Published online June 2, 2008
PEDIATRICS Vol. 121 No. 6 June 2008, pp. 1165-1173 (doi:10.1542/peds.2007-1464)
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ARTICLE

Sleep Patterns and Problems Among Chinese Adolescents

Xianchen Liu, MD, PhDa, Zhongtang Zhao, MDb, Cunxian Jia, PhDb and Daniel J. Buysse, MDa

a Department of Psychiatry, University of Pittsburgh School of Medicine and Western Psychiatric Institute and Clinic, Pittsburgh, Pennsylvania
b Institute of Epidemiology, Shandong University School of Public Health, Jinan, China


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
OBJECTIVES. Little is known about sleep patterns and problems in Chinese adolescents. This study was designed to examine sleep/wake patterns and problems and their associations with parent sleep among adolescents in China.

METHODS. This report represents part of an epidemiological study of sleep and health in 6 high schools in Jinan city, China. A total of 1056 adolescents and 838 parents completed a questionnaire in March or April 2005. Participants consisted of 625 boys and 441 girls, 557 seventh-graders (mean age: 13.5 ± 0.6 years) and 509 tenth-graders (mean age: 16.4 ± 0.7 years), and 603 mothers and 235 fathers. Adolescents and parents reported their own sleep/wake patterns and problems.

RESULTS. Average morning rising time (5:56 AM vs 8:13 AM) and sleep duration (7.5 hours vs 9.4 hours) differed significantly between weekdays and weekends. Compared with seventh-graders, 10th-graders went to bed later and awoke earlier, resulting in ~1 hour of sleep less. Of the adolescents, 18.8% reported their sleep quality as poor, 26.2% were not satisfied with their sleep, 16.1% had insomnia, and 17.9% had daytime sleepiness. Significant but low adolescent-parent correlations were observed for sleep/wake patterns and perceived sleep quality. Difficulty initiating sleep in adolescents was significantly associated with history of insomnia in mothers and fathers.

CONCLUSIONS. Sleep insufficiency, insomnia, and daytime sleepiness are prevalent in Chinese adolescents. Sleep insufficiency on weekdays may be attributable to earlier morning rising to meet school schedules. Parental history of insomnia is associated with elevated risk for insomnia symptoms in adolescent offspring, although adolescent-parent correlations in sleep/wake patterns are relatively low.

Key Words: sleep patterns • insomnia • daytime sleepiness • familial study • Chinese adolescents

Abbreviations: AHQ—Adolescent Health Questionnaire • PFQ—Parent and Family Questionnaire • DIS—difficulty initiating sleep • DRS—difficulty returning to sleep • OR—odds ratio • CI—confidence interval

Adolescence is characterized by tremendous biological, cognitive, emotional, and interpersonal changes. Marked sleep changes in adolescence include going to bed later, getting up earlier, irregular sleep patterns, insufficient sleep, and increased daytime sleepiness.1–3 Adolescents also are vulnerable to sleep disturbances such as insomnia, excessive daytime sleepiness, and circadian sleep disorders.4–6 Epidemiological studies have estimated that between 14% and 33% of adolescents have sleep problems and 10% to 40% of high school students experience moderate or transient sleep deprivation.7 Sleep insufficiency and problems influence school performance, behavior, and mood during daytime hours and increase risks for injuries and accidents, major depression, drug and alcohol use, and suicidal behavior.8–13 Sleep changes during adolescence are associated with multiple biological, developmental, psychosocial, cultural, familial, and school factors.1,6,14–18

However, the aforementioned findings are based on almost exclusively on studies conducted in Western countries. Although Chinese account for one fifth of the total world population, little is known about sleep/wake patterns and sleep problems in this ethnic group of adolescents.4 One comparative study showed that, compared with US peers, school-aged children in China go to bed later, get up earlier, sleep 1 hour less, and have more sleep problems, as reported by parents.19 The authors noted that the differences in sleep patterns between US and Chinese children might be attributable to different family and school environments.19,20 Several studies in Japan and Taiwan concluded that school influences may play a more important role in adolescent sleep/wake patterns for Asian adolescents than for Western peers, because of different school systems.17,21 School influences on sleep may be even greater for adolescent students in China, compared with Japanese and Taiwanese students. In China, limited college resources and the increased need for more and better education lead to keen entrance competition, under which Chinese adolescents face much more academic stress22 and may have more sleep problems. Therefore, the characteristic sleep patterns observed for Western adolescents and several Asian samples may not be generalizable to adolescents in China.

