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Volume 14 No. 04
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Accepted Papers





Scientific Investigations

http://dx.doi.org/10.5664/jcsm.7038

Sleep Patterns in Chinese Preschool Children: A Population-Based Study

Ran Wu, MA1,2; Guang-Hai Wang, PhD3; Hong Zhu, MA2; Fan Jiang, MD, PhD3; Chun-Lei Jiang, MD, PhD1
1Laboratory of Stress Medicine, Faculty of Psychology and Mental Health, Second Military Medical University, China; 2Counseling and Psychological Services Center, East China Normal University, China; 3Department of Developmental and Behavioral Pediatrics, Pediatric Translational Medicine Institute, Shanghai Children's Medical Center, Shanghai Jiaotong University School of Medicine, MOE-Shanghai Key Laboratory of Children's Environmental Health, Shanghai, China

ABSTRACT

Study Objectives:

This study aimed to (1) provide data on normal sleep patterns in Chinese preschool children, (2) identify cross-cultural differences of sleep patterns among children from China and other countries, (3) estimate the prevalence of sleep duration not meeting the optimal amount, and (4) characterize delayed weekend sleep pattern.

Methods:

A population-based sample of 1,610 children aged 3–6 years was recruited from 10 cities across China. Parents completed questions about their child's sleep patterns adapted from the Children's Sleep Habits Questionnaire (CSHQ).

Results:

The mean bedtime was 9:31 PM, wake time was 7:27 AM, nighttime sleep duration was 9 hours 30 minutes, daytime sleep duration was 1 hour 31 minutes, and total sleep duration was 11 hours 2 minutes. The children had a shorter nighttime sleep duration but longer daytime naps, resulting in no differences in total sleep duration compared with counterparts predominantly in the west. Of the children, 85.3% met the recommended amount of sleep of 10 to 13 hours, and 10.8% slept fewer than 10 hours. The prevalence of sleep less than 10 hours was higher in older children and children from eastern China. Children went to bed and woke up more than 30 minutes later on weekends than weekdays, accounting for 40.1% and 50%, respectively. Children in western China showed longer delay than children in eastern China (P < .05).

Conclusions:

Age- and region-specific variability of sleep patterns are reported as well as insufficient sleep and delayed weekend sleep pattern in Chinese preschool children. The cross-cultural difference of sleep patterns was in temporal placement rather than sleep duration.

Citation:

Wu R, Wang GH, Zhu H, Jiang F, Jiang CL. Sleep patterns in Chinese preschool children: a population-based study. J Clin Sleep Med. 2018;14(4):533–540.


BRIEF SUMMARY

Current Knowledge/Study Rationale: To date there have been a limited number of population-based studies that have comprehensively examined sleep patterns specific to preschool children in mainland China. We sought to assess normal sleep patterns in Chinese preschool children and cross-cultural differences among China and other countries, and estimate the prevalence of insufficient sleep and delayed weekend sleep pattern.

Study Impact: Age- and region-specific variability of sleep patterns is reported as well as insufficient sleep and delayed weekend sleep pattern in Chinese preschool children. We found that the cross-cultural difference of sleep patterns was in temporal placement rather than sleep duration.

INTRODUCTION

Adequate and high-quality sleep is important for healthy development and the optimum daytime functioning of children. Unhealthy sleep patterns have been linked to a variety of adverse effects in preschoolers, including emotional behavioral problems, neurodevelopmental problems, fatigue, and accidental injury.1,2 Although sleep problems in young children are considered to be quite common, and have been identified as a specific global public health issue,3 what constitutes a normal sleep pattern in this age group across different countries, especially in China, remains unclear.

Sleep patterns mainly refer to bedtime, wake time, and sleep duration. Previous studies have found that preschool children aged 3 to 6 years slept approximately 10 to 13 in a 24-hour period,4,5 and the length of sleep declines from the age of 3 to 6 years.5,6 However, other studies found that although daytime naps significantly declined within this age range, nighttime sleep duration was not altered.7,8 In addition, sleep patterns of preschool children were found to be different across cultures. Children from predominantly Asian countries go to bed later and get less sleep than those from predominantly western countries.9,10 For example, 70.5% of Chinese preschool children had 9 to 10 hours of sleep per night11 and the average total sleep duration was 10.8 to 11.3 hours.12,13 In comparison, children in Australia and New Zealand were found to have an average total sleep duration that was 2.5 to 3 hours more than that of Chinese children.10 Conversely, other studies indicated no difference in total sleep duration between predominantly western and Asian countries; whereas Chinese preschool children had shorter night sleep due to later bedtime and earlier wake time,14 they had longer daytime naps than children in predominantly western countries.13 Existing studies have ignored cross-cultural differences within China. Geographically, China spans five time zones, but the standard time zone known as Beijing Time is in effect across the entire country. The circadian clock drives endogenous rhythms that modulate the timing, duration, and structure of sleep in humans.15 Taking the sunrise time as the standard, the preschool schedule in western China is approximately 1 hour earlier than in the east (UTC+8/UTC+7 7:30–8:30 AM, UTC+6 8:30–9:30 AM). Moreover, there are also differences in socioeconomic status, culture, and lifestyles of people between the east and the west of China, which further highlights the importance of establishing sleep norm data specified to regions of the east and the west.

