This Is Where Air Pollution Is Tied to a Greater Risk for Parkinson Disease

A region-specific association between Parkinson disease (PD) risk and levels of particulate matter with a diameter <2.5 mm (PM_2.5) has been observed in the United States, according to a population-based analysis published in the journal Neurology.

Fine particulate matter pollution has been associated with risk for neurologic diseases, such as dementia and stroke. However, the association between air pollution and PD risk has been unclear.

To evaluate the region-specific effect fine particulate matter pollution has on PD risk, individuals aged 66 to 90 who were Medicare beneficiaries were included in this analysis. Exposure to average annual PM_2.5 between 1998 and 2000 at the county level and the individual level were compared between individuals who were diagnosed with PD in 2009 (n=65,180; mean age, 79; 51% women; 89% White) and nonPD control individuals (n=15,561,435; mean age, 76; 58% women; 86% White).

Using PM_2.5 levels by ZIP code, areas with the highest PM_2.5 decile were associated with significant PD risk (relative risk [RR], 1.24; 95% CI, 1.19-1.28) relative to the lowest PM_2.5 decile. Similarly, compared with the lowest PM_2.5 decile, all areas with more PM_2.5 pollution were associated with significant PD risk (RR range, 1.11-1.28; P <.0001). Similar trends were observed when data were adjusted for airborne trichloroethylene (RR range, 1.11-1.28; P <.0001).

The overall relationship between PM_2.5 levels and PD was linear up to 13 mg/m³, in which for every 1 mg/m³ increase in PM_2.5, PD risk increased by 4.2% (95% CI, 3.7%-4.8%; P <.0001).

In the hot and cold spot analysis, an S-shaped pattern of high PD risk was observed in the Mississippi-Ohio River Valley with low PD risk observed in a large area in the West. The hot spot in the Mississippi-Ohio River Valley corresponded with a 19% greater risk for PD relative to the rest of the country. At the county level, 118 counties North of the Mississippi-Ohio river were associated with a positive relationship between PM_2.5 levels and PD risk.

Conversely, there were 4 regions (North Dakota-Minnesota border, parts of the Mid-Atlantic, the South Atlantic, and a region spanning Washington, Idaho, and Montana) that showed an inverse relationship between PM_2.5 levels and PD risk.

This study may have been biased by using aggregate data which were subject to ecological fallacy.

“Using state-of-the-art geographic analytic techniques, we identified strong regional associations between PM_2.5 and PD in the United States. A deeper investigation into the subfractions of PM_2.5 in those regions may provide insight into PD risk factors.”