Association of ozone with premature cardiovascular mortality: evidence from a nationwide cohort study

Background Previous studies have found that long-term ozone exposure is associated with an increased risk of cardiovascular mortality, but there remains insufficient analysis regarding the association between ozone and premature death across different populations. Purpose To analyze the association between long-term ozone exposure and the risk of premature cardiovascular mortality, as well as its variations across different population groups. Methods Based on the ChinaHEART (Health Evaluation And risk Reduction through nationwide Teamwork), a nationwide, population-based cohort study, we collected 3,618,867 participants aged 35-75 years, selected as a representative sample of the entire cohort between November 2014 and December 2023. Mortality records were through a linkage of data with the National Mortality Surveillance System and Vital Registration. The mean concentration of ozone during the five-year period preceding the baseline assessment was computed to represent long-term exposure. The Cox proportional hazards model was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs), assessing the association between ozone and the risk of premature cardiovascular disease mortality, as well as its variations across sex, age groups, urbanity and different socioeconomic status (SES). We also assessed the roles of medical history as potential mediators. Results Among the 3,618,867 included participants with an average age of 56·0±10.0 years, 59·4% were female. During the follow-up with a median of 5·3 years, 21,901 premature CVD mortality cases were confirmed. The 10.0 μg/m3 increase in the ozone level was associated with a higher risk of premature CVD in the multivariate model (hazard ratio [HR]: 1.07, 95% confidence interval [CI]: 1.05-1.09). The association between ozone and premature CVD mortality was stronger among older people (HR: 1.14, 95% CI: 1.10-1.19) and participants with lowest SES (HR: 1.09, 95% CI: 1.06-1.12). The association between ozone and premature CVD mortality was mediated by history of hypertension. Conclusion Long-term ozone exposure exerts a significant impact on premature cardiovascular disease mortality, with this association being more pronounced among individuals with older people and low socioeconomic status. Notably, hypertension demonstrates a noteworthy mediating proportion in this pathway. These findings may inform the development of targeted air pollution control strategies.