title: Association between delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan.
abstract: BACKGROUND
  Although delayed sleep timing causes many socio-psycho-biological problems such as sleep loss, excessive daytime sleepiness, obesity, and impaired daytime neurocognitive performance in adults, there are insufficient data showing the clinical significance of a 'night owl lifestyle' in early life. This study examined the association between habitual delayed bedtime and sleep-related problems among community-dwelling 2-year-old children in Japan.
  
  
  METHODS
  Parents/caregivers of 708 community-dwelling 2-year-old children in Nishitokyo City, Tokyo, participated in the study. The participants answered a questionnaire to evaluate their child's sleep habits and sleep-related problems for the past 1 month.
  
  
  RESULTS
  Of the 425 children for whom complete data were collected, 90 (21.2%) went to bed at 22:00 or later. Children with delayed bedtime showed significantly more irregular bedtime, delayed wake time, shorter total sleep time, and difficulty in initiating and terminating sleep. Although this relationship indicated the presence of sleep debt in children with delayed bedtime, sleep onset latency did not differ between children with earlier bedtime and those with delayed bedtime. Rather, delayed bedtime was significantly associated with bedtime resistance and problems in the morning even when adjusting for nighttime and daytime sleep time.
  
  
  CONCLUSIONS
  Even in 2-year-old children, delayed bedtime was associated with various sleep-related problems. The causal factors may include diminished homeostatic sleep drive due to prolonged daytime nap as well as diurnal preference (morning or night type) regulated by the biological clock.
authors: Shingo
authors: S
authors: Kitamura
authors: Minori
authors: M
authors: Enomoto
authors: Yuichi
authors: Y
authors: Kamei
authors: Naoko
authors: N
authors: Inada
authors: Aiko
authors: A
authors: Moriwaki
authors: Yoko
authors: Y
authors: Kamio
authors: Kazuo
authors: K
authors: Mishima
mesh_terms: D000704:Analysis of Variance; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D020920:Dyssomnias / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007223:Infant; D007564:Japan / Q000453:epidemiology; D008297:Male; D015995:Prevalence; D012111:Residence Characteristics; D012890:Sleep; D011795:Surveys and Questionnaires