Long-Term Exposure to Low-Level NO2 and Mortality among the Elderly Population in the Southeastern United States

Background: Mounting evidence has shown that long-term exposure to fine particulate matter [PM <= 2.5 mu m in aerodynamic diameter (PM2.5 )] and ozone (O-3) can increase mortality. However, the health effects associated with long-term exposure to nitrogen dioxide (NO2) are less clear, in particular the evidence is scarce for NO2 at low levels that are below the current international guidelines. Methods: We constructed a population-based full cohort comprising all Medicare beneficiaries (aged = 65 , N = 13,590,387 ) in the southeastern United States from 2000 to 2016, and we then further defined the below-guideline cohort that included only those who were always exposed to low-level NO2 , that is, with annual means below the current World Health Organization guidelines (i.e., = 21 ppb ). We applied previously estimated spatially and temporally resolved NO2 concentrations and assigned annual means to study participants based on their ZIP code of residence. Cox proportional hazards models were used to examine the association between long-term exposure to low-level NO2 and all-cause mortality, adjusting for potential confounders. Results: About 71.1% of the Medicare beneficiaries in the southeastern United States were always exposed to low-level NO2 over the study period. We observed an association between long-term exposure to low-level NO2 and all-cause mortality, with a hazard ratio (HR ) = 1.042 (95% CI: 1.040, 1.045) in single-pollutant models and a HR = 1.047 (95% CI: 1.045, 1.049) in multipollutant models (adjusting for PM2.5 and O-3 ), per 10 -ppb increase in annual NO2 concentrations. The penalized spline indicates a linear exposure-response relationship across the entire NO2 exposure range. Medicare enrollees who were White, female, and residing in urban areas were more vulnerable to long-term NO2 exposure. Conclusion: Using a large and representative cohort, we provide epidemiological evidence that long-term exposure to NO2 , even below the national and global ambient air quality guidelines, was approximately linearly associated with a higher risk of mortality among older adults, independent of PM2.5 and O-3 exposure. Improving air quality by reducing NO2 emissions, therefore, may yield significant health benefits.

Automated summary

Evidence from a large cohort study suggests that long-term exposure to nitrogen dioxide (NO2), even below current international guidelines, is associated with a higher risk of mortality among older adults in a linear manner. White individuals, females, and those living in urban areas are more vulnerable to the effects of long-term NO2 exposure.