University, the corresponding author on the study.

Comparatively less-toxic elemental mercury enters the ocean from natural sources such as volcanic eruptions and also from human activities like the burning of fossil fuels, which accounts for about two-thirds of the mercury that goes into the water.

Once in the ocean, the mercury is methylated, diffuses into phytoplankton and passes up the food chain, accumulating along the way.

A scallop or a shrimp, for example, can have a mercury concentration of less than 0.003 parts per million. A large predator like a tuna, on the other hand, can contain roughly 10 million times as much methylmercury as the water that surrounds it and have a concentration of many parts per million.

Exactly how the mercury in the ocean becomes methylated, scientists don’t know.

Fish advisories are usually aimed at women of childbearing age because a developing fetus has greater sensitivity to the neurotoxic effects of methylmercury. Jointly, the U.S. Environmental Protection Agency and the Food and Drug Administration recommend women in that group eat two meals of low-mercury fish per week.

Using data from the ongoing National Health and Nutrition Examination Survey, Cusack’s research group looked at fish consumption patterns with regard to blood mercury levels in U.S. women of childbearing age from 1999 to 2010.

Findings were recently published in the journal Environmental Health.

Women in the coastal regions, particularly the Northeast, were found to have the highest blood mercury concentrations; women living away from the sea, especially in the inland Midwest, had the lowest.

Coastal residents also ate fish the most frequently, with the species consumed varying by region. The type of fish most often consumed was shellfish in every part of the U.S. except for the inland West and inland Midwest.

As women’s age and household income increased, so did their fish consumption frequency and blood mercury concentrations. Among ethnic groups, Asian Americans, Pacific Islanders, Alaska Natives and Native Americans ate fish the most often and showed the most mercury, and Mexican Americans consumed fish the least often and showed the smallest concentration of mercury.

— source oregonstate.edu

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