Recent epidemiological research investigates associations between exposure to air pollution and neurodegenerative disease, while part of the literature suggests effects on the onset or aggravation of Parkinson’s disease (PD). The goal of this study is to assess the association between exposure to air pollution (NO2, NOx, PM2.5, PM10) and PD through a systematic review and meta-analysis.Methods
We searched studies, published in English, until September 2017 through PubMed, Google Scholar and conference abstracts. References of identified studies were further searched for relevant literature. We initially identified 92 studies, from which 16 were included in the meta-analyses as they provided relevant effect estimates. We extracted descriptive and quantitative information from each study. We applied random-effects models to combine risk estimates and investigated the presence of heterogeneity between studies. We assessed publication bias through funnel plots and the Egger test.Results
We identified 7 articles investigating associations with long term exposure to PM2.5, 5 studies for PM10, 6 for NOx and NO2, while 2 reported associations for short term exposure to PM2.5. The analysis suggested that PD was positively related to long term exposure to nitrogen oxides with relative risk 1.03% (95% CI: 0.99, 1.07%) per 10 µg/m3 increase. Particles’ exposure also displayed weak positive but non-significant associations. There was high heterogeneity between studies for all analysesConclusion
We found weak evidence for an association between air pollution and onset of PD. Although meta-analysis increases power to detect small associations in rare outcomes further research would elaborate our indicative associations, as these may be of public health significance considering the increasing trend in the ageing of the population in developed countries.