Canadian health experts are reacting after a study in southern California concluded that even tiny added concentrations of a key pollutant in wildfire smoke dramatically increase the risk of dementia.
The results of the 10-year study of more than 1.2 million people “suggest the brain health threat posed by wildfire smoke is higher than other forms of air pollution,” far exceeding the risk from factories or automobile exhaust, the Alzheimer’s Society reported [pdf] in a release last month.
“Researchers found that the risk of dementia diagnosis due to exposure to PM2.5 in wildfire smoke was notably stronger—even with less exposure—than the risk due to the other sources of PM2.5 air pollution,” the release stated. “Exposure to non-wildfire PM2.5 raised the risk of dementia diagnosis, but not as much as wildfire smoke.”
It described PM2.5 as “a microscopic mixture of solid and liquid droplets in the air”, about 30 times smaller than the width of the average human hair.
The study found a 21% higher likelihood of a dementia diagnosis for every average increase in PM2.5 concentration of just one microgram—one-millionth of a gram—in a cubic metre of air over a three-year span.
“Previous research has found that exposure to PM2.5 is associated with dementia, but in light of our large, long-term study, it’s apparent the risk from exposure due to wildfire smoke is an even bigger concern,” said first author Holly Elser, M.D., Ph.D., a neurology resident at the Hospital of the University of Pennsylvania in Philadelphia.
And the findings “appeared most pronounced among individuals from racially and ethnically minoritized groups and in high poverty areas,” added senior author Joan A. Casey, Ph.D., assistant professor in the Department of Environmental and Occupational Health Sciences at the University of Washington in Seattle.
After elevated PM2.5 levels during a record wildfire season in 2023, and with residents now beginning to return to the devastated townsite in Jasper, Alberta, Canadian health professionals reacted to the study in a release last week.
“This new research linking wildfire smoke to a disproportionately high risk of dementia—even compared to other forms of air pollution—is deeply concerning,” said Ottawa family physician Dr. Sehjal Bhargava of the Canadian Association of Physicians for the Environment. “It underscores the urgent need for immediate safety measures and ambitious climate action to urgently reduce fossil fuel emissions.”
She added that “protecting our communities—especially those already structurally or personally vulnerable—from the health threats posed by worsening extreme weather events is not just a matter of public health, but of justice for future generations.”
Stephanie Cleland, assistant professor at Simon Fraser University, said the California study “adds to the growing body of evidence that wildfire smoke may pose a significant risk to our cognitive health. It also demonstrates that wildfire smoke has longer-term health implications, which is critical to consider as communities are exposed to more frequent and intense periods of smoke.”
