Is ambient air pollution a risk factor for Parkinson's disease? A meta-analysis of epidemiological evidence.

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 PM 2.5 , PM 10 , O 3 , CO, NO 2 , NO X and SO 2 ; from the beginning until October 2021. The pooled odds ratio (OR) for the effect of NO 2 (per 1 μg/m 3 ) and O 3 (per 1 ppb) on PD was 1.01[95% CI: 1.00,1.02; I 2  = 69% ( p  = .01)] and 1.01 [95% CI: 1.00,1.02; I 2  = 66% ( p  = .03)], respectively. The ORs for the effects of PM 2.5 (per 1 µg/m 3 ) and CO (per 1 ppm) on PD were 1.01 [95% CI: .99,1.03; I 2  = 40%] and 1.64 [95% CI: .96,2.78; I 2  = 75% ( p  = .01)], respectively. The study showed the adverse roles of NO 2 , O 3 , PM 2.5, and CO in increasing the risk for PD.