title: Nocturnal sleep duration and cognitive impairment in a population-based study of older adults.
abstract: OBJECTIVE
  We aimed to investigate the association between nocturnal sleep duration, changes in nocturnal sleep duration and cognitive impairment in older adults.
  
  
  METHODS
  4010 participants of a population-based cohort study provided information on nocturnal sleep duration at baseline (1991-1995) and at follow-up (2002/2003). 792 follow-up participants aged 70+ by 2006 participated in telephone-based cognitive assessments. Several cognitive tests were used including the telephone interview for cognitive status (TICS). Cognitive impairment was defined as <31 points on the TICS (13.0%) and as below this percentile on the other tests. Based on individual tests, a verbal memory score and a total score were constructed. Multivariable prevalence ratios (PRs) of cognitive impairment and 95% confidence intervals (95%CIs) were computed using Poisson regression. Analyses were restricted to those free of depression in 2002/2003 (n = 695).
  
  
  RESULTS
  Sleeping <or=6 or 8 h per night (versus 7 h) were unrelated to cognitive impairment. Sleeping >or=9 h was positively, although imprecisely, associated with impairment of verbal memory (PR = 1.7, 95%CI = 1.0, 3.0), and less pronounced with the other cognitive measures. An increase in sleep duration from 7-8 h in 1992-1995 to >or=9 h 8.5 years later (versus sleeping 7-8 h at both time points) was associated with an increased prevalence of cognitive impairment according to the TICS (PR = 2.1, 95% = 1.0, 4.5) and the verbal memory score (PR = 2.0, 95%CI = 1.0, 3.8).
  
  
  CONCLUSIONS
  Increases in sleep duration are associated with cognitive impairment. A biological explanation for this association is currently lacking. Increases in sleep duration could be a marker of cognitive deficits.
authors: Institute of Psychology, Heidelberg University, Germany. adrian.loerbroks@medma.uni-heidelberg.de
authors: Adrian
authors: A
authors: Loerbroks
authors: Desiree
authors: D
authors: Debling
authors: Manfred
authors: M
authors: Amelang
authors: Til
authors: T
authors: Stürmer
mesh_terms: D000368:Aged; D003072:Cognition Disorders / Q000453:epidemiology*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D012890:Sleep / Q000502:physiology*; D011795:Surveys and Questionnaires; D013997:Time Factors