Environment/Climate Change
Effects of metal mixtures on thyroid function in Bangladeshi children aged 5 to 7 years: Evidence from the BiRCH cohort Yingyue Ni* Yingyue Ni Syed Emdadul Haque Tariqul Islam Mohammad Hasan Shahriar Golam Sarwar Alauddin Ahmed Farzana Jasmine Muhammad G Kibriya Habibul Ahsan Maria Argos
Studies have demonstrated the adverse impact of metals on thyroid function. However, limited research has evaluated this relationship in children despite the importance of thyroid hormones during this stage of development. This study aims to investigate the cross-sectional associations of metal co-exposures on thyroid function in 496 children aged 5 to 7 years participating in the Bangladesh Environmental Research in Children’s Health (BiRCH) cohort. Linear regression models were used to estimate the individual associations of 17 toenail metal concentrations with free thyroxine (FT4), adjusted for potential confounding by sex, age, body mass index and second-hand smoke exposure. Weighted Quantile Sum (WQS) regression was conducted to evaluate the joint effect of the metal co-exposures. Arsenic, zinc, selenium, and cadmium were individually positively associated with FT4 levels (arsenic β=0.03, 95% CI: 0.01, 0.05; zinc β=0.06, 95% CI: 0.01, 0.11; selenium β=0.10, 95% CI: 0.03, 0.17; and cadmium β=0.02, 95% CI: 0.00, 0.04), while mercury was inversely associated (β=-0.05, 95% CI: -0.07, -0.02). In WQS regression, we observed an association with the positive metal mixture index on FT4 (β=0.06, 95% CI: 0.02, 0.10), primarily driven by selenium, arsenic, and zinc. This study provides evidence of early-life associations of metal exposures on thyroid function based on FT4 in children. Further research is needed to elucidate the mechanisms underlying these associations and the potential long-term health impacts across the life course.