Cross-sectional association of arsenic exposure with thyroid function in Bangladeshi children aged 5 to 7 years

BACKGROUND: Arsenic is a pervasive environmental contaminant and a recognized global public health concern. Experimental evidence suggests that arsenic may disrupt endocrine signaling during critical developmental windows, yet epidemiologic data on its effects on thyroid function in early childhood remain limited. METHODS: We investigated the cross-sectional association between arsenic exposure and free thyroxine (fT4) levels among 496 children aged 5 to 7 years enrolled in the Bangladesh Environmental Research in Children's Health (BiRCH) cohort. Arsenic exposure was assessed using urinary total arsenic and toenail arsenic concentrations. Serum fT4 levels were measured by an enzyme-linked immunosorbent assay (ELISA) kit. Associations with fT4 were estimated using multivariable linear regression models adjusted for child age, sex, body mass index, and environmental tobacco smoke exposure. RESULTS: The median urinary and toenail arsenic concentrations were 88.0 µg/L (interquartile range [IQR]: 127.4) and 1.7 µg/g (IQR: 2.0), respectively. Children in the highest quartile (Q4) of arsenic exposure had significantly higher fT4 levels compared to those in the lowest quartile (Q1), for both urinary (β = 0.09; 95% CI: 0.005-0.17) and toenail arsenic (β = 0.10; 95% CI: 0.03-0.17). A significant dose-response trend was observed across quartiles, suggesting a potential linear relationship. CONCLUSIONS: Our findings suggest that thyroid function may be a sensitive target of arsenic toxicity in early childhood. Longitudinal studies are necessary to assess the long-term effects of early-life arsenic exposure on thyroid function across the life course.