title: The association between chronotype and sleep problems in preschool children.
abstract: Adolescents and adults who are evening-types exhibit shorter sleep duration and more sleep problems than individuals with an earlier chronotype. We hypothesized that already at a preschool age, evening-types would exhibit more sleep problems relative to children who are morning or intermediate chronotypes. The aim of this study was to examine the association between chronotype and sleep problems among preschool children.
  
  
  
  We studied a subset of typically-developing 4.5-year-olds taking part in the Growing Up in Singapore Towards healthy Outcomes birth cohort study (n = 244). The Children's Chronotype Questionnaire (CCTQ) was used to categorize children into morning-, intermediate-, and evening-types. Sleep problems were measured using the Children's Sleep Habits Questionnaire (CSHQ), with higher scores corresponding to greater sleep problems. The relation between chronotype, sleep-wake timing, and nocturnal sleep time was also evaluated in a subsample of 117 children using actigraphy recordings with parent-reported sleep diaries.
  
  
  
  After controlling for potential confounders (maternal education, child's sex, birth order, and ethnicity), a significant main effect of chronotype on sleep problems was observed, in which evening-types exhibited greater CSHQ scores compared to morning- and intermediate-types (all p < 0.001). Actigraphy data in the subsample confirmed that evening-types had later bedtimes (p < 0.001) and get-up times (p = 0.02) during weekdays and weekends, but shorter nocturnal sleep time (p = 0.034) only during weekdays, compared to children who had earlier chronotypes.
  
  
  
  In preschool children, sleep problems were greater in evening-types compared to morning- and intermediate-types, suggesting that chronotype could be a contributing factor to sleep disturbances in early childhood.
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore.
authors.forename: Nur K
authors.initials: NK
authors.lastname: Jafar
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore.
authors.forename: Elaine K H
authors.initials: EK
authors.lastname: Tham
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore.
authors.forename: Derric Z H
authors.initials: DZ
authors.lastname: Eng
authors.affiliation: Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Daniel Y T
authors.initials: DY
authors.lastname: Goh
authors.affiliation: Department of Paediatrics, KK Women's and Children's Hospital, Singapore.
authors.forename: Oon-Hoe
authors.initials: OH
authors.lastname: Teoh
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore; Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Yung S
authors.initials: YS
authors.lastname: Lee
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore; Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Lynette Pei-Chi
authors.initials: LP
authors.lastname: Shek
authors.affiliation: Department of Paediatrics, KK Women's and Children's Hospital, Singapore.
authors.forename: Fabian
authors.initials: F
authors.lastname: Yap
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore; Department of Obstetrics & Gynaecology, Yong Loo Lin School of Medicine, National University of Singapore, National University Health System, Singapore.
authors.forename: Yap Seng
authors.initials: YS
authors.lastname: Chong
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Meaney
authors.affiliation: Program in Neuroscience and Behavioral Disorders, Duke-NUS Medical School, Singapore.
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Gooley
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research (A*STAR), Singapore. Electronic address: birit_broekman@sics.a-star.edu.sg.
authors.forename: Birit F P
authors.initials: BF
authors.lastname: Broekman
mesh_terms: D002675:Child, Preschool; D002940:Circadian Rhythm; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D012893:Sleep Wake Disorders
keywords: Actigraphy; Chronotype; Preschool children; Sleep habits; Sleep problems