title: Shift work at young age is associated with increased risk of multiple sclerosis in a Danish population.
abstract: BACKGROUND
  Epidemiological studies suggest an important role for environmental factors in developing multiple sclerosis (MS). Furthermore several studies have indicated that the effect of environmental factors may be especially pronounced in adolescents. Recently only one study investigated and found that shift work at young age is associated with an increased risk of developing MS. In this study we focused on the effect of shift work in the vulnerable period between 15-19 years.
  
  
  OBJECTIVE
  The aim of this study was to investigate the association between shift work at young age and the risk of developing MS.
  
  
  METHODS
  We performed a large case-control study including 1723 patients diagnosed with MS and 4067 controls. MS patients were recruited from the Danish Multiple Sclerosis Biobank and controls from The Danish Blood Donor Study. Information on working patterns and lifestyle factors was obtained using a comprehensive lifestyle-environmental factor questionnaire with participants enrolled between 2009 and 2014. Logistic regression models were used to investigate the association between shift work at age 15-19 years and the subsequent risk of MS and were controlled for effects due to established MS risk factors.
  
  
  RESULTS
  We found a statistically significant association when total numbers of night shifts were compared with non-shift workers. For every additional 100 night shifts the odds ratio (OR) for MS was 1.20 (95% confidence interval (CI), 1.08-1.34, p=0.001). Increasing intensity of shift work also increased MS risk. For every additional night per month the OR was 1.04 (95% CI, 1.01-1.06, p=0.002). Duration of shift work in years was not associated with risk of MS.
  
  
  CONCLUSIONS
  This study supports a statistically significant association between shift work at age 15-19 years and MS risk.
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark. Electronic address: stefan.gustavsen@hotmail.com.
authors.forename: S
authors.initials: S
authors.lastname: Gustavsen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark.
authors.forename: H B
authors.initials: HB
authors.lastname: Søndergaard
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark.
authors.forename: D B
authors.initials: DB
authors.lastname: Oturai
authors.affiliation: The National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Laursen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark.
authors.forename: J H
authors.initials: JH
authors.lastname: Laursen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark; The Danish Multiple Sclerosis Registry, Department of Neurology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Magyari
authors.affiliation: Department of Clinical Immunology, Center of Clinical Investigation, Copenhagen University Hospital, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Ullum
authors.affiliation: Department of Clinical Immunology, Center of Clinical Investigation, Copenhagen University Hospital, Denmark.
authors.forename: M H
authors.initials: MH
authors.lastname: Larsen
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark.
authors.forename: F
authors.initials: F
authors.lastname: Sellebjerg
authors.affiliation: Danish Multiple Sclerosis Center, Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Denmark.
authors.forename: A B
authors.initials: AB
authors.lastname: Oturai
mesh_terms: D000328:Adult; D000367:Age Factors; D016022:Case-Control Studies; D003718:Denmark / Q000453:epidemiology; D004651:Employment; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D009103:Multiple Sclerosis / Q000453:epidemiology*; D016017:Odds Ratio; D012307:Risk Factors
keywords: MS; Multiple sclerosis; Night work; Shift work