Associations between long-term exposure to multiple air pollutants and age at menopause: a longitudinal cohort study

Background: To investigate the associations between long-term exposure to ambient air pollution and age at menopause and the risk of early menopause in two Asian cohorts. Methods: A total of 53,167 female adults were enrolled from two ongoing cohorts, one each in Taiwan and Hong Kong, between 2003 and 2018, yielding 200,000 person-years of follow-up. We performed a Cox regression model with time-dependent covariates to investigate associations between air pollution and menopause. Results: The mean age at baseline and at natural menopause was 34.4 and 51.0 years, respectively. In the single-pollutant models, we found that increase in PM_2.5 and NO₂ was associated a younger age at menopause [hazard ratios (HRs) (95% confidence interval, CI): 1.16 (1.09–1.23) and 1.04 (1.01–1.06), respectively, for each 10 µg/m³ increase in air pollution]. In the multiple-pollutant models, the NO₂–menopause associations were attenuated after adjusting for PM_2.5 and O₃, whereas the associations of menopause with PM_2.5 and O₃ remained stable. Similar associations were observed for the risk of early menopause (age at menopause ≤ 45 years). Conclusions: Long-term exposure to ambient air pollution was associated with the age at menopause and the risk of early menopause. More effective strategies to mitigate air pollution are required.