Research shows that particulate matter with a diameter equal to or less than 2.5 micrometers (PM 2.5) can cross the brain barrier in humans. PM 2.5 can also contain heavy metals such as arsenic and manganese, which are linked to neuropathogenesis. Studies have linked PM 2.5 to neurological conditions such as dementia and stroke.
Until now, however, epidemiological research has delivered mixed results on the link between PM 2.5 and PD. In the present study, researchers thus sought to further investigate the potential link between the two.
For the study, the researchers analyzed healthcare data from over 21.5 million Medicare beneficiaries, of whom over 89,000 had PD in 2009. The analysis also included geographical data to assess nationwide and region-specific correlations with PM 2.5.
"Previous studies have shown fine particulate matter to cause inflammation in the brain, a known mechanism by which Parkinson's disease could develop," said lead study author Brittany Krzyzanowski, PhD, a researcher at Barrow Neurological Institute, in a press release.
"Using state-of-the-art geospatial analytical techniques, we were, for the first time, able to confirm a strong nationwide association between incident Parkinson's disease and fine particulate matter in the US," she added.
Overall, they found that people living in areas with median exposure to PM 2.5 were 56% more likely to develop PD than those in areas with the lowest pollution levels. They further found that people in a region of the Mississippi-Ohio River Valley were 19% more likely to develop PD than the rest of the US. They added that central North Dakota, parts of Texas, Kansas, and Eastern Michigan, as well as the top of Florida, also carried an increased risk of PD. Meanwhile, people in the Western half of the US had a lower risk of PD than the rest of the nation.
To explain their findings, the researchers noted that the Mississippi-Ohio River Valley and the 'Rust Belt'- parts of the Northeast and Midwest of the US- have a relatively high road network density. This means that pollution in these areas may contain more combustion particles from traffic and heavy metals from manufacturing.
"Despite years of research trying to identify the environmental risk factors of Parkinson's disease, most efforts have focused on exposure to pesticides," noted Dr. Krzyzanowski. "This study suggests that we should also be looking at air pollution as a contributor in the development of Parkinson's disease."
The researchers hope their findings will encourage stricter policies to lower pollution levels and decrease the risk of PD and related conditions.
Sources: EurekAlert, Neurology
