Fine particle air pollution tied to Parkinson’s risk in US study

25% rise in disease risk noted in areas with greatest long-term PM2.5 exposure

Steve Bryson, PhD avatar

by Steve Bryson, PhD |

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An illustration of a person coughing surrounded by clouds of smoke.

People living in areas with high levels of an air pollutant called fine particulate matter (PM2.5) — whose sources include power plants, motorized vehicles, and fires — are at greater risk of Parkinson’s disease, according to a U.S. study.

“We found a nationwide association between Parkinson’s disease and air pollution exposure, with people exposed to the highest levels of fine particulate matter having an increased risk of Parkinson’s disease compared to people exposed to the lowest levels,” Brittany Krzyzanowski, PhD, the study’s first author with the Barrow Neurological Institute in Arizona, said in a press release from the American Academy of Neurology (AAN).

The Mississippi-Ohio River Valley is a particular “Parkinson’s disease hot spot,” Krzyzanowski added, with “some of the highest levels of fine particulate matter pollution in the nation.”

Study findings, “Fine Particulate Matter and Parkinson’s Disease Risk in Medicare Beneficiaries,” will be presented at the AAN’s 75th annual meeting, set to run in Boston and virtually on April 22–27.

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Fine particulate matter consists of smoke, aerosols, soot, and the like

“By mapping nationwide levels of Parkinson’s disease and linking them to air pollution, we hope to create a greater understanding of the regional risks and inspire leaders to take steps to lower risk of disease by reducing levels of air pollution,” Krzyzanowski said.

Both genetic and environmental factors appear to influence the risk of Parkinson’s, a progressive neurodegenerative disorder widely known for its movement-related symptoms.

Increasing evidence suggests air pollution is an environmental risk factor for Parkinson’s. A European report also linked long-term exposure to air pollutants such as PM2.5 with a greater risk of dying due to Parkinson’s.

PM2.5 are particles less than 2.5 micrometers in diameter — about 30 times smaller than a strand of human hair — consisting of smoke, soot, aerosols, mold spores, dander, and the like. Such particulates derive from motor vehicles, fossil fuel-fired power plants, other industries, and forest and grass fires.

Krzyzanowski and colleagues investigated the potential links between higher PM2.5 exposure and Parkinson’s risk across the U.S.

“We used geographic methods to examine the rates of Parkinson’s disease across the United States and compared those rates to regional levels of air pollution,” Krzyzanowski said.

Researchers used 2009 data from Medicare, the government-funded health insurance program for people 65 years or older and those with certain disabilities. Among the more than 22.5 million people enrolled in Medicare that year, 83,674 had been newly diagnosed with Parkinson’s.

Disease rates were mapped out and calculated for several U.S. regions. The average air pollution exposure levels, sourced from annual PM2.5 concentrations, were established for this 2009 patient group using their residency ZIP codes and counties.

These people were then divided into four groups based on their average PM2.5 exposure. Those with the highest exposure had an average yearly exposure of 19 micrograms per cubic meter (mcg/m3), while people in the lowest exposure group were exposed, on average, to five mcg/m3 of PM2.5 each year.

Among those in the highest exposure group, 434 in every 100,000 people were newly diagnosed with Parkinson’s compared with 359 new cases in the lowest exposure group.

After adjusting for factors known to influence Parkinson’s risk, such as age, sex, race, smoking, and medical care use, the researchers found the disease’s risk increased by 25% from the lowest to the highest exposure groups.

Exposure risks noted in Rocky Mountain region, Mississippi-Ohio River Valley

Researchers then divided PM2.5 exposure into 10 levels for a more detailed geographic assessment.

The link between PM2.5 exposure and Parkinson’s risk was strongest in the Rocky Mountain region, which included Lake County, Colorado — southwest of Denver — and its neighboring counties. Moving up from one exposure level to the next in these counties was associated with a 16% increase in Parkinson’s risk.

In the Mississippi-Ohio River Valley, which includes Tennessee and Kentucky, higher exposure to PM2.5 was also linked to higher Parkinson’s rates, but this association was weaker than in the Rocky Mountain region.

Here, the risk of Parkinson’s was 4% higher for every exposure level increase.

“Finding a relatively weaker association where we have some of the highest Parkinson’s disease risks and fine particulate matter levels in the nation is consistent with the threshold effect we observed in our data,” Krzyzanowski said.

“In the Mississippi-Ohio River Valley, for example, Parkinson’s disease risk increases with increasing air pollution exposure until about 15 [mcg/m3] of fine particulate matter, where Parkinson’s disease risk seems to plateau,” Krzyzanowski added.

Researchers noted that this weaker link may be due to an apparent plateau effect between 12–19 mcg/m3, and the fact that air pollution is also associated with a greater risk of other health conditions, including dementia, that can affect the likelihood of a Parkinson’s diagnosis.

“Using state-of-the-art geospatial analytical techniques, we identified a nationwide association between PD [Parkinson’s disease] and PM2.5, which varied in strength by region,” the researchers wrote in the abstract.

Since PM2.5 contains a variety of air pollutants, some more toxic than others, “a deeper investigation into the specific subfractions of PM2.5 may provide insight into regional variability in the PM2.5-PD association,” the team added.

This work was supported by the U.S. Department of Defense, the National Institute of Environmental Health Sciences, and the Michael J. Fox Foundation for Parkinson’s Research.