Short-term exposure to warm-season ozone, cardiovascular mortality, and novel high-risk populations: A nationwide time-stratified case-crossover study

A considerable number of previous studies have limitations in evaluating the population-representative relationship between ozone and cardiovascular disease (CVD) mortality risk and revealing high-risk populations due to the limited data availability that could not cover unmonitored areas. To estimate the population-representative association between warm-season (Apr–Sep) ozone and CVD mortality and examine high-risk populations, this study conducted a nationwide case-crossover study in South Korea from 2015 to 2019. Stratified analyses and meta-regression were also performed for each cause of death and demographic characteristics to find high-risk populations. As an exposure, daily modeled warm-season ozone estimated by a machine learning-based ensemble model was used (R² > 0.92). In the total population, warm-season ozone was associated with an increased risk of total CVD death (OR: 1.010, 95% CI: 1.002–1.018), and mortality due to ischemic heart disease showed the highest OR (1.019, 1.003–1.035). The warm-season ozone-related CVD death risk was the highest in younger age groups (0–59 y) across all causes of CVD deaths, except for cerebrovascular disease death. The higher accessibility to hospital beds per 1000 was associated with a lower ozone risk of CVD mortality. The estimated excess CVD mortality fractions and years of life lost from mortality (YLL) attributable to warm-season ozone were 5.10% and 119,353.37 years. Our findings suggest that younger populations should be recognized as novel high-risk populations related to warm-season ozone and CVD mortality, and this study also provides potential benefits for constructing stricter ozone mitigation action plans.