Study: No Link Between Mercury in Fish, Heart Disease
Pregnant Women, Children Should Still Be Cautious About Eating Fish, Experts Say
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Mercury Exposure and Heart Disease: Study Details continued...
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.
It is possible, Solomon and Mozaffarian say, to eat so much fish that side effects from the mercury can develop, such as numbness of the fingers and toes and muscle weakness. But those side effects aren't typical with moderate consumption.
Of the study findings, Solomon says, "it doesn't change my advice to my patients, which is to consume seafood with attention and in moderation."
The Dietary Guidelines for Americans, 2010, suggest adults increase their relatively low intake of seafood, noting that about 8 ounces a week has been linked in some research with reductions in cardiac deaths in healthy people. According to the guidelines, pregnant and breastfeeding women can eat 8 to 12 ounces of seafood per week from a variety of seafood types. They should limit white (albacore) tuna to 6 ounces per week and avoid eating fish with higher mercury levels.
Low-mercury fish and seafood includes salmon, sardines, scallops, and shrimp, among others, Solomon says.