Summary: A Canadian cross-sectional study finds that long-term exposure to common air pollutants—fine particulate matter (PM2.5) and nitrogen dioxide (NO2)—is associated with measurable declines in cognitive performance and with small, visible vascular brain changes on MRI. The analysis, conducted within the Canadian Alliance for Healthy Hearts and Minds (CAHHM) cohort, included nearly 6,900 middle-aged adults across five provinces and shows these associations even at pollution levels well below many international limits.
Researchers report that higher multi-year exposure to traffic- and combustion-related pollution corresponded with lower scores on tests of memory, executive function and mental processing speed. The study also identified a stronger link between traffic-related pollution and MRI-detected covert vascular brain injury in women. These relationships persisted after accounting for established cardiovascular risk factors, suggesting a direct effect of air pollution on the central nervous system.
Key Facts
- Risk at low levels: Unlike earlier studies focused on highly polluted regions, this research shows cognitive and structural brain differences in Canada, where average pollution levels are relatively low.
- Direct brain impact: Associations between pollution and poorer cognition remained after adjusting for high blood pressure, diabetes and body adiposity, indicating pollution may directly affect brain tissue.
- Sex differences: Traffic-related NO2 exposure was linked to MRI-visible covert vascular brain injury, with a more pronounced pattern observed among female participants.
- Pollutants studied: The analysis measured long-term (five-year average) exposure to PM2.5 and NO2, common byproducts of vehicle exhaust, industrial emissions and wildfire smoke.
Source: McMaster University
Air pollution and brain health
New findings from McMaster University, published in the journal Stroke (May 13, 2026), link routine exposure to PM2.5 and NO2 with poorer cognitive performance and subtle vascular brain injury on MRI scans. The research involved 6,878 adults (mean age 57.6 years; 55.6% women) recruited across five Canadian provinces as part of the CAHHM study.
Average five-year pollutant concentrations prior to enrolment were 6.9 μg/m3 for PM2.5 (SD 2.0, range 1.8–11.2) and 12.9 parts per billion for NO2 (SD 5.9, range 0.9–33.9). After adjusting for demographic factors, cardiovascular risk factors and neighborhood greenspace, the investigators found clear statistical links between higher pollutant exposure and lower scores on two established cognitive tests: the Montréal Cognitive Assessment (MoCA) and the Digit Symbol Substitution Test (DSST).
Specifically, a 5 μg/m3 higher PM2.5 concentration was associated with a 0.44-point lower MoCA score (95% CI −0.62 to −0.25) and a 1.31-point lower DSST score (95% CI −2.41 to −0.22). A 5 ppb higher NO2 concentration corresponded to a 0.12-point lower MoCA score (95% CI −0.17 to −0.07) and a 0.38-point lower DSST score (95% CI −0.70 to −0.05). Higher NO2 exposure was also associated with increased odds of covert vascular brain injury on MRI (adjusted OR 1.08 per 5 ppb; 95% CI 1.00–1.17).
Lead and corresponding authors emphasize that cognitive declines and brain injury accumulate over many years. While this cross-sectional analysis does not establish causation, the findings reinforce growing evidence that even relatively low levels of air pollution can contribute to early brain aging and highlight the importance of long-term follow-up to determine whether reducing exposure slows cognitive decline.
“Dementia develops over decades,” says Russell de Souza, associate professor at McMaster and the study’s corresponding author. “Identifying preventable environmental factors that harm the brain in midlife is essential for protecting cognitive health later on.”
Sandi Azab, the study’s lead author, adds: “In countries often considered to have clean air, such as Canada, even modest pollution appears linked to subtle but measurable changes in cognition that can occur quietly years before symptoms emerge.”
Funding: This research was conducted within the Canadian Alliance for Healthy Hearts and Minds (CAHHM) cohort and received support from the Canadian Partnership Against Cancer, the Heart and Stroke Foundation of Canada, and the Canadian Institutes of Health Research.
Key Questions Answered:
A: This study indicates no. Even pollution levels commonly regarded as low were associated with small but meaningful reductions in cognitive test scores and with MRI-detected covert vascular brain injury, suggesting risk exists even in areas with relatively clean air.
A: Cardiovascular conditions are established contributors to cognitive decline. By adjusting for blood pressure, diabetes and body adiposity, the analysis tested whether pollution effects on cognition were independent of these factors. The associations persisted, supporting a direct link between pollution and brain health.
A: The study does not prove that air pollution causes dementia. However, it provides evidence that air pollution accelerates age-related changes in memory and thinking. Because dementia unfolds over decades, reducing avoidable exposures in midlife may be an important preventive strategy.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The full journal paper was reviewed to prepare this summary.
- Additional context and clarification were added by editorial staff to aid reader understanding.
About this pollution and neurology research news
Author: Adam Ward
Source: McMaster University
Contact: Adam Ward – McMaster University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Association of Air Pollution With Brain Health: A Cross-Sectional Analysis in Adults Living in Canada” by Sandi M. Azab et al., published in Stroke.
DOI:10.1161/STROKEAHA.125.054251
Abstract
Association of Air Pollution With Brain Health: A Cross-Sectional Analysis in Adults Living in Canada
BACKGROUND:
Air pollution is increasingly recognized as a modifiable risk factor for dementia, but its role in earlier cognitive dysfunction and in subclinical brain injury requires clarification. This study examined associations between long-term exposure to PM2.5 and NO2 and cognitive outcomes in a Canadian adult cohort, and evaluated whether cardiovascular risk factors or neighborhood greenspace influenced these associations.
METHODS:
The CAHHM cohort enrolled Canadian adults from 2014 to 2018. Five-year average exposures to NO2 and PM2.5 before recruitment were estimated for participants. Cognitive outcomes included the Montréal Cognitive Assessment (MoCA) and the Digit Symbol Substitution Test (DSST). MRI scans were used to detect covert vascular brain injury. Generalized linear mixed models assessed associations between pollutant exposures and outcomes in this cross-sectional analysis, adjusting for demographic, clinical and environmental covariates.
RESULTS:
Among 6,878 participants (mean age 57.6 years; 55.6% women), mean five-year PM2.5 was 6.9 μg/m3 and mean NO2 was 12.9 ppb. In adjusted models, each 5 μg/m3 increase in PM2.5 was associated with 0.44 points lower MoCA and 1.31 points lower DSST. Each 5 ppb increase in NO2 was associated with 0.12 points lower MoCA, 0.38 points lower DSST, and higher odds of covert vascular brain injury (adjusted OR 1.08). Cardiovascular risk factors and greenspace did not materially change these associations.
CONCLUSIONS:
In this large Canadian adult sample, long-term exposure to PM2.5 and NO2 was associated with modest but measurable reductions in cognitive test scores and with increased odds of covert vascular brain injury, independent of cardiovascular risk factors. The findings underscore the need for longitudinal follow-up to assess the impact of air pollution on cognitive decline and to inform prevention strategies for brain health.