Total blood mercury and rubella antibody concentrations in US children aged 6-11 years, NHANES 2003-2004.

Children are susceptible to mercury toxicity, and mercury has immunomodulatory effects. Lower folate and B-12, and higher homocysteine may represent susceptibility cofactors. A large proportion of variability in rubella immune response is attributable to environmental factors. This study aimed to evaluate the interaction between total blood mercury (Hg) and nutritional and homocysteine status on rubella virus antibody concentrations. Cross-sectional data on rubella IgG antibody concentrations, Hg, homocysteine, methylmalonic acid (MMA, an indicator of B-12 deficiency), and folate were obtained from 2003-2004 NHANES for children aged 6-11 years with rubella seropositivity (n=690). Linear regression was used to evaluate relationships between log-transformed rubella concentrations and Hg, stratified by sex, MMA ≥, folate<, and homocysteine ≥ sample medians, adjusted for demographic and nutritional cofactors. Hg was significantly positively associated with rubella antibody concentrations (β=0.24; 95% confidence interval (CI)=0.11, 0.38) in children with higher MMA, lower folate and higher homocysteine (n=110), yet inversely associated among all other children (β=-0.18; 95% CI=-0.34, -0.03) (n=580). Among the former, estimates (β) were positive across all Hg quartiles relative to the lowest (Q1) (Hg<0.30 μg/L): Q2: β=0.23 (-.10, 0.56); Q3: β=0.35 (0.13, 0.57); Q4: β=0.53 (0.21, 0.84); P(trend)<0.01. Findings are consistent with previously reported associations between Hg and measles antibody concentrations, and highlight the importance of considering dynamics between toxicant exposures, pathogens and host susceptibility.