In western countries, normative data of child sleep patterns has been established in several countries,4,16,17 which has contributed to wider research and clinical practice. In China, parents are becoming increasingly concerned about sleep problems in terms of the effect on their child's physical development and school performance. However, to date there have been a limited number of population-based studies that have comprehensively examined sleep patterns, insufficient sleep, and delayed weekend sleep pattern (later bedtime and wake time on weekends), specific to preschool children in mainland China.18 Also, the prevalence of deficit sleep in Chinese preschool children needs to be uncovered to further inform parents, health providers and policy makers. Thus, this study aimed to (1) provide data of normal sleep patterns in Chinese preschool children, (2) identify cross-culture differences of sleep patterns between children from China and other countries, (3) estimate the prevalence of sleep duration not meeting the optimal amount, and (4) characterize delayed weekend sleep pattern.

METHODS

Participants and Procedure

The Shanghai Children's Medical Center Ethics Committee reviewed and approved this study. Taking into consideration the regional distribution, socioeconomic development levels, and other factors, the researchers recruited 1,909 preschool children aged 3 to 6 years from preschools in 10 cities across China between November 2012 and January 2013. All the preschools are in a predominantly Chinese, middle-income, urban school district that also recruits children with a rural registration and were selected both on the basis of accessibility and as representative of a typical preschool system. One teacher from each preschool was trained to distribute questionnaires and instruct the parents on how to complete them within a 1-week period, either in the preschool classroom or at home. Each questionnaire was accompanied by a letter to parents that contained standardized instructional notes, researcher contact details, and further information relating to the content, purpose, and methodology. A total of 1,610 parents completed questionnaires, yielding an overall response rate of 84.3%. Sample characteristics are summarized in Table 1.

Demographic characteristics of study sample (n = 1,610).

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Table 1

Demographic characteristics of study sample (n = 1,610).

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Measures

Sleep patterns were measured using questions adapted from the Children's Sleep Habits Questionnaire (CSHQ). The CSHQ is a parent-report sleep instrument that has been widely used to assess sleep disturbance in children and adolescents aged between 2 and 18 years.19,20 The instrument includes three items about sleep patterns that were used in this study to collect information on bedtime, wake time, and sleep duration on weekdays and weekends. In addition, data regarding sociodemographic variables was collected, including the child's age, sex, regional distribution (time zones), family structure, and annual household income.

Statistical Analysis

The data were mainly analyzed using SPSS 21.0 (IBM Corp., Armonk, New York, United States). The effect sizes and 95% confidence intervals (CI) were analyzed using RevMan 5.3 (The Cochrane Collaboration, London, United Kingdom). Descriptive statistics were applied to depict distributions of the sleep pattern scores with measures of mean and standard deviation. Both t test and analysis of variance were used to compare the bedtime, wake time, and sleep duration separately according to weekday/weekend, region, and age.

In order to identify any statistically significant cross-cultural differences, we compared our data to that of Mindell et al. by calculating effect sizes and 95% CI.13 The data from Mindell et al. were collected between February 2011 and March 2012. Data gathered from different countries except Hong Kong and Thailand were used as experimental group data, and the data from the current study therefore form control group data. The statistical results extracted from all countries were converted into standardized mean difference (d). Results reflected relative weight under the random effects model. The observed variation was evaluated using standardized mean difference.

The proportion of insufficient sleep was estimated based on sleep recommendations of the National Sleep Foundation (NSF) and the American Academy of Sleep Medicine (AASM), which expanded the optimal sleep time for preschoolers to 10 to 13 hours.21,22 NSF indicated that a minimum of 8 to 9 hours and a maximum of 14 hours of sleep time may be more appropriate for some individuals. Distribution of appropriate sleep duration and incidence of insufficient sleep was conducted in this study.

