The Pharmaceutical Journal
Vol 269 No 7227 p799
7 December 2002

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Risk of heart disease following dietary mercury exposure remains unclear

There is no association between dietary mercury exposure and coronary heart disease (CHD) according to the results of an American study. However, a second international study has concluded that mercury is associated with an increased risk of myocardial infarction (MI).

Results from the American case-control study showed that mercury levels within a cohort of 442 men with CHD aged 40 to 75 years and their matched controls, correlated with fish consumption (P<0.001). Mercury levels were highest among dentists, who are exposed occupationally to elemental mercury, rather than the methylmercury found in fish (New England Journal of Medicine 2002;347:1755).

The researchers found that mercury levels within the body were not associated with an increased risk of CHD, but there was a non-statistically significant association when dentists were excluded from the analysis (P=0.43). They conclude that although they found no evidence to support a link between mercury and increased risk of CHD, a weak association between mercury exposure particularly from fish consumption, and heart disease cannot be excluded (ibid, p1747).

The second study involved 684 men from nine countries, who had a first diagnosis of MI. A group of 724 men representative of the same populations were chosen as controls. The average mercury level among controls, measured using toe nail clippings, was 0.25µg/g.

Mercury levels among those diagnosed with a first MI however, were 15 per cent higher (95 per cent confidence interval 5–25 per cent).

Furthermore, those with the highest mercury loading were more than twice as likely to have had a heart attack than those who had the lowest body loading of mercury (odds ratio 2.16, P=0.006). The researchers also found that levels of omega-3 fatty acids were inversely related to the risk of MI. They suggest that the risk of cardiovascular disease may depend on the balance between n-3 fatty acids and methylmercury content of fish consumed, and that high mercury content may diminish the cardioprotective effect of fish intake.

In an accompanying perspective article (ibid, p1735), Dr Michael Bolger and Dr Bernard Schwetz of the American Food and Drug Administration, highlight that methylmercury concentrations are greatest in long-lived species that are high up the food chain, such as king mackerel, shark and swordfish. They say that the idea that mercury contributes to cardiovascular disease is a testable hypothesis that warrants further investigation.

"Robust prospective studies are needed in populations in which fish constitutes a major staple in the diet. Data from such studies are essential if major changes in dietary recommendations for the United States and other populations are to be made," they conclude.