title: Does insomnia predict sick leave? The Hordaland Health Study.
abstract: OBJECTIVE
  The purpose of this study is to prospectively examine the independent contribution of symptoms of insomnia on sick leave.
  
  
  METHODS
  We used a historical cohort design with 4 years of follow-up. Information on sick leave was obtained from Norwegian official registry data and merged with health information from the Hordaland Health Study in Western Norway, 1997 to 1999. Six thousand eight hundred ninety-two participants aged 40 to 45 years were assessed for self-reported symptoms of insomnia, sociodemographic factors, lifestyle behaviors, body mass index, symptoms of sleep apnea, anxiety, depression, as well as a range of somatic diagnoses, somatic symptoms, and pain. The outcome was the total number of sick days during a 4-year follow-up period, as registered in the official registries by the National Insurance Administration.
  
  
  RESULTS
  Overall, insomnia was found to be a significant predictor of sick leave [odds ratio (OR)=2.20; 95% confidence interval (CI), 1.77-2.74], and the effect remained significant when adjusting for possible confounders (OR=1.51; 95% CI, 1.19-1.94). The effect increased with longer durations of sickness leave.
  
  
  CONCLUSIONS
  This is the first study to demonstrate that insomnia is an independent risk factor for long-term sick leave.
authors.affiliation: Department of Clinical Psychology, University of Bergen, Bergen, Norway. borge.sivertsen@psykp.uib.no
authors.forename: Børge
authors.initials: B
authors.lastname: Sivertsen
authors.forename: Simon
authors.initials: S
authors.lastname: Overland
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bjorvatn
authors.forename: John Gunnar
authors.initials: JG
authors.lastname: Maeland
authors.forename: Arnstein
authors.initials: A
authors.lastname: Mykletun
mesh_terms: D000041:Absenteeism; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D016017:Odds Ratio; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors; D018582:Sick Leave / Q000706:statistics & numerical data*; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology* / Q000523:psychology; D013223:Statistics as Topic; D011795:Surveys and Questionnaires