This paper [1] will be useful for those of us interested in the aetiology of PD. It uses meta-analysis to quantify about 75 PD risk factors: from smoking, RR=0.64, to vitamin D, OR=0.67.
Reference:
[1] "Environmental risk factors and Parkinson's disease: An umbrella review of meta-analyses"
Parkinsonism and Related Disorders, Feb 2016.
Vanesa Bellou, Lazaros Belbasis, Ioanna Tzoulaki, Evangelos Evangelou, John P.A. Ioannidis
http://www.prd-journal.com/article/S...15)30061-4/pdf
John