Sleep behavior has a strong familial aggregation and some degree of genetic transmission.16,23 Twin studies have generally shown modest levels of genetic determination, with heritability estimates in the range of 20% to 57% for various aspects of sleep, including bedtime, sleep duration, overall sleep quality, and polysomnographic sleep parameters.24,25 Twin studies also demonstrated that genetic effects contribute to 40% to 70% of the variance in childhood parasomnias and 35% to 80% in adults.26 Family studies demonstrated significant genetic effects on insomnia,15,25 snoring, and sleep-related breathing symptoms and disorders.27,28 However, almost all of those family studies of sleep also were conducted in Western countries, and most of those studies reported on only a single sleep behavior, such as sleep duration, snoring, or excessive daytime sleepiness, because the studies were not initially designed to study sleep.29 In addition, previous family studies of sleep problems used only probands as informants for the history of sleep problems among relatives.15 This might have overestimated or underestimated family history for sleep problems, because of recall bias.

The goals of the present study were to describe sleep/wake patterns and sleep problems across grade (seventh-graders versus 10th-graders), gender, and area of residence (urban versus rural) in a sample of adolescents in China and to explore the associations between adolescent and parent sleep. On the basis of previous studies,4,16,17,22,25 we expected that (1) senior high school students (10th-graders) would be more likely than junior students (seventh-graders) to have sleep debt, assessed as the difference between reported sleep duration and sleep need; (2) adolescent and parent sleep/wake patterns would demonstrate low/moderate correlation; and (3) adolescents whose parents reported sleep problems would be at elevated risk for sleep problems.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Participants and Procedures
This report represents part of an epidemiological project on sleep and adolescent health in 6 public high schools, conducted in March and April 2005 in Jinan city of Shandong Province, China. The 6 high schools included 3 junior high schools and 1 senior high school in an urban school district and 1 junior high school and 1 senior high school in a rural school district of Jinan. These schools were selected for representativeness of students in this area and for logistic reasons (eg, convenient transportation and time and financial constraints). The 6 high schools had different starting and ending times on school days; the 3 urban junior high schools started at 7:30 AM and ended at 5:30 PM, the urban senior high school started at 7:30 AM and ended at 8:30 PM, and the 2 rural schools started at 6:30 AM and ended at 9:30 PM.

This study was initially designed to obtain a sample of ~1000 participants, with ~500 seventh-graders and ~500 tenth-graders. We restricted our participants to seventh-graders and 10th-graders, to monitor them for 2 years before graduation. After we obtained permission from the principals of the target schools before initiation of the study, we randomly selected 16 classes of seventh-graders and 10 classes of 10th-graders, on the basis of the class sizes of the 6 target schools. All of the students in the target classes were recruited as potential participants.

Self-administered paper-and-pencil questionnaires were used to collect data on adolescent and parent sleep, through the Adolescent Health Questionnaire (AHQ) and Parent and Family Questionnaire (PFQ) developed especially for this study. Adolescents were asked to complete the AHQ within 1.5 hours in the classroom setting, during school days. Students who returned the AHQ were asked to bring the PFQ to their parents after school. One of the parents (either the mother or the father, as chosen by the family) was invited to fill out the PFQ. The PFQ asked about that parent's sleep patterns and the history of sleep problems for both parents and was completed by the parent within 2 weeks. This procedure for data collection was approved by the research ethics committee of Shandong University and target school principals. Students and parents were invited to participate in the survey and their participation was voluntary, without any penalties for nonparticipation. This is the most commonly used procedure to conduct school-based surveys in China.4,19

