Associations of ozone exposure and residential greenness with early chronic kidney disease in young adults from the Tianshan cohort.

The relationship between environmental factors and early chronic kidney disease (CKD) in young adults remains unclear, particularly regarding the joint effects and climatic modifying factors. Here, by analyzing data from the Tianshan Cohort of 2,517,928 adults (aged 18-40 years) linked with satellite-derived ozone (O3) and the Normalized Difference Vegetation Index (NDVI), and using Cox models, we quantified their associations with incident early CKD (eGFR ≥60 mL/min/1.73 m2 with proteinuria). Over a median follow-up period of 4.53 years, 264,195 incident cases were identified. Higher O3 exposure increased the risk of early CKD (HR for Q4 vs. Q1 = 1.60, 95% CI: 1.58-1.63), while higher residential greenness (NDVI) decreased the risk (HR for Q4 vs. Q1 = 0.95, 95% CI: 0.93-0.96). Notably, the exposure-response relationships were nonlinear. The risk of early CKD increased sharply when O3 levels exceeded 100.94 μg/m3, whereas a marked protective effect of NDVI emerged once its value surpassed 0.27. Mediation analysis indicated that 57.57% of NDVI's protective effect was mediated by reduced O3 exposure. Stratified analyses revealed that high temperature (HR for O3≥Q4 = 1.62, 95% CI: 1.59-1.64) and low precipitation (HR for O3≥Q4 = 1.73, 95% CI: 1.70-1.77) exacerbated O3-associated risk. Furthermore, the protective effect of NDVI was enhanced under low temperature (HR for NDVI ≥ Q4 = 0.91, 95% CI: 0.89-0.92) and high precipitation (HR for NDVI ≥ Q4 = 0.75, 95% CI: 0.73-0.76). Thus, O3 exposure is associated with an increased risk of early CKD, whereas residential greenness exerts a protective effect partly mediated by reducing O3; these nonlinear associations are intensified by high temperature and low precipitation. Integrated strategies for air quality improvement, urban greening, and climate adaptation may help mitigate CKD incidence in young adults.