Abstract
BACKGROUND: Adult-onset neurodegenerative diseases affect millions and negatively impact health care systems worldwide. Evidence suggests that air pollution may contribute to aggravation of neurodegeneration, but studies have been limited. OBJECTIVE: We examined the potential association between long-term exposure to particulate matter ≤ 2.5 μm in aerodynamic diameter [fine particulate matter (PM2.5)] and disease aggravation in Alzheimer's (AD) and Parkinson's (PD) diseases and amyotrophic lateral sclerosis (ALS), using first hospitalization as a surrogate of clinical aggravation. METHODS: We used data from the New York Department of Health Statewide Planning and Research Cooperative System (SPARCS 2000-2014) to construct annual county counts of first hospitalizations with a diagnosis of AD, PD, or ALS (total, urbanicity-, sex-, and age-stratified). We used annual PM2.5 concentrations estimated by a prediction model at a 1-km2 resolution, which we aggregated to population-weighted county averages to assign exposure to cases based on county of residence. We used outcome-specific mixed quasi-Poisson models with county-specific random intercepts to estimate rate ratios (RRs) for a 1-y PM2.5 exposure. We allowed for nonlinear exposure-outcome relationships using penalized splines and accounted for potential confounders. RESULTS: We found a positive nonlinear PM2.5 - PD association that plateaued above 11 μg/m3 (RR = 1.09, 95% CI: 1.04, 1.14 for a PM2.5 increase from 8.1 to 10.4 μg/m3). We also found a linear PM2.5 - ALS positive association (RR = 1.05, 95% CI: 1.01, 1.09 per 1-μg/m3 PM2.5 increase), and suggestive evidence of an association with AD. We found effect modification by age for PD and ALS with a stronger positive association in patients < 70 years of age but found insufficient evidence of effect modification by sex or urbanization level for any of the outcomes. CONCLUSION: Our findings suggest that annual increase in county-level PM2.5 concentrations may contribute to clinical aggravation of PD and ALS. Importantly, the average annual PM2.5 concentration in our study was 8.1 μg/m3, below the current American national standards, suggesting the standards may not adequately protect the aging population. https://doi.org/10.1289/EHP7425.