Mercury Exposure and Antinuclear Antibodies among Females of Reproductive Age in the United States: NHANES

Abstract

Background: Immune dysregulation associated with mercury has been suggested, though data in the general population are lacking. Chronic exposure to low levels of methylmercury (organic) and inorganic mercury is common, such as through fish consumption and dental amalgams.

Objective: To examine associations between mercury biomarkers and antinuclear antibody (ANA) positivity and titer strength.

Methods: Among females 16-49 years (n=1352) from the National Health and Nutrition Examination Survey (NHANES) 1999-2004, we examined cross-sectional associations between mercury and ANAs (indirect immunofluorescence; cutoff ≥1:80). Three biomarkers of mercury exposure were utilized: hair (available 1999-2000) and total blood (1999-2004) predominantly represented methylmercury, and urinary (1999-2002) inorganic. Survey statistics were used. Multivariable modeling adjusted for several covariates, including age and omega-3 fatty acids.

Results: 16% of females were ANA-positive; 96% of ANA-positives had a nuclear staining pattern of speckled. Mercury geometric means (standard deviations) were: 0.22 (0.03) ppm hair, 0.92 (0.05) µg/L blood, and 0.62 (0.04) µg/L urinary. Hair and blood, but not urinary, mercury were associated with ANA positivity (sample sizes 452, 1352, and 804, respectively), adjusting for confounders: hair odds ratio (OR)=4.10 (95% CI: 1.66, 10.13); blood OR=2.32 (95% CI: 1.07, 5.03) comparing highest versus lowest quantiles. Magnitudes of association were strongest for high-titer (≥1:1280) ANA: hair OR=11.41 (95% CI: 1.60, 81.23); blood OR=5.93 (95% CI: 1.57, 22.47).

Conclusions: Methylmercury, at low levels generally considered safe, was associated with subclinical autoimmunity among reproductive-age females. Autoantibodies may predate clinical disease by years, thus methylmercury exposure may be relevant to future autoimmune disease risk.