Of 1090 students who were asked to participate, 1066 (97.8%) returned the AHQ and 838 parents (76.9% of families) returned the PFQ. Adolescent participants consisted of 625 boys (58.6%) and 441 girls (41.4%), with 420 urban students (38.4%) and 646 rural students (60.6%). The sample included 557 seventh-graders (mean age: 13.5 ± 0.6 years) and 509 tenth-graders (mean age: 16.4 ± 0.7 years,), with an overall median age of 14.5 years. Parent participants were 603 mothers (72.0%; mean age: 40.7 ± 3.8 years; education: middle school or less, 47%; high school, 30%; college or above, 23%) and 235 fathers (28.0%; mean age: 41.8 ± 4.4 years; education: middle school or less, 38%; high school, 36%; college or above, 26%).

Adolescents whose parents did not return the PFQ did not differ in grade or any sleep parameter, compared with adolescents whose parents completed the PFQ (P > .05). However, the proportion of girls was greater among adolescents whose parents completed the PFQ, compared with adolescents whose parents did not complete the PFQ (43.1% vs 35.1%; {chi}2 = 4.72; P = .030).

Measures of Sleep
Adolescent sleep patterns and problems during the past month were assessed with the AHQ, which includes a set of items designed to elicit information about sleep, social demographic features, health history, lifestyle factors, and behavioral and emotional problems. All of the sleep items were derived from various questionnaires used to study sleep patterns and sleep problems in children and adolescents, including the School Sleep Habits Survey,30 Teen Health 2000,11 the Children's Sleep Habits Questionnaire,31 and the Sleep Health Survey for Chinese adolescents.4,10

Questions on sleep/wake patterns inquired about usual bedtime ("During the past month, on an average school day/weekend, when did you go to bed at night?") and wake-up time (". . . when did you get up in the morning?"), nocturnal sleep duration (". . . how many hours of actual sleep did you get at night?") on weekdays and weekends, usual sleep latency ("How many minutes has it usually taken you to fall asleep after you go to bed at night?"), and perceived sleep need ("How much sleep do you need to be at your best during the day?"). One item assessed overall sleep quality ("During the past month, how would you rate the quality of your sleep overall?"), and another item assessed overall sleep satisfaction. Sleep debt was estimated by subtracting actual nocturnal sleep duration from perceived sleep need.

Four items were used to evaluate insomnia, that is, difficulty initiating sleep (DIS) ("During the past month, how often would you say you have had difficulty falling asleep?"), difficulty maintaining sleep (". . . wake up frequently but usually fall back to sleep?"), difficulty returning to sleep (DRS) once awake (". . . wake up in the middle of night and find it hard to get back to sleep?"), and early morning awaking (". . . wake up very early and cannot get back to sleep?"). Three items were used to indicate daytime sleepiness, namely, feeling very sleepy during the day, falling asleep very easily, and feeling physically tired during the day. Three items addressed sleep-related breathing symptoms (ie, snoring loudly, holding breath/having breathing pauses, and snorting/choking/gasping during sleep), 1 item addressed nightmares, and 2 items addressed use of hypnotics ("How often do you use prescribed/nonprescribed sleep pills?"). All of the problem items were answered with frequency responses of less than once per week, 1 or 2 times per week, 3 to 5 times per week, or almost every day. Insomnia and daytime sleepiness were considered clinically significant if the problem occurred ≥3 times per week.

