Occupational mercury exposure in association with prevalence of multiple sclerosis and tremor among US dentists.

BACKGROUND

The effects of chronic occupational exposure to elemental mercury (Hg(0)) are largely unknown. The objective was to evaluate the association of occupational Hg(0) exposure with multiple sclerosis (MS) and tremor.

METHODS

The study included 13,906 dentists who attended the American Dental Association's annual meeting over 24 years (1986-2007 and 2011-2012). Participants reported MS and tremor and provided urine specimens for Hg(0) analysis. The authors estimated mean Hg(0) exposures over time and used logistic regression to estimate the associations of 3 Hg(0) exposure measures with MS or tremor.

RESULTS

Among participants, 0.18% reported MS and 1.24% reported tremor. Hg(0) exposure was not associated with MS (odds ratio [OR] per 191 micrograms per liter in cumulative Hg(0) exposure, 0.85; 95% confidence interval [CI], 0.39-1.85). Increased prevalent risk of tremor was found with exposure to both urinary Hg(0) exposure (OR, 1.10 [95% CI, 1.00-1.22]) and cumulative Hg(0) exposure among younger dentists (< 51 years; OR, 1.13 [95% CI, 1.05-1.22]).

CONCLUSIONS

Occupational Hg(0) exposure in US dentists decreased over time and now is approaching that of the general population. Our results suggest a positive association between Hg(0) exposure and tremor.

PRACTICAL IMPLICATIONS

Studies with more sophisticated outcome and exposure measures, and including more retired dentists, would provide critical information toward understanding the relation of Hg(0) exposures to MS and tremor risk.