Yet Another Study Links Dementia to Air Pollution

The traffic that passes you by every day could be a contributing factor in developing Alzheimer’s disease, at least if you live in a large city.

Researchers with Emory University in Atlanta recently found a correlation between increased exposure to traffic-related air pollution and higher incidences of amyloid plaques in the brain. These plaques are associated with the development of Alzheimer’s disease, the most common type of dementia.

The findings were published in Neurology, the medical journal of the American Academy of Neurology.

The researchers examined brain tissue from 224 people who had consented to donate their brains to dementia research after death. Their average age at death was 76.

Researchers then looked at data on traffic-related air pollution based on the people’s home addresses at the time of death, all of which were in the Atlanta area.

Their focus was on a type of air pollution known as fine particulate matter or PM2.5, which is composed of pollutant particles that are smaller than 2.5 microns in diameter. That’s far less than the width of a strand of human hair. PM2.5 is a major source of air pollution in urban areas like Atlanta.

The observational study showed that the people with more exposure to air pollution one and three years before death were more likely to have higher levels of amyloid plaques in their brains than others.

More specifically, people with significantly higher PM2.5 exposure in the year before death were almost twice as likely to have more amyloid plaques at death. Those with significantly higher exposure in the three years before death were 87% more likely to have plaques.

The increased risk of amyloid plaque associated with pollution wasn’t just the case among study subjects who had the main gene variant associated with Alzheimer’s disease (APOE e4).

Among subjects without APOE e4, the relationship between air pollution and amyloid plaque was actually strongest.

In a summary of the findings, study co-author Anke Huels says:

“This suggests that environmental factors such as air pollution could be a contributing factor to Alzheimer’s in patients in which the disease cannot be explained by genetics.”

The researchers cannot say for sure that PM2.5 directly causes amyloid plaques to develop, only that increased exposure to PM2.5 is associated with an increased likelihood of having plaques. Due to the observational nature of their study, they could not rule out other factors that might contribute to amyloid plaque.

The study has other limitations as well. The subjects were primarily white and highly educated. Because of this, scientists can’t say for certain that these findings are representative of other populations. Also, the study only considered participants’ addresses at the time of death.

Emory’s researchers aren’t the first to note a correlation between air pollution and dementia, though.

For example, a 2023 study based on 18 years of health records on about 30,000 people found that emissions from wildfires and farming — including PM2.5 — were “robustly associated with greater rates of dementia.”

Going further back, a 2020 study of brain scans of some 18,000 seniors concluded that living in areas with greater air pollution, such as from PM2.5, was associated with an increased likelihood of developing amyloid plaques.

The 2023 and 2020 studies were both published in journals of the American Medical Association.

While changing the air you breathe isn’t by any means a straightforward task, there are lifestyle changes you can make to lower your risk of dementia. To learn more, check out “7 Lifestyle Changes That May Help Prevent Dementia.”