Smoking and Its Relation with Amyotrophic Lateral Sclerosis: A Systematic Review and Meta-Analysis

Epidemiologic investigations have provided unpredictable consequences on the relation of cigarette smoking with the prevalence of amyotrophic lateral sclerosis (ALS). In this systematic review and meta-analysis study, we evaluated this association. A systematic search was done using Embase, PubMed, Google Scholar and Science Direct for publications from 2012 to 2017. All retrospective, or prospectiveobservational studies and cross-sectional studies, of amyotrophic lateral sclerosis in relation to smoking exposure were included. Data extraction was done using a standardized data extraction tool in Microsoft Office Excel 2013. All the analyses were done usingStata V.15.0. . 15 investigations reported the relation between ALS and smoking risk in 3 cohort studies and 12 case control studies. The pooled RR (95% CI) of ALS was 1.46 (0.80 to 1.78) for present vs. nonsmokers and 1.52 (0.59 to 1.63) for ever vs. nonsmokers. The estimated RR of ALS for ever vs. nonsmokers was 0.69 (0.53 to 1.19) in men and 1.36 (1.20 to 2.15) in women. Conclusion: According to the results, smoking increases the risk of ALS especially in women.