Long-term effects of traffic-related air pollution on mortality in the Southeastern US

Abstract

Background Mounting evidence has shown that the long-term exposure to fine particulate matter and ozone can increase mortality. However, the health effects associated with long-term exposure to nitrogen dioxide (NO2) are less clear. Methods We conducted a large population-based cohort study that included all Medicare beneficiaries (aged ≥65, N=15,646,962) in the Southeastern US from 2000-2016, with 124,019,974 person-years of follow-up. We applied previously estimated spatially- and temporally-resolved NO2 concentrations and assigned annual means to study subjects based on ZIP code of residence. Cox proportional hazards models were used to examine the association between long-term exposure to NO2 and all-cause mortality, adjusting for potential confounders. Results We observed a statistically significant association between long-term exposure to NO2 and all-cause mortality, with a hazard ratio (HR) of 1.036 (95% CI: 1.029, 1.043) in two-pollutant models (adjusting for PM2.5) and a HR of 1.032 (95% CI: 1.021, 1.043) in multi-pollutant models (adjusting for PM2.5 and ozone), per 10 ppb increase in annual NO2 concentrations. The penalized spline indicates a linear dose-response relationship across the entire NO2 exposure range. Subjects who are female, Black, Medicaid-eligible, and residing in urban areas are more vulnerable to long-term NO2 exposure. Conclusion Using a large cohort, we provide epidemiological evidence that long-term exposure to NO2 was significantly associated with a higher risk of mortality, independent of PM2.5 and ozone. Improving air quality by reducing NO2 emissions may yield substantial health benefits.