Long-term Exposure to Ozone and Cause-Specific Mortality Risk in the U.S.

RATIONALE: Many studies have linked short-term exposure to ozone (O3) with morbidity and mortality, but epidemiological evidence of associations between long-term ozone exposure and mortality is more limited.

OBJECTIVES: We investigated associations of long-term (annual or warm season average) 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 2002-2010) and multiple causes of death were evaluated using multivariate Cox proportional hazards models, adjusted for both individual- and census tract-level covariates, as well as potentially confounding co-pollutants and temperature.

MEASUREMENTS AND MAIN RESULTS: Long-term annual average exposure to O3 was significantly associated with deaths due to cardiovascular disease (per 10 ppb, HR=1.03; 95% 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 co-pollutants (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 standard(s) are needed to more adequately protect public health from ambient O3 exposures.