The adolescent sleep questionnaire showed acceptable psychometric properties. The internal consistency (Cronbach {alpha}) was .83 for daytime sleepiness items, .71 for sleep-related breathing items, and .50 for insomnia items with the current sample. Two classes of students (n = 87) were randomly selected in a high school, to examine 2-week test-retest reliability.31 Test-retest reliability (Pearson correlation coefficient) were .53 for weekday bedtime, .60 for weekday morning rising time, .68 for weekday sleep duration, .43 for weekend bedtime, .54 for weekend morning rising time, .53 for weekend sleep duration, .63 for sleep latency, .60 for sleep need, .59 for perceived sleep quality, and .60 for sleep satisfaction, and all were significant at P < .001. The 2-week test-retest agreement as measured with the {kappa} statistic was 0.40 for insomnia symptoms, 0.49 for sleep-related breathing problems, and 0.13 for daytime sleepiness.

Parent sleep/wake patterns and family history of sleep disorders were assessed with the PFQ, which includes questions regarding current sleep/wake patterns, parental history of sleep problems, and family demographic information. The parent respondent was asked to report his or her own sleep/wake patterns on weekdays and weekends, perceived sleep need, sleep latency, perceived sleep quality, and sleep satisfaction by using the same questions as in the AHQ. The respondent was also asked to report the history of sleep problems and use of hypnotics for himself or herself and for his or her spouse. Sleep problems included insomnia ("Do you often have sleep problems, such as difficulty falling sleep, difficulty maintaining sleep, or early morning awaking?"), daytime sleepiness ("Do you often feel sleepy, tired, or fall asleep during the day?"), sleep-related breathing symptoms ("Do you often snore loudly?" and "Do you often hold your breath, pause breathing, or stop breathing while sleeping?), nightmares ("Do you often have nightmares?"), and use of hypnotics ("Do you often use sleep pills?"). Each question was answered with a simple yes/no choice, to reduce the parent's burden to fill out the questionnaire.

Statistical Analyses
General linear models were used to examine grade (seventh versus 10th), residence (urban versus rural), and gender effects on sleep/wake patterns (bedtime, waking time, and night sleep duration) on weekdays and weekends, as well as perceived sleep need, among adolescents. A similar analysis was conducted to examine differences in sleep/wake patterns between mothers and fathers, with parental age as the covariate. Student's t tests were used to examine sleep parameter differences between weekdays and weekends. Stratified {chi}2 tests were used to examine the differences in the frequencies of sleep quality, sleep satisfaction, and sleep problems between seventh-graders and 10th-graders, between urban and rural adolescents, between boys and girls, and between mothers and fathers. Partial correlations were computed to estimate the associations between adolescent and parent sleep, with adjustment for the potential effects of adolescent age, gender, and school.

Multiple logistic regressions were used to examine the associations between parent sleep problems and corresponding sleep problems among adolescent offspring, that is, insomnia symptoms predicted by mother's or father's insomnia, loud snoring predicted by mother's or father's snoring, nightmares predicted by mother's or father's nightmares, and daytime sleepiness predicted by mother's or father's daytime sleepiness. Adolescent age, gender, and school were adjusted in the logistic regressions. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to quantify these associations. Age and gender were considered covariates, because of their potential effects on adolescent sleep. School was statistically controlled because the 6 target schools had different starting and ending hours.

The false-discovery rate-controlling procedure32 was used to correct for multiple testing as appropriate. According to this procedure, the null hypothesis is rejected for P/(n – i) < .05, where n is the number of P values for multiple testing and i is the ascending order of P values.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Sleep/Wake Patterns
Table 1 shows weekday and weekend sleep patterns, perceived sleep need, and estimated sleep debt among adolescents according to residence and grade. Compared with seventh-graders, 10th-graders went to bed later and awoke earlier on weekdays, resulting in ~1 hour of sleep less. On the weekend, 10th-graders again went to bed later than seventh-graders, but they also awoke later; as a result, average weekend sleep duration showed no significant difference between grades. Compared with urban children, rural children went to bed earlier and also awoke earlier, with no significant difference in average nocturnal sleep duration on weekdays or weekends. Compared with boys, girls went to bed slightly later on weekdays (10:12 PM ± 0.83 hours vs 10:06 PM ± 0.74 hours; F = 6.49; P < .05) and slept longer (9.55 ± 1.48 vs 9.21 ± 1.60 hours; F = 11.97; P < .001) on the weekend.


