title: Epidemiology and etiology of Parkinson's disease: a review of the evidence.
abstract: The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden. karin.wirdefeldt@ki.se
authors.forename: Karin
authors.initials: K
authors.lastname: Wirdefeldt
authors.forename: Hans-Olov
authors.initials: HO
authors.lastname: Adami
authors.forename: Philip
authors.initials: P
authors.lastname: Cole
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Trichopoulos
authors.forename: Jack
authors.initials: J
authors.lastname: Mandel
mesh_terms: D000367:Age Factors; D000428:Alcohol Drinking / Q000009:adverse effects; D015897:Comorbidity; D003937:Diagnosis, Differential; D004032:Diet; D004781:Environmental Exposure / Q000009:adverse effects*; D020022:Genetic Predisposition to Disease; D006801:Humans; D008280:Magnetics; D008670:Metals / Q000633:toxicity; D016273:Occupational Exposure / Q000009:adverse effects; D009930:Organic Chemicals / Q000633:toxicity; D010300:Parkinson Disease / Q000453:epidemiology* / Q000209:etiology* / Q000235:genetics; D010575:Pesticides / Q000633:toxicity; D011110:Polymorphism, Genetic; D012111:Residence Characteristics; D012737:Sex Factors; D012907:Smoking / Q000009:adverse effects; D014881:Water Supply
chemical_list: D008670:Metals; D009930:Organic Chemicals; D010575:Pesticides