Associations Between Ambient PM 2.5 and Thyroid Hormones in Pregnant Persons in Puerto Rico

Introduction: This study investigates associations between fine particulate air pollution (PM 2.5 ) exposure and thyroid hormone levels during pregnancy in Puerto Rican individuals, a vulnerable population facing socioeconomic and environmental disparities. Methods: This research draws on data from the PROTECT cohort study and involves 1040 participants to measure the effect of PM 2.5 on developmentally important thyroid hormones (TSH, T3, T4, and FT4). Pollution concentrations were linked to participant locations using EPA air quality data and analyzed across two visits during gestational weeks 16–20 and 24–28. Results: The results suggest that PM 2.5 exposure is positively associated with maternal T3, T4, and FT4 levels but not TSH. These effects vary by timing, with T3 showing stronger associations later in pregnancy and T4/FT4 earlier. Nonlinear dose–response relationships were observed, suggesting thresholds for certain hormones. Discussion: These findings support previous studies linking altered thyroid hormones to adverse birth outcomes and highlight the potential role of air pollution in disrupting maternal thyroid function and its implications for fetal development, calling for further research into mechanisms and interventions to mitigate these risks.