Long-Term Exposure to Ozone and Cause-Specific Mortality Risk in the United States

Rationale: Many studies have linked short-term exposure to ozone (O₃) with morbidity and mortality, but epidemiologic evidence of associations between long-term O₃ exposure and mortality is more limited.Objectives: To investigate associations of long-term (annual or warm season average of daily 8-h maximum concentrations) O₃ exposure with all-cause and cause-specific mortality in the NIH-AARP Diet and Health Study, a large prospective cohort of U.S. adults with 17 years of follow-up from 1995 to 2011.Methods: The cohort (n = 548,780) was linked to census tract-level estimates for O₃. Associations between long-term O₃ exposure (averaged values from 2002 to 2010) and multiple causes of death were evaluated using multivariate Cox proportional hazards models, adjusted for individual- and census tract-level covariates, and potentially confounding copollutants and temperature.Measurements and Main Results: Long-term annual average exposure to O₃ was significantly associated with deaths caused by cardiovascular disease (per 10 ppb; hazard ratio [HR], 1.03; 95% confidence interval [CI], 1.01-1.06), ischemic heart disease (HR, 1.06; 95% CI, 1.02-1.09), respiratory disease (HR, 1.04; 95% CI, 1.00-1.09), and chronic obstructive pulmonary disease (HR, 1.09; 95% CI, 1.03-1.15) in single-pollutant models. The results were robust to alternative models and adjustment for copollutants (fine particulate matter and nitrogen dioxide), although some evidence of confounding by temperature was observed. Significantly elevated respiratory disease mortality risk associated with long-term O₃ exposure was found among those living in locations with high temperature (P_interaction < 0.05).Conclusions: This study found that long-term exposure to O₃ is associated with increased risk for multiple causes of mortality, suggesting that establishment of annual and/or seasonal federal O₃ standards is needed to more adequately protect public health from ambient O₃ exposures.