The Protective Effect of the Composite Dietary Antioxidant Index on Hypertension Risk Associated with Long-term Exposure to PM 2.5 and Its Constituents: A 10-Year Cohort Study in Southwest China

Background Fine particulate matter (PM _2.5 ) has been established as a significant environmental risk factor for cardiovascular disease. However, evidence linking its chemical constituents to the incidence of hypertension remains limited, and additionally, critical gaps persist in this field regarding the protective potential of nutritional interventions. Objectives Evaluate the effects of long-term exposure to PM _2.5 and its constituents on the risk of incident hypertension, and explore the protective effects of the Composite Dietary Antioxidant Index (CDAI) on these associations. Methods A baseline survey enrolled 9,280 permanent residents aged ≥ 18 years from 12 counties or districts in Guizhou Province, China. After follow-up from 2016 to 2020, 5,270 participants were included in the final analysis. Time-dependent Cox proportional hazards regression models were employed to estimate hazard ratios ( HRs ) and 95% confidence intervals ( CIs ) for incident hypertension per 1-standard deviation (SD) µg/m ³ increase in long-term exposure to PM _2.5 and its chemical constituents. Restricted cubic spline models were used to visualize exposure-response relationships between PM _2.5 and its constituents with hypertension risk at different CDAI levels. Results (1) During a median follow-up of 6.58 years, 1,156 incident cases of hypertension were identified, yielding an incidence density of 31.32 per 1,000 person-years. (2) After multivariable adjustment, each 1-SD µg/m ³ increase in PM _2.5 exposure was associated with a hazard ratio ( HR ) of 1.532 (95% CI: 1.410–1.665) for hypertension. Among its chemical constituents, sulfate (SO ₄ ^2- ) and black carbon (BC) demonstrated the strongest associations ( HR  = 1.625; 95% CI : 1.474–1.790 and HR  = 1.641; 95% CI : 1.478–1.823, respectively). These associations remained robust after further adjustment for ozone (O ₃ ), nitrogen dioxide (NO ₂ ), and the normalized difference vegetation index (NDVI). (3) Exposure-response curves derived from restricted cubic spline models demonstrated significantly lower hypertension risk at the highest tertile of CDAI (Q3 vs. Q1/Q2), with risk thresholds for PM _2.5 and its constituents shifting toward higher concentrations, a significant interaction between PM _2.5 constituents and CDAI was also observed. (4) Stratified analyses revealed significant effect modification by urban-rural residence, ethnicity, and smoking status ( P for interaction < 0.05). Conclusion This study demonstrates that long-term exposure to PM₂.₅ and its constituents significantly elevates hypertension risk. Crucially, it provides the first direct evidence that a higher CDAI level can attenuate this risk, revealing a novel "nutrition-environment" interaction mechanism in hypertension prevention that holds pivotal public health significance.