Study: No Link Between Mercury in Fish, Heart Disease
Pregnant Women, Children Should Still Be Cautious About Eating Fish, Experts Say
Mercury Exposure and Heart Disease: Study Details continued...
Every two years, the participants answered questions about their medical history, risk factors, disease, and lifestyle.
The researchers zeroed in on 3,427 participants who did not develop heart disease during the follow-up and another 3,427 who did. Mercury levels were evaluated from toenail clippings the participants provided. Toenail clippings are an excellent biomarker for mercury, Mozaffarian says, because mercury binds tightly to the protein in the toenail.
They also evaluated levels of selenium, a trace nutrient some think protects against mercury toxicity, in the clippings.
The median follow-up (half were longer, half less) from time of sampling to the time of an event was 11.3 years. Men's average age at the study start was 61; women, 53.
Those with higher levels of mercury concentration did not have a higher risk of cardiovascular events. Levels of selenium, whether high or low, weren't linked with adverse effects.
When the researchers compared those who had the highest mercury levels with the lowest, they found a trend toward lower cardiovascular disease risk with the higher mercury levels. They speculate that is because of the other beneficial effects of eating fish.
Before they adjusted for such factors as age, the researchers found higher mercury levels linked with high cholesterol. But Mozafarian says that finding could simply be because of age or that those with high cholesterol were eating more fish to get healthier.
"If you are not pregnant, nursing, or trying to become pregnant, there is no reason to be concerned about mercury levels in fish," Mozaffarian tells WebMD. "Fish is part of a healthy diet."
He does suggest that people who eat fish very often -- say, five times a week or more -- eat a variety and not just fish that have higher mercury levels. Among those varieties with higher mercury levels are shark, swordfish, king mackerel, and tile fish.
Mozaffarian reports funding from GlaxoSmithKline, Sigma-Tau Pharmaceuticals, and Pronova BioPharma (which makes omega-3 derived pharmaceutical products).
Mercury Exposure and Heart Disease: Perspective
The study shows that "the levels of mercury in the fish most Americans are eating are not high enough to offset the positive effects,'' says Solomon, who is also an associate clinical professor of medicine at the University of California, San Francisco.