Incident COPD and Its Disparities Associated with Low-concentration Air Pollution in American Older Adults: A National Cohort Analysis

BACKGROUND: Risk of air pollution-related Chronic Obstructive Pulmonary Disease (COPD) and corresponding disparities associated with air pollutant exposures are less clear at concentrations below current National Ambient Air Quality Standards (NAAQS). METHODS: We constructed a national U.S. population-based cohort of those aged ≥65 from the Medicare Chronic Conditions Warehouse (2000-2016), combined with high-resolution population-weighted air pollution datasets, to investigate the association of long-term exposure to low-level air pollution and incident COPD. We defined four distinct low-exposure sub-cohorts comprised of individuals who were always exposed to low-levels of: (1) PM2.5 (annual mean ≤12-μg/m³), (2) NO2 (annual mean ≤53-ppb), (3) O3 (warm-season mean ≤50-ppb), and (4) low levels of all three air pollutants. We further tested effect modification by individual- and community-level characteristics. RESULTS: Of the 18.8 million individuals, 64.2% (12.1-million), 99.3% (18.7-million), 75.4% (14.2-million), and 54.1% (10.2-million) were always exposed to low-level annual PM2.5, NO2, O3, and all three air pollutants, respectively. Among the single-pollutant low-exposure cohorts, a 5-μg/m³ increase in PM2.5, 5-ppb increase in NO2, and 5-ppb increase in warm-season O3 were associated with an increase in COPD rate ranging between 9-12%, 1-2%, and 11-12%. Associations with each individual pollutant were also significant in the cohort exposed to low-levels of all three pollutants. There was evidence of linearity in concentration-response relationships for NO2 and O3 at levels below the current NAAQS. For PM2.5, there was a sharp increase in risks at levels above 10-μg/m³. Further, individuals in communities with lower household incomes, lower educational attainment, and lower numbers of active doctors experienced higher risk. CONCLUSIONS: Our study suggests exposures to low-level PM2.5, NO2, and warm-season O3 were associated with incident COPD. Subgroup differences suggest individual and contextual factors contributed to COPD disparities under effects of air pollutant exposures. KEYWORDS: Chronic obstructive pulmonary disease (COPD), air pollution, low concentration, disparities