A study of stored toenail clippings reveals that mercury levels from eating fish pose no heart disease or stroke hazard. Measuring mercury levels in toenails is a good indicator of long-term exposure to mercury from eating fish, according to the investigators. They analyzed two studies of 173,229 health professionals whose toenail clippings had been stored. After an average of 11 years, 3,427 developed heart disease or suffered a stroke. After adjustment for potential confounders, they found no differences in the rate of coronary heart disease and stroke among the participants with the highest concentrations of mercury in their toenails compared with those with the lowest concentrations.