Long-term Effects of Fine Particulate Matter on Neurological Disorders in the US Medicare Population: A Nationwide Analysis

Abstract

Background. Accumulated evidence links fine particulate matter (PM2.5) to mortality, cardiovascular and respiratory disease. However, less is known about the impact of PM2.5 on neurological disorders, including Parkinson’s disease (PD), Alzheimer’s disease and related dementias (AD/ADRD).Methods. We constructed a population-based nationwide open cohort comprised of all fee-for-service Medicare beneficiaries (aged ≥65, N=63,038,019) in the contiguous US (2000-2016). We assigned PM2.5 zip code concentrations based on annually-averaged predictions from a high-resolution model. To accommodate our massive dataset, we applied Cox-equivalent Poisson models utilizing parallel computing to estimate hazard ratios (HR) for first PD and AD/ADRD hospitalization, adjusting for confounding.Results. We identified ~1.0 million cases of PD and ~3.4 million cases of AD/ADRD. For each 5 μg/m3 increase in annual PM2.5 concentrations, the HRs were 1.14 (95% confidence interval [CI]: 1.13, 1.15) and 1.15 (95% CI: 1.14, 1.16) for first PD and AD/ADRD hospitalization, respectively. For both outcomes there was strong evidence of linearity below 16 μg/m3 (95th percentile of the PM2.5 distribution), followed by a plateaued association with increasingly larger confidence bands.Conclusions. Using a large nationwide cohort and robust epidemiologic analyses, we provide strong evidence that exposure to PM2.5 was significantly associated with an increase in the hazard of first admission with PD and AD/ADRD. For the aging US population, improving air quality to PM2.5 levels below current national standards may yield substantial health benefits by reducing the burden of neurological disorders among the elderly.