Air pollution tied to higher risk of dementia due to Lewy body diseases

GAINESVILLE, Fla. — Long-term exposure to common air pollutants may increase the risk of developing Parkinson’s disease-related dementia and Lewy body dementia, according to new research led by University of Florida Health.

The study, published May 14 in JAMA Network Open, examined whether exposure to fine particulates in the air and nitrogen dioxide is linked to these dementias.

Researchers found that higher exposure to either pollutant is associated with an increased risk for the conditions. Fine particulates are tiny airborne particles invisible to the naked eye, generated mostly by combustion. Nitrogen dioxide is a reddish-brown toxic gas most often created by burning fossil fuels. “These are pollutants most people are exposed to every day,” said Dimitry S. Davydow, M.D., M.P.H., the Lauren and Lee Fixel Professor at the Norman Fixel Institute for Neurological Diseases at UF Health. “They come from things like traffic, shipping and other forms of combustion.”

The study, which included researchers at Aarhus University, involved de-identified records from more than 2.1 million people in Denmark between the ages of 65 and 95. Researchers identified people diagnosed with Lewy body or Parkinson’s-related dementia and compared them with control subjects similar in age and sex. The team estimated each person’s exposure to air pollution over a decade before their diagnosis using national registry data, home addresses and data from centralized healthcare records.

They found that even small increases in pollution exposure were associated with higher risk. For every increase in air pollution exposure, the risk of developing Lewy body dementia was nearly four times higher, while the risk of Parkinson’s-related dementia was more than twice as high after accounting for demographic, medical and socioeconomic factors.

Nitrogen dioxide was also associated with increased risk, although the effect was smaller compared to the risk associated with small particulate matter. Even so, higher exposure was still linked to nearly double the risk of developing Lewy body dementia, with a more modest increase observed for Parkinson’s-related dementia.

The researchers noted the association was stronger for Lewy body dementia than for Parkinson’s dementia, though the two conditions are closely related and cause similar changes in the brain.

“While this research does not establish causation, it does show a clear association between air pollution exposure and increased risk of these dementias,” said Gregory Pontone, M.D., M.H.S., the Louis and Roberta Fixel Endowed Chair. “It’s an important step in understanding how environmental factors may contribute to disease development.”

Air pollutants like those studied are small enough to be inhaled deep into the lungs, where they enter the bloodstream and reach the brain by crossing the blood-brain barrier. There, they may contribute to other conditions, such as inflammation, that are being studied for their potential effects on the brain. Previous research has suggested these exposures may trigger immune responses in the brain or affect proteins linked to Parkinson’s disease.

Because the study relied on nationwide registry data, researchers were able to follow individuals over time and account for factors such as income, education, medical history and psychiatric conditions.

The data primarily captured diagnoses made in hospital or specialty care settings, which could miss milder or undiagnosed cases. The study did not capture details about lifestyle factors or occupational exposures that could affect risk.

Still, the findings point to a potential link between long-term air pollution exposure and brain health, particularly for diseases involving α-synuclein (alpha sin-YOO-klee-uhn), the protein associated with Parkinson’s disease and other Lewy body dementias.