Ambient PM2.5 and thyroid health: A cross-sectional study of 24,333 participants in Zhejiang, China.
TL;DR
Higher ambient PM2.5 exposure was associated with lower thyroid function, and exposure to PM2.5 was not clearly associated with autoimmune thyroiditis.
Abstract
Evidence on the association between ambient fine particulate matter (PM2.5) exposure and thyroid dysfunction remains inconsistent, with limited evidence from community-based populations encompassing both minors and adults while accounting for iodine nutrition. We aimed to evaluate the associations of ambient PM2.5 exposure with complementary dimensions of thyroid health in a community-based population in Zhejiang Province, China. We conducted a cross-sectional study of 24,333 participants between 2022 and 2025. PM2.5 exposure was estimated using participants' geocoded residential addresses. Linear and generalised linear mixed-effects models were used to estimate the associations of PM2.5 with free thyroxine (FT4), thyroid-stimulating hormone (TSH), subclinical hypothyroidism, and autoimmune thyroiditis. Stratified analyses were conducted by age, sex, and body mass index (BMI). Our results showed that each 10 μg/m3 increase in PM2.5 was associated with lower FT4 [-3.57% (95% confidence interval (CI): -4.39%, -2.75%)], higher TSH [12.15% (95% CI: 7.92%, 16.56%)], and higher odds of subclinical hypothyroidism [odds ratio (OR) 1.27 (95% CI: 1.06, 1.51)]. Exposure to PM2.5 was not clearly associated with autoimmune thyroiditis. The association with lower FT4 was more pronounced among participants aged < 18 years and those with BMI < 18.5 kg/m2, whereas the associations with higher TSH and higher odds of subclinical hypothyroidism were more pronounced among participants aged ≥ 50 years and those with BMI ≥ 24.0 kg/m2. Overall, our findings suggest that higher ambient PM2.5 exposure was associated with lower thyroid function.