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Sleep duration, insomnia and behavioral problems among Chinese adolescents
Psychiatry Research 111 (2002) 75–85
Sleep duration, insomnia and behavioral problems among Chinese adolescents Xianchen Liua,b,*, Haibo Zhouc a
Department of Family and Human Development and Program for Prevention Research, Arizona State University, P.O. Box 876005, Tempe, AZ 85287, USA b Shandong University School of Public Health, Jinan, PR China c Department of Biostatics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Received 11 October 2001; received in revised form 5 April 2002; accepted 19 May 2002
Abstract This study examined the associations among sleep duration, insomnia, and behavioral problems in a sample of 1359 Chinese adolescents. Participants completed a self-administrated questionnaire that included questions on sleep duration and insomnia symptoms and the Youth Self-Report of Child Behavior Checklist. It was found that adolescents who complained of insomnia reported sleep duration only half an hour shorter than did those without insomnia. Sleep duration did not differ among adolescents reporting three different types of insomnia (difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening). Adolescents with insomnia reported more behavioral problems than did those without complaints of insomnia. After adjustment for age and sex, sleep duration of less than 7 h a day was significantly associated with most behavioral problems in those without complaints of insomnia but with only a few behavioral problems in adolescents reporting insomnia. Results suggest that sleep duration in adolescents with insomnia is short, but not as short as reported in previous clinical studies. Insomnia and short sleep duration are associated with a wide range of behavioral and emotional problems in adolescents. 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Behavioral problems; Emotional problems; Insomnia; Sleep duration
1. Introduction Numerous studies have consistently reported that adolescents do not get enough sleep and that their sleep patterns are characterized by staying up late (e.g. Straugh and Meier, 1988; Carskadon, *Corresponding author. Tel.: q1-480-727-6145; fax: q1480-965-5430. E-mail address: [email protected] (X. Liu).
1990; Wolfson and Carskadon, 1998; Laberge et al., 2001). Shorter sleep duration in adolescents possibly results from a combination of early school start times, late afternoonyevening jobs and activities, academic and social pressure, a physiological sleep requirement that does not decrease with puberty (Carskadon, 1990; Wolfson and Carskadon, 1998), and sleep disorders (e.g. chronic nightmares, sleep-disordered breathing, delayed sleep
0165-1781/02/$ - see front matter 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 5 - 1 7 8 1 Ž 0 2 . 0 0 1 3 1 - 2
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X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
phase syndrome) (Stores, 1996; Ohayon et al., 2000; Krakow et al., 2001). Most studies have demonstrated that the way adolescents sleep and their tendency to get insufficient sleep result in negative effects on their ability to think and concentrate in school, school performance, behavior, and mood during daytime hours, increased risk for injuries and accidents, use of drugs and alcohol, and circadian sleep disorders (Carskadon, 1990; Carskadon et al., 1998; Wolfson and Carskadon, 1998; Laberge et al., 2001). A few studies of adolescent sleep reported that sleep quality but not sleep quantity (time in bed or time asleep) was correlated with school functioning, physical complaints, or negative mood (Pilcher et al., 1997; Meijer et al., 2000). Insomnia is one of the most common sleep disturbances in adolescents. Ohayon et al. (2000) reported 25% of adolescents had insomnia symptoms. The association between insomnia and mental disorders has long been concerned. Clinically, insomnia is a principal symptom of major depression and anxiety, and is considered a precursor of onset or relapse of many mental disorders, such as schizophrenia, mania, and major depression, drug abuse, and anxiety disorder (American Psychiatric Association, 1994). Many cross-sectional studies have found that insomnia is associated with various mental health problems in the general population of adults and adolescents (Ford and Kamerow, 1989; Stores, 1996; Vignau et al., 1997; Ohayon et al., 1997, 2000; Roberts et al., 2001). Recent prospective studies of adults indicate that insomnia predicts the development of major depression, anxiety, or alcohol abuse (Ford and Kamerow, 1989; Breslau et al., 1996; Chang et al., 1997). However, one study of 823 children did not find a prospective association between trouble sleeping at age 6 and parent-reported anxietyydepression at age 11 years (Johnson et al., 2000). No prospective studies have reported the association between sleep disturbance and mental disorders in adolescents. However, one of the disappointing aspects of research in this area is that the aforementioned findings are based almost exclusively on studies in Western countries. The findings from Western samples may not generalize to Chinese adolescents, because sleep behavior, sleep schedules and
mental disorders are all influenced by potential environmental and cultural factors. For example, Chinese adolescents have to get up earlier for morning class before breakfast (Liu et al., 2000b). Compared with Western adolescents, Chinese adolescents have been reported to have fewer externalizing problems but more internalizing problems (Liu et al., 2001). This study with a large population sample of Chinese adolescents was carried out in 1993 (Liu et al., 2000b). In our previous report, we found that 17% of Chinese adolescents had complaints of insomnia symptoms and that multiple psychosocial and biological factors were associated with an increased risk for sleep problems (Liu et al., 2000b). In this report, we aimed to examine the relationships between self-reported sleep duration and complaints of insomnia. Clinical patients with insomnia often have depressive or anxious symptoms, overestimate sleep latency, and underestimate total sleep time (Bliwise et al., 1993; Chervin and Guilleminault, 1996; Vanable et al., 2000), but the relationship between self-reported sleep duration and insomnia symptoms in the general population has been less addressed. We also aimed to examine the association between reported sleep duration and a wide range of behavioral problems measured by the Youth Self-Report of the Achenbach Child Behavior Checklist (Achenbach, 1991). If the association was detected, we wanted to find a threshold of sleep duration, which is associated with a significantly increased risk for behavioral problems. Finally, we aimed to test the hypothesis that insomnia would be associated with increased risks for behavioral or emotional problems in Chinese adolescents. If the association were found, we proposed to identify which behavioral or emotional problems would be most strongly associated with insomnia. 2. Methods 2.1. Subjects and procedure This cross-sectional survey was carried out in Hezhe Prefecture of Shandong Province, in eastern China. The details of the study design and procedure were described elsewhere (Liu et al.,
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2000a,b). Briefly, after considering the geographic distribution, population size, time and financial constraints, and representatives of the sample, we planned to recruit a total of 1300 students (250– 300 for each grade) from five or six public high schools in this area. According to our requirement, the prefecture education committee selected five high schools (three junior and two senior), which could represent average schools of the area. After obtaining permission from the principals of the target schools, we randomly recruited half of the classes for each grade in each target school. As a result of the procedure, 1400 students in the target classes on the day of survey were recruited as potential participants. It is a standard procedure in China to obtain consent from the principals, not the parents, since schools in China act in loco parentis. The 12th graders were not included in the survey because they were preparing for university entrance examinations. Of 1400 students who were asked to participate, 1359 completed the questionnaire (97%). Participants consisted of 814 junior high school and 546 senior high school students, and 822 boys (60%) and 537 girls (40%). Participants had a mean age of 14.6 years (S.D.s3.4), with a range of 12–18 years. The average family size (including the subject) was 5.8 (S.D.s3.0). Most of the fathers (80%) and mothers (83%) were farmers. Sixtyeight percent of the fathers and 90% of the mothers had only primary or junior high school education. Mean maternal age was 40.1 years (S.D.s12.2) and mean paternal age was 41.3 years (S.D.s 11.9). With the help of teachers, trained psychiatrists administered the questionnaire to the sample of students in their classrooms during regular school hours. All the students attending school on the day of the survey gave their consent even though they were given the option of not participating. Before completing the questionnaire, the students were told to read the instructions carefully and to ask about anything they did not understand. The psychiatrists monitored the session and answered questions as needed to ensure that all questionnaires would be completed as accurately as possible. Approximately 30 min were required to complete the questionnaire.
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2.2. Measures A self-administered questionnaire was developed to investigate mental health problems in adolescents attending school. Four generalized questions were included in the questionnaire with regard to sleep behavior: ‘On the average, how many hours do you sleep at night?’ ‘Do you have difficulty getting to sleep at night?’ ‘Do you awaken during the night and have trouble getting back to sleep?’ ‘Do you awaken too early in the morning and have trouble getting back to sleep?’ The time frame for the questions was the past month and the response categories for questions 2–4 were: (1) never or rarely; (2) sometimes; and (3) often. Questions 2, 3 and 4 were used to estimate insomnia resulting from difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS) and early morning awakening (EMA). If an adolescent answered ‘often’ to at least one of the three questions, he or she was defined as a ‘case’ of insomnia. We used the Youth Self-Report (YSR; Achenbach, 1991) of the Child Behavior Checklist to measure adolescents’ behavioral problems. Due to its sufficient psychometric properties, the YSR has been widely applied in clinical assessment and research in many countries, including China (Achenbach, 1991; Liu et al., 1997, 2000a). The YSR is composed of 103 problem items to which the respondent can answer ‘0’ if the problem is not true of him or her, ‘1’ if the item is somewhat or sometimes true, and ‘2’ if it is very true or often true. Respondents were asked to select the response that described their behaviors or feelings at the time they completed the questionnaire or within the past 6 months. The YSR includes eight subscales: Withdrawn (seven items), Somatic Complaints (nine items), AnxiousyDepressed (16 items), Social Problems (eight items), Thought Problems (seven items), Attention Problems (nine items), Delinquent Behavior (11 items), and Aggressive Behavior (19 items). To identify more specifically the nature of the behavioral or emotional problems associated with insomnia and sleep duration, the eight subscales were used for analyses. The Chinese YSR has satisfactory reliability,
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X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
and a total YSR score of 70 as cut-off has been reported to be indicative of significant mental health problems (Liu et al., 1997). Cronbach’s alpha coefficients with the present sample were 0.93 for the total scale; mean Cronbach’s alpha for eight subscales was 0.65. 2.3. Statistical analysis Analysis of variance (ANOVA) was performed to examine age differences in sleep duration and overall behavior problem scores, and to compare sleep duration among groups with different insomnia symptoms (DIS, DMS, EMA, two symptoms) and those without insomnia. Student’s t-tests were used to compare sleep duration and behavior problem scores between boys and girls. Chi-square tests were used to compare frequencies of insomnia symptoms in relation to age, gender, and sleep duration. As previous studies have shown that age and gender of adolescents are associated with sleep duration, insomnia symptoms and behavior problems as well (Vignau et al., 1997; Wolfson and Carskadon, 1998), age and gender were adjusted for in examinations of the associations between sleep duration, insomnia, and behavior problems. Multiple linear regression analyses were performed to examine the relationships between insomnia and behavioral problems and to determine whether sleep duration could predict behavioral problems after adjustment for age and sex. To estimate the clinical relevance of the associations of sleep duration and insomnia with behavioral problems, multiple logistic regression analyses were performed on a binary outcome variable indicating whether an individual’s behavioral score was above or below the 90th percentiles (Byrd et al., 1996; Liu et al., 1999). Odds ratios (ORs) and their 95% confidence intervals (CI) were calculated to show the association. All the analyses were performed with SPSS 10.1 for Windows. The threshold of statistical significance was set at P-0.05. 3. Results Of the sample, 16.9% reported insomnia symptoms, including difficulty initiating sleep (10.8%),
Table 1 Sleep duration (hours), insomnia and behavior problems according to age Age (years)
n
Sleep duration Insomnia Mean"S.D. %
Behavior problemsa Mean"S.D.
