Association between Air Pollutants and Circadian Syndrome in China: A Longitudinal Cohort Study Based on CHARLS

Circadian syndrome (CircS) is a multisystem metabolic disorder related to circadian disruption, characterized by sleep disturbance, central obesity, hypertension, and impaired glucose and lipid metabolism. Evidence linking ambient air pollution to CircS in middle-aged and older adults remains limited. Using the nationally representative China Health and Retirement Longitudinal Study (CHARLS), we examined the individual and joint effects of seven pollutants (PM1, PM2.5, PM10, NO2, SO2, CO, and O3) on incident CircS. We followed 2,975 participants aged ≥45 years who were free of CircS at baseline (2011–2012) through 2015–2016. Long-term residential exposures were assigned using CHAP-based estimates. Multivariable logistic regression and subgroup analyses assessed associations, and several complementary mixture models evaluated joint effects. In fully adjusted models, per-SD increases in pollutants were associated with higher odds of incident CircS (ORs 1.10–1.16), whereas the highest versus lowest quartile yielded ORs of 1.26–1.64. Mixture analyses consistently showed a harmful overall joint effect, with O3 and SO2 contributing most and PM10 also showing a notable role. Associations were stronger among older adults and current smokers, and results were robust across multiple modeling strategies and sensitivity analyses. These findings support prioritizing targeted pollution control for circadian-metabolic health in ageing populations.