title: Sleep duration, schedule and quality among urban Chinese children and adolescents: associations with routine after-school activities.
abstract: BACKGROUND
  With rapid urbanization accompanied by lifestyle changes, children and adolescents living in metropolitan areas are faced with many time use choices that compete with sleep. This study reports on the sleep hygiene of urban Chinese school students, and investigates the relationship between habitual after-school activities and sleep duration, schedule and quality on a regular school day.
  
  
  METHODS
  Cross-sectional, school-based survey of school children (Grades 4-8) living in Shanghai, China, conducted in 2011. Self-reported data were collected on students' sleep duration and timing, sleep quality, habitual after-school activities (i.e. homework, leisure-time physical activity, recreational screen time and school commuting time), and potential correlates.
  
  
  RESULTS
  Mean sleep duration of this sample (mean age: 11.5-years; 48.6% girls) was 9 hours. Nearly 30% of students reported daytime tiredness. On school nights, girls slept less (p<0.001) and went to bed later (p<0.001), a sex difference that was more pronounced in older students. Age by sex interactions were observed for both sleep duration (p=0.005) and bedtime (p=0.002). Prolonged time spent on homework and mobile phone playing was related to shorter sleep duration and later bedtime. Adjusting for all other factors, with each additional hour of mobile phone playing, the odds of daytime tiredness and having difficulty maintaining sleep increased by 30% and 27% among secondary students, respectively.
  
  
  CONCLUSIONS
  There are sex differences in sleep duration, schedule and quality. Habitual activities had small but significant associations with sleep hygiene outcomes especially among secondary school students. Intervention strategies such as limiting children's use of electronic screen devices after school are implicated.
authors.affiliation: School of Public Health and Key Laboratory of Public Health Safety, Fudan University, Shanghai, China; Prevention Research Collaboration, School of Public Health, University of Sydney, Sydney, Australia.
authors.forename: Xiaoxiao
authors.initials: X
authors.lastname: Jiang
authors.affiliation: Prevention Research Collaboration, School of Public Health, University of Sydney, Sydney, Australia.
authors.forename: Louise L
authors.initials: LL
authors.lastname: Hardy
authors.affiliation: Prevention Research Collaboration, School of Public Health, University of Sydney, Sydney, Australia.
authors.forename: Louise A
authors.initials: LA
authors.lastname: Baur
authors.affiliation: Prevention Research Collaboration, School of Public Health, University of Sydney, Sydney, Australia.
authors.forename: Ding
authors.initials: D
authors.lastname: Ding
authors.affiliation: School of Public Health and Key Laboratory of Public Health Safety, Fudan University, Shanghai, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Wang
authors.affiliation: School of Public Health and Key Laboratory of Public Health Safety, Fudan University, Shanghai, China.
authors.forename: Huijing
authors.initials: H
authors.lastname: Shi
mesh_terms: D000293:Adolescent; D002648:Child; D002681:China; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D011998:Recreation; D012727:Sex Characteristics; D012890:Sleep; D014505:Urban Population; D014937:Work