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  		TABLE 1 Sleep/Wake Patterns, Sleep Need, and Sleep Debt in Adolescents According to Residence and Grade

 
As a group, adolescents went to bed slightly later (t = 3.82; P < .001), awoke ~2.5 hours later (t = 49.62; P < .001), and slept ~2 hours longer (t = 33.00; P < .001) on the weekend than on weekdays. Perceived sleep need was significantly less in 10th-graders than in seventh-graders, but weekday sleep debt was significantly greater in 10th-graders than in seventh-graders. Sleep need and sleep debt showed no significant differences between boys and girls and between urban and rural adolescents (P > .05). After adjustment for age, gender, and grade, school start time was significantly related to weekday bedtime (r = 0.33; P < .001) and morning rising time (r = 0.28; P < .001) but was not related to nocturnal sleep duration (r = –0.004; P > .05).

On average, parents went to bed at 9:59 PM (SD: 1.08 hours), awoke at 6:29 AM (SD: 0.96 hours), and slept ~7.75 hours (SD: 1.22 hours) on weekdays. On the weekend, they went to bed at 10:11 PM (SD: 1.25 hours), awoke at 7:31 AM (SD: 1.22 hours), and slept ~8.43 hours (SD: 1.48 hours). Perceived sleep need was 8.07 hours (SD: 1.37 hours). None of the sleep/wake parameters was significantly different between mothers and fathers (P > .05).

Partial correlations between adolescent and parent sleep parameters, after adjustment for age, gender, and school, are presented in Table 2. Although the correlations were low to moderate, most of them were significant. After correction for multiple testing, all of the correlations that were significant at P < .001 remained significant. Correlations between adolescent and parent sleep were very similar across mothers and fathers, except for weekend bedtime.


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  		TABLE 2 Partial Correlations Between Adolescent and Parent Sleep After Adjustment for Age, Gender, and School

 
Sleep Latency and Perceived Sleep Quality
Tables 3 and 4 show reported sleep latency, sleep quality, and sleep satisfaction in adolescents and parents, respectively. The majority of adolescents fell asleep within 30 minutes (85.7%), reported their sleep quality as good or excellent (81.3%), and was satisfied or very satisfied with their sleep (73.9%). For both urban and rural adolescents, 10th-graders were more likely than seventh-graders to report poor or very poor sleep quality (P < .001) and to be unsatisfied with their sleep (P < .01). Compared with urban peers, rural seventh-graders were more likely to report sleep latency of >30 minutes (P < .001). Girls rated their sleep quality as better than boys overall ({chi}2 = 9.78; P = .021), with 20.6% of boys and 16.0% of girls reporting poor sleep quality. No other sleep parameters demonstrated grade, residence, or gender differences.


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  		TABLE 3 Perceived Sleep, Selected Sleep Problems, and Hypnotic Use According to Residence and Grade

 

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  		TABLE 4 Perceived Sleep, Selected Sleep Problems, and Hypnotic Use in Parents

 
Parents rated their sleep quality at least as good as their adolescent children; 90.0% fell asleep within 30 minutes, 91.7% rated their sleep quality as good or excellent, and 91.9% described themselves as satisfied or very satisfied with their sleep. As shown in Table 4, mothers rated their sleep quality better than fathers ({chi}2 = 20.39; P < .001) and were more likely to be satisfied with their sleep ({chi}2 = 16.40; P < .001).

As presented in Table 2, the correlations between adolescent and parent sleep latency and sleep quality were low but statistically significant. The highest correlation was observed for perceived sleep quality between adolescents and fathers (r = 0.247).

