The association between PM_2.5 exposure and neurological disorders: A systematic review and meta-analysis

Background: Recent systematic review and meta-analyses have tried to identify an association between PM _2.5 exposure and stroke, but few could find a conclusive and comprehensive evidence. Moreover, the associations between PM _2.5 , neurodegenerative diseases and neurodevelopmental disorders have never been reviewed. We aimed to assess the effects of PM _2.5 exposure on stroke, dementia, Alzheimer's disease, autism spectrum disorder (ASD), Parkinson's disease, and mild cognitive impairment (MCI). Methods: We searched PubMed and CNKI databases for articles published until June 2018. Studies were eligible for analysis if they were human studies and provided risk estimates with 95% CI. We screened 1645 articles and identified 80 eligible studies covering 26 countries across all continents except Antarctica. Risks of incidence and mortality were extracted and stratified by types of neurological disorders, PM _2.5 concentration and duration of PM _2.5 exposure. Results: We found significant association between PM _2.5 exposure and stroke, dementia, Alzheimer's disease, ASD, Parkinson's disease. The risks of ischemic and hemorrhagic stroke were higher than that of stroke in general, and that hemorrhagic stroke had by far the highest mortality. The risk of stroke for heavily polluted countries was significantly higher than that of lightly polluted countries. Short- and long-term PM _2.5 exposure was associated with increased risks of stroke (short-term odds ratio 1.01 [per 10 μg/m ³ increase in PM _2.5 concentrations], 95% CI 1.01–1.02; long-term 1.14, 95% CI 1.08–1.21) and mortality (short-term 1.02, 95% CI 1.01–1.04; long-term 1.15, 95% CI 1.07–1.24) of stroke. Long-term PM _2.5 exposure was associated with increased risks of dementia (1.16, 95% CI 1.07–1.26), Alzheimer's disease (3.26, 95% 0.84–12.74), ASD (1.68, 95% CI 1.20–2.34), and Parkinson's disease (1.34, 95% CI 1.04–1.73). Conclusions: There is a strong association between PM _2.5 exposure and neurological disorders. National governments should exert greater efforts to improve air quality given its health implications.