Mediated relationships between multiple metals exposure and fasting blood glucose by reproductive hormones in Chinese men

Previous studies have reported metals exposure contribute to the change of fasting blood glucose (FBG) level. However, the roles of reproductive hormones in their associations have not been fully elucidated. The aim of the study is to investigate the associations of multiple serum metals with reproductive hormones, and to further explore potential roles of reproductive hormones in relationships between metals exposure and FBG level. A total of 1911 Chinese Han men were analyzed by a cross-sectional study. We measured serum levels of 22 metals by inductively coupled plasma mass spectrometer (ICP-MS). FBG, total testosterone (TT), estradiol (E2), follicle stimulating hormone (FSH), and sex hormone-binding globulin (SHBG) levels were determined. Least absolute shrinkage and selection operator (LASSO) regression models were conducted to select important metals, and restricted cubic spline models were then used to estimate dose-response relationships between selected metals and reproductive hormones. We also conducted mediation analyses to evaluate whether reproductive hormones played mediating roles in the associations between metals and FBG. We found significant inverse dose-dependent trends of copper, tin and zinc with E2; zinc with SHBG; copper and nickel with TT, while significant positive dose-dependent trend of iron with E2, respectively. Moreover, approximately inverted U-shaped associations existed between lead and SHBG, iron and TT. In addition, E2, SHBG and TT were negatively associated with FBG level. In mediation analyses, the association of copper with FBG was mediated by E2 and TT, with a mediation ratio of 10.4% and 22.1%, respectively. Furthermore, E2 and SHBG mediated the relationship of zinc with FBG, with a mediation ratio of 7.8% and 14.5%, respectively. E2 mediated 11.5% of positive relationship between tin with FBG. Our study suggested that the associations of metals exposure with FBG may be mediated by reproductive hormones.