Mercury, fish oil, and risk of heart disease

Is it necessary to eat fish to reduce risk of heart disease? Although some groups have recommended this, recent studies raise concern about the mercury levels in fish. Fish, especially fatty fish and fish oil, are significant dietary sources of mercury, which may predispose people to heart disease. Two studies examined whether the mercury content of fish counteracts the beneficial effects that the omega-3 fatty acids found in fish have on the heart.

The first study (Guallar) examined close to 700 men throughout Europe and Israel who had had a heart attack. They were compared to almost 700 men who had not had a heart attack. The toenail mercury level in men who had a heart attack was 15% higher than in those who had not. The level of mercury in the men was related to blood levels of DHA, a fatty acid found mainly in fish. This suggests that high levels of mercury were due to higher fish consumption. A beneficial effect of higher blood levels of DHA was not seen unless mercury levels were controlled for. This suggests that the high mercury content of some fish may markedly reduce any beneficial effects of fish oil on risk of heart disease.

The second study (Yoshzawa) was smaller but may have had similar results if only a large number of dentists had not been included. Dentists would be expected to have higher levels of mercury due to their exposure to mercury in their practice. However, this form of mercury is different from the methylmercury found in fish and may have a different effect on the risk of heart disease. These studies suggest that there should be some rethinking of recommendations to eat fish for your heart. (For more information about recommendations related to fish consumption, see Vegetarian Journal Sept/Oct 2001, American Heart Association Calls for Eating Fish Twice Per Week--What's a Vegetarian To Do? This article is on the web at <www. vrg.org/journal/vj2001sep/2001sepomega3.htm>.)

Guallar E, Sanz-Gallardo I, Van't Veer P, et al. 2002. Mercury, fish oils, and the risk of myocardial infarction. N Engl J Med 347:1747-54.

Yoshzawa K, Rimm EB, Morris JS, et al. 2002. Mercury and the risk of coronary heart disease in men. N Engl J Med 347:1755-60.

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