title: Sleep duration and health among older adults: associations vary by how sleep is measured.
abstract: BACKGROUND
  Cohort studies have found that short and long sleep are both associated with worse outcomes, compared with intermediate sleep times. While demonstrated biological mechanisms could explain health effects for short sleep, long-sleep risk is puzzling. Most studies reporting the U shape use a single question about sleep duration, a measurement method that does not correlate highly with objectively measured sleep. We hypothesised that the U shape, especially the poor outcomes for long sleepers, may be an artefact of how sleep is measured.
  
  
  METHODS
  We examined the cross-sectional prevalence of fair/poor health by sleep hour categories (≤ 6, ≤ 7, ≤ 8, ≤ 9, > 9 h) in a national US sample of adults aged 62-90 that included several types of sleep measures (n = 727). Survey measures were: a single question; usual bedtimes and waking times; and a 3-day sleep log. Actigraphy measures were the sleep interval and total sleep time. Fair/poor health was regressed on sleep hour categories adjusted for demographics, with tests for both linear trend and U shape.
  
  
  RESULTS
  Adjusted OR of fair/poor health across sleep hour categories from the single question were 4.6, 2.2, referent (8 h), 1.8 and 6.9. There was high prevalence of fair/poor health for ≤ 6 h for all sleep measures, but the long-sleep effect was absent for sleep logs and actigraphy measures.
  
  
  CONCLUSIONS
  Associations between long sleep and poor health may be specific to studies measuring sleep with survey questions. As cohorts with actigraphy mature, our understanding of how sleep affects health may change.
authors.affiliation: Department of Public Health Sciences, University of Chicago, Chicago, Illinois, USA.
authors.forename: Diane S
authors.initials: DS
authors.lastname: Lauderdale
authors.affiliation: Department of Health Sciences, University of Missouri, Columbia, Missouri, USA.
authors.forename: Jen-Hao
authors.initials: JH
authors.lastname: Chen
authors.affiliation: Department of General Medical Disciplines, Stanford University School of Medicine, Palo Alto, California, USA.
authors.forename: Lianne M
authors.initials: LM
authors.lastname: Kurina
authors.affiliation: Department of Sociology, University of Chicago, Chicago, Illinois, USA.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Waite
authors.affiliation: Department of Public Health Sciences, University of Chicago, Chicago, Illinois, USA.
authors.forename: Ronald A
authors.initials: RA
authors.lastname: Thisted
mesh_terms: D056044:Actigraphy; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003430:Cross-Sectional Studies; D005260:Female; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D012307:Risk Factors; D012890:Sleep; D013997:Time Factors; D014481:United States
keywords: MEASUREMENT; SELF-RATED HEALTH; SLEEP