Fine Particulate Matter and Parkinson Disease Risk Among Medicare Beneficiaries
Brittany Krzyzanowski, Susan Searles Nielsen, Jay R. Turner, Brad A. Racette
Abstract
<h3>Background and Objectives:</h3> Numerous studies suggest that environmental exposures play a critical role in Parkinson disease (PD) pathogenesis, and large, population-based studies have the potential to advance substantially the identification of novel PD risk factors. We sought to study the nationwide geographic relationship between PD and air pollution, specifically PM<sub>2.5</sub> (particulate matter with a diameter <2.5 micrometers), using population-based, United States (U.S.) Medicare data. <h3>Methods:</h3> We conducted a population-based geographic study of Medicare beneficiaries aged 66-90 geocoded to U.S. counties and zip+4. We used integrated nested Laplace approximation to create age, sex, race, smoking, and healthcare utilization adjusted relative risk (RR) at the county-level for geographical analyses with PM<sub>2.5</sub> as the primary exposure of interest. We also performed an individual-level analysis using logistic regression with cases and controls with zip+4 centroid PM<sub>2.5</sub>. We adjusted <i>a priori</i> for the same covariates and verified no confounding by indicators of socioeconomic status or neurologist density. <h3>Results:</h3> Among 21,639,190 Medicare beneficiaries, 89,390 had incident PD in 2009. There was a nationwide association between average annual PM<sub>2.5</sub> and PD risk whereby the RR for PD was 56% (95% CI 47%-66%) greater for those exposed to the median level of PM<sub>2.5</sub> compared to those with the lowest level of PM<sub>2.5</sub>. This association was linear up to 13 μg/m<sup>3</sup> corresponding to a 4.2% (95% CI 3.7%-4.8%) greater risk of PD for each additional μg/m<sup>3</sup> of PM<sub>2.5</sub> (p<sub>trend</sub><0.0001). We identified a region with high PD risk in the Mississippi-Ohio River Valley, where the risk for PD was 19% greater compared to the rest of the nation. The strongest association between PM<sub>2.5</sub> and PD was found in a region with low PD risk in the Rocky Mountains. PM<sub>2.5</sub> was also associated with PD in the Mississippi-Ohio River Valley where the association was relatively weaker, due to a possible ceiling effect at average annual PM<sub>2.5</sub> levels of ∼13 μg/m<sup>3</sup>. <h3>Discussion:</h3> State-of-the-art geographic analytic techniques revealed an association between PM<sub>2.5</sub> and PD that varied in strength by region. A deeper investigation into the specific subfractions of PM<sub>2.5</sub> may provide additional insight into regional variability in the PM<sub>2.5</sub>-PD association.