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. Materials 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. Conclusion. Smoking is associated with MS risk. Research using animal models can help to fully understand the mechanisms behind the association.