Tobacco smoking, but not Swedish snuff use, increases the risk of multiple sclerosis

OBJECTIVE: The aim of this study was to estimate the influence of tobacco smoking and Swedish snuff use on the risk of developing multiple sclerosis (MS). METHODS: A population-based case-control study was performed in Sweden, using incident cases of MS (902 cases and 1,855 controls). A case was defined as a subject from the study base who had received a diagnosis of MS, and controls were randomly selected from the study base. The incidence of MS among smokers was compared with that of never-smokers. We also investigated whether the use of Swedish snuff had an impact on the risk of developing MS. RESULTS: Smokers of both sexes had an increased risk of developing MS (odds ratio OR 1.4, 95% confidence interval CI 1.2-1.7 for women, and OR 1.8, 95% CI 1.3-2.5 for men). The increased risk was apparent even among subjects who had previously smoked moderately (< or =5 pack-years) prior to index, and the risk increased with increasing cumulative dose (p < 0.0001). The increased risk for MS associated with smoking remained up to 5 years after stopping smoking. In contrast, taking Swedish snuff for more than 15 years decreased the risk of developing MS (OR 0.3, 95% CI 0.1-0.8). CONCLUSIONS: Smokers of both sexes run an increased risk of developing multiple sclerosis (MS), and the risk increases with cumulative dose of smoking. However, the use of Swedish snuff is not associated with elevated risk for MS, which may indicate that nicotine is not the substance responsible for the increased risk of developing MS among smokers.