title: Sleep disturbances as predictors of hospitalization for back disorders-a 28-year follow-up of industrial employees.
abstract: METHODS
  A prospective cohort study.
  
  
  OBJECTIVE
  To study the relationship of sleep disturbances with severe back disorders leading to hospitalization.
  
  
  BACKGROUND
  Sleep disturbances are associated with persistent pain syndromes, but little is known about their relationship with back disorders.
  
  
  METHODS
  The first hospital admission for back disorders from 1973 to 2000 was studied in a cohort of metal industry workers (n = 902). The occurrence of sleep disturbances at baseline was categorized as: none; 1 type (either difficulties in falling asleep/waking up at night or nightmares); or both types. Cox proportional hazards regression was used to estimate the time between the assessment of risk factors and first hospital admission for back disorders.
  
  
  RESULTS
  Those individuals who had 1 type of sleep disturbance had a 2.1-fold (95% confidence interval 1.1-3.8) risk of back-related hospitalization, and those with both types of disturbance a 2.4-fold (1.2-4.6) risk, compared with those with no sleep disturbances. The hazard ratios were 2.1; 1.0-4.6 and 2.9; 1.2-7.1, respectively, when patients with chronic back disease or recurrent back symptoms at baseline were excluded from the analyses.
  
  
  CONCLUSIONS
  These findings suggest that sleep disturbances are predictive of hospitalization for back disorders. The mechanism underlying this association warrants further study.
authors.affiliation: Finnish Institute of Occupational Health, Helsinki, Finland. Leena.Kaila-Kangas@ttl.fi
authors.forename: Leena
authors.initials: L
authors.lastname: Kaila-Kangas
authors.forename: Mika
authors.initials: M
authors.lastname: Kivimäki
authors.forename: Mikko
authors.initials: M
authors.lastname: Härmä
authors.forename: Hilkka
authors.initials: H
authors.lastname: Riihimäki
authors.forename: Ritva
authors.initials: R
authors.lastname: Luukkonen
authors.forename: Juhani
authors.initials: J
authors.lastname: Kirjonen
authors.forename: Päivi
authors.initials: P
authors.lastname: Leino-Arjas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001416:Back Pain / Q000150:complications* / Q000453:epidemiology / Q000523:psychology; D004651:Employment; D005260:Female; D005387:Finland / Q000453:epidemiology; D005544:Forecasting; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016272:Occupational Health / Q000706:statistics & numerical data*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012893:Sleep Wake Disorders / Q000453:epidemiology / Q000209:etiology* / Q000523:psychology