Mercury Exposure and Risk of Hypertension in US Men and Women in 2 Prospective Cohorts

Cross-sectional studies and animal-experiments suggest that methylmercury exposure could increase risk of hypertension. This relationship has not been evaluated in large prospective studies. Using data from prior nested case-control studies in two separate prospective cohorts, we measured toenail mercury, a valid biomarker of long-term methylmercury exposure, among 6,045 US men and women free of hypertension at baseline. Median toenail mercury concentrations were 0.09 μg/g in the lowest quintile and 0.64 μg/g in the highest quintile, the latter corresponding to exposures about 1.7-fold higher than the EPA reference dose (RfD). Participants were followed prospectively (mean±SD=14.9±7.9 years) for a new self-report of physician-diagnosed hypertension (3,540 cases), shown to be >95% sensitive and specific for diagnosing hypertension in these cohorts as compared with review of medical records and direct blood pressure measurement, respectively. After adjustment for demographic, clinical, and lifestyle risk factors, the hazard ratio (95% CI) for incident hypertension in the highest vs. lowest quintile of mercury exposure was 0.96 (0.84–1.09) in women, 0.82 (0.62–1.08) in men, and 0.94 (0.84–1.06) in both cohorts combined. Findings were similar when more extreme categories of mercury were compared (across deciles, with median levels in highest decile about 2.5-fold higher than the RfD); and in analyses stratified by fish or omega-3 consumption, selenium levels, body mass index, and age. These findings from two separate large prospective cohort studies do not support any clinically apparent adverse effects of methylmercury exposure on risk of hypertension in men or women, including at levels up to 2.5-fold higher than the RfD