12 13 14 15 16 17 18 Statistical tests
88 125 207 323 315 242 60
8.3"0.7 8.1"0.8 7.7"0.8 7.6"0.9 7.4"0.9 7.5"0.7 7.5"0.7 Fs24.13***
30.6"20.0 36.1"11.2 41.3"21.7 43.2"16.5 46.3"21.7 46.6"22.5 50.2"21.8 Fs10.58***
a
10.2 11.2 10.1 16.5 21.6 20.2 23.3 x2s21.19***
Total score of the Youth Self-Report. ***P-0.001.
difficulty maintaining sleep (6.3%), and early morning awakening (2.1%); mean sleep duration at night was 7.6"0.8 hours; mean YSR total problems score was 43.1"22.1, and 10.7% of the students scored higher than the cutoff score of 70 (Liu et al., 1997). Mean sleep duration significantly declined between 12 and 16 years of age, while insomnia symptoms significantly increased between 14 and 18 years of age (Table 1). Girls reported sleep duration a little shorter than boys (7.6"0.8 vs. 7.7"0.9 hours, ts2.04, Ps0.04). There was no significant gender difference in overall prevalence of insomnia (x2s0.02, P) 0.05). Mean behavior problem scores significantly increased across age (Fs10.58, d.f.s6, P0.001), but did not significantly differ between boys and girls (ts1.50, d.f.s1357, Ps0.13). 3.1. Insomnia symptoms and sleep duration Mean sleep duration was significantly shorter in adolescents with insomnia than in those without complaints of insomnia (7.7"0.8 h vs. 7.3"0.9 h; ts5.83, d.f.s1357, P-0.001), but the difference was less than 30 min. To further examine the association between insomnia symptoms and sleep duration, we divided the subjects into five groups: DIS, DMS, EMA, two insomnia symptoms, and non-insomnia. Adolescents with two symptoms reported shortest sleep duration (7.0"0.9 h), followed by EMA (7.3"0.7 h), DIS (7.4"0.9 h), DMS (7.5"1.0 h), and non-insomnia (7.7"0.8
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
Fig. 1. Prevalence (%) of insomnia in different sleep-duration groups.
h). ANOVA showed that sleep duration significantly differed among the five groups (Fs9.90, d.f.s3, P-0.001). Post-hoc Tukey tests showed significant differences in sleep duration only between non-insomnia and DIS (mean differences0.32 h, Ps0.001) or two symptoms (mean differences0.73 h, P-0.001). Fig. 1 shows the prevalence of insomnia in different sleep-duration groups. The prevalence of insomnia ranged from 11% for those sleeping 8 h a day to 32% for those sleeping less than 7 h and differed significantly among the four sleep-duration groups (x2s49.39, d.f.s3, P-0.001). Logistic regression analysis showed that the adolescents with sleep duration of less than 7 h were over three times as likely to report insomnia as those with sleep duration of 8 or more h (ORs3.6, 95% CIs2.3-5.7, Walds9.49, P-0.001). 3.2. Sleep duration and behavioral problems We performed multiple linear and logistic regression analyses to examine the dose–response relationships between sleep duration and behavioral problems after adjustment for age and sex. As shown in Table 2, most behavioral problem scores significantly declined with longer sleep duration with the exceptions of thought problems and delinquent behavior. Compared with sleep duration of 9 h, sleep duration of less than 7 h was significantly associated with increased risk for most
79
behavioral problems; sleep duration of 7 h was associated only with increased risk for withdrawn and anxiousydepressed symptoms; sleep duration of 8 h was not associated with any behavioral problems. The association of short sleep duration with anxiousydepressed syndrome was stronger than that with any other behavioral problems. To examine whether the effects of sleep duration on behavioral problems differed between insomniacs and non-insomniacs, we performed multiple linear and logistical regression analyses for insomniacs and non-insomniacs separately (Table 3). For insomniacs, only anxiousydepressed and aggressive behavior significantly decreased with increased sleep duration. For non-insomniacs, however, most behavioral problems except for thought problems and delinquent behavior significantly decreased with increased sleep duration. Short sleep duration accounted for the largest portion of the variance in anxiousydepressed (13%). Logistic regression models showed only two problems among non-insomniacs and no problems among insomniacs to be associated with decreased sleep duration. Compared with sleep duration of 9 h a day, sleep duration of less than 7 h was associated with increased risk of anxiousy depressed (ORs4.5, 95% CIs1.7–11.7, Walds 9.68, P-0.001) and for social problems (ORs 2.7, 95% CIs1.1–6.7, Walds4.91, P-0.02). 3.3. Insomnia and behavioral problems Table 4 presents mean scores and frequencies of behavioral problems for insomniacs and noninsomniacs. Multiple linear regression analyses indicated that mean scores on all behavior problem scales were significantly higher in insomniacs than in non-insomniacs at P-0.01. Chi-square tests showed that the frequencies of all behavior problems were significantly higher in insomniacs than in non-insomniacs (Table 4). Logistic regression models showed that insomnia was significantly associated with increased risk for all behavioral problems except for delinquent behavior. Odds ratios and 95% confidence intervals are presented to show the association (Fig. 2). As seen in Fig. 2, the strongest associations of insomnia were with anxiousydepressed (ORs2.9,
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
80
Table 2 YSR scale scores and percentages of behavioral problems (P90th percentiles) in relation to sleep duration Behavioral problems
a
Withdrawn Mean"S.D. % OR (95% CI) Somatic complaints Mean"S.D. % OR (95% CI) Anxiousydepressed Mean"S.D. % OR (95% CI) Social problems Mean"S.D. % OR (95% CI) Thought problems Mean"S.D. % OR (95% CI) Attention problems Mean"S.D. % OR (95% CI) Delinquent behavior Mean"S.D. % OR (95% CI) Aggressive behavior Mean"S.D. % OR (95% CI)
Sleep duration (h)
b
-7 (ns110)
7 (ns428)
8 (ns644)
9 (ns177)
(S.E.)b
5.8"2.8 15.5 2.4 (1.0–5.7)*
5.3"2.8 15.1 2.3 (1.1–4.9)*
4.6"2.7 7.6 1.2 (0.6–2.5)
3.9"2.6 5.1 1.0
y0.43 (y0.12)***
4.3"3.5 15.5 2.0 (0.9–4.5)
3.9"3.3 13.7 1.8 (0.9–3.5)
3.4"2.7 9.2 1.2 (0.6–2.2)
3.4"3.0 7.3 1.0
y0.28 (y0.07)*
9.6"5.9 25.5 4.4 (2.0–9.6)***
8.4"5.5 16.3 2.5 (1.2–5.1)**
7.0"4.6 9.6 1.5 (0.7–3.0)
5.9"4.6 5.6 1.0
y0.98 (y0.15)***
4.8"2.8 17.3 2.2 (1.0–4.6)*
4.5"2.4 11.4 1.3 (0.7–2.5)
4.1"2.3 8.9 1.1 (0.6–2.0)
3.5"2.5 7.9 1.0
y0.31 (y0.10)***
2.7"2.5 13.6 2.0 (0.9–4.4)
2.6"2.4 12.6 1.7 (0.9–3.3)
2.4"2.1 9.6 1.3 (0.7–2.5)
2.1"2.1 7.3 1.0
y0.15 (y0.05)
6.2"3.3 17.3 2.3 (1.0–5.1)*
6.2"3.1 14.2 1.7 (0.9–3.5)
5.4"3.0 10.2 1.4 (0.7–2.7)
4.6"3.0 6.2 1.0
y0.38 (y0.10)***
3.1"2.6 15.5 2.3 (1.1–5.1)*
2.8"2.1 10.5 1.3 (0.7–2.5)
2.7"2.2 11.3 1.5 (0.8–2.7)
2.4"2.7 7.9 1.5 (0.8–2.7)
y0.12 (y0.42)
8.3"5.2 16.4 2.4 (1.1–5.3)*
7.5"4.6 12.1 1.5 (0.8–3.0)
6.8"4.4 9.5 1.3 (0.7–2.5)
5.6"4.8 6.8 1.0
y0.59 (y0.10)***
YSR, Youth Self-Report; OR, odds ratio; CI, confidence interval. a All ORs were adjusted for age and sex. b Standardized regression coefficients using multiple linear regression analysis after controlling for age and sex. *P-0.05; **P0.01; ***P-0.001.
