Association of Air Pollution With Brain Health: A Cross-Sectional Analysis of Adults Living in Canada

Air pollution is a risk factor for dementia, but its role in early cognitive dysfunction is not clear. We aimed to investigate the association of air pollution with cognitive function, and the role of cardiovascular risk factors and greenspace in this association.

The CAHHM (Canadian Alliance for Healthy Hearts and Minds Cohort Study) is a cohort of Canadian adults recruited between 2014 and 2018, for whom averages of exposures to NO₂ and fine particulate matter were estimated for 5 years before recruitment. Outcomes included the Montréal Cognitive Assessment and Digit Symbol Substitution Test for cognitive function, and magnetic resonance imaging-measured covert vascular brain injury. Generalized linear mixed models assessed pollutant associations with outcomes in this cross-sectional analysis.

A total of 6878 adults participated in the study, with a mean age of 57.6 years (SD=8.8), and 55.6% were women. Mean (SD; range) 5-year pollutant concentrations preceding enrollment for fine particulate matter were 6.9 μg/m³ (2.0 [1.8-11.2]), and for NO₂ were 12.9 parts per billion (5.9 [0.9-33.9]). In adjusted models, a 5 μg/m³ higher fine particulate matter concentration was associated with 0.44 points lower Montréal Cognitive Assessment (95% CI, -0.62 to -0.25) and 1.31 points lower Digit Symbol Substitution Test (95% CI, -2.41 to -0.22) scores. A 5 parts per billion higher NO₂ concentration was associated with 0.12 points lower Montréal Cognitive Assessment (95% CI, -0.17 to -0.07) and 0.38 points lower Digit Symbol Substitution Test (95% CI, -0.70 to -0.05) scores. A 5 parts per billion higher NO₂ concentration was associated with higher odds of covert vascular brain injury (adjusted odds ratio, 1.08 [95% CI, 1.00-1.17]). Cardiovascular risk factors and greenspace did not change these associations.

Fine particulate matter and NO₂ were associated with lower cognitive function scores in middle-aged adults living in Canada, independent of cardiovascular risk factors. Our results warrant longitudinal follow-up to study the impact of air pollution on cognitive decline.