Air pollution from traffic is linked to some of the more severe forms of dementia, and may be a significant cause of the condition among those who are not already genetically predisposed to it, research suggests.
Research conducted in Atlanta, Georgia found that people with greater exposure to traffic-related fine particulate air pollution are more likely to have high amounts of amyloid plaques in their brains that are associated with Alzheimer’s disease.
The findings, which will alarm anyone living in a town or city, but especially those living near busy roads, add to the damage already known to be caused by road traffic pollution, ranging from climate change to respiratory disease .
A team of researchers from Atlanta’s Emory University specifically investigated the effects on people’s brains of exposure to the type of fine particles known as PM2.5.
Consisting of particles less than 2.5 microns in diameter – about one-hundredth the thickness of a human hair – suspended in the air, they are known to penetrate deep into living tissue, including the blood-brain barrier. Traffic-related PM2.5 concentrations are a major source of environmental pollution in the metro Atlanta area, and also in urban centers around the planet.
The Emory researchers examined the brain tissue of 224 people from Atlanta, 90% of whom had a diagnosis of some form of dementia, who agreed to donate their brains to medical science after their death. They also investigated the traffic-related exposure to PM2.5 pollution at subjects’ homes in the years before their death.
The average level of exposure in the year before death was 1.32 micrograms per cubic meter (µg/m)3) and 1.35 µg/m3 in the three years before death.
“We found that donors living in areas with high concentrations of traffic-related exposure to air pollution, especially exposure to PM2.5, had higher levels of Alzheimer’s disease neuropathology in their brains,” says Anke Huels, an assistant professor at the Emory University in Atlanta, who was the lead author of the study.
“In particular, we looked at … a score used to evaluate amyloid plaques in the brain, in autopsy samples, and we showed that donors living in areas with higher levels of air pollution, and also higher levels of amyloid plaques in their brain.”
There was a positive relationship between exposure to high levels of PM2.5 and levels of amyloid plaques in the brains of the subjects the team investigated. They found that people with a 1 µg/m3 higher PM2.5 exposure in the year before death was nearly twice as likely to have higher levels of amyloid plaques in their brains, while those with higher exposure in the three years before death were 87% more likely to have higher levels of plaques have.
Huels and her team also investigated whether the main gene variant associated with Alzheimer’s disease, ApoE4, had any effect on the relationship between air pollution and signs of Alzheimer’s disease in the brain.
“We found that the association between In air pollution and severity of Alzheimer’s disease was stronger among those who did not carry an ApoE4 allele, those who did not have as strong a genetic risk for Alzheimer’s disease,” Huels said. “Which kind of suggests that environmental exposures like air pollution may explain some of the Alzheimer’s risk in people whose risk can’t be explained by genetic risk factors.”
The findings are published in the February 21, 2024, online edition of Neurology®the medical journal of the American Academy of Neurology.