95% CIs2.0–4.2, Walds32.73, P-0.001), withdrawn (ORs2.9, 95% CIs1.9–4.3, Walds27.73, P-0.001), somatic complaints (ORs2.8, 95% CIs1.9–4.1, Walds26.97, P-0.001), attention problems (ORs2.7, 95% CIs1.9–4.0, Walds 27.26, P-0.001), and social problems (ORs2.7, 95% CIs1.9–4.1, Walds25.04, P-0.001). 4. Discussion In this study, we investigated a sample of 1359
Chinese adolescents attending school to examine the associations among reported sleep duration, insomnia and behavioral problems. The main findings of our study are: (1) sleep duration in Chinese adolescents was short (7.6 h), and declined with advancing age; (2) sleep duration was shorter in adolescents with insomnia complaints than those without insomnia, but by less than half an hour; (3) insomnia and shorter sleep duration (less than 7 h a day) were significantly associated with a wide range of behavioral or emotional problems.
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
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Table 3 Sleep duration and behavioral problems (Mean"S.D.) in insomnia and non-insomnia adolescents b (S.E.)a
Sleep duration (h)
Insomnia (ns228) Anxiousydepressed Aggressive behavior Non-insomnia (ns1132) Withdrawn Somatic complaints Anxiousydepressed Social problems Attention problems Aggressive behavior
-7
7
8
9
11.2"6.9 10.5"5.9
11.0"6.2 8.7"5.1
8.4"5.3 7.3"4.0
8.2"6.7 8.1"7.1
y1.04 (y0.15)* y0.85 (y0.14)*
5.4"2.7 4.0"3.3 8.9"5.3 4.7"2.8 5.7"2.9 7.3"4.5
5.0"2.7 3.6"3.0 7.6"4.9 4.2"2.3 5.8"2.9 7.2"4.4
4.4"2.6 3.3"2.6 6.8"4.5 4.0"2.3 5.3"2.9 6.7"4.4
3.8"2.5 3.1"2.6 5.5"4.1 3.4"2.4 4.4"2.9 5.2"4.2
y0.33 y0.37 y0.76 y0.25 y0.30 y0.41
(y0.10)** (y0.08)* (y0.13)*** (y0.08)** (y0.08)* (y0.07)*
a
Standardized regression coefficients using multiple regression analysis after controlling for age and sex. *P-0.05; **P-0.01; ***P-0.001.
Table 4 YSR scale scores and percentages of behavioral problems (P90th percentiles) in relation to insomnia in Chinese adolescents Behavioral problems Withdrawn Mean"S.D. % Somatic complaints Mean"S.D. % Anxiousydepressed Mean"S.D. % Social problems Mean"S.D. % Thought problems Mean"S.D. % Attention problems Mean"S.D. % Delinquent behavior Mean"S.D. % Aggressive behavior Mean"S.D. %
Insomnia (ns228)
Non-insomnia (ns1131)
tayx2
6.3"3.0 21.5
4.5"2.6 8.0
7.69*** 37.13***
5.0"3.7 21.5
3.4"2.8 8.8
7.37*** 31.73***
10.0"6.2 25.4
7.0"4.7 9.9
7.59*** 41.85***
5.1"2.7 20.2
4.0"2.4 8.2
5.66*** 29.52***
3.1"2.4 17.1
2.3"2.2 9.3
4.41*** 12.25***
6.9"3.4 23.2
5.4"3.0 9.2
6.19*** 36.66***
3.2"2.5 14.9
2.6"2.2 10.2
2.79** 4.38*
8.5"5.2 17.5
6.7"4.4 9.1
4.68*** 14.35***
YSR, Youth Self-Report. a Multiple regression analysis after controlling for age and sex. *P-0.05; **P-0.01; ***P-0.001.
Mean sleep duration of our sample was short (7.6 h), comparable with a group of 965 Taipei high school students (Gau and Soong, 1995) and a recent survey of 3120 American high school students in which the authors found the average self-reported total sleep time on school nights was 7 h and 20 min (Wolfson and Carskadon, 1998). Short sleep duration in Chinese adolescents may be attributed to staying up later and rising earlier as a result of early morning class before breakfast (06:30 h), heavy evening homework and late
Fig. 2. Odds ratios (ORs) and 95% confidence intervals of behavioral syndromes in relation to insomnia. I denotes Withdrawn, II Somatic complaints, III Anxiousydepressed, IV Social problems, V Thought problems, VI Attention problems, VII Delinquent behavior, and VIII Aggressive behavior. All ORs were adjusted for age and sex.
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X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
evening activities (Gau and Soong, 1995; Liu et al., 2000a), and biological changes that take place during puberty (Carskadon et al., 1993). Beyond increased homework and other psychosocial demands, short sleep duration in Chinese adolescents may also be attributed to sleep disorders including chronic nightmares, sleep-disordered breathing, restless legs and periodic limb movements, and delayed sleep phase syndrome in addition to psychophysiological insomnia (Stores, 1996; Ohayon et al., 2000; Krakow et al., 2001). Further studies are needed to examine the main determinants of short sleep duration in Chinese adolescents. Our results indicated that self-reported sleep duration was significantly shorter in adolescents who reported insomnia symptoms than in those without insomnia, but the difference was less than half an hour. Our findings differ from those of most previous clinical studies, which reported markedly shorter sleep duration in insomnia patients than in those without insomnia (e.g. Frankel et al., 1976). Because insomniacs may go to bed earlier and get up later than non-insomniacs, we speculate that the total time they are in bed is markedly longer and total sleep time may not be less than non-insomniacs despite the fact that sleep efficiency in insomniacs is poor. In addition, most clinical patients with insomnia often have depressive or anxious symptoms, overestimate sleep latency, but underestimate total sleep time (Bliwise et al., 1993; Chervin and Guilleminault, 1996; Vanable et al., 2000). It is also possible that clinical patients with insomnia suffer from more severe sleep disturbance or are more concerned about their poor sleep than those with insomnia in the general population because most insomniacs in the general population do not seek professional help (Rosekind, 1992). Our results may help explain why most insomniacs complain of sleep loss when, in fact, their total sleep time differs only slightly from that of non-complaining normal sleepers (Coates and Thoresen, 1981). Many experimental studies in healthy humans have found that sleep deprivation may result in a wide range of psychological or physiological impairments, such as anxiety, aggressive behavior, daytime sleepiness, lowered cognitive function,
and endocrine or immunological changes (Devoto et al., 1999; Spiegel et al., 1999; Vgontzas et al., 1999). However, the association between sleep duration and psychosocial well-being in the general population remains unclear (Jean-Louis et al., 2000; Ferrara and Gennaro, 2001). We found that sleep duration of less than 7 h per day was significantly associated with increased risk of behavioral or emotional problems, particularly for anxious or depressed syndrome. Sleep duration of 8 h was not related to any behavioral problems. Thus, sleep duration of 7 h might be considered a threshold for behavioral or emotional problems in Chinese adolescents. Stratified analysis showed that short sleep duration was significantly associated with most behavioral problems in adolescents without insomnia but not in those with complaints of insomnia. That is, for adolescents with insomnia symptoms, short sleep duration was not as likely to predict behavioral problems as it was in those without insomnia complaints. Recently, a few studies indicated that sleep quality rather than sleep quantity could predict adolescents’ school functioning (Meijer et al., 2000), negative mood, or physical complaints (Pilcher et al., 1997). Unfortunately, we did not measure sleep quality of our sample. The association between sleep quality and behavioral problems and the extent to which the association between sleep duration and behavioral problems would be changed after controlling for the effects of sleep quality need to be further investigated with Chinese adolescents. Insomnia was associated with a wide range of behavioral or emotional problems in our sample, consistent with most previous cross-sectional studies of adolescents in Western countries (Morrison et al., 1992; Vignau et al., 1997; Alapin et al., 2000; Johnson et al., 2000; Roberts et al., 2001). The fact that insomnia was most strongly associated with depressionyanxiety is not surprising, because insomnia is a cardinal symptom of major depression (American Psychiatric Association, 1994). The link between disturbed sleep and depression has long been demonstrated in most cross-sectional and a few prospective studies of adolescents and adults (Kirmil-Gray et al., 1984; Ford and Kamerow, 1989; Breslau et al., 1996; Chang et al., 1997; Johnson et al., 2000; Roberts
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
et al., 2001). Clinical studies have shown that patients with insomnia often have symptoms of depression or anxiety and that patients with mental disorders often complain of insomnia (Ford and Kamerow, 1989; Benca et al., 1992; Buysse et al., 1994). However, a mere association between disturbed sleep and mental disorders tells us little about cause and effect. Disturbed sleep may prompt mental disorders; mental disorders may contribute to disturbed sleep; or both may be caused by common factors that predispose to both disturbed sleep and mental disorders. Many psychosocial and biological factors, such as family psychiatric history, substance use, or stressful life events, may be associated with both insomnia and mental disorders. Thus, it is difficult to disentangle whether insomnia is a precursor, sequel, or comorbidity of mental disorders. Replication of these results and ultimately naturalistic prospective studies will shed more light on the association between insomnia and behavioral problems in adolescents. In interpreting these results, it is important to consider some methodological limitations of this study. One of the obvious limitations is that we did not have objective data on sleep duration and insomnia symptoms such as electroencephalography (EEG), which is of great importance in ruling out other sleep disorders causing insomnia (Krakow et al., 2001). We defined sleep duration as the adolescent’s perceived sleep time, and insomnia symptoms as the adolescent’s positive responses to three questions. Although objective measures of sleep duration and sleep problems are desirable, self-reports and interview measures remain the measures of choice in large-scale epidemiologic studies (Ohayon et al., 2000; Roberts et al., 2001) and there is evidence that subjective measures of sleep from children and adolescents are correlated with objective measures (Sadeh et al., 1995). Second, based on a self-report questionnaire with four generalized questions of sleep behavior, we could neither differentiate DIS insomnia from delayed sleep phase syndrome nor differentiate some poor sleepers (e.g. hypersomnia due to physiological sleep disorders) from non-insomniacs. This may cause biased estimation of sleep duration for insomniacs and non-insomniacs and the asso-
