Maternal blood metal levels during pregnancy and body mass index z-score, overweight, and obesity among children: Findings of the Japan Environment and Children's Study.

This study explored the association between maternal blood lead, cadmium, mercury, and manganese concentrations during pregnancy and body mass index z-scores (zBMI), overweight, and obesity among children aged 0-4 years based on data from the Japan Environment and Children's Study (JECS). After data selection, 93,782 mother-child pairs were selected for analysis. Associations between prenatal metal exposure and obesity in children were explored using the generalized estimating equation (GEE), latent class growth analysis (LCGA), and quantile g-computation models. After adjusting for confounders, mercury (Hg) showed a very weak opposite association with zBMI, overweight, and obesity according to the GEE model. A one-unit increase in the log2(Hg) was associated with an approximately 3 % reduction in the odds of obesity. Similarly, lead and cadmium were associated with a slight reduction in zBMI. Results from the LCGA model showed that increased mercury exposure was associated with reduced odds of belonging to the late-onset or persistent obesity trajectory groups. The mixture effect from the quantile g-computation model indicated the same direction of association. A one-quartile simultaneous increase in the lead, cadmium, mercury, and manganese concentrations was associated with a 0.024 reduction in zBMI and the risk of overweight and obesity (approximately 4.6 % and 6.4 %, respectively). Extremely weak negative associations were observed between prenatal metal exposure and zBMI, overweight, and obesity during early childhood. However, given the weak effect size, we acknowledge that prenatal metal exposure does not significantly influence childhood obesity from a public health and clinical perspective.