Studies Conflict on Health Effect of Mercury-Laden Fish

Eating fish with high levels of toxic mercury does not lead to heart attacks, a study by the Harvard School of Public Health (SPH) has found, directly contradicting another major study of mercury consumption and heart disease.

Both studies were published in last Thursday’s issue of the New England Journal of Medicine. The two research teams—one from SPH and the other from the Bloomberg School of Public Health at Johns Hopkins University—join an ongoing debate over fish in human diets.

“To suggest that there’s a high risk is really too premature at this point,” said Eric B. Rimm, an associate professor of epidemiology and nutrition, who co-directed the SPH study. “I don’t think there’s enough data out there to say mercury causes heart disease.”

The findings come after the American Heart Association recently reiterated its recommendation to eat at least two servings of fish per week, supported by research that certain fatty acids found in fish help reduce risk of heart disease.

In the Harvard study, researchers measured mercury content in the toenails of two groups of middle-aged to elderly American men. The men in one group had never suffered from heart problems, while those in the other had either suffered from a heart attack or had heart surgery.

Mercury levels increased consistently with the amount of fish the men had reported eating. But there was no clear link between mercury consumption and vulnerability to heart problems.

However, in its research on groups of heart-healthy and heart attack-prone European men, the Johns Hopkins team found that men with high mercury levels were 2.2 times more likely to suffer a heart attack. Correspondingly, heart attack victims had mercury levels that were 15 percent higher than men who had never suffered from heart problems.

Some researchers have speculated that mercury may damage artery walls, making them more susceptible to clogging.

Like the Harvard team, the Johns Hopkins researchers analyzed mercury content in the men’s toenails, which are known to harbor mercury.

Rimm and other researchers speculate that the experiments’ different conclusions may be due to differences between fish on the European and American coastlines.

But the researchers agree that fish should not be entirely eliminated from a diet. Some fish, such as salmon and shrimp, may provide healthy fatty acids and minerals while containing little or no mercury. But predators, such as sharks and swordfish, which are more concentrated with mercury, may pose a greater threat.

“There’s clearly a much greater benefit from eating them than taking them out of your diet,” Rimm said. But “you would be ill-advised to have tuna fish every day.”

Research has shown that mercury from fish can damage the developing brain of a fetus or young child, so the Food and Drug Administration currently advises pregnant women to limit their consumption of mercury-laden fish.

The Harvard researchers say they plan to repeat their study on women in several years.