83
ciation between insomnia and behavioral problems. This limitation of our study should be addressed in future studies. Furthermore, although our sample was large, the fact that local officials selected the schools from which classes could be selected for assessment and that the students absent on the day of survey were not further tested is a potential biasing factor. Because absentees tend to have higher rates of mental health problems, the absence of these students possibly underestimates insomnia symptoms and their association with behavior problems. To our best knowledge, this is the first attempt to systematically relate sleep duration, insomnia symptoms, and behavioral problems in a large general population sample of Chinese adolescents. Our findings have important implications for public health and clinical relevance. First, we found that adolescents who present with complaints of insomnia and sleep duration of less than 7 h a day were at higher risk for significant behavioraly emotional problems, particularly for depression and anxiety. Because Chinese adolescents with psychopathology rarely seek professional help and those who do seek help are often referred to physicians or neurologists for complaints of insomnia (Parker et al., 2001), we suggest that those adolescents who complain of insomnia andyor short sleep duration (less than 7 h a day) need further psychiatric assessment for early detection and intervention of mental health problems. Second, our results indicated that adolescents with insomnia in the general population reported sleep duration only approximately half an hour less than those without insomnia. These results underline the importance of sleep hygiene education in sleep clinics to reassure patients with insomnia that their sleep duration is not as short as they perceive because clinical insomniacs often underestimate their sleep duration, which, in turn, leads to anxiety and exacerbates insomnia. Acknowledgments This research was supported in part by the Shandong Medical Research Foundation, People’s Republic of China, and the Multi-Investigator Proposal Development Grant Program, Arizona State
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University. The authors thank Dr Andrew Rowland, Epidemiology Branch, National Institute of Environmental Health Sciences, for his comments on the manuscript. References Achenbach, T.M., 1991. Manual for the Youth Self-Report and 1991 Profile. University of Vermont, Department of Psychology, Burlington. Alapin, I., Fichten, C.S., Libman, E., Creti, L., Bailes, S., Wright, J., 2000. How is good and poor sleep in older adults and college students related to daytime sleepiness, fatigue, and ability to concentrate? Journal of Psychosomatic Research 49, 381–390. American Psychiatric Association, 1994. Diagnostic and Statistical Manual of Mental Disorders, fourth ed. American Psychiatric Press, Washington, DC. Benca, R.M., Obermeyer, W.H., Thisted, R.A., Gillin, J.C., 1992. Sleep and psychiatric disorders. A meta-analysis. Archives of General Psychiatry 49, 651–668. Bliwise, D.L., Friedman, L.Y., Jerome, A., 1993. Depression as a confounding variable in the estimation of habitual sleep time. Journal of Clinical Psychology 49, 471–477. Breslau, N., Roth, T., Rosenthal, L., Andreski, P., 1996. Sleep disturbance and psychiatric disorders: a longitudinal epidemiological study of young adults. Biological Psychiatry 39, 411–418. Buysse, D.J., Reynolds, C.F., Hauri, P.J., Roth, T., Stepanski, E.J., Thorpy, M.J., Bixler, E.O., Kales, A., Manfredi, R.L., Vgontzas, A.N., Stapf, D.M., Houck, P.R., Kupfer, D.J., 1994. Diagnostic concordance for DSM-IV sleep disorders: a report from the APAyNIMH DSM-IV field trial. American Journal of Psychiatry 15, 1351–1360. Byrd, R.S., Weitzman, M., Lanphear, N.E., Auinger, P., 1996. Bedwetting in US children: epidemiology and related behavior problems. Pediatrics 98, 414–419. Carskadon, M.A., 1990. Patterns of sleep and sleepiness in adolescents. Pediatrician 17, 5–12. Carskadon, M.A., Vieira, C., Acebo, C., 1993. Association between puberty and delayed phase preference. Sleep 16, 258–262. Carskadon, M.A., Wolfson, A.R., Acebo, C., Tzischinsky, O., Seife, R., 1998. Adolescent sleep patterns, circadian timing, and sleepiness at a transition to early school days. Sleep 21, 871–881. Chang, P.P., Ford, D.E., Mead, L.A., Cooper-Patrick, L., Klag, M.J., 1997. Insomnia in young men and subsequent depression. The Johns Hopkins Precursors Study. American Journal of Epidemiology 146, 105–114. Chervin, R.D., Guilleminault, C., 1996. Overestimation of sleep latency by patients with suspected hypersomnolence. Sleep 19, 94–100. Coates, T.J., Thoresen, C.E., 1981. Treating sleep disorders: few answers, some suggestions, and many questions. In: Turner, S.M., Calhoun, K.S., Adams, H.E. (Eds.), Handbook
of Clinical Behavior Therapy. Wiley, New York, pp. 240–289. Devoto, A., Lucidi, F., Violani, C., Bertini, M., 1999. Effects of different sleep reductions on daytime sleepiness. Sleep 22, 336–343. Ferrara, M., Gennaro, L.D., 2001. How much sleep do we need? Sleep Medicine Review 5, 155–179. Ford, D.E., Kamerow, D.B., 1989. Epidemiologic study of sleep disturbances and psychiatric disorders: an opportunity for prevention? Journal of the American Medical Association 262, 1479–1484. Frankel, B.L., Coursey, R.D., Buchbinder, R., Snyder, F., 1976. Recorded and reported sleep in chronic primary insomnia. Archives of General Psychiatry 33, 615–623. Gau, S.F., Soong, W.T., 1995. Sleep problems of junior high school students in Taipei. Sleep 18, 667–673. Jean-Louis, G., Kripke, D.F., Ancoli-Israel, S., 2000. Sleep and quality of well-being. Sleep 23, 1115–1121. Johnson, E.O., Chilcoat, H.D., Breslau, N., 2000. Trouble sleeping and anxietyydepression in childhood. Psychiatry Research 94, 93–102. Kirmil-Gray, K., Eaglestone, J.R., Gibson, E., Thoresen, C.E., 1984. Sleep disturbance in adolescents: sleep quality, sleep habits, beliefs about sleep, and daytime functioning. Journal of Youth and Adolescence 13, 375–384. Krakow, B., Melendrez, D., Ferreira, E., Clark, J., Warner, T.D., Sisley, B., Sklar, D., 2001. Prevalence of insomnia symptoms in patients with sleep-disordered breathing. Chest 120, 1923–1929. Laberge, L., Petit, D., Simard, C., Vitaro, F., Tremblay, R.E., 2001. Development of sleep patterns in early adolescence. Journal of Sleep Research 10, 59–67. Liu, X., Guo, C., Liu, L., Sun, L., 1997. Reliability and validity of the Youth Self-Report in Chinese adolescents. Chinese Journal of Mental Health 11, 200–203. Liu, X., Kurita, H., Guo, C., Miyake, Y., Ze, J., Cao, H., 1999. Prevalence and risk factors of behavioral problems among Chinese children aged 6–11. Journal of the American Academy of Child and Adolescent Psychiatry 38, 708–715. Liu, X., Kurita, H., Uchiyama, M., Okawa, M., Liu, L., Ma, D., 2000a. Life events, locus of control, and behavioral problems among Chinese adolescents. Journal of Clinical Psychology 56, 1565–1577. Liu, X., Uchiyama, M., Okawa, M., Kurita, H., 2000b. Prevalence and correlates of self-reported sleep problems among Chinese adolescents. Sleep 23, 27–33. Liu, X., Sun, Z., Neiderhiser, J.M., Uchiyama, M., Okawa, M., Rogan, W., 2001. Behavioral and emotional problems in Chinese adolescents: parent and teacher reports. Journal of the American Academy of Child and Adolescent Psychiatry 40, 828–836. Meijer, A.M., Habekothe, H.T., Van Den Wittenboer, G.L.H., 2000. Time in bed, quality of sleep and school functioning of children. Journal of Sleep Research 9, 145–153. Morrison, D.N., McGee, R., Stanton, W.R., 1992. Sleep problems in adolescence. Journal of the American Academy of Child and Adolescent Psychiatry 31, 94–99.
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85 Ohayon, M.M., Caulet, M., Priest, R.G., Guilleminault, C., 1997. DSM-IV and ICD-10 insomnia symptoms and sleep dissatisfaction. British Journal of Psychiatry 171, 382–388. Ohayon, M.M, Roberts, R.E., Zulley, J., Smirne, S., Priest, R., 2000. Prevalence and patterns of problematic sleep among older adolescents. Journal of the American Academy of Child and Adolescent Psychiatry 39, 1549–1556. Parker, G., Gladstone, G., Chee, K.T., 2001. Depression in the planet’s largest ethic group: the Chinese. American Journal of Psychiatry 158, 857–864. Pilcher, J.J., Ginter, D.R., Sadowsky, B., 1997. Sleep quality versus sleep quantity: relationships between sleep and measures of health, well-being and sleepiness in college students. Journal of Psychosomatic Research 42, 583–596. Roberts, R.E., Roberts, C.R., Chen, I.G., 2001. Functioning of adolescents of disturbed sleep. Journal of Youth and Adolescence 30, 1–18. Rosekind, M.R., 1992. The epidemiology and occurrence of insomnia. Journal of Clinical Psychiatry 53, 4–6. Sadeh, A., McGuire, J.P., Sachs, H., Seifer, R., Tremblay, A., Civita, R., Hayden, R.M., 1995. Sleep and psychological characteristics of children on a psychiatric inpatient unit. Journal of the American Academy of Child and Adolescent Psychiatry 34, 813–819.
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Spiegel, K., Leproult, R., Cauter, E.V., 1999. Impact of sleep debt on metabolic and endocrine function. Lancet 354, 1435–1439. Stores, G., 1996. Practitioner review: assessment and treatment of sleep disorders in children and adolescents. Journal of Child Psychology and Psychiatry 37, 907–925. Straugh, I., Meier, B., 1988. Sleep need in adolescents: a longitudinal approach. Sleep 11, 378–386. Vanable, P.A., Aikens, J.E., Tadimeti, L., Caruana-Montaldo, B., Mendelson, W.B., 2000. Sleep latency and duration estimates among sleep disorder patients: variability as a function of sleep disorder diagnosis, sleep history, and psychological characteristics. Sleep 23, 71–79. Vgontzas, A.N., Mastorakos, G., Bixler, E.O., Kales, A., Gold, P.W., Chrousos, G.P., 1999. Sleep deprivation effects on the activity of the hypothalamic-pituitary-adrenal and growth axes: potential clinical implications. Clinical Endocrinology 51, 205–215. Vignau, J., Bailly, D., Duhamel, A., Vervaecke, P., Beuscart, R., Collinet, C., 1997. Epidemiologc study of sleep quality and troubles in French secondary school adolescents. Journal of Adolescent Health 21, 343–350. Wolfson, A.R., Carskadon, M.A., 1998. Sleep schedules and daytime functioning in adolescents. Child Development 69, 875–887.
