Is Air Pollution Associated with Increased Risk of Dementia? A Meta-Analysis of Epidemiological Research
Vikas Dhiman, Tanwi Trushna, Dharma Raj, RajnarayanR Tiwari
Abstract
Background: There are prevailing inconsistencies in epidemiological research about air pollution being a risk factor for dementia. Objective: We performed meta-analyses to calculate the pooled estimates of the risk of developing dementia due to air pollution exposure. Methods and Materials: We performed a systematic search in PubMed, Google Scholar, The Cochrane Library, and J-GATEPLUS databases for peer-reviewed epidemiological studies reporting the risk of developing all-cause dementia, cognitive decline, Alzheimer's disease (AD), and vascular dementia (VaD) due to exposure to particulate matter with an aerodynamic diameter less than 2.5 μm (PM 2.5 ) and less than 10 μm (PM 10 ), ozone (O 3 ), carbon monoxide (CO), nitrogen dioxide (NO 2 ), nitrogen oxides (NO X ) and sulfur dioxide (SO 2 ) from the beginning until December 2020. Meta-analysis was performed by adopting the random-effects model using Meta-XL. Results: In all-cause dementia, the pooled hazard ratio (HR) for PM 2.5 and NO 2 exposure was 1.03 [(95%CI: 1.01–1.06; I 2 = 99% ( P < 0.001)] and 1.00 [(95%CI: 1.00–1.01; I 2 = 96% ( P < 0.001)], respectively. The pooled HR for NO X was 1.00 [(95%CI: 1.00–1.01; I 2 = 61% ( P = 0.05)]. In AD, the pooled HRs for PM 2.5 and O 3 was 1.08 (95%CI: 1.01–1.15; I 2 = 99% ( P < 0.001)]) and 1.02 (95%CI: 0.96–1.08; I 2 = 100% ( P < 0.001)], respectively. In VaD, the pooled HR for PM 2.5 exposure was 1.03 (95%CI: 1.01–1.06; I 2 = 91% ( P < 0.001)]. In NO 2 /NO X , the results were found to be equivocal. Meta-analysis could not be performed in cognitive decline because of wide variations in assessments methods. Conclusions: The present study showed exposure to PM 2.5 as a risk factor for all-cause dementia, AD, and VaD and exposure to O 3 as a possible risk factor for AD. These findings can be used for policy measures and further research.