Sleep Problems
Table 3 also presents the prevalence rates of sleep problems during the past month in adolescents. Daytime sleepiness and insomnia were prevalent, endorsed by 17.9% and 16.1% of adolescents, respectively. Approximately 13% endorsed nightmares, 3% to 8% sleep-related breathing symptoms, and 2.5% hypnotic use.

With regard to insomnia symptoms, urban 10th-graders reported more problems with DIS and DRS than seventh-graders, but rural seventh-graders reported more problems with DIS and difficulty maintaining sleep than 10th-graders. Daytime sleepiness was more prevalent in 10th-graders than in seventh-graders. Rural seventh-graders reported more nightmares than rural 10th-graders. Compared with urban seventh-graders, rural seventh-graders reported more problems with DIS, difficulty maintaining sleep, early morning awaking, sleep breathing problems, nightmares, and use of hypnotics. After correction for multiple comparisons, all sleep problems that were significant at P < .01 remained significant.

Compared with girls, boys were more likely to report loud snoring (10.6% vs 4.7%; {chi}2 = 10.72; P = .001), breathing pauses (3.5% vs 1.3%; {chi}2 = 4.69; P = .030), and difficulty breathing (5.9% vs 2.7%; {chi}2 = 5.37; P = .020). However, no significant gender differences were observed in insomnia symptoms, nightmares, daytime sleepiness, or use of hypnotics (P > .05).

Logistic regression showed that school start time (OR: 0.59; 95% CI: 0.45–0.78; P < .001) and total time in school (OR: 1.22; 95% CI: 1.12–1.34; P < .001) were significantly associated with insomnia, after adjustment for age, gender, and grade. The earlier the school start time and the longer the time in school, the higher was the risk for insomnia. However, school start time and total time in school were not associated with daytime sleepiness (P > .05).

As shown in Table 4, compared with mothers, fathers were significantly more likely to have loud snoring (P < .001) but were less likely to have nightmares (P = .015). Sleep problems such as chronic insomnia, excessive daytime sleepiness, and nightmares showed no significant differences between mothers and fathers (P > .05).

Figure 1 presents ORs of adolescent insomnia symptoms associated with parental history of insomnia. Paternal insomnia was significantly associated with DIS (OR: 7.09; P < .001) and DRS (OR: 8.44; P < .05) after adjustment for age, gender, and school. Maternal insomnia was significantly associated only with DIS (OR: 5.69; P < .01). No other adolescent sleep problems were significantly related to corresponding sleep problems in parents.


Figure 1
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  		FIGURE 1 Associations of parental history of insomnia and insomnia symptoms in adolescent offspring after adjustment for age, gender, and school. EMA indicates early morning awaking. a P < .01; b P < .001; c P < .05.

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
This study was designed to address sleep/wake patterns and problems and their associations with parent sleep behavior among adolescents in China. Our major findings are summarized as follows. First, adolescent sleep/wake patterns were markedly different between weekdays and weekends and between seventh-graders and 10th-graders, consistent with those observed in Western peers.1,33 Second, urban adolescents were more likely to go to bed later and to awake later than rural peers. Third, sleep insufficiency, insomnia, and daytime sleepiness were prevalent sleep problems among Chinese adolescents, with 10th-graders being approximately twice as likely as seventh-graders to report daytime sleepiness. Fourth, school start time was related to sleep/wake pattern but was not related to nocturnal sleep duration. Fifth, adolescents and parents had low to moderate correlations in sleep/wake patterns, sleep latency, reported sleep quality, and perceived sleep need. Finally, parental history of insomnia was associated with insomnia symptoms in adolescent offspring.

Consistent with previous findings in Western countries1,34 and several studies in Asian countries or regions,17,21 our results indicated that Chinese adolescents went to bed later and awoke later in the morning on weekends than on weekdays. The discrepancy in sleep duration between weeknights and weekend nights was markedly increased from 1.4 hours in seventh-graders to 2.4 hours in 10th-graders. The longer sleep duration on weekends, compared with weeknights, suggests that adolescents are relatively sleep deprived on weekdays. Longer weekend sleep duration may reflect their actual sleep need or may be an indicator of "catch-up" sleep to compensate for sleep insufficiency on weekdays.

