Associations between metals and anemia indicator: mixed exposure effects and mediation analysis

Exposure to metals is an important cause of anemia. The effects of mixed metal exposure on hemoglobin have been less studied, and the existing research conclusions are inconsistent. Body mass index (BMI) is associated with both metal levels and hemoglobin and may play a mediating role in the association between metals and hemoglobin. This study selected 832 children from the National Health and Nutrition Examination Survey database and further analyzed the association between metals and hemoglobin, an indicator of anemia. We found that zinc (Zn), selenium (Se) and thallium (Tl) were associated with increased hemoglobin levels in children. Copper (Cu), cobalt (Co), and lead (Pb) were associated with decreased hemoglobin levels. Both Bayesian kernel machine regression (BKMR) and Quantile g-computation (Qgcomp) analysis showed that mixed metal exposure levels were positively correlated with hemoglobin levels, and both found that Zn played a major role in this relationship. Stratified analysis showed that mixed metal exposure had a more significant effect on older children and boys. Our analysis suggested BMI as an intermediary in the associations of Pb, Mn, and Tl with hemoglobin, with mediating proportions being 100, 12.6, and 14%, respectively. The mediation analysis also suggested that the relationship between metals and hemoglobin could be explained, in part, by their correlations with other metals. In this study, the impact of mixed metal exposure on hemoglobin, as well as the possible biological mediating pathways involved, was further clarified.