Mercury in fish linked to heart attacks

People who eat fish with a high mercury content run a greater risk of coronary heart disease than previously thought, a European study has found. But scientists add that a fish diet is still healthy, provided the fish has safe levels of mercury.

In a collaborative study of eight European countries, scientists have found that eating fish from mercury contaminated waters may counteract the health benefits of omega3 fatty acids also present in fish. The findings, published in the latest issue of the New England Journal of Medicine, suggest warnings on mercury exposure should not be confined to high-risk groups like pregnant women (see related story).

By measuring mercury in toenail clippings in heart attack patients and healthy volunteers across Europe, scientists correlated mercury intake with docosahexaenoic acid (DHA) body levels. DHA in body fat is a marker of fatty fish intake. Mercury and DHA levels were found to be related, indicating that fish is likely to be the main source of toenail mercury in the populations studied, with mercury levels 15% higher in coronary patients than in the healthy volunteers.

The new study contradicts the general belief that eating fish may reduce the risk of heart disease. Fish with relatively high methylmercury – the form of mercury most toxic to man – include swordfish, shark, tilefish, king mackerel, and fish from locally contaminated areas, while tuna, marlin and red snapper have intermediate concentrations.

Although the effect of long-term exposure to mercury is not well known, a previous study suggested that fish from a mercury-contaminated lake in Finland predisposed people to cardiovascular disease. The latest research indicates a more general problem that may also occur at lower mercury concentrations more typical of levels in the Western diet, say the scientists.

“We do not advise people to stop eating fish,” says Professor Rudolph Riemersma, of the University of Edinburgh Cardiovascular Research Unit. “Our analyses are consistent with a protective effect of dietary fish, as long as it is not heavily contaminated by mercury. 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 a salmon and small oceanic fish, is consistent with current advice for reducing cardiovascular risk.”

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