Sleep duration, insomnia and behavioral problems among Chinese adolescents Xianchen Liua,b,*, Haibo Zhouc a
Department of Family and Human Development and Program for Prevention Research, Arizona State University, P.O. Box 876005, Tempe, AZ 85287, USA b Shandong University School of Public Health, Jinan, PR China c Department of Biostatics, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Received 11 October 2001; received in revised form 5 April 2002; accepted 19 May 2002
Abstract This study examined the associations among sleep duration, insomnia, and behavioral problems in a sample of 1359 Chinese adolescents. Participants completed a self-administrated questionnaire that included questions on sleep duration and insomnia symptoms and the Youth Self-Report of Child Behavior Checklist. It was found that adolescents who complained of insomnia reported sleep duration only half an hour shorter than did those without insomnia. Sleep duration did not differ among adolescents reporting three different types of insomnia (difficulty initiating sleep, difficulty maintaining sleep, and early morning awakening). Adolescents with insomnia reported more behavioral problems than did those without complaints of insomnia. After adjustment for age and sex, sleep duration of less than 7 h a day was significantly associated with most behavioral problems in those without complaints of insomnia but with only a few behavioral problems in adolescents reporting insomnia. Results suggest that sleep duration in adolescents with insomnia is short, but not as short as reported in previous clinical studies. Insomnia and short sleep duration are associated with a wide range of behavioral and emotional problems in adolescents. 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Behavioral problems; Emotional problems; Insomnia; Sleep duration
1. Introduction Numerous studies have consistently reported that adolescents do not get enough sleep and that their sleep patterns are characterized by staying up late (e.g. Straugh and Meier, 1988; Carskadon, *Corresponding author. Tel.: q1-480-727-6145; fax: q1480-965-5430. E-mail address: [email protected] (X. Liu).
1990; Wolfson and Carskadon, 1998; Laberge et al., 2001). Shorter sleep duration in adolescents possibly results from a combination of early school start times, late afternoonyevening jobs and activities, academic and social pressure, a physiological sleep requirement that does not decrease with puberty (Carskadon, 1990; Wolfson and Carskadon, 1998), and sleep disorders (e.g. chronic nightmares, sleep-disordered breathing, delayed sleep
0165-1781/02/$ - see front matter 䊚 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 5 - 1 7 8 1 Ž 0 2 . 0 0 1 3 1 - 2
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phase syndrome) (Stores, 1996; Ohayon et al., 2000; Krakow et al., 2001). Most studies have demonstrated that the way adolescents sleep and their tendency to get insufficient sleep result in negative effects on their ability to think and concentrate in school, school performance, behavior, and mood during daytime hours, increased risk for injuries and accidents, use of drugs and alcohol, and circadian sleep disorders (Carskadon, 1990; Carskadon et al., 1998; Wolfson and Carskadon, 1998; Laberge et al., 2001). A few studies of adolescent sleep reported that sleep quality but not sleep quantity (time in bed or time asleep) was correlated with school functioning, physical complaints, or negative mood (Pilcher et al., 1997; Meijer et al., 2000). Insomnia is one of the most common sleep disturbances in adolescents. Ohayon et al. (2000) reported 25% of adolescents had insomnia symptoms. The association between insomnia and mental disorders has long been concerned. Clinically, insomnia is a principal symptom of major depression and anxiety, and is considered a precursor of onset or relapse of many mental disorders, such as schizophrenia, mania, and major depression, drug abuse, and anxiety disorder (American Psychiatric Association, 1994). Many cross-sectional studies have found that insomnia is associated with various mental health problems in the general population of adults and adolescents (Ford and Kamerow, 1989; Stores, 1996; Vignau et al., 1997; Ohayon et al., 1997, 2000; Roberts et al., 2001). Recent prospective studies of adults indicate that insomnia predicts the development of major depression, anxiety, or alcohol abuse (Ford and Kamerow, 1989; Breslau et al., 1996; Chang et al., 1997). However, one study of 823 children did not find a prospective association between trouble sleeping at age 6 and parent-reported anxietyydepression at age 11 years (Johnson et al., 2000). No prospective studies have reported the association between sleep disturbance and mental disorders in adolescents. However, one of the disappointing aspects of research in this area is that the aforementioned findings are based almost exclusively on studies in Western countries. The findings from Western samples may not generalize to Chinese adolescents, because sleep behavior, sleep schedules and
mental disorders are all influenced by potential environmental and cultural factors. For example, Chinese adolescents have to get up earlier for morning class before breakfast (Liu et al., 2000b). Compared with Western adolescents, Chinese adolescents have been reported to have fewer externalizing problems but more internalizing problems (Liu et al., 2001). This study with a large population sample of Chinese adolescents was carried out in 1993 (Liu et al., 2000b). In our previous report, we found that 17% of Chinese adolescents had complaints of insomnia symptoms and that multiple psychosocial and biological factors were associated with an increased risk for sleep problems (Liu et al., 2000b). In this report, we aimed to examine the relationships between self-reported sleep duration and complaints of insomnia. Clinical patients with insomnia often have depressive or anxious symptoms, overestimate sleep latency, and underestimate total sleep time (Bliwise et al., 1993; Chervin and Guilleminault, 1996; Vanable et al., 2000), but the relationship between self-reported sleep duration and insomnia symptoms in the general population has been less addressed. We also aimed to examine the association between reported sleep duration and a wide range of behavioral problems measured by the Youth Self-Report of the Achenbach Child Behavior Checklist (Achenbach, 1991). If the association was detected, we wanted to find a threshold of sleep duration, which is associated with a significantly increased risk for behavioral problems. Finally, we aimed to test the hypothesis that insomnia would be associated with increased risks for behavioral or emotional problems in Chinese adolescents. If the association were found, we proposed to identify which behavioral or emotional problems would be most strongly associated with insomnia. 2. Methods 2.1. Subjects and procedure This cross-sectional survey was carried out in Hezhe Prefecture of Shandong Province, in eastern China. The details of the study design and procedure were described elsewhere (Liu et al.,
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2000a,b). Briefly, after considering the geographic distribution, population size, time and financial constraints, and representatives of the sample, we planned to recruit a total of 1300 students (250– 300 for each grade) from five or six public high schools in this area. According to our requirement, the prefecture education committee selected five high schools (three junior and two senior), which could represent average schools of the area. After obtaining permission from the principals of the target schools, we randomly recruited half of the classes for each grade in each target school. As a result of the procedure, 1400 students in the target classes on the day of survey were recruited as potential participants. It is a standard procedure in China to obtain consent from the principals, not the parents, since schools in China act in loco parentis. The 12th graders were not included in the survey because they were preparing for university entrance examinations. Of 1400 students who were asked to participate, 1359 completed the questionnaire (97%). Participants consisted of 814 junior high school and 546 senior high school students, and 822 boys (60%) and 537 girls (40%). Participants had a mean age of 14.6 years (S.D.s3.4), with a range of 12–18 years. The average family size (including the subject) was 5.8 (S.D.s3.0). Most of the fathers (80%) and mothers (83%) were farmers. Sixtyeight percent of the fathers and 90% of the mothers had only primary or junior high school education. Mean maternal age was 40.1 years (S.D.s12.2) and mean paternal age was 41.3 years (S.D.s 11.9). With the help of teachers, trained psychiatrists administered the questionnaire to the sample of students in their classrooms during regular school hours. All the students attending school on the day of the survey gave their consent even though they were given the option of not participating. Before completing the questionnaire, the students were told to read the instructions carefully and to ask about anything they did not understand. The psychiatrists monitored the session and answered questions as needed to ensure that all questionnaires would be completed as accurately as possible. Approximately 30 min were required to complete the questionnaire.
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2.2. Measures A self-administered questionnaire was developed to investigate mental health problems in adolescents attending school. Four generalized questions were included in the questionnaire with regard to sleep behavior: ‘On the average, how many hours do you sleep at night?’ ‘Do you have difficulty getting to sleep at night?’ ‘Do you awaken during the night and have trouble getting back to sleep?’ ‘Do you awaken too early in the morning and have trouble getting back to sleep?’ The time frame for the questions was the past month and the response categories for questions 2–4 were: (1) never or rarely; (2) sometimes; and (3) often. Questions 2, 3 and 4 were used to estimate insomnia resulting from difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS) and early morning awakening (EMA). If an adolescent answered ‘often’ to at least one of the three questions, he or she was defined as a ‘case’ of insomnia. We used the Youth Self-Report (YSR; Achenbach, 1991) of the Child Behavior Checklist to measure adolescents’ behavioral problems. Due to its sufficient psychometric properties, the YSR has been widely applied in clinical assessment and research in many countries, including China (Achenbach, 1991; Liu et al., 1997, 2000a). The YSR is composed of 103 problem items to which the respondent can answer ‘0’ if the problem is not true of him or her, ‘1’ if the item is somewhat or sometimes true, and ‘2’ if it is very true or often true. Respondents were asked to select the response that described their behaviors or feelings at the time they completed the questionnaire or within the past 6 months. The YSR includes eight subscales: Withdrawn (seven items), Somatic Complaints (nine items), AnxiousyDepressed (16 items), Social Problems (eight items), Thought Problems (seven items), Attention Problems (nine items), Delinquent Behavior (11 items), and Aggressive Behavior (19 items). To identify more specifically the nature of the behavioral or emotional problems associated with insomnia and sleep duration, the eight subscales were used for analyses. The Chinese YSR has satisfactory reliability,
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and a total YSR score of 70 as cut-off has been reported to be indicative of significant mental health problems (Liu et al., 1997). Cronbach’s alpha coefficients with the present sample were 0.93 for the total scale; mean Cronbach’s alpha for eight subscales was 0.65. 2.3. Statistical analysis Analysis of variance (ANOVA) was performed to examine age differences in sleep duration and overall behavior problem scores, and to compare sleep duration among groups with different insomnia symptoms (DIS, DMS, EMA, two symptoms) and those without insomnia. Student’s t-tests were used to compare sleep duration and behavior problem scores between boys and girls. Chi-square tests were used to compare frequencies of insomnia symptoms in relation to age, gender, and sleep duration. As previous studies have shown that age and gender of adolescents are associated with sleep duration, insomnia symptoms and behavior problems as well (Vignau et al., 1997; Wolfson and Carskadon, 1998), age and gender were adjusted for in examinations of the associations between sleep duration, insomnia, and behavior problems. Multiple linear regression analyses were performed to examine the relationships between insomnia and behavioral problems and to determine whether sleep duration could predict behavioral problems after adjustment for age and sex. To estimate the clinical relevance of the associations of sleep duration and insomnia with behavioral problems, multiple logistic regression analyses were performed on a binary outcome variable indicating whether an individual’s behavioral score was above or below the 90th percentiles (Byrd et al., 1996; Liu et al., 1999). Odds ratios (ORs) and their 95% confidence intervals (CI) were calculated to show the association. All the analyses were performed with SPSS 10.1 for Windows. The threshold of statistical significance was set at P-0.05. 3. Results Of the sample, 16.9% reported insomnia symptoms, including difficulty initiating sleep (10.8%),
Table 1 Sleep duration (hours), insomnia and behavior problems according to age Age (years)
n
Sleep duration Insomnia Mean"S.D. %
Behavior problemsa Mean"S.D.
