xray image of human head with cloud inside to illustrate the effect of air pollution on the brain
Credit: the-lightwriter/Getty Images

Results from a U.S. study led by the University of Michigan School of Public Health show that long-term exposure to particulate air pollution increases the risk of developing dementia in older adults.

As reported in the journal JAMA Internal Medicine, Boya Zhang, a researcher at the University of Michigan, and colleagues found that the association between exposure to fine particulate matter (PM2.5) air pollution and incident dementia was strongest when it came from agriculture and wildfires.

Approximately 10% of U.S. adults over the age of 70 have dementia. Exposure to air pollution has recently been recognized as a risk factor for dementia, but the details of the connection, such as whether certain sources of pollution are worse than others, are unclear.

The Health and Retirement Study is a nationally representative, population-based cohort study in the U.S. The current study used data collected from about 27,857 participants of the Health and Retirement Study, aged 50 years or older, between 1998 and 2016.

The researchers measured total PM2.5 exposure over 10 years and monthly exposure to nine different sources of PM2.5 at the participant areas of residence. These included PM2.5 exposure from agriculture, road traffic, nonroad traffic, coal combustion for energy production, other energy production, coal combustion for industry, other industry, wildfires, and windblown dust.

Overall median 10-year total PM2.5 exposure ranged from 9.5–13.2 μg/m3. PM2.5 exposure from different sources varied by region, with higher concentrations in the Midwest and lower concentrations in the West.

During the follow-up period, 4105 (15%) individuals in the cohort developed dementia. Exposure to higher concentrations of PM2.5 over the 10-year follow-up period was linked to an 8% higher risk of incident dementia.

When the researchers looked at the different sources of air pollution, all were associated with incident dementia except for dust with the strongest links to pollution from agriculture, traffic, coal combustion, and wildfires. After controlling for PM2.5 from all other sources and co-pollutants, PM2.5 from agriculture and wildfires significantly increased risk by 13% and 5%, respectively.

“According to our estimation, nearly 188,000 new cases per year of dementia were attributable to total PM2.5 exposure in the U.S., suggesting that reducing PM2.5 through actions such as regulations, technological advances, or use of personal air purifiers may promote healthy cognitive aging,” write the authors.

“Our data further indicate that intervening on key emission sources might have value, although we cannot conclude causality, and more research is needed to confirm these findings.”

Also of Interest