Air Pollution and Alzheimer's Disease: A Systematic Review and Meta-Analysis

Background: Ambient air pollution has been associated with Alzheimer's disease (AD) in the elderly. However, its effects on AD have not been meta-analyzed comprehensively. Objective: We conducted a systematic review and meta-analysis to assess the associations between air pollution and AD incidence. Methods: We searched PubMed and Web of Science for indexed publications up to March 2020. Odds risk (OR) and confidence intervals (CI) were estimated for particulate matter (PM)10 (PM 10), PM 2.5, ozone (O 3), nitrogen dioxide (NO 2), sulfur dioxide (SO 2), and carbon monoxide (CO). The subgroup analysis was conducted based on the pollution levels. Results: Nine studies were included in the meta-analysis and review. The OR per 10 μg/m 3 increase of PM 2.5 was 1.95 (95% CI: 0.88-4.30). The corresponding values per 10 μg/m3 increment of other pollutants were 1.03 (95% CI: 0.68-1.57) for O 3, 1.00 (95% CI: 0.89-1.13) for NO 2, and 0.95 (95% CI: 0.91-0.99) for PM 10 (only one study), respectively. Overall OR of the five air pollutants above with AD was 1.32 (95% CI: 1.09-1.61), suggesting a positive association between ambient air pollution and AD incidence. The sub-analysis indicated that the OR (2.20) in heavily polluted regions was notably higher than that in lightly polluted regions (1.06). Although AD risk rate data related to SO 2 or CO exposure are still limited, the epidemiologic and toxicological evidence indicated that higher concentration of SO 2 or CO exposure increased risks of dementia, implying that SO 2 or CO might have a potential impact on AD. Conclusion: Air pollution exposure may exacerbate AD development.