12 13 14 15 16 17 18 Statistical tests
88 125 207 323 315 242 60
8.3"0.7 8.1"0.8 7.7"0.8 7.6"0.9 7.4"0.9 7.5"0.7 7.5"0.7 Fs24.13***
30.6"20.0 36.1"11.2 41.3"21.7 43.2"16.5 46.3"21.7 46.6"22.5 50.2"21.8 Fs10.58***
a
10.2 11.2 10.1 16.5 21.6 20.2 23.3 x2s21.19***
Total score of the Youth Self-Report. ***P-0.001.
difficulty maintaining sleep (6.3%), and early morning awakening (2.1%); mean sleep duration at night was 7.6"0.8 hours; mean YSR total problems score was 43.1"22.1, and 10.7% of the students scored higher than the cutoff score of 70 (Liu et al., 1997). Mean sleep duration significantly declined between 12 and 16 years of age, while insomnia symptoms significantly increased between 14 and 18 years of age (Table 1). Girls reported sleep duration a little shorter than boys (7.6"0.8 vs. 7.7"0.9 hours, ts2.04, Ps0.04). There was no significant gender difference in overall prevalence of insomnia (x2s0.02, P) 0.05). Mean behavior problem scores significantly increased across age (Fs10.58, d.f.s6, P0.001), but did not significantly differ between boys and girls (ts1.50, d.f.s1357, Ps0.13). 3.1. Insomnia symptoms and sleep duration Mean sleep duration was significantly shorter in adolescents with insomnia than in those without complaints of insomnia (7.7"0.8 h vs. 7.3"0.9 h; ts5.83, d.f.s1357, P-0.001), but the difference was less than 30 min. To further examine the association between insomnia symptoms and sleep duration, we divided the subjects into five groups: DIS, DMS, EMA, two insomnia symptoms, and non-insomnia. Adolescents with two symptoms reported shortest sleep duration (7.0"0.9 h), followed by EMA (7.3"0.7 h), DIS (7.4"0.9 h), DMS (7.5"1.0 h), and non-insomnia (7.7"0.8
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
Fig. 1. Prevalence (%) of insomnia in different sleep-duration groups.
h). ANOVA showed that sleep duration significantly differed among the five groups (Fs9.90, d.f.s3, P-0.001). Post-hoc Tukey tests showed significant differences in sleep duration only between non-insomnia and DIS (mean differences0.32 h, Ps0.001) or two symptoms (mean differences0.73 h, P-0.001). Fig. 1 shows the prevalence of insomnia in different sleep-duration groups. The prevalence of insomnia ranged from 11% for those sleeping 8 h a day to 32% for those sleeping less than 7 h and differed significantly among the four sleep-duration groups (x2s49.39, d.f.s3, P-0.001). Logistic regression analysis showed that the adolescents with sleep duration of less than 7 h were over three times as likely to report insomnia as those with sleep duration of 8 or more h (ORs3.6, 95% CIs2.3-5.7, Walds9.49, P-0.001). 3.2. Sleep duration and behavioral problems We performed multiple linear and logistic regression analyses to examine the dose–response relationships between sleep duration and behavioral problems after adjustment for age and sex. As shown in Table 2, most behavioral problem scores significantly declined with longer sleep duration with the exceptions of thought problems and delinquent behavior. Compared with sleep duration of 9 h, sleep duration of less than 7 h was significantly associated with increased risk for most
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behavioral problems; sleep duration of 7 h was associated only with increased risk for withdrawn and anxiousydepressed symptoms; sleep duration of 8 h was not associated with any behavioral problems. The association of short sleep duration with anxiousydepressed syndrome was stronger than that with any other behavioral problems. To examine whether the effects of sleep duration on behavioral problems differed between insomniacs and non-insomniacs, we performed multiple linear and logistical regression analyses for insomniacs and non-insomniacs separately (Table 3). For insomniacs, only anxiousydepressed and aggressive behavior significantly decreased with increased sleep duration. For non-insomniacs, however, most behavioral problems except for thought problems and delinquent behavior significantly decreased with increased sleep duration. Short sleep duration accounted for the largest portion of the variance in anxiousydepressed (13%). Logistic regression models showed only two problems among non-insomniacs and no problems among insomniacs to be associated with decreased sleep duration. Compared with sleep duration of 9 h a day, sleep duration of less than 7 h was associated with increased risk of anxiousy depressed (ORs4.5, 95% CIs1.7–11.7, Walds 9.68, P-0.001) and for social problems (ORs 2.7, 95% CIs1.1–6.7, Walds4.91, P-0.02). 3.3. Insomnia and behavioral problems Table 4 presents mean scores and frequencies of behavioral problems for insomniacs and noninsomniacs. Multiple linear regression analyses indicated that mean scores on all behavior problem scales were significantly higher in insomniacs than in non-insomniacs at P-0.01. Chi-square tests showed that the frequencies of all behavior problems were significantly higher in insomniacs than in non-insomniacs (Table 4). Logistic regression models showed that insomnia was significantly associated with increased risk for all behavioral problems except for delinquent behavior. Odds ratios and 95% confidence intervals are presented to show the association (Fig. 2). As seen in Fig. 2, the strongest associations of insomnia were with anxiousydepressed (ORs2.9,
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Table 2 YSR scale scores and percentages of behavioral problems (P90th percentiles) in relation to sleep duration Behavioral problems
a
Withdrawn Mean"S.D. % OR (95% CI) Somatic complaints Mean"S.D. % OR (95% CI) Anxiousydepressed Mean"S.D. % OR (95% CI) Social problems Mean"S.D. % OR (95% CI) Thought problems Mean"S.D. % OR (95% CI) Attention problems Mean"S.D. % OR (95% CI) Delinquent behavior Mean"S.D. % OR (95% CI) Aggressive behavior Mean"S.D. % OR (95% CI)
Sleep duration (h)
b
-7 (ns110)
7 (ns428)
8 (ns644)
9 (ns177)
(S.E.)b
5.8"2.8 15.5 2.4 (1.0–5.7)*
5.3"2.8 15.1 2.3 (1.1–4.9)*
4.6"2.7 7.6 1.2 (0.6–2.5)
3.9"2.6 5.1 1.0
y0.43 (y0.12)***
4.3"3.5 15.5 2.0 (0.9–4.5)
3.9"3.3 13.7 1.8 (0.9–3.5)
3.4"2.7 9.2 1.2 (0.6–2.2)
3.4"3.0 7.3 1.0
y0.28 (y0.07)*
9.6"5.9 25.5 4.4 (2.0–9.6)***
8.4"5.5 16.3 2.5 (1.2–5.1)**
7.0"4.6 9.6 1.5 (0.7–3.0)
5.9"4.6 5.6 1.0
y0.98 (y0.15)***
4.8"2.8 17.3 2.2 (1.0–4.6)*
4.5"2.4 11.4 1.3 (0.7–2.5)
4.1"2.3 8.9 1.1 (0.6–2.0)
3.5"2.5 7.9 1.0
y0.31 (y0.10)***
2.7"2.5 13.6 2.0 (0.9–4.4)
2.6"2.4 12.6 1.7 (0.9–3.3)
2.4"2.1 9.6 1.3 (0.7–2.5)
2.1"2.1 7.3 1.0
y0.15 (y0.05)
6.2"3.3 17.3 2.3 (1.0–5.1)*
6.2"3.1 14.2 1.7 (0.9–3.5)
5.4"3.0 10.2 1.4 (0.7–2.7)
4.6"3.0 6.2 1.0
y0.38 (y0.10)***
3.1"2.6 15.5 2.3 (1.1–5.1)*
2.8"2.1 10.5 1.3 (0.7–2.5)
2.7"2.2 11.3 1.5 (0.8–2.7)
2.4"2.7 7.9 1.5 (0.8–2.7)
y0.12 (y0.42)
8.3"5.2 16.4 2.4 (1.1–5.3)*
7.5"4.6 12.1 1.5 (0.8–3.0)
6.8"4.4 9.5 1.3 (0.7–2.5)
5.6"4.8 6.8 1.0
y0.59 (y0.10)***
YSR, Youth Self-Report; OR, odds ratio; CI, confidence interval. a All ORs were adjusted for age and sex. b Standardized regression coefficients using multiple linear regression analysis after controlling for age and sex. *P-0.05; **P0.01; ***P-0.001.
