Mercury May Counteract DHA Benefits From Fish

BALTIMORE--The mercury content of fish may counteract the heart-healthy properties of docosahexaenoic acid (DHA), an omega-3, according to a case-control study in the Nov. 28 issue of The New England Journal of Medicine (347, 22:1747-54, 2002) (www.nejm.org). Researchers from the Johns Hopkins Medical Institutions noted that while DHA levels were inversely related to myocardial infarction, patients with the highest mercury levels exhibited the highest risk of myocardial infarction.

Researchers started their case-control study based on the evidence that mercury increases the risk of cardiovascular disease. They stated that the mercury content of fish may counteract the beneficial effects of its omega-3 fatty acids, including DHA.

Researchers compared the joint association of mercury levels in toenail clippings and DHA levels in adipose tissue with the risk of a first myocardial infarction in men. There were 684 men with a first diagnosis of myocardial infarction and 724 male controls. After researchers adjusted data for DHA levels and coronary risk factors, it was found that mercury levels in the men who suffered a first myocardial infarction were 15-percent higher than in the controls. And, after researchers adjusted for mercury levels, DHA levels were inversely related to the risk of myocardial infarction. Researchers concluded that while DHA seems to have a protective effect, mercury levels might diminish the protective effects of fish intake.

"There is a general consensus of concern not only among scientists but also health authorities around the world regarding intake of mercury through fish," said Morten Bryhn, M.D., Ph.D., director of R&D at Pronova Biocare. "The industry devoted to working with marine omega-3 fatty acids as food supplements and pharmaceuticals have had removal of mercury from their products as a primary objective together with other man-made pollutants. ... Marine omega-3 fatty acids are essential fatty acids important for a series of organ functions and a regular intake has recently been identified as protective against cardiovascular diseases by the American Heart Association (AHA). New guidelines issued by AHA present an equal choice between eating fish or taking omega-3 supplements. Consumers uncertain of the mercury content in fish sold locally may use omega-3 concentrates as a substitute for eating fish."