Smoking is a major preventable risk factor for multiple sclerosis

Background:Both smoking and exposure to passive smoking have repeatedly been associated with increased multiple sclerosis (MS) risk, but have never before been studied together. We assessed the public health impact of these factors.Methods:In a Swedish population-based case-control study (2455 cases, 5336 controls), we calculated odds ratios of developing MS associated with different categories of tobacco smoke exposure, together with 95% confidence intervals, by using logistic regression. The excess proportion of cases attributable to smoking and passive smoking was calculated as a percentage.Results:Both smoking and exposure to passive smoking contribute to MS risk in a dose-dependent manner. At the population level, 20.4% of all cases were attributable to smoke exposure. Among subjects carrying the genetic risk factor HLA-DRB1*15 but lacking HLA-A*02, 41% of the MS cases were attributable to smoking.Conclusions:From a public health perspective, the impact of smoking and passive smoking on MS risk is co...