Tenth-graders thought they needed 1.5 hours more sleep than they were getting on school nights to be at their best, whereas seventh-graders thought they would be at their best with almost 1 hour more sleep. In an early longitudinal study, Strauch and Meier35 reported that between 55% and 75% of their subjects thought they needed more sleep. A recently released study of sleep in adolescents in the United States by the National Sleep Foundation reported that 45% of adolescents get insufficient amounts of sleep (<8 hours) on school nights.33 Differences in the desire for more sleep do not seem to be the result of just greater reduction in total sleep time or more-irregular sleep habits.34 Carskadon et al36 suggested that a delayed sleep phase tends to occur during middle adolescence and seems to be associated with biological factors, rather than the psychosocial ones that govern sleep and waking times. Therefore, the fact that 10th-graders tend to go to bed later and need to get up earlier to meet school schedules, despite the fact that their physiologic sleep requirement does not decrease,1,3,8 may result in more-severe sleep debt and daytime sleepiness, compared with seventh-graders.

A total of 16% of Chinese adolescents had insomnia and 18% had daytime sleepiness ≥3 times a week. The prevalence of insomnia symptoms was comparable to values reported for Western peers5,6 and in one study in mainland China.4 Although insomnia rates were similar between seventh-graders and 10th-graders in urban schools and the rate was slightly higher in seventh-graders than in 10th-graders in rural schools, the daytime sleepiness rate was approximately twofold higher in 10th-graders than in seventh-graders. This is consistent with previous observations that daytime sleepiness is more common in middle or late adolescents than in young children or early adolescents.1,17 Increased daytime sleepiness among 10th-graders may be explained by more-severe sleep debt on weekdays, as discussed above. In addition, daytime sleepiness may be explained by poorer sleep quality in 10th-graders (21%) than in seventh-graders (13%). Poorer sleep quality in 10th-graders may be attributable to more academic stresses for senior high school students than for junior high school students. High academic stress levels are particularly true for senior high school students in China, because of high parental academic expectations of success and great pressure to enter better universities.4,19,22

Urban adolescents went to bed later than rural peers and also awoke later on both schooldays and weekends. Urban adolescents may have more night activities than rural adolescents and more opportunities to access electronic media and/or the Internet, because of social and economic developmental disparities between rural and urban areas in China.37 Unfortunately, we did not collect data on daytime and nighttime social activities for urban and rural adolescents in the current study. Additional studies to examine the effects of nighttime social activities on sleep among rural and urban adolescents in China are warranted.

Our results indicated that adolescents and parents had low to moderate correlations in sleep/wake patterns, independent of age and gender. These results suggest that genetic and/or parental factors play relatively minor roles in sleep changes during adolescence. Sleep/wake patterns among adolescents may be largely attributable to biological changes and environmental influences/events, such as early school start, schoolwork overload, life events, and psychological and physical changes during adolescence.1,4,17 In addition, the relatively uniform and restricted lifestyles among adolescent students may result in correlation estimates lower than expected, because genetic variance could not be fully expressed within environmental restrictions.38

However, the prevalence of insomnia symptoms among adolescent offspring of parents with a history of insomnia was increased. After controlling for the potential confounding effects of age and gender, the elevated risk for insomnia among adolescent offspring of parents with insomnia was only slightly attenuated, which suggests that it was unlikely that parent-offspring associations could be explained by demographic factors. Additional studies are needed to examine whether the parent-adolescent association of insomnia is determined by family environment, genetic effects, or both.

