People living in heavily polluted areas of the United States may be more vulnerable to Parkinson's disease, a new study suggests.
Specifically, the culprit is a type of air pollution called fine particulate matter (PM2.5), which is less than 2.5 microns in diameter and comes from car exhaust, burning of fuels in power plants and other industries, and forest and grass fires, researchers say.
"We found an association between Parkinson's disease and exposure to fine particulate matter. In specific, people in the highest exposure have a 25% greater risk of Parkinson's disease compared to people with the lowest exposure," said lead researcher Brittany Krzyzanowski, from the Barrow Neurological Institute in Phoenix, Ariz.
"We also found that the regions with the strongest association between particulate matter and Parkinson's disease were the Mississippi-Ohio River Valley and the Rocky Mountain region," she said.
"Our findings suggest that the regional differences in Parkinson's disease might reflect that the composition of the particulate matter in some areas may be more toxic than others," Krzyzanowski added. "We know that air pollution causes inflammation in the brain, which is linked to Parkinson's disease."
Krzyzanowski said that lowering levels of air pollution might help lower the risk of Parkinson's, especially in areas where pollution levels are high.
"Despite 30 years of research trying to identify the environmental risk factors of Parkinson's disease, most efforts have focused on exposure to pesticides," she said. "Our work suggests that air pollution may be a key contributor in the development of Parkinson's disease."
For the study, Krzyzanowski and her colleagues collected data on more than 22.5 million Medicare patients in 2009. Of these, nearly 84,000 had Parkinson's disease. The research team mapped where the participants lived and calculated the rates of Parkinson's disease for various regions. They also calculated average air pollution levels.
The investigators found that 434 people per 100,000 who were exposed to the highest levels of PM2.5 developed Parkinson's disease, compared with 359 per 100,000 among those who lived in areas with the lowest levels of PM2.5.
After taking into account other risks for Parkinson's — such as age, smoking and use of medical care — the researchers found that people with the highest exposure to air pollution had a 25% increased risk of Parkinson's disease, compared to people with the lowest exposure.
The strongest association was in the Rocky Mountain region, including Lake County, Colo., southwest of Denver and its surrounding counties. The risk for Parkinson's in those counties increased by 16% when moving up from one level of fine particulate matter exposure to the next level, the findings showed.
Air pollution was also linked with higher rates of Parkinson's in the Mississippi-Ohio River Valley, which includes Tennessee and Kentucky, but the association was weaker, with a 4% increase in risk when moving up one level of fine particulate matter exposure to the next, the research group found.
The findings are scheduled for presentation April 22 at the annual meeting of the American Academy of Neurology, in Boston. Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.
While the association found in the study does not prove a cause-and-effect link, one expert thinks the association between air pollution and the risk for Parkinson's disease needs to be seriously considered.
"The idea that a hotspot in the Mississippi-Ohio River Valley was potentially associated with increasing the risk of Parkinson's disease by 25% is staggering," said Dr. Michael Okun, a medical advisor to the Parkinson's Foundation and director of the Norman Fixel Institute for Neurological Diseases at the University of Florida Health, in Gainesville.
"The identification of Parkinson's disease 'hot spots,' which could help us understand how the environment contributes to the development of neurodegenerative diseases, may provide another critical piece to the environmental risk factor puzzle," Okun said.
For more on Parkinson's, head to the Parkinson's Foundation.
SOURCES: Brittany Krzyzanowski, PhD, Barrow Neurological Institute, Phoenix, Ariz.; Michael Okun, MD, medical advisor, Parkinson's Foundation, and director, Norman Fixel Institute for Neurological Diseases, University of Florida Health, Gainesville; April 22, 2023, presentation, American Academy of Neurology annual meeting, Boston