Evidence mounts linking air pollution to Parkinson’s disease

New research adds to evidence that people living in areas with high air pollution are at a higher risk of developing Parkinson’s disease, a progressive neurological disorder.

The research found a nationwide association between incidents of Parkinson’s and annual average particulate matter air pollution, also known as PM 2.5. Researchers found that at the highest annual exposure level, participants were 25% more likely to develop Parkinson’s disease, compared to those with the lowest exposure. 

The findings are expected to be presented at the American Academy of Neurology’s meeting in April and published in the journal Neurology. The work was funded by grants from the US Department of Defense, the National Institutes of Health National Institute of Environmental Health Sciences, and the Michael J. Fox Foundation for Parkinson’s Research.

“It’s a very compelling story that we see,” said Brittany Krzyzanowski, a scientist at the Barrow Neurological Institute and lead author on the new study. 

Researchers used data from over 22 million Americans, 83,674 of whom had reported a Parkinson’s diagnosis. They analyzed that data alongside geographical data showing the amount of PM 2.5 in the atmosphere. PM 2.5 is a type of air pollution that comes from vehicle exhaust, forest and grass fires, and other industrial processes, meaning that communities near highways and industrial areas are most likely to have high exposure. 

Evidence building

The link between the disease and PM 2.5 has been suggested in numerous other studies, including a 2022 review of existing research that found air pollution to be “an emerging risk factor in the development of Parkinson’s disease.” 

As well, a 2018 study of more than 2 million Ontario adults found that long-term exposure to PM 2.5 was associated with a 4% increase in instances of Parkinson’s, while a 2020 study of 63 million US adults found an association between PM 2.5 exposure and hospitalization for Parkinson’s. 

The particles that make up PM 2.5 air pollution are small enough that they can enter the bloodstream via the lungs, then travel to the brain. There, they cause inflammation of the nervous system, which increases the accumulation of a protein in the brain known to cause Parkinson’s. 

Hot spots of disease

The researchers named the Mississippi-Ohio River Valley as a disease “hot spot” — saying they found Parkinson’s occurred more frequently there than anywhere else in the country. This is probably because the Mississippi-Ohio River Valley has a number of different sources of heavy air pollution, generally from high roadway density and industry in the region, said Krzyzanowski.

“There is a lot of traffic related pollution in that area,” she said. “Power plants and steel and iron manufacturing are also contributing to the air pollution in that area, as well.”

The Rocky Mountain region, especially southwest of Denver, had the strongest association between pollution and disease, meaning that every increase in PM 2.5 exposure in that region correlated with a greater jump in Parkinson’s risk. 

Experts say the link between pollution and Parkinson’s is an environmental justice issue, since many communities dealing with high levels of PM 2.5 are made up of large percentages of people of color, majority low-income, or both. 

“There might be cause to consider taking steps to reduce levels of air pollution in order to lower risk of Parkinson’s disease, especially in high risk areas,” said Krzyzanowski.