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Heart Risks Tied Directly To Mercury In Nine-Country Study

High mercury content in some fish may diminish the cardioprotective effects associated with consumption of omega-three fatty acids fish, write researchers from Johns Hopkins Medical Institutions, Baltimore, Maryland, United States.

Currently, specific high-risk groups, such as pregnant women and women who may become pregnant, are cautioned against eating fish species with the highest average amounts of methylmercury, to avoid associated conditions.

Findings in this study raise the possibility of broadening the advice to the general population, say the authors, led by Dr. Eliseo Guallar. While they suggest eliminating fish with a high mercury content from the diet, they do not recommend total abstinence.

"A weekly intake of two to four servings of fish from a variety of species, with special emphasis on fatty fish with low mercury content, such as salmon and small oceanic fish, is consistent with current advice for reducing cardiovascular risk," they write.

This case-control study was conducted in eight European countries and Israel for the Heavy Metals and Myocardial Infarction Study Group. They used toenail clippings and adipose tissue samples to measure mercury exposure and levels of fish oils (docosahexaenoic acid C22:6n-3, or DHA), respectively, in 684 men with first diagnosis of myocardial infarction and 724 controls. The mercury and fish oil levels were then correlated with risk of heart attack.

Mercury levels in patients with myocardial infarction were 15 percent higher than were those in healthy controls living in the same areas. While the toenail mercury level was directly associated with risk of myocardial infarction, the fish oil level was inversely associated with this risk.

Fish with relatively high methylmercury content include swordfish, shark, tilefish, king mackerel and fish from locally contaminated areas. Fresh or frozen tuna, marlin and red snapper contain intermediate concentrations.
N Engl J Med 2002;347:1747-54.

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