Descriptive statistics were applied to depict the delayed weekend sleep pattern including delay of bedtime, delay of wake time, and delay of sleep midpoint with measures of mean and standard deviation. The sleep midpoint is the midpoint between bedtime and wake time which is used for chronotype assessment.18 Both t test and analysis of variance were used to compare the delayed weekend sleep pattern by region and age.

RESULTS

Sleep Patterns

Descriptive data on sleep patterns by age and region on both weekdays and weekends are listed in Table 2. Three-year-old children go to bed and wake up earlier than other age groups, on both weekdays and weekends. Six-year-old children wake up later than other children within the sample, which made them sleep longer at night. However, younger children had longer total sleep duration because of their longer daytime sleep.

Sleep patterns in different age and region groups on weekdays and weekends.

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Table 2

Sleep patterns in different age and region groups on weekdays and weekends.

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Children from eastern China were found to go to bed and wake up earlier than children from western China; however, the difference mostly does not exceed 1 hour, whereas their sunrise time is 1 to 2 hours earlier. Their nighttime and total sleep duration are both significantly shorter than for children from western China.

On weekdays, children were found to go to bed and wake up earlier than on weekends. They sleep less on weekdays than on weekends at night and in total, whereas there was no difference in nap time.

Cross-Cultural Differences in Sleep Patterns of Preschool Children

Table 3 shows comparisons between sleep pattern data from this study and data from other countries reported by Mindell and colleagues.18 For comparison purposes, we weighed the sleep data of weekdays and weekends in this study to obtain average data for a 1-week period. The average sleep pattern of Chinese preschool children in 1 week is shown in the aforementioned tables. Comparing with the study by Mindell et al., the bedtime of Chinese children in this study was about 1 to 2 hours later than the results of predominantly western countries and approximately 0.5 hours earlier than in India and Malaysia. The wake time of Chinese preschool children was just 10 to 20 minutes later than in western countries, and 30 minutes earlier than in South Korea and the Philippines. Chinese preschool children were found to take more daytime naps, which were significantly longer than in the western countries included: Australia and New Zealand, Canada, Japan, and the United States. However, the nighttime sleep of Chinese preschool children was found to be significantly shorter than these countries, consequently resulting in no significant difference in total sleep duration.

Cross-cultural differences in sleep patterns of preschool children.

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Table 3

Cross-cultural differences in sleep patterns of preschool children.

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Appropriate Sleep in Preschool Children

Distribution of Appropriate Sleep Duration

In the current study, 85.3% of children slept 10 to 13 hours per day on weekdays. 10.8% of children slept 8 to 9 hours, and 0.7% children slept 14 hours, which are possibly acceptable hours according to the NSF. No child slept fewer than 8 hours and 0.8% of children slept more than 14 hours. The proportion of children who had an optimal sleep duration decreased from 90.0% to 72.3% with age (Figure 1).

Distribution of sleep duration based on NSF- and AASM-recommended criterion for preschool children (n = 1,341).

AASM = American Academy of Sleep Medicine, NSF = National Sleep Foundation.

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Figure 1

Distribution of sleep duration based on NSF- and AASM-recommended criterion for preschool children (n = 1,341).

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The Incidence of Insufficient Sleep

Based on the latest recommendations of NSF and AASM, insufficient sleep for preschool children means less than 10 hours of sleep per day, on weekdays or weekends. On the whole, 10.8% of preschool children slept fewer than 10 hours per day on weekdays or weekends. In addition, 10.4% of children had insufficient sleep during the weekdays, 0.4% fewer during weekends. The incidence of insufficient sleep was found to increase with age and was significantly higher in children aged 5 and 6 years (15%, 16%) than in children aged 3 and 4 years (6.4%, 8.6%). The incidence of children in eastern China (16.9%) was higher than in children in western China (9.3%).

Delayed Weekend Sleep Pattern

The percentage of bedtime and wake time delay was evaluated in order to identify the distribution of delayed weekend sleep pattern. The results showed that only 26.5% of preschool children had no bedtime delay or delay shorter than 15 minutes. More than 30% of children slept 15 to 30 minutes later at night and 40.1% of children slept more than 30 minutes later at night, on weekends. About 25% of children woke up at a similar time during weekdays and on weekends, whereas 50% of children woke up more than 30 minutes later in the morning on weekends. More descriptive statistics and comparisons can be seen in Table 4.

Delayed weekend sleep patterns in different age and region groups.

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Table 4

Delayed weekend sleep patterns in different age and region groups.

