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Current evidence shows inconsistencies about ambient air pollution (AAP) exposure as a risk factor for Parkinson's disease (PD). We performed meta-analyses to estimate the pooled risk of PD due to AAP exposure. 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 PD due to exposure to PM2.5, PM10, O3, CO, NO2, NOX and SO2; from the beginning until October 2021. The pooled odds ratio (OR) for the effect of NO2 (per 1 μg/m3) and O3 (per 1 ppb) on PD was 1.01[95% CI: 1.00,1.02; I2 = 69% (p =.01)] and 1.01 [95% CI: 1.00,1.02; I2 = 66% (p =.03)], respectively. The ORs for the effects of PM2.5 (per 1 µg/m3) and CO (per 1 ppm) on PD were 1.01 [95% CI:.99,1.03; I2 = 40%] and 1.64 [95% CI:.96,2.78; I2 = 75% (p =.01)], respectively. The study showed the adverse roles of NO2, O3, PM2.5, and CO in increasing the risk for PD. [ABSTRACT FROM AUTHOR]

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 (PM2.5) and less than 10 μm (PM10), ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), nitrogen oxides (NOX) and sulfur dioxide (SO2) 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 PM2.5 and NO2 exposure was 1.03 [(95%CI: 1.01-1.06; I2 = 99% (P < 0.001)] and 1.00 [(95%CI: 1.00-1.01; I2 = 96% (P < 0.001)], respectively. The pooled HR for NOX was 1.00 [(95%CI: 1.00-1.01; I2 = 61% (P = 0.05)]. In AD, the pooled HRs for PM2.5 and O3 was 1.08 (95%CI: 1.01-1.15; I2 = 99% (P < 0.001)]) and 1.02 (95%CI: 0.96-1.08; I2 = 100% (P < 0.001)], respectively. In VaD, the pooled HR for PM2.5 exposure was 1.03 (95%CI: 1.01-1.06; I2 = 91% (P < 0.001)]. In NO2/NOX, 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 PM2.5 as a risk factor for all-cause dementia, AD, and VaD and exposure to O3 as a possible risk factor for AD. These findings can be used for policy measures and further research. [ABSTRACT FROM AUTHOR]