Long-Term Association of Air Pollution and Incidence of Lung Cancer in American Elderly Population: A National Study in Medicare Cohort

BACKGROUND AND AIM Despite growing evidence of the association of fine particulate matter [PM2.5] to an increased risk of lung cancer mortality, few studies have investigated associations of multiple pollutants simultaneously. We aim to investigate the long-term effects of PM2.5, nitrogen dioxide [NO2], and warm-season (i.e. May to October) ozone [O3] on lung cancer incidence in a large national cohort. METHODS We conducted a prospective study in a nationwide cohort with Medicare beneficiaries (aged ≥ 65 years) enrolled in the fee-for-service program in the contiguous US from 2000 to 2016. Air pollution exposure was averaged across three years and assigned to each subject based on their ZIP code of residence. We fitted single-, bi-, and tri-pollutant Cox proportional hazards models to estimate the hazard ratios (HRs) for lung cancer incidence, adjusted for potential confounders. RESULTS Over the study period, we identified 172,371 lung cancer cases (n= 12,827,068). We found a significant increase in lung cancer risk for all three pollutants in the single-pollutants model. HRs associated with 1 μg/m3 increase in PM2.5 (μg/m3) was 1.015 (1.013, 1.018), and with 1 ppb increase in NO2 and O3 was 1.013 (1.012, 1.014) and 1.007 (1.006, 1.009) respectively. In bi- and tri-pollutant models, we observed potential confounding by NO2 on PM2.5¬, which was no longer significantly associated with lung cancer incidence. Subgroup analysis revealed significantly stronger effects for PM2.5 for those who were men, aged ≥ 75 years, black, eligible for Medicaid, and living in neighborhoods at the lowest quartile of median household income. CONCLUSIONS Long-term exposure to elevated concentrations of PM2.5, NO2, and O3 was significantly associated with an increased risk of lung cancer incidence among the Medicare population. Improving air quality in the US could yield substantial health benefits for the aging American population. KEYWORDS: air pollution, lung cancer, Medicare