Emory University epidemiologist explains how air pollution could increase the risk of developing dementia and why she’s hopeful research into this association could help promote clean air policies.
Wildfires, gasoline, oil, and wood fuels release plumes of pollutants that negatively impact lung and brain health. Most of these health risks come from breathing in tiny toxic particles smaller than 2.5 microns (PM2.5). These toxic particles are associated with the development of asthma or respiratory problems, impaired thinking and executive function, and an increased risk of developing Alzheimer’s and other forms of dementia.
A 2023 study tracked the cognitive health of over 27,000 adults over 50 for more than 10 years. The researchers found that exposure to PM2.5 increased the risk of developing dementia, and as many as 188,000 cases each year could be attributed to breathing in PM2.5 pollutants. Low-income Black and Hispanic Americans, who are already at a higher risk of dementia, are also most affected as they are more likely to live in areas with higher exposure to this pollution.
Experts, like Emory University epidemiologist Anke Huels, think that clean air policies could prevent some of these cases.
How does air pollution affect the brain?
PM2.5 particles are so small that they cross the blood-brain barrier, where they become neurotoxic, Huels explained. These particles activate the brain’s immune cells, the microglia, which cause inflammation and damage to other brain cells.
These effects also accelerate the brain’s aging and increase the levels of Alzheimer’s biomarkers like amyloid and tau. A 2021 study found that older women who lived in areas with higher levels of PM2.5 air pollution experienced more memory loss and brain shrinkage than women living in areas with cleaner air.
In research published earlier this year, Huels and colleagues found that cognitively healthy adults living in areas with higher levels of PM2.5 were more likely to develop biomarkers of amyloid plaques in their cerebrospinal fluid, which increases the chances of developing Alzheimer’s later on.
From research to public policy
This year, the Environmental Protection Agency (EPA) changed its guidelines, lowering the limit of PM2.5 pollution particles from 12 to nine micrograms per cubic meter. The new limit is almost double the recommended safe limit of five micrograms set by the World Health Organization.
According to Huels’ research, exposure, even at these lower levels of air pollution, is still linked to higher levels of Alzheimer’s disease biomarkers.
“We expect that when we successfully decrease concentrations of air pollution, we will hopefully also see fewer dementia cases,” Huels said, adding that interventions that promote better public transportation and bicycle adoption could help by taking more vehicles off the road.
With more evidence linking dementia to pollution, Huels thinks it could encourage policymakers to take action, which could also mitigate some of the effects of climate change.