Study details and key findings

For the study, researchers from Emory University analyzed data from almost 28 million U.S. Medicare recipients ages 65 and older collected between 2000 and 2018. The researchers examined the participants' exposure to air pollution and whether they developed Alzheimer's disease.

The researchers focused specifically on fine particulate air pollution, which is also known as PM2.5. According to the American Lung Association, PM2.5 particles come from car exhaust, power plants, wildfires, and burning fuels. These particles are small enough to enter deep into the lungs and reach the bloodstream.

Overall, the researchers found that long-term exposure to air pollution was linked to an increased risk of developing Alzheimer's even after accounting for other common health conditions.

Previous studies have shown a connection between air pollution and Alzheimer's, but this link has mostly been associated with the impact of air pollution on other health conditions, such as hypertension, stroke, and depression. Air pollution can contribute to these conditions, which can then cause dementia.

"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 researchers wrote.

Commentary                                  

According to Masashi Kitazawa, a professor of environmental and occupational health at the University of California, Irvine, the study strengthens evidence of a potential causal relationship between air pollution and Alzheimer's disease.

"Remarkably, results from this study predict a possibly direct toxic mechanism of [particulate matter] to [Alzheimer's disease]," Kitazawa said.

To help people reduce their contributions and exposure to air pollution, health experts have several recommendations:

• When possible, take public transportation, carpool with others, or use a ride share to decrease vehicle emissions
• Wear a mask or other face covering in areas with high air pollution
• Check your local air quality report to limit time outside on high pollution days
• Limit your time near busy roads and avoid going out during peak traffic hours
• Invest in a high-quality air filter to reduce air pollution in your home
• Plant trees and increase greenery around you to help filter pollutants and increase oxygen levels

Ultimately, "[t]he best thing that people can do is educate themselves about these risks [of Alzheimer's]," Steenland said, noting that both genetic and environmental factors can contribute to the disease.