Impacts of environmental tobacco smoke on the onset and progression of multiple sclerosis: a systematic review

Abstract

Background Unlike cigarette smoking, environmental tobacco smoke (ETS) has not been as well described as an environmental risk for Multiple sclerosis (MS) nor as a risk factor for disease progression. Objective We systematically reviewed the association between ETS and the risk of onset and/or progression of MS. Methods We systematically screened MedLine/PubMed, Science Direct, LILACs, and SciELO searching for publications between January 1st, 2010, and July 5, 2021, with the following keywords: “multiple sclerosis and smoking”; “multiple sclerosis and passive smoking”; “multiple sclerosis and secondhand smoking”. Results Fifteen articles were included in this review, which consisted of systematic reviews with meta-analysis (N = 2), systematic reviews (N = 2), and observational studies (N = 11). Both meta-analyses reported an impact of ETS on MS onset among secondhand smokers. One of the systematic reviews selected two observational studies showing the association between ETS and MS development, and one study that did not find a significant association between ETS and the risk of MS development. The other systematic review identified selected eight articles showing a relationship between ETS and MS. Seven observational studies reported higher odds of MS onset when associated with ETS. Four observational studies did not show a relationship between ETS and MS onset or progression. Conclusion Most articles showed a positive association between ETS exposure and the risk of developing MS. On the other hand, an association between ETS and a higher risk for MS progression could not be established.