Toenail metal concentrations and age at menopause: A prospective study

Menopause timing is related to cancer, cardiovascular disease, and mortality. Lead has been associated with an earlier age at menopause, but no study has considered exposure to other metals or multiple metals simultaneously.

At baseline, we measured toenail concentrations of 16 metals for 903 premenopausal women in the Sister Study (2003-2009). Age at menopause was ascertained through follow-up questionnaires. Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations between individual metals and age at menopause. We used quantile-g-computation to examine the association between age at menopause and the joint effect of a simultaneous increase in (1) all metals and for subgroups of metals categorized as (2) essential or (3) non-essential.

For individual metals, we observed negligible associations except for an interquartile range increase in lead which was modestly associated with an earlier age at menopause (HR = 1.03, 95% CI = 1.01, 1.05). In the mixture analyses, a quartile increase in all metals was associated with a later age at menopause (HR = 0.81, 95% CI = 0.64, 1.02). The metals with the largest negative contributions (i.e., associated with a later age at menopause) were chromium and nickel. The joint effect for the essential metals remained inverse (HR = 0.83, 95% CI = 0.64, 1.07), but was attenuated for nonessential metals (HR = 0.98, 95% CI = 0.76, 1.24).

Although no individual metal was strongly associated with age at menopause, our joint effect analysis suggests that having low levels of essential metals could be associated with an earlier age at menopause.