Reducing Inflammation Levels and Ensuring Adequate Iodine Intake May Mitigate Thyroid Hormone Alterations in Youth Exposed to Multiple Endocrine-Disrupting Chemicals

Exposure to environmental endocrine-disrupting chemicals (EDCs) is ubiquitous and inevitable; exploring the association between multiple types of EDCs and thyroid hormone levels allows for a comprehensive understanding of the potentially cumulative and synergistic effects of EDCs on endocrine function. Moreover, investigating the roles of inflammation and urinary iodine in these associations enhances our understanding of the possible mechanisms and aids in developing targeted interventions. This study assessed the exposure to multiple EDCs, polycyclic aromatic hydrocarbons, phthalates, and pesticides in 234 children and adolescents aged 6–17 years by determining urinary metabolite concentrations, and concurrently measured urinary iodine concentrations. Thyroid hormones, C-reactive protein, and white blood cell counts were measured in the paired blood. We systematically evaluated the individual dose–response relationships and joint effects of the EDC exposure on thyroid hormone levels using multiple statistical methodologies. The results revealed significant associations between higher concentrations of metabolites of EDCs and elevated triiodothyronine and tetraiodothyronine levels. Significant nonlinear associations were obtained between specific individual metabolites and thyroid hormones. 1-hydroxypyrene was the particular compound that contributed significantly to the elevated levels of triiodothyronine and tetraiodothyronine. Moderation analysis revealed that the association between EDC exposure and thyroid hormone alterations strengthens with increasing C-reactive protein levels, but weakens and even becomes non-significant as the levels of urinary iodine concentration increase. The results demonstrated significant thyroid disrupting effects of exposure to multiple EDCs, and ensuring sufficient iodine intake and lowing systemic inflammation levels may attenuate the association between EDCs exposure and thyroid hormone alterations.