The air pollution we breathe daily could be harming more than just our lungs and hearts. New research from McMaster University suggests that fine particles from traffic, industry and wildfire smoke is linked to worse cognitive function.
The study, published online in the journal Stroke on May 13, 2026, found that people living in areas with higher air pollution scored worse on tests of memory, understanding and mental speed. This finding was true for places where air pollution is considered low by international standards.
Higher levels of traffic-related pollution were also linked to small but visible signs of damage to the brain seen on MRI scans, and more so in women. These relationships remained even after accounting for heart-health risk factors like high blood pressure, diabetes, and body adiposity, suggesting that air pollution may be directly affecting the brain.
"Dementia doesn't happen overnight," says Russell de Souza , associate professor with McMaster's Department of Health Research Methods, Evidence, and Impact and the study's corresponding author. "It develops over decades. Identifying factors that may damage the brain early, and that are potentially preventable, is critical for protecting brain health later in life."
While the study doesn't prove air pollution causes dementia, it does add to a growing body of evidence that air quality may impact age-related changes in memory or thinking.
Unlike many previous studies conducted in regions with heavy pollution, this research focused on Canada, a country with some of the lowest average air pollution levels in the world. Researchers studied nearly 7,000 middle-aged adults across five Canadian provinces to see if long-term exposure to common air pollutants was linked to how well people think and remember.
To do this, researchers compared people's exposure over several years with their performance on cognitive tests. They focused on two pollutants: fine particles in the air known as fine particulate matter or PM2.5 and nitrogen dioxide. Both are common byproducts of vehicle exhaust, with PM2.5 particles also common within fumes from wildfires and industry.
"Canada's air is often described as clean, but our findings suggest that even low levels of air pollution are linked to worse brain health," says lead author Sandi Azab , an assistant professor with McMaster's Department of Medicine. "These are changes that can happen quietly, years before any noticeable symptoms appear."
Researchers say long‑term follow‑up studies are needed to better understand how ongoing exposure to air pollution may influence cognitive decline over time, and whether improving air quality can help protect brain health.
The research was conducted as part of the Canadian Alliance for Healthy Hearts and Minds (CAHHM) study and was supported by funding from the Canadian Partnership Against Cancer, the Heart and Stroke Foundation of Canada, and the Canadian Institutes of Health Research.
