Mercury exposure, cardiovascular disease, and mortality: A systematic review and dose-response meta-analysis

Background: There is evidence that exposure to mercury (Hg) may be a risk factor for cardiovascular disease (CVD). Objective: To conduct a systematic review of published studies and a meta-analysis of the results to examine the associations between chronic Hg exposure and CVD outcomes. Methods: We searched PubMed, Embase, and TOXLINE using previously developed strategies. Studies were selected according to a priori-defined inclusion criteria, and their qualities were assessed. Study estimates were extracted, and subgroup analyses were conducted to explore potential sources of heterogeneity: 1) fatal vs. nonfatal events, 2) cohort study vs. non-cohort study, and 3) inorganic Hg vs. methyl mercury (MeHg). Dose response meta-analyses were conducted for MeHg exposure and fatal/nonfatal ischemic heart disease (IHD), stroke, and all CVD. Results: A total of 14 studies reporting results collected from more than 34,000 participants in 17 countries were included in the meta-analysis. Hg exposure was associated with an increase in nonfatal IHD (relative risk (RR): 1.21 (0.98, 1.50)), all-cause mortality (RR: 1.21 (0.90, 1.62)), CVD mortality (RR: 1.68 (1.15, 2.45)), and mortality due to other heart diseases (RR: 1.50 (1.07, 2.11)). No association was observed between Hg exposure and stroke. A heterogeneous relationship was found between studies reporting fatal and nonfatal outcomes and between cohort and non-cohort studies. However, these differences were mainly due to differences in Hg exposure level. Occupational inorganic Hg exposure was associated with similar increases in different mortality outcomes. A J-shaped relationship between Hg exposure and different fatal/nonfatal outcomes was observed, with turning points at hair Hg concentrations of 1 mu g/g for IHD and 2 mu g/g for stroke and all CVD. Conclusion: Chronic exposure to Hg was associated with an increased risk of all-cause mortality and fatal/ nonfatal IHD. The risk of multiple cardiovascular endpoints starts to increase consistently at a hair Hg concentration of 2 mu g/g.