2 Studies Differ on Effect of Mercury on Risk of Heart Disease

BOSTON —  Two studies have yielded contradictory findings about the possible heart dangers of eating mercury-laden fish.

Plenty of research shows that mercury accumulated from fish can harm the developing brain of a fetus or child. Far less is known about how the toxic, widespread pollutant affects the heart.

Two studies in today’s New England Journal of Medicine on the long-term effects of mercury exposure on the hearts of middle-aged and elderly men had opposite findings.

One found no clear link between mercury levels in the body and the risk of developing heart disease; the other found men who had suffered a heart attack had higher mercury levels than similar men who had not.

That left the researchers, Food and Drug Administration officials and other experts agreeing on just two things: More research is needed, and people should not stop eating fish, because minerals and fatty acids in fish protect the heart. Also, many fish, such as salmon and shrimp, contain little or no mercury.

“The bottom line is, yes, you should eat fish, and, yes, you should know which fish have mercury” levels considered unsafe, said Dr. Daniel M. Shindler, a cardiologist at Robert Wood Johnson Medical School in New Brunswick, N.J., who was not involved in either study.

The FDA, Environmental Protection Agency and many state agencies report such information. For years, they have warned women who are pregnant, nursing or of childbearing age to avoid fish from mercury-contaminated waterways, and large, long-lived predators such as sharks and swordfish, which accumulate mercury from all the smaller fish they eat.

The American Heart Assn., citing new research showing the omega-3 fatty acids in fish reduce the risk of heart disease, last week reiterated its guidelines that people eat at least two servings of fish per week, preferably fatty fish.

One of the New England Journal studies indicated that the mercury contamination in fish offsets the benefits of a key fatty acid, DHA.

Researchers at the Johns Hopkins Bloomberg School of Public Health reviewed data and tissue samples from an earlier, nine-country European cardiac study. They compared 684 middle-aged men who had had one heart attack with 724 similar men who had not had a heart attack. They looked at the men’s health history, use of tobacco and alcohol, and toenail clippings and fat withdrawn from their buttocks.

Toenails hold accumulated mercury, and fatty tissue accumulates DHA; their levels in each subject were measured.

Those with the highest mercury levels were nearly 2.2 times more likely than those with the lowest levels to have had a heart attack, said Dr. Eliseo Guallar, assistant professor of epidemiology at Hopkins.

Researchers at Harvard School of Public Health studied 470 men who had had heart surgery or a heart attack, comparing each with a similar man without heart disease. Dr. Walter C. Willett, a professor of epidemiology and nutrition, said mercury levels in the men’s toenails corresponded well with the levels of fish they reported eating, but his team found no association between mercury exposure and risk of heart disease.

Willett and Guallar said there could be several explanations for their disparate results, from differences in the fish eaten in America and Europe to how the patient and comparison groups were picked in each study.

Both studies followed up on a 1995 Finnish study that found an increased risk of heart disease in people whose hair had high mercury levels.

The new studies looked only at men, and Shindler said the findings can not necessarily be applied to women.