Associations of air pollutant exposures with Cardio-Kidney-Metabolic syndrome in Chinese middle-aged and older adults: a cross-sectional study based on CHARLS.

BACKGROUND: Cardio-Kidney-Metabolic (CKM) syndrome is a prevalent systemic disorder, but evidence linking it to air pollution is scarce. We investigated the association between long-term exposure to multiple air pollutants and CKM syndrome severity in Chinese adults. METHODS: In this cross-sectional study of 3,937 participants from the China Health and Retirement Longitudinal Study (CHARLS), we estimated long-term (2013-2015) residential exposures to PM₁, PM₂.₅, PM₁₀, NO₂, O₃, and SO₂. CKM syndrome was staged per American Heart Association criteria. We used ordered logistic, Weighted Quantile Sum (WQS), and restricted cubic spline regression to assess associations. RESULTS: After full adjustment, each one-standard-deviation (SD) increase in pollutant concentration was significantly associated with higher odds of a more advanced CKM stage. The association was strongest for PM₁₀ (per 33.3 µg/m³ SD increase; OR = 1.16, 95% CI: 1.07-1.27), with significant positive associations also found for SO₂, PM₂.₅, NO₂, and O₃. The overall pollutant mixture was also positively associated with CKM progression (OR = 1.20, 95% CI: 1.02-1.41 per quartile increase in the WQS index). Older adults (≥ 60 years) and residents of eastern China were identified as particularly susceptible subgroups (P for interaction < 0.05). CONCLUSION: Long-term exposure to ambient air pollutants, individually and as a mixture, is associated with advanced CKM syndrome in Chinese adults. Our findings identify air pollution as a critical modifiable factor and underscore the need for targeted public health interventions to mitigate the burden of this multisystem disease, especially for vulnerable populations.