The new study included more than 22.5 million people enrolled in Medicare. Within this cohort, researchers identified 83,674 individuals who had Parkinson’s disease. To determine the prevalence of Parkinson’s disease in different regions, researchers analyzed the geographic distribution of the study participants throughout the United States.
Today, a preliminary study has revealed that residing in regions of the United States with elevated levels of air pollution is linked to a greater likelihood of developing Parkinson’s disease.
The research focused on PM2.5, or tiny particulate matter, which has a diameter of fewer than 2.5 millimeters. Fine particles are produced by motor vehicle exhaust, fuel combustion in power plants and other businesses, and forest and grass fires.
The study’s lead author, Brittany Krzyzanowski said: they “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.”
And they discovered a significant link between Parkinson’s disease and air pollution exposure, with those who were exposed to the greatest concentrations of fine particulate matter having a higher chance of developing the condition than those who were exposed to the lowest concentrations.
“We also identified a Parkinson’s disease hot spot in the Mississippi-Ohio River Valley, which is a region that has some of the highest levels of fine particulate matter pollution in the nation.”
More than 22.5 million Medicare beneficiaries from 2009 participated in the research. Researchers found 83,674 individuals with Parkinson’s disease within this cohort. Researchers plotted the locations of study participants throughout the United States and computed the prevalence rates of Parkinson’s disease for distinct geographic areas.
Researchers also assessed annual air pollution exposure levels for study subjects using ZIP codes and counties where they resided, as well as data from an air pollution data source on average yearly fine particulate matter concentrations.
After that, individuals were separated into four groups depending on their average exposure to air pollution. In the highest exposure group, the average yearly exposure to fine particulate matter was 19 micrograms per cubic meter (g/m3). The average yearly exposure for those in the lowest exposure category was five g/m3.
In the group with the greatest exposure, 434 new instances of Parkinson’s disease emerged per 100,000 persons, compared to 359 cases in the group with the lowest exposure.
Having accounted for other variables that could influence the probability of developing Parkinson’s disease, such as age, smoking, and healthcare utilization, the researchers discovered a correlation between Parkinson’s disease and the yearly average exposure to fine particulate matter. Individuals in the highest exposure category had a 25% higher chance of developing Parkinson’s disease than those in the lowest exposure category.
Researchers classified exposure to fine particulate matter into 10 levels for geographic study.
Lake County, Colorado, and the counties to the southwest of Denver had the highest levels of air pollution and the highest rates of Parkinson’s disease, according to the study’s authors. After going up from one level of exposure to fine particulate matter to the next level, the risk of Parkinson’s disease in those counties rose by 16%.
The Mississippi-Ohio River Valley hot region, which encompasses Tennessee and Kentucky, also showed a stronger relationship between air pollution and a higher prevalence of Parkinson’s disease, with a 4% increase in risk when going from one level of fine particulate matter exposure to the next.
“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 added. “In the Mississippi-Ohio River Valley, for example, Parkinson’s disease risk increases with increasing air pollution exposure until about 15 µg/m3 of fine particulate matter, where Parkinson’s disease risk seems to plateau.”
Krzyzanowski added: “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 the risk of disease by reducing levels of air pollution.”
The study’s drawback was that it concentrated only on fine particulate matter, a mixture of airborne pollutants, some of which may be more harmful than others. Krzyzanowski pointed out that air pollution is also linked to various other health hazards, including dementia, which might decrease the possibility of a Parkinson’s diagnosis. This could clarify why the connection between Parkinson’s disease and particulate matter in the Mississippi-Ohio River Valley is relatively weaker.
The study was funded by the U.S. Department of Defense, the National Institutes of Health, the National Institute of Environmental Health Sciences, and the Michael J. Fox Foundation for Parkinson’s Research.
The study will be presented at the 75th Annual Meeting of the American Academy of Neurology, which will be held in Boston and live online from April 22-27, 2023.
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