Mercury and the risk of coronary heart disease in men

Background: A high dietary intake of mercury from consumption of fish has been hypothesized to increase the risk of coronary heart disease. Methods: Using a nested case-control design, we investigated the association between mercury levels in toenails and the risk of coronary heart disease among male health professionals with no previous history of cardiovascular disease or cancer who were 40 to 75 years of age in 1986. Toenail clippings were collected in 1987 from 33,737 cohort members, and during five years of follow-up, we documented 470 cases of coronary heart disease (coronary-artery surgery, nonfatal myocardial infarction, and fatal coronary heart disease). Each patient was matched according to age and smoking status with a randomly selected control subject. Results: The mercury level was significantly correlated with fish consumption (Spearman r = 0.42, P<0.001), and the mean mercury level was higher in dentists than in nondentists (mean, 0.91 and 0.45 microg per gram, respectively; P<0.001). After age, smoking, and other risk factors for coronary heart disease had been controlled for, the mercury level was not significantly associated with the risk of coronary heart disease. When the highest and lowest quintiles of mercury level were compared, the relative risk of coronary heart disease was 0.97 in the highest level (95 percent confidence interval, 0.63 to 1.50; P value for trend = 0.78). Adjustment for intake of n-3 fatty acids from fish did not appreciably change these results. Conclusions: Our findings do not support an association between total mercury exposure and the risk of coronary heart disease, but a weak relation cannot be ruled out.