Metals and trace elements in relation to body mass index in a prospective study of US women

Epidemiologic studies on the association between metals and body mass index (BMI) have been cross-sectional and have demonstrated inconsistent associations. Our study prospectively examined whether metals measured at baseline were associated with later BMI. We considered metals individually and as joint exposure to pre-defined metal groupings. We measured concentrations of 16 metals in toenails collected at baseline (2003–2009) in a subset of 1221 women from the Sister Study. We calculated BMI from height and weight reported on a follow-up questionnaire an average of 5.2 years (range = 3.5–8.3) after baseline. Multivariable linear regression was used to estimate β coefficients and 95% confidence intervals (CIs) for associations between BMI and individual metals (with estimates given per interquartile range (IQR) increase or in quartiles). Quantile g-computation was used to examine joint associations between groups of metals and BMI. Groups considered were (1) all metals combined, and metals classified as (2) non-essential or (3) essential. In individual metal models we found that, with the exception of cobalt, no single metal was strongly related to BMI. In our mixture analyses, a quartile increase in all non-essential metals was associated with higher BMI (β = 0.32; 95%CI: 0.00, 0.63 kg/m2), whereas essential metals were suggestively associated with lower BMI (β = −0.25; 95%CI: −0.58, 0.07 kg/m2). In this population of women who were, on average, overweight, essential metals were jointly associated with slightly healthier, lower BMI whereas non-essential metals were jointly associated with slightly higher, unhealthier BMI, after controlling for other health indicators and predictors of metals exposures. •This study prospectively examined whether metals were associated with BMI.•In single metal models cobalt was inversely associated with BMI.•Other metals were not strongly related to BMI individually.•Increasing all non-essential metals jointly was positively associated with BMI.•Results show the importance of a prospective design and examining metal mixtures.