title: Age-related reduction in daytime sleep propensity and nocturnal slow wave sleep.
abstract: OBJECTIVE
  To investigate whether age-related and experimental reductions in SWS and sleep continuity are associated with increased daytime sleep propensity.
  
  
  METHODS
  Assessment of daytime sleep propensity under baseline conditions and following experimental disruption of SWS. Healthy young (20-30 y, n = 44), middle-aged (40-55 y, n = 35) and older (66-83 y, n = 31) men and women, completed a 2-way parallel group study. After an 8-h baseline sleep episode, subjects were randomized to 2 nights with selective SWS disruption by acoustic stimuli, or without disruption, followed by 1 recovery night. Objective and subjective sleep propensity were assessed using the Multiple Sleep Latency Test (MSLT) and the Karolinska Sleepiness Scale (KSS).
  
  
  RESULTS
  During baseline sleep, SWS decreased (P < 0.001) and the number of awakenings increased (P < 0.001) across the 3 age groups. During the baseline day, MSLT values increased across the three age groups (P < 0.0001) with mean values of 8.7 min (SD: 4.5), 11.7 (5.1) and 14.2 (4.1) in the young, middle-aged, and older adults, respectively. KSS values were 3.7 (1.0), 3.2 (0.9), and 3.4 (0.6) (age-group: P = 0.031). Two nights of SWS disruption led to a reduction in MSLT and increase in KSS in all 3 age groups (SWS disruption vs. control: P < 0.05 in all cases).
  
  
  CONCLUSIONS
  Healthy aging is associated with a reduction in daytime sleep propensity, sleep continuity, and SWS. In contrast, experimental disruption of SWS leads to an increase in daytime sleep propensity. The age-related decline in SWS and reduction in daytime sleep propensity may reflect a lessening in homeostatic sleep requirement. Healthy older adults without sleep disorders can expect to be less sleepy during the daytime than young adults.
authors.affiliation: Surrey Sleep Research Centre, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK. d.j.dijk@surrey.ac.uk
authors.forename: Derk-Jan
authors.initials: DJ
authors.lastname: Dijk
authors.forename: John A
authors.initials: JA
authors.lastname: Groeger
authors.forename: Neil
authors.initials: N
authors.lastname: Stanley
authors.forename: Stephen
authors.initials: S
authors.lastname: Deacon
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002540:Cerebral Cortex / Q000503:physiopathology; D002940:Circadian Rhythm / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D017286:Polysomnography; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult