The influence of obesity on blood mercury levels for U.S. non-pregnant adults and children: NHANES 2007–2010

• Blood mercury was inversely related to body mass index (for non-pregnant adults).
• Blood mercury was 22% lower for obese compared to overweight/normal weight adults.
• Methylmercury metabolism possibly differed between adults and children.
• Obesity may contribute to inter-individual variability in mercury metabolism.

BackgroundIn animal studies obesity is associated with higher blood and tissue mercury concentrations; however human studies are lacking. Although the mechanism underlying this association is uncertain, obesity may alter the metabolism and distribution of methylmercury.ObjectivesWe determined whether obesity influenced blood mercury levels, the majority of which was methylmercury, for U.S. non-pregnant adults (≥20 years) and children (2–19 years) after controlling for methylmercury intake through fish and shellfish consumption, and other confounders.MethodsWe completed secondary data analysis of the National Health and Nutrition Examination Survey (NHANES) (2007–2010) for participants who consumed fish/shellfish within 24 h of blood collection for mercury analysis. Weighted least squares regression models related blood mercury levels (the dependent variable) to methylmercury exposure (μg) from fish consumed in the previous 24 h, body mass index (BMI) (for adults), BMI z-scores (for children), and other confounders.ResultsIn adjusted models, blood mercury levels were inversely correlated with BMI for adults [β, 95% confidence interval (CI)=−0.54 (−0.90, −0.18)]. For children, blood mercury levels were inversely correlated with BMI z-scores but the trend was not significant [β (95% CI)=−0.016 (−0.066, 0.035)]. When obese adults or children were compared with those who were overweight/normal weight, blood mercury averaged 22% lower for obese adults (95% CI: −33%, −8.2%), while blood mercury did not differ significantly for obese children [β (95% CI)=−1.7% (−31%, +39%)].ConclusionsAfter adjusting for the main, if not exclusive, exogenous source of methylmercury exposure (through fish/shellfish intake) and other confounders, our results support potential changes in the metabolism, distribution or excretion of methylmercury with increasing BMI (for adults).