title: Insomnia as a predictor of depression: a meta-analytic evaluation of longitudinal epidemiological studies.
abstract: BACKGROUND
  In many patients with depression, symptoms of insomnia herald the onset of the disorder and may persist into remission or recovery, even after adequate treatment. Several studies have raised the question whether insomniac symptoms may constitute an independent clinical predictor of depression. This meta-analysis is aimed at evaluating quantitatively if insomnia constitutes a predictor of depression.
  
  
  METHODS
  PubMed, Medline, PsycInfo, and PsycArticles databases were searched from 1980 until 2010 to identify longitudinal epidemiological studies simultaneously investigating insomniac complaints and depressed psychopathology. Effects were summarized using the logarithms of the odds ratios for insomnia at baseline to predict depression at follow-up. Studies were pooled with both fixed- and random-effects meta-analytic models in order to evaluate the concordance. Heterogeneity test and sensitivity analysis were computed.
  
  
  RESULTS
  Twenty-one studies met inclusion criteria. Considering all studies together, heterogeneity was found. The random-effects model showed an overall odds ratio for insomnia to predict depression of 2.60 (confidence interval [CI]: 1.98-3.42). When the analysis was adjusted for outliers, the studies were not longer heterogeneous. The fixed-effects model showed an overall odds ratio of 2.10 (CI: 1.86-2.38).
  
  
  CONCLUSIONS
  The main limit is that included studies did not always consider the role of other intervening variables.
  
  
  CONCLUSIONS
  Non-depressed people with insomnia have a twofold risk to develop depression, compared to people with no sleep difficulties. Thus, early treatment programs for insomnia might reduce the risk for developing depression in the general population and be considered a helpful general preventive strategy in the area of mental health care.
authors.affiliation: Department of Psychiatry & Psychotherapy, University of Freiburg Medical Center, Hauptstrasse 5, 79104 Freiburg, Germany. chiara.baglioni@uniklinik-freiburg.de
authors.forename: Chiara
authors.initials: C
authors.lastname: Baglioni
authors.forename: Gemma
authors.initials: G
authors.lastname: Battagliese
authors.forename: Bernd
authors.initials: B
authors.lastname: Feige
authors.forename: Kai
authors.initials: K
authors.lastname: Spiegelhalder
authors.forename: Christoph
authors.initials: C
authors.lastname: Nissen
authors.forename: Ulrich
authors.initials: U
authors.lastname: Voderholzer
authors.forename: Caterina
authors.initials: C
authors.lastname: Lombardo
authors.forename: Dieter
authors.initials: D
authors.lastname: Riemann
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D002648:Child; D003863:Depression / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D003866:Depressive Disorder; D016021:Epidemiologic Studies; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D012107:Research Design; D012306:Risk; D012680:Sensitivity and Specificity; D007319:Sleep Initiation and Maintenance Disorders