Long-Term Exposure to PM2.5 and Risk of Incident Dementia: A Systematic Review and Meta-Analysis of Cohort Studies

Exposure to ambient fine particulate matter (PM2.5) is associated with cardiovascular and inflammatory pathways implicated in neurodegeneration. However, epidemiologic findings linking PM2.5 exposure to dementia incidence remain heterogeneous. We conducted a systematic review and meta-analysis of existing cohort studies evaluating the association between PM2.5 exposure and incident dementia. A literature search yielded 909 records, of which 15 cohort studies, including approximately 65 million participants in Europe, Asia, and North America, were included in the meta-analysis. Hazard ratios were standardized to a 1 μg/m3 increase in PM2.5 exposure using logarithmic transformation. Effect estimates were then pooled using a random-effects model. Long-term PM2.5 exposure was associated with an increased risk of incident dementia (pooled HR 1.04, 95% confidence interval 1.01-1.06). Substantial heterogeneity was observed across studies (I2 = 88.3%). These findings support growing evidence that chronic exposure to fine particulate air pollution may contribute to the development of dementia and highlight air pollution as a potentially modifiable environmental risk factor for neurodegenerative disease.