Smoking As a Risk Factor for Developing Multiple Sclerosis: A Meta-Analysis of Observational Studies.

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.MATERIAL AND 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.