Lead author Dariush Mozaffarian of Boston's Harvard School of Public Health, Brigham and Women's Hospital and Harvard Medical School says previous studies suggested mercury exposure from fish consumption may be linked to higher risk of cardiovascular disease.
Mozaffarian and colleagues analyzed data from two studies including 51,529 men in the Health Professionals Follow-up Study and 121,700 women in the Nurses' Health Study.
The researchers measured mercury concentrations in stored toenail clippings -- an excellent biomarker of long-term mercury exposure -- of some 7,000 participants who did and did not have cardiovascular event.
In the top 20 percent of exposure, average toenail mercury levels were 0.7 micrograms per gram -- U.S. advisories aim at keeping mercury exposures below 0.4 micrograms per gram.
After adjusting for age, gender and heart disease risk factors, the study found no association between mercury exposure and higher risk of cardiovascular disease; in fact, there were trends toward lower heart risk with higher mercury levels which the researchers attribute to the beneficial effects of eating fish.
The findings are published in the New England Journal of Medicine.