title: Mortality related to actigraphic long and short sleep.
abstract: BACKGROUND
  The folk belief that we should sleep 8 h seems to be incorrect. Numerous studies have shown that self-reported sleep longer than 7.5 h or shorter than 6.5 h predicts increased mortality risk. This study examined if prospectively-determined objective sleep duration, as estimated by wrist actigraphy, was associated with mortality risks.
  
  
  METHODS
  From 1995-1999, women averaging 67.6 years of age provided one-week actigraphic recordings. Survival could be estimated from follow-up continuing until 2009 for 444 of the women, with an average of 10.5 years before censoring. Multivariate age-stratified Cox regression models were controlled for history of hypertension, diabetes, myocardial infarction, cancer, and major depression.
  
  
  RESULTS
  Adjusted survival functions estimated 61% survival (54-69%, 95% C.I.) for those with sleep less than 300 min and 78% survival (73-85%, 95% C.I.) for those with actigraphic sleep longer than 390 min, as compared with survival of 90% (85-94%, 95% C.I.) for those with sleep of 300-390 min. Time-in-bed, sleep efficiency and the timing of melatonin metabolite excretion were also significant mortality risk factors.
  
  
  CONCLUSIONS
  This study confirms a U-shaped relationship between survival and actigraphically measured sleep durations, with the optimal objective sleep duration being shorter than the self-report optimums. People who sleep five or six hours may be reassured. Further studies are needed to identify any modifiable factors for this mortality and possible approaches to prevention.
authors.affiliation: Department of Psychiatry, University of California, San Diego, La Jolla, CA 92037, USA. DKripke@UCSD.edu
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Kripke
authors.forename: Robert D
authors.initials: RD
authors.lastname: Langer
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Elliott
authors.forename: Melville R
authors.initials: MR
authors.lastname: Klauber
authors.forename: Katharine M
authors.initials: KM
authors.lastname: Rex
mesh_terms: D056044:Actigraphy; D000368:Aged; D005260:Female; D006801:Humans; D009026:Mortality; D015999:Multivariate Analysis; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012890:Sleep / Q000502:physiology; D013997:Time Factors