Long-term air pollution exposure and incident stroke in American elderly population: a national cohort study

Abstract

BACKGROUND AND AIM: Literature has linked air pollution and cerebrovascular diseases including stroke. However, evidence is limited for the simultaneous effects of multiple air pollutants on stroke incidence. METHODS: A nationwide population-based open cohort study was used to estimate the association between long-term exposure to PM2.5, NO2, ozone, and stroke incidence. The study population included all free-for-service Medicare enrollees (aged ≥65 years) in the contiguous United States from 2000-2017. We estimated the hazard ratios (HRs) for the first diagnosis with stroke using single-, bi-, and tri-pollutant Cox proportional hazards models that controlled for demographic characteristics, Medicaid eligibility, and area-level covariates. We further looked at this relationship in two sub-cohorts of enrollees who were always exposed to pollutant levels below the US EPA National Ambient Air Quality Standards [NAAQS] (annual PM2.5 ≤12 μg/m³, annual NO2 ≤53 ppb, and warm-season ozone ≤50 ppb) and the WHO air quality guideline (annual PM2.5 ≤10 μg/m³, annual NO2 ≤20 ppb, and warm-season ozone ≤40 ppb). RESULTS:Increases of 10 μg/m³ in PM2.5, 10 ppb in NO2, and 10 ppb in ozone were associated with increased risk of first diagnosis with stroke, with HRs of 1.063 (95% CI, 1.048-1.077), 1.048 (1.043-1.052), and 1.031 (1.026-1.037), respectively. Among the below EPA low-exposure sub-cohort, the corresponding HRs were 1.041 (95% CI, 1.008-1.075), 1.067 (1.056-1.077), and 1.123 (1.108-1.138), respectively. When restricting analyses to levels below the WHO air quality guidelines, increasing pollution levels were consistently associated with a greater hazard estimate. CONCLUSIONS:Long-term exposure to air pollution, even at concentrations below NAAQS or international standards, was significantly associated with increased stroke incidence among the US elderly population. KEYWORDS: Air pollution, Multi-pollutant, Stroke