Association Between Particulate Matter Exposure and Thyroid Hormone Levels in Early Childhood: Results from JECS

Background Particulate matter (PM) exposure is associated with adverse health outcomes. However, the association between PM exposure and thyroid hormone (TH) concentrations in children is not comprehensively evaluated. Objectives Using an ongoing birth cohort dataset, the association between PM exposure and blood free thyroxine (fT4) and thyroid-stimulating hormone (TSH) concentrations in children aged 2–4 years was assessed. Methods Data were obtained from the Japan Environment and Children’s Study. Children aged 2 years and those aged 4 years were analyzed separately, with 3,599 and 3,431 cases included in each dataset. The generalized linear model and the quantile g-computation models were fitted. Results Neither indoor nor outdoor PM exposures at 1.5 years were significantly associated with fT4 and TSH levels at 2 years of age. Indoor and outdoor PM10-2.5 exposures at 3 years of age were negatively associated with fT4 concentrations at 4 years of age. A simultaneous increase in PM concentrations by one quartile at 3 years of age resulted in a significant decrease in fT4 levels of 0.011 ng/dL at 4 years of age. Conclusion Using a large sample, the statistical modeling results suggested an opposite association between PM exposure and fT4. However, since this association is very weak, from a clinical and epidemiological point of view, we can entirely ignore the effect of PM exposure on fT4. Therefore, we conclude that PM does not significantly influence thyroid parameters in daily life.