title: Smoking as a risk factor for developing Multiple Sclerosis: A meta-analysis of observational studies.
abstract: OBJECTIVE
  The aim of this study was to improve and update the pool of available studies included in the previous meta-analyses, and to provide further evidence about smoking as a risk factor for MS.
  
  
  METHODS
  PubMed and Scopus searches were undertaken to identify studies investigating the association between cigarette smoking and MS. Odds ratio (OR), relative risk (RR) together with 95% confidence intervals (CIs) were calculated for case-control and cohort studies and prevalence rate for cross sectional.
  
  
  RESULTS
  33 studies were suitable for the meta-analysis. The summary OR for case control studies (ever versus never) was 1.40 (95% CI, 1.29 to 1.52) and 1.42 (1.26-1.60) for current vs. no-smokers.
  
  
  CONCLUSIONS
  Smoking is associated with MS risk. Research using animal models can help to fully understand the mechanisms behind the association.
authors.affiliation: CAPHRI School of Public Health and Primary Care, Maastricht University, Maastricht, the Netherlands - Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Backhaus
authors.affiliation: Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Mannocci
authors.affiliation: CAPHRI School of Public Health and Primary Care, Maastricht University, Maastricht, the Netherlands.
authors.forename: P H H M
authors.initials: PH
authors.lastname: Lemmens
authors.affiliation: Department of Public Health and Infectious Diseases, Sapienza University of Rome, Rome, Italy.
authors.forename: G
authors.initials: G
authors.lastname: La Torre
mesh_terms: D006801:Humans; D009103:Multiple Sclerosis / Q000453:epidemiology*; D064887:Observational Studies as Topic; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*
keywords: Meta-analysis; Multiple sclerosis; Observational studies; Risk factor; Smoking