title: Smoking is a major preventable risk factor for multiple sclerosis.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  From a public health perspective, the impact of smoking and passive smoking on MS risk is considerable. Preventive measures in order to reduce tobacco smoke exposure are, therefore, essential. In particular, individuals with a history of MS in the family should be informed regarding the impact of smoking on the risk of MS, and the importance of preventing their children from being exposed to passive smoke.
authors.affiliation: Institute of Environmental Medicine, Karolinska Institute, Sweden anna.hedstrom@ki.se.
authors.forename: A K
authors.initials: AK
authors.lastname: Hedström
authors.affiliation: Neuroimmunology Unit, Department of clinical neuroscience and Center for Molecular Medicine, Karolinska Institute at Karolinska University Hospital, Sweden.
authors.forename: T
authors.initials: T
authors.lastname: Olsson
authors.affiliation: Institute of Environmental Medicine, Karolinska Institute, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Alfredsson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D015789:HLA-A2 Antigen / Q000235:genetics / Q000276:immunology; D059811:HLA-DRB1 Chains / Q000235:genetics / Q000276:immunology; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics / Q000517:prevention & control*; D016017:Odds Ratio; D065840:Protective Factors; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D040242:Risk Reduction Behavior; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology; D000074606:Smoking Prevention / Q000379:methods*; D013548:Sweden / Q000453:epidemiology; D014028:Tobacco Smoke Pollution / Q000009:adverse effects* / Q000517:prevention & control*; D055815:Young Adult
chemical_list: C524866:HLA-A*02 antigen; D015789:HLA-A2 Antigen; D059811:HLA-DRB1 Chains; C507799:HLA-DRB1*15 antigen; D014028:Tobacco Smoke Pollution
keywords: Multiple sclerosis; epidemiology; passive smoking; smoking