Air pollution and risk of autoimmune thyroid diseases in children and adolescents: Findings from a nationwide cohort study in Korea

Epidemiological evidence on the association between long-term air pollution exposure and the incidence of autoimmune thyroid diseases (AITD) in children and adolescents remains limited. This study aimed to examine the relationship between long-term exposure to air pollution and the onset of AITD in children and adolescents in South Korea. This nationwide cohort study included 1,400,433 children aged 6 years at baseline (2008-2010) from the National Health Information Database, with follow-up until 19 years of age. The onset of AITD was defined based on the 10th revision of the International Classification of Diseases (Hashimoto's thyroiditis: E063; Graves' disease: E050). Individuals with missing data on age, residence, income level, or underlying conditions such as congenital hypothyroidism were excluded. Exposure concentrations of particulate matter (PM₁₀ and PM_2.5), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and ozone (O₃) were categorized into quartiles. Hazard ratios (HRs) with 95% confidence intervals (CIs) were estimated using Cox proportional hazards models, comparing the lowest quartile with higher quartiles. Among the 1,400,433 children analyzed (boys: 729,367; girls: 671,066), 2344 cases (0.17%) of Hashimoto's thyroiditis and 3424 cases (0.24%) of Graves' disease were identified during follow-up. The total person-years for both diseases were approximately 19.6 million. Among girls, annual mean PM_2.5 exposure (HR_3rd quartile: 1.245, 95% CI: 1.035-1.497; HR_4th quartile: 1.286, 95% CI: 1.052 -1.571) was significantly associated with the onset of Graves' disease, as was SO₂ exposure (HR_2nd quartile: 1.131, 95% CI: 1.003 -1.277). Among boys, a significant association was observed between higher annual NO₂ exposure (HR_4th quartile: 2.153, 95% CI: 1.214 -3.818) and the onset of Hashimoto's thyroiditis. These findings provide evidence that long-term exposure to air pollution, particularly PM_2.5, NO₂, and SO₂, is associated with the incidence of AITD in children and adolescents.