Cleaner Air, Healthier Brains: Study Links Air Pollution to Alzheimer’s Plaques and Tangles

Across developed countries, the rates of dementia are going down. Dr. Edward Lee, a neuropathologist and associate professor at the University of Pennsylvania wanted to know why. The answer may be in the air: Over the last few decades, as air quality improved in the U.S. and Europe, dementia rates have dropped.  

Pollution from wildfires, gasoline exhaust, oil, and other fumes pose risks for the lungs, heart, and brain. Toxic pollutant particles smaller than 2.5 microns (PM2.5) have also been shown to affect brain function, including diminished memory, impaired thinking and executive function, and a higher risk of Alzheimer’s and dementia. 

So far, most of the evidence has been indirect: People living in polluted areas are more likely to be diagnosed with dementia. A new study, published in JAMA Neurology, provides more direct evidence. Lee and his colleagues examined 602 autopsied brains, linking the average levels of air pollution to Alzheimer’s-related proteins in the brain — beta-amyloid plaques and tau tangles. 

“Air pollution was associated with worse cognitive outcomes,” Lee told Being Patient. The effect was tied to Alzheimer’s proteins, suggesting that air pollution increased amyloid and tau, worsening symptoms.

Does more pollution mean more plaques?

Does more pollution mean more plaques? To answer the question, the researchers examined autopsied brains of people with various dementias. 

Most donors were white Americans who lived, on average, until 78, and over half carried at least one copy of the Alzheimer’s risk gene ApoE4. Nearly half (47.3 percent) had Alzheimer’s, while 14.1% were diagnosed with Parkinson’s disease dementia. 

The researchers looked at the air quality in the area where each donor lived, taking the average level of PM2.5 across the final year of their life. Every one unit increase (measured in μg/m3) was linked to 17 to 20 percent higher levels of beta-amyloid plaques and tau tangles, and a 16 percent higher risk of stroke. 

Among 287 donors with neurological assessments, Lee’s team saw that higher levels of PM2.5 lead to more cognitive and functional impairment. 

However, pollution was not linked to Parkinson’s disease dementia-associated proteins, known as Lewy bodies. 

“We were surprised to see that it seemed to be specific to Alzheimer’s disease pathology,” Lee said. He noted that future research might still uncover a link.

Marc Weisskopf, a professor at the Harvard T.H. Chan School of Public Health told Being Patient that the results were “very intriguing,” since they tied PM2.5 directly to Alzheimer’s proteins. While he wasn’t involved in this study, he has collaborated with the authors on other research.

How certain is the link?

While the study provides direct evidence, strengthening previous observations, the study does have limitations. 

The proteins involved in Alzheimer’s disease build up over decades, but the main analysis only connected the person’s final year’s exposure to air pollution with the autopsy findings. Lee explained their team found similar results when they looked at two to seven years before death. 

The problem: They didn’t have data on each participant going back several years to understand their exposure over time. Weisskopf also thought that the data on PM2.5 in the last year of life provides a good proxy measure of longer-term exposure. 

Many people who are at a higher risk of Alzheimer’s disease because of their ethnicity or socioeconomic status live in more polluted areas. Lee’s team accounted for socioeconomic status, but since all of the brains came from the University of Pennsylvania brain bank, it only included people living in urban areas.

Blood tests will let Lee and other researchers conduct a similar analysis on thousands of people in the future. But this research would need steady funding.

Clear the air, clear the brain

Air pollution is a societal issue. Many people don’t have the money or resources to address it at a personal level. Many apartment or home renters have little control over air filtration and sometimes can’t afford respirators or air purifiers. 

But policymakers are taking notice.

In 2024, the Environmental Protection Agency (EPA) changed its guidelines, lowering the U.S. limit of PM2.5 pollution particles from 12 to nine micrograms per cubic meter. Although an improvement, the new limit is almost double the recommended safe limit of five micrograms set by the World Health Organization. Lowering these levels further could have additional benefits, potentially preventing as many as 188,000 cases of dementia annually.  

For Lee, the important question is how do we reduce PM2.5 levels across the world? In the U.S. and Europe, PM2.5 reductions have led to a drop in dementia. Lowering levels even further, and targeting developing countries that have higher levels of PM2.5 could make a global dent, he said.