Characteristics and Transition of Sleep-Wake Rhythm in Nursery School Children: The Importance of Nocturnal Sleep

Abstract

In this study, we investigated the sleep-wake rhythm of nursery school children with the aim of supporting their health and mental/physical development. We analyzed 4881 children from infancy to 6 years of age, using 2 week sleep tables recorded by their guardians. The tables contained night bedtimes, wake times, nighttime/daytime sleep duration, and the differences in these between weekdays and weekends. The total sleep decrement of children with increasing age is attributed to a decrease in daytime sleep, while nighttime sleep duration remains almost unchanged at about 10 h, which is, therefore, referred to as the nighttime basic sleep duration (NBSD). Although bedtime stabilizes at around 9:30 p.m. by the age of 2, wake-up times tend to be before 7 a.m., which results in sleep insufficiency during weekdays. This lack of sleep is compensated for by long naps on weekdays and by catching up on sleep on weekend mornings, which may contribute to future social jet lag. Guardians are encouraged to know their children's exact NBSD and set an appropriate bedtime to be maintained on weekdays. This helps to prevent sleep debt and fosters a consistent daily rhythm of waking up at the same time both on weekdays and weekends. These conditions are believed to support mental/physical development and school and social adaptation.

Keywords: catch-up sleep; nighttime basic sleep duration; nursery children; sleep–wake rhythm; social jet lag.

Figure 1

Night bedtime and morning wake time of each age group on weekdays and weekends. The bottom and top edges of the boxes represent the 25th and 75th percentile of the data, respectively. The lines in the boxes represent the median of the data. The lower and upper ends of the error bars represent the minimum and maximum values, excluding outliers, respectively.

Figure 2

Nocturnal sleep duration and daytime sleep duration of different age groups on weekdays and weekends. The bottom and top edges of the boxes represent the 25th and 75th percentile of the data, respectively. The lines in the boxes represent the median of the data. The lower and upper ends of the error bars represent the minimum and maximum values, excluding outliers, respectively.

Figure 3

Relationship between bedtime on weekdays and wake time on weekdays and weekends. The graph is a heat map, with the x-axis representing the bedtime of all of the participants on weekdays and the y-axis showing the wake time of all of the participants on weekdays (A) and weekends (B). The vertical line separates the groups that slept no later than 21:00 and after 21:00, and the horizontal line separates the groups that woke no later than 7:00 and after 7:00. The lower right quarter of the graph suggests a tendency of chronic sleep deprivation, and the upper right quarter suggests a backward shift in life (chronobiological) rhythm.