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DISCUSSION

The current study is a population-based sleep survey of Chinese preschool children from 10 cities across different time zones. For comparison with other samples across a wide spectrum of pediatric populations, the current study chose widely used instruments, and adopted the latest sleep duration recommendations of the NSF and the AASM. The study measured sleep patterns separately by age, regional distribution and weekdays/ weekends, and reported the variability of sleep patterns as well as sleep problems of insufficient sleep and delayed weekend sleep pattern. This study highlights differences in sleep patterns among different countries.

Sleep Patterns in Chinese Preschool Children and Cross-Cultural Difference

On average, preschool children in China are getting an appropriate amount of sleep. Compared with other studies of Chinese preschool children in the same period,12,13 the 24-hour sleep duration reported in this study was considered to be consistent. However, compared with a previous study sampled in communities of 12 Chinese cities 12 years ago,23 preschool children of each age group in the current study slept 0.5 to 1 hour less per day. The difference of the total sleep duration was mainly caused by shorter daytime naps rather than changes in nighttime sleep. It might signal a decrease in sleep duration during a 10-year period among Chinese preschool children, because of the increased social competition and the pressure of enrollment, increased use of electronic products, and changes in parenting values.1,12 However, differences might partly be because of sampling and not the factor of time.

Previous studies generally found that young children from predominantly Asian countries had less sleep overall than children from western countries.5,9,10 However, the current study found that the difference between sleep of children from China and western countries is not the sleep duration but the temporal placement. Children in the current study and the predominantly Asian countries of the study by Mindell et al. have been found to have significantly shorter nighttime sleep but longer daytime sleep, as most children continue to nap, resulting in no differences in 24-hour total sleep time across cultures. On average, Chinese preschool children were found to be waking up earlier than children in other Asian countries in the study by Mindell et al., similar to children from western countries.

There are major differences in sleep patterns between the east and west of China. Preschool children in western China were going to sleep 20 minutes earlier and waking 40 minutes later than children in eastern China. Considering the sunrise time of western China is 1 to 2 hours later than that of eastern China, children in western China are in the habit of early hours. The sleep-wake cycle is important for preschool children in the cognitive processes of learning, such as attention and memory.24,25 The sleep patterns of Chinese preschool children who go to sleep late and wake up early on weekdays might have a negative effect on their morning school performance.26 In addition, children in western China slept 20 minutes longer at night and the same time in the daytime, making their total sleep duration 20 minutes longer per day than children from eastern China.

Previous studies found that children living in neighborhoods associated with low socioeconomic status are more likely to obtain shorter sleep duration and later bedtime.27 Children from economically poorer districts often have suboptimal sleep environments, such as shared rooms with parents and falling asleep with the TV on.27,28 However, eastern China is more developed than western China; thus, the current study came to the opposite conclusion.29 In fact, the per capita housing area of the western residents is not smaller than that of the residents of the east. Other differences between the east and west of China such as culture, parenting, and use of electronics might also be the reason for their shorter sleep duration.30 For example, children in eastern China are more likely to participate in mathematics tutoring, piano lessons, and other extracurricular activities at night in order to gain entry to a better primary school. Digital technology use is more popular among children in eastern China.

In eastern China, the daytime, nighttime, and total sleep duration decreased significantly from 3 to 6 years, which was consistent with the results of previous studies.5,6 Conversely, in western China, sleep duration of 6-year-old children increased both on weekdays and weekends, which may be explained by the relatively lower level of economic development and social competition stress. Three-year-old children were found to sleep early at night and wake early in the morning, and 6-year-old children were found to sleep late and wake later. This is prompted by the 24-hour rhythm in sleep-wake behavior developed during 3 to 6 years of age. The development may be driven by the changes of both circadian and homeostatic sleep-wake processes, and by changes of parental daily activities, increased independent locomotion, and cognitive development.6

Insufficient Sleep and Delayed Weekend Sleep Pattern

The latest NSF and AASM recommendation for the United States has a wider variation in sleep duration than the previous version, ranging from 10 to 13 hours for preschoolers. In the current study, there were 10.8% of preschool children who slept fewer than 10 hours per day, whereas most children (85.3%) slept for the recommended 10 to 13 hours per day. Previous studies have indicated that the incidence of insufficient sleep increases as children grow up.4,7,8 The current study obtained a similar result, in that the insufficient sleep incidence of 5- and 6-year-old children was twice as high than that of 3- and 4-year-old children.

