Long-Term Ozone Exposure and Mortality in a Large Prospective Study

Abstract

Rationale: Tropospheric ozone (O ₃) is potentially associated with cardiovascular disease risk and premature death. Results from long-term epidemiological studies on O ₃ are scarce and inconclusive.

Objectives: In this study, we examined associations between chronic ambient O ₃ exposure and all-cause and cause-specific mortality in a large cohort of U.S. adults.

Methods: Cancer Prevention Study II participants were enrolled in 1982. A total of 669,046 participants were analyzed, among whom 237,201 deaths occurred through 2004. We obtained estimates of O ₃ concentrations at the participant’s residence from a hierarchical Bayesian space–time model. Estimates of fine particulate matter (particulate matter with an aerodynamic diameter of up to 2.5 μm [PM _2.5]) and NO ₂ concentrations were obtained from land use regression. Cox proportional hazards regression models were used to examine mortality associations adjusted for individual- and ecological-level covariates.

Measurements and Main Results: In single-pollutant models, we observed significant positive associations between O ₃, PM _2.5, and NO ₂ concentrations and all-cause and cause-specific mortality. In two-pollutant models adjusted for PM _2.5, significant positive associations remained between O ₃ and all-cause (hazard ratio [HR] per 10 ppb, 1.02; 95% confidence interval [CI], 1.01–1.04), circulatory (HR, 1.03; 95% CI, 1.01–1.05), and respiratory mortality (HR, 1.12; 95% CI, 1.08–1.16) that were unchanged with further adjustment for NO ₂. We also observed positive mortality associations with both PM _2.5 (both near source and regional) and NO ₂ in multipollutant models.

Conclusions: Findings derived from this large-scale prospective study suggest that long-term ambient O ₃ contributes to risk of respiratory and circulatory mortality. Substantial health and environmental benefits may be achieved by implementing further measures aimed at controlling O ₃ concentrations.