Air pollution may directly increase Alzheimer’s risk, study finds

Exposure to air pollution may directly increase your risk for Alzheimer’s disease, according to a new study.

In the study, published Feb. 17 in the open-access journal PLOS Medicine, researchers found a five-year average exposure to fine particulate air pollution was associated with an increased risk of the brain ​disorder.

The study used data from more than 27.8 million U.S. Medicare recipients aged 65 years and older from 2000 to 2018. The study looked specially at fine particulate matter called PM 2.5, ⁠which the Environmental Protection Agency defines as fine inhalable particles with diameters generally 2.5 micrometers and smaller that can cause serious ‌health problems and even enter the bloodstream.

Previous studies have ​found a connection between air pollution and Alzheimer’s, but typically via other chronic health conditions such as hypertension, stroke and depression. Until these findings, it was unclear whether air pollution causes these chronic conditions, which then lead to dementia, or if air pollution directly impacted ⁠brain health.

“We found that long-term exposure to fine particulate air pollution ‌was associated with a higher risk ‌of Alzheimer’s disease, largely through direct effects on the brain rather than through common chronic conditions,” the authors noted in a news release.

Masashi Kitazawa, professor ⁠of Environmental & Occupational Health at UC Irvine, said the study further strengthens the possible causal link between particulate matter and Alzheimer’s disease.

“Remarkably, results from this study predict a ‌possibly direct toxic mechanism of (particulate matter) to (Alzheimer’s ‌disease),” said Kitazawa, who was not involved in the study.

Dr. Haroon Ahmad, a neurologist at the University of Maryland Medical Center, said studies like these are important for understanding how disease processes ⁠develop, but he emphasizes that this study is observational, which shows a ​correlation, not causation. 

“While research like this ⁠points ​us in the right direction for future studies, we should be cautious not to jump to conclusions,” Ahmad, who was not involved in this study, added.

The authors also found that the association between air pollution and Alzheimer’s risk was slightly stronger ⁠in individuals who had experienced a stroke.

“Our findings suggest that individuals with a history of stroke may be particularly vulnerable to the harmful effects of air pollution on brain health, highlighting an important intersection ⁠between environmental and vascular risk factors,” the authors added.

It’s not clear why this is, though, Ahmad added.

“It could be related to a previously damaged brain − from stroke − being weaker in fighting off toxins,” suggested Ahmad, who is also an assistant professor at ⁠the University of Maryland School of Medicine.

A ‌2025 report found up to 7.2 million Americans ages 65 ​and older are ‌living with Alzheimer’s disease, an increase of about 300,000 cases from the previous year.

The authors ​hope these findings will highlight the need for air quality interventions as part of dementia prevention strategies in aging populations.