title: Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies.
abstract: BACKGROUND
  Increasing evidence suggests an association between both short and long duration of habitual sleep with adverse health outcomes.
  
  
  OBJECTIVE
  To assess whether the population longitudinal evidence supports the presence of a relationship between duration of sleep and all-cause mortality, to investigate both short and long sleep duration and to obtain an estimate of the risk.
  
  
  METHODS
  We performed a systematic search of publications using MEDLINE (1966-2009), EMBASE (from 1980), the Cochrane Library, and manual searches without language restrictions. We included studies if they were prospective, had follow-up >3 years, had duration of sleep at baseline, and all-cause mortality prospectively. We extracted relative risks (RR) and 95% confidence intervals (CI) and pooled them using a random effect model. We carried out sensitivity analyses and assessed heterogeneity and publication bias.
  
  
  RESULTS
  Overall, the 16 studies analyzed provided 27 independent cohort samples. They included 1,382,999 male and female participants (followup range 4 to 25 years), and 112,566 deaths. Sleep duration was assessed by questionnaire and outcome through death certification. In the pooled analysis, short duration of sleep was associated with a greater risk of death (RR: 1.12; 95% CI 1.06 to 1.18; P < 0.01) with no evidence of publication bias (P = 0.74) but heterogeneity between studies (P = 0.02). Long duration of sleep was also associated with a greater risk of death (1.30; [1.22 to 1.38]; P < 0.0001) with no evidence of publication bias (P = 0.18) but significant heterogeneity between studies (P < 0.0001).
  
  
  CONCLUSIONS
  Both short and long duration of sleep are significant predictors of death in prospective population studies.
authors.affiliation: University of Warwick, Warwick Medical School, Clinical Sciences Research Institute, Coventry, UK. f.p.cappuccio@warwick.ac.uk
authors.forename: Francesco P
authors.initials: FP
authors.lastname: Cappuccio
authors.forename: Lanfranco
authors.initials: L
authors.lastname: D'Elia
authors.forename: Pasquale
authors.initials: P
authors.lastname: Strazzullo
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Miller
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002423:Cause of Death; D006970:Disorders of Excessive Somnolence / Q000401:mortality; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012306:Risk; D012890:Sleep; D012892:Sleep Deprivation / Q000401:mortality; D012893:Sleep Wake Disorders / Q000401:mortality*; D013997:Time Factors; D055815:Young Adult
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