Brief CommunicationThe association between chronotype and sleep problems in preschool children
Introduction
Sleep problems that start in early childhood often persist across development [1], [2], [3], and have been associated with negative behavioral, cognitive, and emotional health consequences [2], [4]. It is known that sleep problems are often caused by irregular sleep habits [5], [6], [7] and poorly enforced bedtime routines [5], [6] such as irregular sleep–wake schedules. In adolescents and adults, chronotype is thought to be a stable trait that contributes to individual differences in sleep–wake timing [8], [9]. A person's chronotype reflects his or her preferred timing of sleep and waking activities [7], which is linked to psychosocial behavior and specific properties of the circadian clock [8], [9], [10].
In children, chronotype is often divided into three different categories: “morning,” “intermediate,” and “evening” chronotypes. Evening-types exhibit later habitual bedtimes and sleep onset times independent of environmental factors (such as parenting), in comparison to morning-types, as evidenced by actigraphy [7], [11]. However, little is known about whether individual differences in chronotype contribute to sleep problems in preschool children who have yet to be exposed to the formal education system and fixed school start times. In the present study, we therefore aimed to assess whether typically developing Singaporean preschoolers who are evening-types exhibit greater sleep problems than those who are morning- or intermediate-types.
Section snippets
Study design and sample
The present study was carried out as part of the Growing Up in Singapore Towards healthy Outcomes (GUSTO) birth cohort study, which recruited 1247 pregnant women aged ≥18 years during the first trimester of pregnancy. Socio-demographic information was collected upon enrollment. Women were recruited from two major public hospitals in Singapore: KK Women's and Children's Hospital, and the National University Hospital. All births occurred between 30 November 2009 and 1 May 2011. Further details
Sleep–wake timing
The actigraphy-estimated average (standard deviation [SD] in hours) bedtime and get-up time based on mother-reported child sleep diaries were respectively 23:01 (0:59) and 08:02 (01:00). Average bedtimes for morning-, intermediate-, and evening-types during weekdays were respectively 21:55 (01:00), 22:44 (0:48), 23:02 (0:58), and during weekends were respectively 22:21 (01:23), 23:12 (01:03), and 23:34 (01:15). Average wake for morning-, intermediate-, and evening-types during weekdays were
Discussion
We found that Singaporean preschoolers who were evening-types had greater parent-reported sleep problems in comparison to morning- and intermediate-types. Additionally, in a subsample, sleep diaries and actigraphy were used to confirm that children who were categorized as evening chronotypes on the CCTQ indeed had later bedtimes and get-up times during weekdays and weekends, and shorter nocturnal sleep time during weekdays compared to morning- and intermediate-types. Our results are consistent
Acknowledgments
We thank the GUSTO study group and all of the participants in this study. We also thank Mr. Desmond Neo for his assistance in coding of the actigraphy data and questionnaires. This research was supported by the Singapore National Research Foundation (NMRC/TCR/004-NUS/ 2008; NMRC/TCR/012-NUHS/2014) under its Translational and Clinical Research (TCR) Flagship Programme and administered by the Singapore Ministry of Health's National Medical Research Council (NMRC), Singapore-NMRC/TCR/004-NUS/2008;
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