Several limitations should be considered in the interpretation of our results. First, as with any self-report measure, the data reported in the article may have estimation bias. For example, snoring may be underreported if the participant does not know that he or she is snoring. On the basis of self-reported sleep duration and sleep need, the estimation of sleep debt is arbitrary. Test-retest reliability of the adolescent sleep questionnaire was moderate across all sleep variables. This indicates that the responses received might have been related to the date completed (eg, after a holiday period), sleep behaviors in adolescents are more state-like than trait-like, or possibly this is a reflection on the validity of self-report measures that ask about the past month. In addition, although most of the sleep items in the parent questionnaire were used in our previous project in China,39 we did not formally assess their psychometric properties for the current study. Objective measurement of sleep, such as nocturnal polysomnography, actigraphy, and multiple sleep latency testing, would add an important dimension to our understanding of sleep patterns and disturbances. Second, this was an epidemiological survey without control for the effects of environment and/or daytime/nighttime activities. Although the association between adolescent and parent sleep may result from a gene-environment interaction, it is not clear to what extent the variance in sleep behavior can be attributed to genetic or environmental factors; family studies are limited, in that they cannot separate the common environment from genetic factors. It is well known that sleep is related to psychiatric status and psychiatric disorders are genetically transmitted,13,40 but we did not have psychiatric diagnostic information for parents and adolescents. Third, although the demographic characteristics of this sample were similar those of to the school population in the area, it is not known whether our findings can be generalized to the entire adolescent population in China. Finally, we could not control for the effects of age when examining the differences in sleep parameters between seventh-graders and 10th-graders, because almost all of the participants in the same grade were in the same age group. We also could not distinguish between pubertal developmental and chronologic effects, because we did not include measures of pubertal development staging in the current study.


   CONCLUSIONS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Sleep insufficiency, insomnia, and daytime sleepiness are common sleep problems in Chinese adolescents. Sleep insufficiency and daytime sleepiness are more prevalent in senior high school students than in junior high school peers. Sleep insufficiency on weekdays may be attributable to earlier morning rising to meet school schedules. Parental history of insomnia increases the risk for insomnia symptoms in adolescent offspring, although adolescent-parent correlations in sleep/wake patterns are relatively low. These findings provide initial evidence of familial linkage (parent-offspring) of sleep patterns and problems in a sample of Chinese adolescents. However, environmental factors and biological changes associated with puberty may play major roles, compared with genetic and/or parental factors in adolescent sleep patterns. Additional studies are required to examine how and the extent to which genetic and environmental factors interact in adolescent sleep changes and disturbances.


   ACKNOWLEDGMENTS
 
This study was supported in part by the Multi-Investigator Proposal Development Grant Program, Arizona State University.

We thank all participating schools, parents, and students for data collection in the study and Dr Lan Gong, Department of Biostatistics, University of Pittsburgh, for statistical comments.


   FOOTNOTES
 
Accepted Oct 1, 2007.

Address correspondence to Xianchen Liu, MD, PhD, Western Psychiatric Institute and Clinic, Webster Hall-134, 3811 O'Hara St, Pittsburgh, PA 15213. E-mail: xcliu{at}pitt.edu or Zhongtang Zhao, MD, Shangdong University School of Public Health, Jinan, China. E-mail: ztzhao{at}sedu.edu.cn

Financial Disclosure: Dr Buysse serves as a consultant for Actelion, Arena, Cephalon, Eli Lilly, GlaxoSmithKline, Merck, Neurocrine, Neurogen, Pfizer, Repironics, Sanofi-Aventis, Sepracor, Servier, Stress Eraser, Takeda, and Transcept Pharmaceuticals.


What's Known on This Subject

Adolescents experience marked sleep changes. Sleep insufficiency, daytime sleepiness, and insomnia are very common in adolescents. Inadequate sleep influences daytime functioning and health. Sleep changes during adolescence are associated with multiple biological, developmental, psychosocial, cultural, familial, and school factors.

 

What This Study Adds

This represents the first report on sleep-wake patterns among adolescents in China. Sleep patterns and problems in Chinese adolescents are similar to those reported for Western peers. Parental history of insomnia is associated with insomnia symptoms in adolescent offspring.

 


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
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PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics

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