title: Vitamin A and carotenoids and the risk of Parkinson's disease: a systematic review and meta-analysis.
abstract: BACKGROUND
  Vitamin A and carotenoids are involved in signalling pathways regulating gene expression in many organs, including the brain. The dopaminergic system is a target of retinoic acid action in the central nervous system. The aim of this review is to assess the epidemiological evidence on the association between blood levels or dietary intakes of vitamin A and carotenoids and risk of Parkinson's disease (PD).
  
  
  METHODS
  PubMed and ISI Web of Science were searched for relevant papers from 1990 to April 2013. Data reported in epidemiological studies assessing the association between vitamin A and/or carotenoids (α-carotene, β-carotene, β-cryptoxanthin, lutein, lycopene, zeaxanthin and canthaxanthin) and PD were extracted for a narrative synthesis and meta-analysis.
  
  
  RESULTS
  Thirteen papers were included out of a total of 362 potentially relevant; of these, eight contributed to the meta-analysis. No statistically significant pooled estimate between micronutrient and PD was detected. Forest plots suggest possible non-significant inverse pooled estimates of α-carotene and β-carotene and risk of PD. A significant association between lutein intake and PD risk was detected in case-control studies only.
  
  
  CONCLUSIONS
  Data published to date are insufficient for drawing definite conclusions about the epidemiological evidence on the association between blood levels or dietary intakes of vitamin A and carotenoids and the risk of PD. Results should be interpreted particularly cautiously given the limitation of the present meta-analysis and the potential publication bias. Authors are urged to follow more closely the recommendations for reporting epidemiological studies in order to enhance the capacity for synthesising the evidence.
authors.affiliation: Centre for Primary Care and Public Health, Blizard Institute, Queen Mary University of London, London, UK.
authors.forename: Andrea
authors.initials: A
authors.lastname: Takeda
authors.forename: Olga P
authors.initials: OP
authors.lastname: Nyssen
authors.forename: Asmat
authors.initials: A
authors.lastname: Syed
authors.forename: Eugene
authors.initials: E
authors.lastname: Jansen
authors.forename: Bas
authors.initials: B
authors.lastname: Bueno-de-Mesquita
authors.forename: Valentina
authors.initials: V
authors.lastname: Gallo
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000009:adverse effects / Q000097:blood*; D016022:Case-Control Studies; D006801:Humans; D010300:Parkinson Disease / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology*; D012307:Risk Factors; D014801:Vitamin A / Q000009:adverse effects / Q000097:blood*; D019207:beta Carotene / Q000097:blood
chemical_list: D019207:beta Carotene; D014801:Vitamin A; D002338:Carotenoids; C041635:alpha-carotene