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

Mounting evidence has shown that long-term exposure to fine particulate matter [PM $$ in aerodynamic diameter ($$)] and ozone ($$) can increase mortality. However, the health effects associated with long-term exposure to nitrogen dioxide ($$) are less clear, in particular the evidence is scarce for $$ at low levels that are below the current international guidelines.

We constructed a population-based full cohort comprising all Medicare beneficiaries (aged $$, $$) 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 $$, that is, with annual means below the current World Health Organization guidelines (i.e., $$). We applied previously estimated spatially and temporally resolved $$ concentrations and assigned annual means to study participants based on their ZIP code of residence. Cox proportional hazards models were used to examine the association between long-term exposure to low-level $$ and all-cause mortality, adjusting for potential confounders.

About 71.1% of the Medicare beneficiaries in the southeastern United States were always exposed to low-level $$ over the study period. We observed an association between long-term exposure to low-level $$ and all-cause mortality, with a $$ 1.042 (95% CI: 1.040, 1.045) in single-pollutant models and a $$ 1.047 (95% CI: 1.045, 1.049) in multipollutant models (adjusting for $$ and $$), per $$ increase in annual $$ concentrations. The penalized spline indicates a linear exposure-response relationship across the entire $$ exposure range. Medicare enrollees who were White, female, and residing in urban areas were more vulnerable to long-term $$ exposure.

Using a large and representative cohort, we provide epidemiological evidence that long-term exposure to $$, even below the national and global ambient air quality guidelines, was approximately linearly associated with a higher risk of mortality among older adults, independent of $$ and $$ exposure. Improving air quality by reducing $$ emissions, therefore, may yield significant health benefits. https://doi.org/10.1289/EHP9044.