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Harvard Toenail Study Shows No Heart Risk From Mercury in Fish

White tuna fish for sale at the fish market in Bermeo, near Bilbao, Spain. Photographer: Markel Redondo/Bloomberg
White tuna fish for sale at the fish market in Bermeo, near Bilbao, Spain. Photographer: Markel Redondo/Bloomberg

March 24 (Bloomberg) -- The heart benefits from eating most fish outweigh the potential risks of ingesting mercury found in the seafood, according to a Harvard study of people’s toenail clippings.

Higher mercury exposure didn’t boost the incidence of coronary heart disease, stroke or cardiovascular disease, according to a study from Harvard Medical School, in Boston. The report, published yesterday in the New England Journal of Medicine, analyzed toenails because they are an indicator of the body’s absorption of mercury over the years, researchers wrote.

Eating fatty fish such as albacore tuna, mackerel, sardines and herring may reduce the risk of cardiovascular disease because they have nutrients that can boost heart wellness, according to the study. In adults, mercury is also linked to a risk of heart ailments. The research shows the heart benefits are greater than any drawbacks from exposure to mercury found in almost all fish, the U.S. Food and Drug Administration said.

“These findings suggest that people need not worry about cardiovascular harm from mercury exposure when deciding whether or not to consume fish,” Dariush Mozaffarian, the lead author and associate professor in the department of epidemiology at the Harvard School of Public Health, and in the division of cardiovascular medicine at Harvard Medical School, said in a statement.

Pregnancy Risks

Mercury is also known to stunt neurological development in children. In 2004, the Environmental Protection Agency and FDA recommended that children and women who are pregnant or might become pregnant avoid certain kinds of fish and limit their fish intake. Mercury exposure in the womb can affect a fetus’s developing brain and nervous system, according to the Environmental Protection Agency’s website.

This study’s failure to find an association between mercury exposure and increased risk of cardiovascular disease in adults shouldn’t alter public-health and policy efforts to lower mercury contamination in fish and the environment, which could still partly have the potential to “offset the net cardiovascular benefits of fish consumption,” the authors wrote.

“Our findings should also not alter advisories directed toward women who are or may become pregnant or who are nursing,” the researchers said in the report, citing the potential for neurodevelopmental harm from mercury.

Long-Term Studies

The researchers analyzed data from two long-term studies, the Health Professionals Follow-Up Study composed of men, and the Nurses’ Health Study composed of women. Both groups have been answering questions every two years about their medical history and lifestyle.

Harvard researchers analyzed 3,427 patients who had coronary artery disease or stroke and matched them to similar controls. To compare levels of mercury, researchers divided the participants into five groups, from lowest to highest exposure. Those with the highest mercury concentration were no more likely to have heart disease than those with the lowest levels in their toenails.

Fish is a source of omega-3 fatty acids, which have been shown to benefit heart health, according to the American Heart Association. Unlike many meats, it isn’t high in saturated fats.

To contact the reporter on this story: Elizabeth Lopatto in New York at

To contact the editor responsible for this story: Reg Gale at

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