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 (PM₁₀), PM_2.5, ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO₂), 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 10μg/m³ increase of PM2.5 was 1.95 (95% CI: 0.88-4.30). The corresponding values per 10μg/m³ increment of other pollutants were 1.03 (95% CI: 0.68-1.57) for O₃, 1.00 (95% CI: 0.89-1.13) for NO₂, and 0.95 (95% CI: 0.91-0.99) for PM₁₀ (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 SO₂ or CO exposure are still limited, the epidemiologic and toxicological evidence indicated that higher concentration of SO₂ or CO exposure increased risks of dementia, implying that SO₂ or CO might have a potential impact on AD. 

Conclusion: Air pollution exposure may exacerbate AD development. Copyright © 2021 The authors and IOS Press.