title: [Parkinson's disease, tobacco and age: meta analysis].
abstract: BACKGROUND
  Epidemiological studies have demonstrated contradictory results about the association between smoking and the risk of Parkinson s disease (PD).
  
  
  OBJECTIVE
  Examine the hypothesis of the EUROPARKINSON group that smoking protects against PD only in patients below 75 years of age.
  
  
  METHODS
  We conducted a meta analysis including all observational studies that were published about this association before January 2001. All languages were included with no restriction for year of publication. Risk estimate and its 95% confidence interval (95% CI) were extracted or calculated for all localized studies in patients below or above 75 years of age.
  
  
  RESULTS
  Seventeen studies investigated the association between PD risk and smoking in patients below 75 years of age. Meanwhile, only seven studies investigated the association in patients above 75 years of age. The fixed effect pooled analysis in patients below 75 years of age was 0.59 (95% CI: 0.52 0.67), with insignificant homogeneity test. Patients above 75 years of age had fixed effect pooled analysis of 0.76 (95% CI: 0.59 0.99), with insignificant homogeneity test.
  
  
  CONCLUSIONS
  The pooled analysis in patients below 75 years of age clearly demonstrates that smoking is inversely associated with PD risk. The 95% CI of the pooled analysis in patients above 75 years of age is nearly overlapping unity. This result is not in favor for the negative association in old patients, and confirms the hypothesis of the EUROPARKINSON group.
authors.affiliation: Departamento de Medicina preventiva y Salud Pública, Facultad de Medicina, Universidad de Córdoba. Córdoba, España. fm2faahm@lucano.uca.es
authors.forename: M F
authors.initials: MF
authors.lastname: Allam
authors.forename: A S
authors.initials: AS
authors.lastname: del Castillo
authors.forename: R F-C
authors.initials: RF
authors.lastname: Navajas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging; D006801:Humans; D010300:Parkinson Disease / Q000453:epidemiology*; D012307:Risk Factors; D012907:Smoking; D014026:Nicotiana