95% CIs2.0–4.2, Walds32.73, P-0.001), withdrawn (ORs2.9, 95% CIs1.9–4.3, Walds27.73, P-0.001), somatic complaints (ORs2.8, 95% CIs1.9–4.1, Walds26.97, P-0.001), attention problems (ORs2.7, 95% CIs1.9–4.0, Walds 27.26, P-0.001), and social problems (ORs2.7, 95% CIs1.9–4.1, Walds25.04, P-0.001). 4. Discussion In this study, we investigated a sample of 1359
Chinese adolescents attending school to examine the associations among reported sleep duration, insomnia and behavioral problems. The main findings of our study are: (1) sleep duration in Chinese adolescents was short (7.6 h), and declined with advancing age; (2) sleep duration was shorter in adolescents with insomnia complaints than those without insomnia, but by less than half an hour; (3) insomnia and shorter sleep duration (less than 7 h a day) were significantly associated with a wide range of behavioral or emotional problems.
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85
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Table 3 Sleep duration and behavioral problems (Mean"S.D.) in insomnia and non-insomnia adolescents b (S.E.)a
Sleep duration (h)
Insomnia (ns228) Anxiousydepressed Aggressive behavior Non-insomnia (ns1132) Withdrawn Somatic complaints Anxiousydepressed Social problems Attention problems Aggressive behavior
-7
7
8
9
11.2"6.9 10.5"5.9
11.0"6.2 8.7"5.1
8.4"5.3 7.3"4.0
8.2"6.7 8.1"7.1
y1.04 (y0.15)* y0.85 (y0.14)*
5.4"2.7 4.0"3.3 8.9"5.3 4.7"2.8 5.7"2.9 7.3"4.5
5.0"2.7 3.6"3.0 7.6"4.9 4.2"2.3 5.8"2.9 7.2"4.4
4.4"2.6 3.3"2.6 6.8"4.5 4.0"2.3 5.3"2.9 6.7"4.4
3.8"2.5 3.1"2.6 5.5"4.1 3.4"2.4 4.4"2.9 5.2"4.2
y0.33 y0.37 y0.76 y0.25 y0.30 y0.41
(y0.10)** (y0.08)* (y0.13)*** (y0.08)** (y0.08)* (y0.07)*
a
Standardized regression coefficients using multiple regression analysis after controlling for age and sex. *P-0.05; **P-0.01; ***P-0.001.
Table 4 YSR scale scores and percentages of behavioral problems (P90th percentiles) in relation to insomnia in Chinese adolescents Behavioral problems Withdrawn Mean"S.D. % Somatic complaints Mean"S.D. % Anxiousydepressed Mean"S.D. % Social problems Mean"S.D. % Thought problems Mean"S.D. % Attention problems Mean"S.D. % Delinquent behavior Mean"S.D. % Aggressive behavior Mean"S.D. %
Insomnia (ns228)
Non-insomnia (ns1131)
tayx2
6.3"3.0 21.5
4.5"2.6 8.0
7.69*** 37.13***
5.0"3.7 21.5
3.4"2.8 8.8
7.37*** 31.73***
10.0"6.2 25.4
7.0"4.7 9.9
7.59*** 41.85***
5.1"2.7 20.2
4.0"2.4 8.2
5.66*** 29.52***
3.1"2.4 17.1
2.3"2.2 9.3
4.41*** 12.25***
6.9"3.4 23.2
5.4"3.0 9.2
6.19*** 36.66***
3.2"2.5 14.9
2.6"2.2 10.2
2.79** 4.38*
8.5"5.2 17.5
6.7"4.4 9.1
4.68*** 14.35***
YSR, Youth Self-Report. a Multiple regression analysis after controlling for age and sex. *P-0.05; **P-0.01; ***P-0.001.
Mean sleep duration of our sample was short (7.6 h), comparable with a group of 965 Taipei high school students (Gau and Soong, 1995) and a recent survey of 3120 American high school students in which the authors found the average self-reported total sleep time on school nights was 7 h and 20 min (Wolfson and Carskadon, 1998). Short sleep duration in Chinese adolescents may be attributed to staying up later and rising earlier as a result of early morning class before breakfast (06:30 h), heavy evening homework and late
Fig. 2. Odds ratios (ORs) and 95% confidence intervals of behavioral syndromes in relation to insomnia. I denotes Withdrawn, II Somatic complaints, III Anxiousydepressed, IV Social problems, V Thought problems, VI Attention problems, VII Delinquent behavior, and VIII Aggressive behavior. All ORs were adjusted for age and sex.
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evening activities (Gau and Soong, 1995; Liu et al., 2000a), and biological changes that take place during puberty (Carskadon et al., 1993). Beyond increased homework and other psychosocial demands, short sleep duration in Chinese adolescents may also be attributed to sleep disorders including chronic nightmares, sleep-disordered breathing, restless legs and periodic limb movements, and delayed sleep phase syndrome in addition to psychophysiological insomnia (Stores, 1996; Ohayon et al., 2000; Krakow et al., 2001). Further studies are needed to examine the main determinants of short sleep duration in Chinese adolescents. Our results indicated that self-reported sleep duration was significantly shorter in adolescents who reported insomnia symptoms than in those without insomnia, but the difference was less than half an hour. Our findings differ from those of most previous clinical studies, which reported markedly shorter sleep duration in insomnia patients than in those without insomnia (e.g. Frankel et al., 1976). Because insomniacs may go to bed earlier and get up later than non-insomniacs, we speculate that the total time they are in bed is markedly longer and total sleep time may not be less than non-insomniacs despite the fact that sleep efficiency in insomniacs is poor. In addition, most clinical patients with insomnia often have depressive or anxious symptoms, overestimate sleep latency, but underestimate total sleep time (Bliwise et al., 1993; Chervin and Guilleminault, 1996; Vanable et al., 2000). It is also possible that clinical patients with insomnia suffer from more severe sleep disturbance or are more concerned about their poor sleep than those with insomnia in the general population because most insomniacs in the general population do not seek professional help (Rosekind, 1992). Our results may help explain why most insomniacs complain of sleep loss when, in fact, their total sleep time differs only slightly from that of non-complaining normal sleepers (Coates and Thoresen, 1981). Many experimental studies in healthy humans have found that sleep deprivation may result in a wide range of psychological or physiological impairments, such as anxiety, aggressive behavior, daytime sleepiness, lowered cognitive function,
and endocrine or immunological changes (Devoto et al., 1999; Spiegel et al., 1999; Vgontzas et al., 1999). However, the association between sleep duration and psychosocial well-being in the general population remains unclear (Jean-Louis et al., 2000; Ferrara and Gennaro, 2001). We found that sleep duration of less than 7 h per day was significantly associated with increased risk of behavioral or emotional problems, particularly for anxious or depressed syndrome. Sleep duration of 8 h was not related to any behavioral problems. Thus, sleep duration of 7 h might be considered a threshold for behavioral or emotional problems in Chinese adolescents. Stratified analysis showed that short sleep duration was significantly associated with most behavioral problems in adolescents without insomnia but not in those with complaints of insomnia. That is, for adolescents with insomnia symptoms, short sleep duration was not as likely to predict behavioral problems as it was in those without insomnia complaints. Recently, a few studies indicated that sleep quality rather than sleep quantity could predict adolescents’ school functioning (Meijer et al., 2000), negative mood, or physical complaints (Pilcher et al., 1997). Unfortunately, we did not measure sleep quality of our sample. The association between sleep quality and behavioral problems and the extent to which the association between sleep duration and behavioral problems would be changed after controlling for the effects of sleep quality need to be further investigated with Chinese adolescents. Insomnia was associated with a wide range of behavioral or emotional problems in our sample, consistent with most previous cross-sectional studies of adolescents in Western countries (Morrison et al., 1992; Vignau et al., 1997; Alapin et al., 2000; Johnson et al., 2000; Roberts et al., 2001). The fact that insomnia was most strongly associated with depressionyanxiety is not surprising, because insomnia is a cardinal symptom of major depression (American Psychiatric Association, 1994). The link between disturbed sleep and depression has long been demonstrated in most cross-sectional and a few prospective studies of adolescents and adults (Kirmil-Gray et al., 1984; Ford and Kamerow, 1989; Breslau et al., 1996; Chang et al., 1997; Johnson et al., 2000; Roberts
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et al., 2001). Clinical studies have shown that patients with insomnia often have symptoms of depression or anxiety and that patients with mental disorders often complain of insomnia (Ford and Kamerow, 1989; Benca et al., 1992; Buysse et al., 1994). However, a mere association between disturbed sleep and mental disorders tells us little about cause and effect. Disturbed sleep may prompt mental disorders; mental disorders may contribute to disturbed sleep; or both may be caused by common factors that predispose to both disturbed sleep and mental disorders. Many psychosocial and biological factors, such as family psychiatric history, substance use, or stressful life events, may be associated with both insomnia and mental disorders. Thus, it is difficult to disentangle whether insomnia is a precursor, sequel, or comorbidity of mental disorders. Replication of these results and ultimately naturalistic prospective studies will shed more light on the association between insomnia and behavioral problems in adolescents. In interpreting these results, it is important to consider some methodological limitations of this study. One of the obvious limitations is that we did not have objective data on sleep duration and insomnia symptoms such as electroencephalography (EEG), which is of great importance in ruling out other sleep disorders causing insomnia (Krakow et al., 2001). We defined sleep duration as the adolescent’s perceived sleep time, and insomnia symptoms as the adolescent’s positive responses to three questions. Although objective measures of sleep duration and sleep problems are desirable, self-reports and interview measures remain the measures of choice in large-scale epidemiologic studies (Ohayon et al., 2000; Roberts et al., 2001) and there is evidence that subjective measures of sleep from children and adolescents are correlated with objective measures (Sadeh et al., 1995). Second, based on a self-report questionnaire with four generalized questions of sleep behavior, we could neither differentiate DIS insomnia from delayed sleep phase syndrome nor differentiate some poor sleepers (e.g. hypersomnia due to physiological sleep disorders) from non-insomniacs. This may cause biased estimation of sleep duration for insomniacs and non-insomniacs and the asso-
