Clusters of Parkinson’s disease correlated significantly with air quality in urban versus more rural areas, a study spanning the Geneva canton of Switzerland reports, lending support to the idea that air pollution contributes to the disorder.
The study, “Geospatial analysis of individual-based Parkinson’s disease data supports a link with air pollution: A case-control study,” was published in the journal Parkinsonism and Related Disorders.
Parkinson’s is a complex disorder, whose exact cause defies simple explanation. Many experts believe that it evolves from a combination of genetic susceptibility and environmental factors.
Air pollution is one suggested environmental factor, but evidence supporting its inclusion has been inconsistent. Such data often comes from large, aggregated datasets whose large-scale trends can obscure important local effects.
To search for these kind of individual-level interactions, researchers with the École Polytechnique Fédéral de Lausanne, in Switzerland, examined clusters of Parkinson’s patients in Geneva canton — equivalent to a state or province, with a mix of cities and more rural communities. They compared each cluster to air pollution levels, drinking water sources, and pesticide use in its geographic location.
“The Canton of Geneva … is characterized by a well-defined urban centre surrounded by nearly a third of its territory devoted to agriculture,” the researchers wrote.
The team chose this canton because, as Vanessa Fleury said in a university press release, another neurologist “had noticed that several of his patients lived close together, and thought there might be localized clusters of the disease in the canton. Then I worked with him to find a way to scientifically substantiate his hypothesis.”
Fleury, the study’s lead author, and colleagues collected data on 1,115 people with Parkinson’s and 12,614 healthy controls, all canton residents with personal home addresses.
From this, they identified six “hotspots” of increased Parkinson’s occurrence and eight “coldspots” of lower-than-average occurrence. These locations did not overlap each other, and did not appear to be randomly distributed.
Most hotspots were in urban centers closer to downtown Geneva, whereas coldspots occurred both in urban and less urban areas, but more often along the canton’s outskirts.
Water sources and pesticides did not show a correlation to Parkinson’s occurrence, but air quality — as measured by nitrogen dioxide (NO2) and fine particulate matter — did.
Although the number of people with Parkinson’s living in these areas amounted to 6% of the study population, their location and disease diagnosis tightly correlated with their local air quality.
“There is a significant positive correlation between these hotspots and the degree of air pollution, which leads us to suspect that there is a link between Parkinson’s and atmospheric pollution,” Fleury said.
One cold spot, the investigators mentioned, was located in an area with high NO2 levels, for which they have no good explanation as yet. They suggested that while air pollution as an environmental factor in Parkinson’s may dominate in many areas, it is likely not the only culprit.
“We will now try to identify one or more possible explanatory factors and publish them in a new paper,” said Stéphane Joost, PhD, a study author.
Nonetheless, the contribution of air quality to Parkinson’s prevalence appeared strong enough for the study’s researchers to suggest that policymakers consider it when adjusting public health plans.
“PD [Parkinsons’s disease] prevalence hotspots were concentrated in the [canton’s] urban centre and were associated with atmospheric air pollution,” they concluded.
“Our findings,” they added, “emphasize the multifactorial nature of PD and the importance of air quality improvement in PD prevention which could be of substantial public health significance.”
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