A Nationwide Association Exists Between Parkinson Disease and PM2.5

In the United States, a nationwide association has been reported between Parkinson disease (PD) and PM_2.5 (ie, particles of ≤2.5 microns in diameter), according to study results presented at the 2023 American Academy of Neurology (AAN) Annual Meeting, held from April 22 to 27, in Boston, Massachusetts.

Environmental exposures have been shown to play a key role in the pathogenesis of PD. As the only population-based national health care system in the United States, Medicare is an optimal way in which to evaluate nationwide geographic studies of PD risk factors.

Researchers sought to identify geographic patterns of PD, as well as to examine nationwide and region-specific associations with PM_2.5. The current population-based geographic study comprised a total of 22,546,965 Medicare beneficiaries, among whom 83,674 had been recognized in 2009 as having incident PD. All of the beneficiaries were geocoded based on county and ZIP+4 code of residence in the contiguous US.

The researchers used a multimethod strategy that involved R-INLA, in an effort to generate sex, age, race, smoking, and health care utilization–adjusted relative risk (RR) for geographic and country-level regression analyses. PM_2.5 was the exposure of interest. Additionally, individual-level case-control analysis via logistic regression was used to confirm all county-level PM_2.5 results.

The Mississippi-Ohio River Valley was recognized as a PD hot spot, with a nationwide association reported between incident PD and average annual PM_2.5. In fact, in this location, the RR for PD increased by 25% (95% CI, 23%-26%)in a comparison of the lowest vs highest quartile of PM_2.5.

In the Rocky Mountain region, the strongest association was observed between PD and PM_2.5. Although PM_2.5 was also related to PD in the Mississippi-Ohio River Valley region, the association was weaker. When the lowest and the highest deciles of PM_2.5 were compared, individual-level results verified that PD increased by 25% (95% CI, 20%-29%).

“A deeper investigation into the specific subfractions of PM_2.5 may provide insight into regional variability in the PM_2.5-PD association,” the researchers concluded.