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

BACKGROUND: 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.
OBJECTIVE: This study aimed to evaluate the interaction between total blood mercury (Hg) and nutritional and homocysteine status on rubella virus antibody concentrations.
DESIGN: 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.
RESULTS: 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.
CONCLUSION: 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.