Is Air Pollution Associated with Increased Risk of Dementia? A Meta-Analysis of Epidemiological Research.

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) and less than 10 μm (PM), ozone (O), carbon monoxide (CO), nitrogen dioxide (NO), nitrogen oxides (NO) and sulfur dioxide (SO) 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 and NO exposure was 1.03 [(95%CI: 1.01-1.06; I = 99% (P < 0.001)] and 1.00 [(95%CI: 1.00-1.01; I = 96% (P < 0.001)], respectively. The pooled HR for NO was 1.00 [(95%CI: 1.00-1.01; I = 61% (P = 0.05)]. In AD, the pooled HRs for PM and O was 1.08 (95%CI: 1.01-1.15; I = 99% (P < 0.001)]) and 1.02 (95%CI: 0.96-1.08; I = 100% (P < 0.001)], respectively. In VaD, the pooled HR for PM exposure was 1.03 (95%CI: 1.01-1.06; I = 91% (P < 0.001)]. In NO/NO, 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 as a risk factor for all-cause dementia, AD, and VaD and exposure to O as a possible risk factor for AD. These findings can be used for policy measures and further research.