In this study, children's nighttime and total sleep duration were found to both be significantly longer on weekends than on weekdays. They sleep later and wake up later on weekends, which is referred to as a delayed weekend sleep pattern. A previous study found weekend sleep data to be generally consistent worldwide, with 2-hour-later bedtimes and more total sleep duration on weekends being the norm.31 However, this pattern has been most typically seen in cohorts of school-aged children or adolescents, because of their weekly obligations.6,31 In this study, delayed weekend sleep pattern was shown in preschoolers, and children had an approximately 0.5- to 1-hour delay of bedtime and wake time on weekends, similar to the results of a study of German children. However, half of the German children were found to have a sleep onset latency of 15 minutes or shorter; only 16.8% went to sleep more than 30 minutes later at night on weekends.18 In this study, only 26.5% of children had no sleep onset latency or it was shorter than 15 minutes. The percentage of delay more than 30 minutes was 41.1%, which might indicate that delayed weekend sleep of preschoolers is more common in China, especially children in western China and 6-year-old children. The delayed weekend sleep pattern might be due to the early school time in China (7:30–8:00 AM) on weekdays and a trend of engaging children in evening activities on weekends.18 Postponing the morning school hours may help children to get better sleep. In addition, during the stage of preschool, bedtimes during the week are usually set by parents. Parental monitoring and setting of bedtimes that lead to earlier bedtimes may be beneficial because parental behavior and family schedules have an important influence on children's sleep patterns.18 Delayed weekend sleep pattern might have a negative influence on emotional and behavioral development of preschool children. Future research could explore the causes of weekend sleep delay and its effects on preschool children.

Limitations

The current study has some limitations. First, the data were collected through parent-report questionnaires that largely depend on subjective parental observations. Parents tend to report times for going to bed and rising, rather than times for falling asleep and waking, and they might also miss nighttime wakefulness of their children. Although a comparison of self-reported sleep time to actigraphy found high correlations of the two measures32,33 and we had reminded parents to avoid overestimation and watch their child's sleep carefully for 2 days before they filled out the questionnaire, systematic overestimation of sleep time might still exist in self-reported studies. Second, there was no concern about the individual differences in sleep pattern and its influence on children's physical and psychological development. In this study we cannot identify the relationship between sleep patterns and the development of preschool children, such as their height and weight, school performance, and emotional or behavior regulation. Third, our study was limited by potential sampling bias, as we did not use a rigorous random sampling procedure. Finally, factors such as ethnicity, sleep environments, parenting practice, and seasonal differences may also affect sleep patterns, which should be considered in future studies.

CONCLUSIONS

On average, Chinese preschool children were found to be getting an appropriate amount of sleep. Total sleep duration and daytime sleep episodes decline progressively with age, without an increase in nighttime sleep except for in 6-year-old children. Children in western China were found to be sleeping approximately 20 minutes longer than children in eastern China. The difference of sleep patterns between children from China and western countries is not the sleep duration but the temporal placement. Compared with the western countries in the study by Mindell et al., children in this study were found to have shorter nighttime sleep and longer daytime naps, resulting in no differences in total sleep duration per day across cultures. A total of 85.3% of Chinese children met the recommended sleep duration of 10 to 13 hours, and 10.8% slept less than 10 hours. The prevalence of insufficient sleep was higher in older children and children from eastern China. Children, especially children in western China, were found to be waking up early on weekdays for school, but sleeping 0.5 to 1 hours later on weekends, which might have a negative effect on their cognitive learning and morning school performance. It is recommended that parents in China allow and support their children to get enough sleep according to the recommended NSF sleep time through the maintenance of a stable sleep pattern throughout the week, in order to avoid misalignment.

DISCLOSURE STATEMENT

Funding/support: For the work, Chun-Lei Jiang was supported by the Military Medical Research Foundation (grant number: BWS17J027) and National Natural Science Foundation of China (grant numbers: 31371200, 81571169); Guang-Hai Wang was supported by the National Natural Science Foundation of China (grant number: 81601162), Shanghai Municipal Commission of Health and Family Planning (grant number: 20164Y0001), Shanghai Children's Medical Center (grant number: YJY-SCMC2016-5), and the Project of Shanghai Children's Health Service Capacity Construction (grant number: GDEK201708).

ABBREVIATIONS

AASM

American Academy of Sleep Medicine

CI

confidence interval

CSHQ

Children's Sleep Habits Questionnaire

NSF

National Sleep Foundation

ACKNOWLEDGMENTS

The authors thank the staff at ELG (www.chinaelg.com) for their support, including insightful input into this paper and refining the language.

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