Association of air pollution with brain health: A cross-sectional analysis in adults living in Canada

Abstract Background 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. Methods The Canadian Alliance for Healthy Hearts and Minds Cohort Study (CAHHM) is a cohort of Canadian adults recruited between 2014-2018, for whom averages of exposures to nitrogen dioxide (NO 2 ) and fine particulate matter (PM 2.5 ) were estimated for five years prior to recruitment. Outcomes included the Montréal Cognitive Assessment (MoCA) and Digit Symbol Substitution Test (DSST) for cognitive function, and magnetic resonance imaging-measured covert vascular brain injury. Generalized linear mixed models assessed pollutant associations with outcomes. Results 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 enrolment (Figure S1) for PM 2.5 was 6.9 μg/m³ (2.0; 1.8-11.2), and for NO 2 was 12.9 ppb (5.9; 0.9-33.9). In adjusted models, a 5 μg/m 3 higher PM 2.5 concentration was associated with 0.44-points lower MoCA (95% confidence intervals (CI) −0.62, −0.25) and 1.31-points lower DSST (95% CI −2.41,-0.22) scores. A 5-ppb higher NO 2 concentration was associated with 0.12-points lower MoCA (95% CI −0.17, −0.07) and 0.38 lower DSST (95% CI −0.70, −0.05) scores. A 5-ppb higher NO 2 concentration was associated with higher odds of covert vascular brain injury (adjusted Odds Ratio (OR)=1.08; 95% CI 1.00, 1.17). Cardiovascular risk factors and greenspace did not change these associations. Conclusions PM 2.5 and NO 2 were associated with lower cognitive function scores in middle-aged adults living in Canada, independent of cardiovascular risk factors. This study suggests that air pollution mitigation efforts may help preserve cognitive function.