title: Prevalence and correlates of delayed sleep phase in high school students.
abstract: OBJECTIVE
  To investigate prevalence and correlates of delayed sleep phase, characterized by problems falling asleep in the evening and rising at adequate times in the morning, in a large sample of Norwegian high school students.
  
  
  METHODS
  A randomized sample of 1285 high school students (aged 16-19 years) participated in an internet based study answering questions about sleep habits, height, weight, smoking, alcohol use, school grades, and anxiety and depression symptoms. Delayed sleep phase was operationalized as difficulties falling asleep before 2 a.m. at least three nights per week together with much or very much difficulty waking up in the morning.
  
  
  RESULTS
  The results show a prevalence of delayed sleep phase of 8.4%. In all, 68% of these students (5.7% of the total sample) also reported problems advancing their sleep period as well as one daytime consequence (oversleeping at least two days a week or experiencing much/very much sleepiness at school). Delayed sleep phase was associated with lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.
  
  
  CONCLUSIONS
  Delayed sleep phase appears to be common amongst Norwegian adolescents and is associated with negative outcomes such as lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.
authors.affiliation: Department of Public Health and Primary Health Care, University of Bergen, Postboks 7804, 5020 Bergen, Norway. ingvild.saxvig@isf.uib.no
authors.forename: Ingvild W
authors.initials: IW
authors.lastname: Saxvig
authors.forename: Ståle
authors.initials: S
authors.lastname: Pallesen
authors.forename: Ane
authors.initials: A
authors.lastname: Wilhelmsen-Langeland
authors.forename: Helge
authors.initials: H
authors.lastname: Molde
authors.forename: Bjørn
authors.initials: B
authors.lastname: Bjorvatn
mesh_terms: D000293:Adolescent; D000428:Alcohol Drinking / Q000453:epidemiology; D001007:Anxiety / Q000453:epidemiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003863:Depression / Q000453:epidemiology*; D004522:Educational Status; D005260:Female; D006801:Humans; D008297:Male; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D020178:Sleep Disorders, Circadian Rhythm / Q000453:epidemiology* / Q000503:physiopathology* / Q000523:psychology; D012894:Sleep Stages / Q000502:physiology; D012907:Smoking / Q000453:epidemiology; D013334:Students / Q000706:statistics & numerical data; D011795:Surveys and Questionnaires; D055815:Young Adult