Association of Ozone Exposures with the risk of thyroid nodules in Hunan Province: a population-based cohort study

BACKGROUND: Increasing evidence associates air pollution with thyroid dysfunction, whereas the potential relationship between exposure to ozone (O(3)) and Thyroid Nodules (TNs) is unclear. METHODS: This retrospective cohort study investigated the association between O(3) exposure and TNs in Hunan province, enrolling 191,357 Chinese adults who lived in Hunan province from January 2009 to December 2019 and received voluntary medical examinations. Individual exposure levels to O(3) from 2010 to 2019 were measured on account of participants’ residential addresses at the district level. Associations of O(3) exposure with the risk of incidental TNs were assessed by restricted cubic splines and surveyed as odds ratios after adjusting for demographic factors. RESULTS: In total, 81,900 adults were newly diagnosed with TNs during the study period. Age-standardized TNs detection rate in Hunan province increased from 25.9 to 46.3% between 2010 and 2019, with the greatest annual percent change being 8.1 [95% CI, 7.3–8.8]. A similar trend has been found in all tumor sizes, ages, and both sexes. O(3) exposure presented a statistically significant dose-dependent positive correlation (greater than 0.036 ppm) with TNs. Similarly, long-term exposure to high levels of O(3) (1-year average O(3) concentrations exceeding 0.0417 ppm) was found positively associated with increased TSH levels. CONCLUSIONS: High-level O(3) exposure in the long term was associated with an increase in TSH. Consequently, increased TSH was related to the increased risk of TNs. Being exposed to high-level O(3) in the long term was related to the increased detection rates of TNs in Hunan province, which could be mediated by TSH. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12940-022-00874-8.