A study of nearly 28 million older Americans has found a direct link between long-term exposure to fine particulate air pollution – known as PM2.5 – and an increased risk of developing Alzheimer’s disease, researchers at Emory University announced February 20, 2026.
The research, published in the open access journal PLOS Medicine, analyzed data from Medicare beneficiaries aged 65 and older between 2000 and 2018. Researchers examined participants’ exposure to PM2.5, a common component of car exhaust, power plant emissions, wildfires, and fuel combustion, and tracked the incidence of Alzheimer’s diagnoses.
Unlike previous research suggesting air pollution’s impact on Alzheimer’s was indirect – through conditions like hypertension, stroke, or depression – the Emory team found that over 95% of the increased risk stemmed from the direct impact of breathing polluted air, likely through inflammation or damage to brain cells, according to a statement released by ABC News.
“The relationship between PM2.5 and AD [Alzheimer’s disease] has been shown to be pretty much linear,” said Kyle Steenland, a professor in the departments of environmental health and epidemiology at the Rollins School of Public Health at Emory University, in a statement to ABC News.
The study builds on earlier work demonstrating an association between PM2.5 and neurodegenerative diseases. A 2021 study led by Emory University’s Rollins School of Public Health, in collaboration with Georgia Tech and Harvard T.H. Chan School of Public Health, was the first nationwide analysis linking key air pollutants – including PM2.5, nitrogen dioxide (NO2), and ozone (O3) – to neurodegeneration incidence in the U.S. Medicare population. That earlier research indicated that PM2.5 and NO2 posed the greatest risk, with effects strongest for PM2.5.
According to the Emory study, a difference of 3 micrograms per cubic meter of air (ug/m3) in PM2.5 levels between cities would lead to a predicted 7 percent increase in Alzheimer’s diagnoses. The national average PM2.5 level is around 7 ug/m3, but cities like Houston and Los Angeles experienced levels above 10 ug/m3 in 2020.
Researchers noted that no safe levels of PM2.5 exposure appear to exist when it comes to the risk of neurodegeneration. Liuhua Shi, ScD, assistant professor at Rollins and co-lead author of the 2021 study, stated the need for further investigation into the specific components of PM2.5 that contribute to these conditions.
The Emory team’s latest findings suggest traffic emissions are a primary source of the harmful PM2.5 particles. Yanling Deng of Emory University led the most recent research, which examined data from 27.8 million older adults.
