Long-term ozone exposures and cause-specific mortality in a US Medicare cohort

We examined the association of long-term, daily 1-h maximum O(3) (ozone) exposures on cause-specific mortality for 22.2 million US Medicare beneficiaries between 2000–2008. We modeled the association between O(3) and mortality using age-gender-race stratified log-linear regression models, adjusted for state of residence. We examined confounding by (1) adjusting for PM(2.5) (particles with aerodynamic diameters <2.5 μm) and NO(2) (nitrogen dioxide) exposures, temperature, and neighborhood-level characteristics and behaviors, and (2) decomposing O(3) into its temporal and spatio-temporal components and comparing estimated risk ratios. We also examined sensitivity of our results to alternate exposure measures based on warm-season 8-h daily maximum and 24-h average exposures. We found increased risks from long-term O(3) exposures to be strongest and most consistent for mortality from respiratory disease (1.030, 95% CI: 1.027, 1.034) (including COPD (chronic obstructive pulmonary disease)), CHF (congestive heart failure), and lung cancer (1.015, 95% CI: 1.010, 1.020), with no evidence of confounding by PM(2.5), NO(2), and temperature and with results similar across O(3) exposure measures. While significant, associations between long-term O(3) exposures and CVD (cardiovascular)-related mortality (1.005, 95% CI: 1.003, 1.007) were confounded by PM(2.5) and varied with the exposure measure, with associations no longer significantly positive when warm-season 8-h maximum or 24-h average O(3) was used to assess exposures. In this large study, we provide strong evidence that O(3) exposure is associated with mortality from respiratory-related causes and for the first-time, lung cancer, but raise questions regarding O(3)-related impacts on CVD mortality. Our findings demonstrate the need to further identify potential confounders.