Kenneth Glad
Researchers analyzing health data from millions of older adults say long-term exposure to polluted air may be associated with a greater likelihood of developing certain neurodegenerative disorders. The findings add to ongoing research into how environmental factors could influence brain health later in life.
A study published in JAMA Network Open examined whether exposure to fine particulate matter and nitrogen dioxide was associated with higher rates of dementia with Lewy bodies and Parkinson’s disease-related dementia.
The research was conducted by scientists from the University of Florida, Aarhus University and Aarhus University Hospital using Danish nationwide registry data.
According to Aarhus University Hospital, the researchers analyzed anonymized information from more than 2.1 million Danish residents between the ages of 65 and 95.
The team identified individuals diagnosed with dementia with Lewy bodies and Parkinson’s disease-related dementia, then compared them with control groups matched by age and sex.
Researchers estimated each person’s exposure to pollution based on residential address data during the decade before diagnosis.
Pollutants under review
The study focused on two common forms of air pollution: PM2.5, which refers to microscopic airborne particles, and nitrogen dioxide, a gas commonly linked to fossil fuel combustion.
According to Aarhus University Hospital, these pollutants are frequently produced by road traffic, shipping activity and other combustion-related sources.
Dimitry S. Davydow of the University of Florida said, according to Danish broadcaster DR: “These are pollutants that most people are exposed to every day.”
“They come from traffic, shipping and other forms of combustion,” he added.
The researchers reported that even relatively small increases in pollution exposure were associated with higher risks of both neurological conditions.
Stronger association for Lewy bodies
JAMA Network Open reported that every increase of 5 micrograms per cubic meter in PM2.5 exposure was associated with nearly four times greater risk of dementia with Lewy bodies and more than double the risk of Parkinson’s disease-related dementia after adjustments for demographic, medical and socioeconomic factors.
The study also found elevated risks linked to nitrogen dioxide exposure, although the association was smaller than the one observed for fine particles.
Researchers noted that the relationship appeared stronger for dementia with Lewy bodies than for Parkinson’s disease-related dementia, despite similarities between the disorders.
According to the paper, both diseases are associated with abnormal accumulation of the protein alpha-synuclein in the brain.
Researchers urge caution
The authors stressed that the findings do not prove air pollution directly causes these conditions.
Jakob Christensen, professor at Aarhus University and consultant at Aarhus University Hospital, said: “Although the research cannot establish a direct causal relationship, it shows a clear association between air pollution and increased dementia risk.”
He added: “Our findings suggest that air pollution may be one of the environmental factors contributing to the development of these diseases.”
The study also discussed possible biological explanations. According to the researchers, very small airborne particles may enter the bloodstream after inhalation and potentially cross into the brain, where they could contribute to inflammation.
Earlier research in both animals and humans has suggested that pollution exposure may trigger immune responses in the brain and affect proteins linked to Parkinson’s disease.
Study limitations
The researchers acknowledged several limitations in the study.
Because the analysis relied on diagnoses recorded in hospital data, milder cases may not have been included.
The study also lacked detailed information about smoking habits, occupational exposure and pesticide exposure, which may also influence neurological disease risk.
Still, the authors said the findings point to a potential connection between long-term pollution exposure and brain health, particularly in diseases involving alpha-synuclein.
The paper concluded that further research is needed to better understand the biological mechanisms involved and whether reducing exposure to pollution could lower future disease risk.
Sources: Aarhus University Hospital, DR, JAMA Network Open.
