title: The bidirectional association between depression and insomnia: the HUNT study.
abstract: OBJECTIVE
  Depression and insomnia are closely linked, yet our understanding of their prospective relationships remains limited. The aim of the current study was to investigate the directionality of association between depression and insomnia.
  
  
  METHODS
  Data were collected from a prospective population-based study comprising the most recent waves of the Nord-Trøndelag Health Study (HUNT) (the HUNT2 in 1995-1997 and the HUNT3 in 2006-2008). A total of 24,715 persons provided valid responses on the relevant questionnaires from both surveys. Study outcomes were onset of depression or insomnia at HUNT3 in persons not reporting the other disorder in HUNT2.
  
  
  RESULTS
  Both insomnia and depression significantly predicted the onset of the other disorder. Participants who did not have depression in HUNT2 but who had insomnia in both HUNT2 and HUNT3 had an odds ratio (OR) of 6.2 of developing depression at HUNT3. Participants who did not have insomnia in HUNT2 but who had depression in both HUNT2 and HUNT3 had an OR of 6.7 of developing insomnia at HUNT3. ORs were only slightly attenuated when adjusting for potential confounding factors.
  
  
  CONCLUSIONS
  The results support a bidirectional relationship between insomnia and depression. This finding stands in contrast to the previous studies, which have mainly focused on insomnia as a risk factor for the onset of depression.
authors.affiliation: Division of Mental Health, Norwegian Institute of Public Health, Christiesgt 13, 5020 Bergen, Norway. borge.sivertsen@fhi.no
authors.forename: Børge
authors.initials: B
authors.lastname: Sivertsen
authors.forename: Paula
authors.initials: P
authors.lastname: Salo
authors.forename: Arnstein
authors.initials: A
authors.lastname: Mykletun
authors.forename: Mari
authors.initials: M
authors.lastname: Hysing
authors.forename: Ståle
authors.initials: S
authors.lastname: Pallesen
authors.forename: Steinar
authors.initials: S
authors.lastname: Krokstad
authors.forename: Inger Hilde
authors.initials: IH
authors.lastname: Nordhus
authors.forename: Simon
authors.initials: S
authors.lastname: Øverland
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015897:Comorbidity; D003863:Depression / Q000453:epidemiology*; D003866:Depressive Disorder / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D016017:Odds Ratio; D011446:Prospective Studies; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology*; D011795:Surveys and Questionnaires; D013997:Time Factors