83
ciation between insomnia and behavioral problems. This limitation of our study should be addressed in future studies. Furthermore, although our sample was large, the fact that local officials selected the schools from which classes could be selected for assessment and that the students absent on the day of survey were not further tested is a potential biasing factor. Because absentees tend to have higher rates of mental health problems, the absence of these students possibly underestimates insomnia symptoms and their association with behavior problems. To our best knowledge, this is the first attempt to systematically relate sleep duration, insomnia symptoms, and behavioral problems in a large general population sample of Chinese adolescents. Our findings have important implications for public health and clinical relevance. First, we found that adolescents who present with complaints of insomnia and sleep duration of less than 7 h a day were at higher risk for significant behavioraly emotional problems, particularly for depression and anxiety. Because Chinese adolescents with psychopathology rarely seek professional help and those who do seek help are often referred to physicians or neurologists for complaints of insomnia (Parker et al., 2001), we suggest that those adolescents who complain of insomnia andyor short sleep duration (less than 7 h a day) need further psychiatric assessment for early detection and intervention of mental health problems. Second, our results indicated that adolescents with insomnia in the general population reported sleep duration only approximately half an hour less than those without insomnia. These results underline the importance of sleep hygiene education in sleep clinics to reassure patients with insomnia that their sleep duration is not as short as they perceive because clinical insomniacs often underestimate their sleep duration, which, in turn, leads to anxiety and exacerbates insomnia. Acknowledgments This research was supported in part by the Shandong Medical Research Foundation, People’s Republic of China, and the Multi-Investigator Proposal Development Grant Program, Arizona State
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University. The authors thank Dr Andrew Rowland, Epidemiology Branch, National Institute of Environmental Health Sciences, for his comments on the manuscript. References Achenbach, T.M., 1991. Manual for the Youth Self-Report and 1991 Profile. University of Vermont, Department of Psychology, Burlington. Alapin, I., Fichten, C.S., Libman, E., Creti, L., Bailes, S., Wright, J., 2000. How is good and poor sleep in older adults and college students related to daytime sleepiness, fatigue, and ability to concentrate? Journal of Psychosomatic Research 49, 381–390. American Psychiatric Association, 1994. Diagnostic and Statistical Manual of Mental Disorders, fourth ed. American Psychiatric Press, Washington, DC. Benca, R.M., Obermeyer, W.H., Thisted, R.A., Gillin, J.C., 1992. Sleep and psychiatric disorders. A meta-analysis. Archives of General Psychiatry 49, 651–668. Bliwise, D.L., Friedman, L.Y., Jerome, A., 1993. Depression as a confounding variable in the estimation of habitual sleep time. Journal of Clinical Psychology 49, 471–477. Breslau, N., Roth, T., Rosenthal, L., Andreski, P., 1996. Sleep disturbance and psychiatric disorders: a longitudinal epidemiological study of young adults. Biological Psychiatry 39, 411–418. Buysse, D.J., Reynolds, C.F., Hauri, P.J., Roth, T., Stepanski, E.J., Thorpy, M.J., Bixler, E.O., Kales, A., Manfredi, R.L., Vgontzas, A.N., Stapf, D.M., Houck, P.R., Kupfer, D.J., 1994. Diagnostic concordance for DSM-IV sleep disorders: a report from the APAyNIMH DSM-IV field trial. American Journal of Psychiatry 15, 1351–1360. Byrd, R.S., Weitzman, M., Lanphear, N.E., Auinger, P., 1996. Bedwetting in US children: epidemiology and related behavior problems. Pediatrics 98, 414–419. Carskadon, M.A., 1990. Patterns of sleep and sleepiness in adolescents. Pediatrician 17, 5–12. Carskadon, M.A., Vieira, C., Acebo, C., 1993. Association between puberty and delayed phase preference. Sleep 16, 258–262. Carskadon, M.A., Wolfson, A.R., Acebo, C., Tzischinsky, O., Seife, R., 1998. Adolescent sleep patterns, circadian timing, and sleepiness at a transition to early school days. Sleep 21, 871–881. Chang, P.P., Ford, D.E., Mead, L.A., Cooper-Patrick, L., Klag, M.J., 1997. Insomnia in young men and subsequent depression. The Johns Hopkins Precursors Study. American Journal of Epidemiology 146, 105–114. Chervin, R.D., Guilleminault, C., 1996. Overestimation of sleep latency by patients with suspected hypersomnolence. Sleep 19, 94–100. Coates, T.J., Thoresen, C.E., 1981. Treating sleep disorders: few answers, some suggestions, and many questions. In: Turner, S.M., Calhoun, K.S., Adams, H.E. (Eds.), Handbook
of Clinical Behavior Therapy. Wiley, New York, pp. 240–289. Devoto, A., Lucidi, F., Violani, C., Bertini, M., 1999. Effects of different sleep reductions on daytime sleepiness. Sleep 22, 336–343. Ferrara, M., Gennaro, L.D., 2001. How much sleep do we need? Sleep Medicine Review 5, 155–179. Ford, D.E., Kamerow, D.B., 1989. Epidemiologic study of sleep disturbances and psychiatric disorders: an opportunity for prevention? Journal of the American Medical Association 262, 1479–1484. Frankel, B.L., Coursey, R.D., Buchbinder, R., Snyder, F., 1976. Recorded and reported sleep in chronic primary insomnia. Archives of General Psychiatry 33, 615–623. Gau, S.F., Soong, W.T., 1995. Sleep problems of junior high school students in Taipei. Sleep 18, 667–673. Jean-Louis, G., Kripke, D.F., Ancoli-Israel, S., 2000. Sleep and quality of well-being. Sleep 23, 1115–1121. Johnson, E.O., Chilcoat, H.D., Breslau, N., 2000. Trouble sleeping and anxietyydepression in childhood. Psychiatry Research 94, 93–102. Kirmil-Gray, K., Eaglestone, J.R., Gibson, E., Thoresen, C.E., 1984. Sleep disturbance in adolescents: sleep quality, sleep habits, beliefs about sleep, and daytime functioning. Journal of Youth and Adolescence 13, 375–384. Krakow, B., Melendrez, D., Ferreira, E., Clark, J., Warner, T.D., Sisley, B., Sklar, D., 2001. Prevalence of insomnia symptoms in patients with sleep-disordered breathing. Chest 120, 1923–1929. Laberge, L., Petit, D., Simard, C., Vitaro, F., Tremblay, R.E., 2001. Development of sleep patterns in early adolescence. Journal of Sleep Research 10, 59–67. Liu, X., Guo, C., Liu, L., Sun, L., 1997. Reliability and validity of the Youth Self-Report in Chinese adolescents. Chinese Journal of Mental Health 11, 200–203. Liu, X., Kurita, H., Guo, C., Miyake, Y., Ze, J., Cao, H., 1999. Prevalence and risk factors of behavioral problems among Chinese children aged 6–11. Journal of the American Academy of Child and Adolescent Psychiatry 38, 708–715. Liu, X., Kurita, H., Uchiyama, M., Okawa, M., Liu, L., Ma, D., 2000a. Life events, locus of control, and behavioral problems among Chinese adolescents. Journal of Clinical Psychology 56, 1565–1577. Liu, X., Uchiyama, M., Okawa, M., Kurita, H., 2000b. Prevalence and correlates of self-reported sleep problems among Chinese adolescents. Sleep 23, 27–33. Liu, X., Sun, Z., Neiderhiser, J.M., Uchiyama, M., Okawa, M., Rogan, W., 2001. Behavioral and emotional problems in Chinese adolescents: parent and teacher reports. Journal of the American Academy of Child and Adolescent Psychiatry 40, 828–836. Meijer, A.M., Habekothe, H.T., Van Den Wittenboer, G.L.H., 2000. Time in bed, quality of sleep and school functioning of children. Journal of Sleep Research 9, 145–153. Morrison, D.N., McGee, R., Stanton, W.R., 1992. Sleep problems in adolescence. Journal of the American Academy of Child and Adolescent Psychiatry 31, 94–99.
X. Liu, H. Zhou / Psychiatry Research 111 (2002) 75–85 Ohayon, M.M., Caulet, M., Priest, R.G., Guilleminault, C., 1997. DSM-IV and ICD-10 insomnia symptoms and sleep dissatisfaction. British Journal of Psychiatry 171, 382–388. Ohayon, M.M, Roberts, R.E., Zulley, J., Smirne, S., Priest, R., 2000. Prevalence and patterns of problematic sleep among older adolescents. Journal of the American Academy of Child and Adolescent Psychiatry 39, 1549–1556. Parker, G., Gladstone, G., Chee, K.T., 2001. Depression in the planet’s largest ethic group: the Chinese. American Journal of Psychiatry 158, 857–864. Pilcher, J.J., Ginter, D.R., Sadowsky, B., 1997. Sleep quality versus sleep quantity: relationships between sleep and measures of health, well-being and sleepiness in college students. Journal of Psychosomatic Research 42, 583–596. Roberts, R.E., Roberts, C.R., Chen, I.G., 2001. Functioning of adolescents of disturbed sleep. Journal of Youth and Adolescence 30, 1–18. Rosekind, M.R., 1992. The epidemiology and occurrence of insomnia. Journal of Clinical Psychiatry 53, 4–6. Sadeh, A., McGuire, J.P., Sachs, H., Seifer, R., Tremblay, A., Civita, R., Hayden, R.M., 1995. Sleep and psychological characteristics of children on a psychiatric inpatient unit. Journal of the American Academy of Child and Adolescent Psychiatry 34, 813–819.
85
Spiegel, K., Leproult, R., Cauter, E.V., 1999. Impact of sleep debt on metabolic and endocrine function. Lancet 354, 1435–1439. Stores, G., 1996. Practitioner review: assessment and treatment of sleep disorders in children and adolescents. Journal of Child Psychology and Psychiatry 37, 907–925. Straugh, I., Meier, B., 1988. Sleep need in adolescents: a longitudinal approach. Sleep 11, 378–386. Vanable, P.A., Aikens, J.E., Tadimeti, L., Caruana-Montaldo, B., Mendelson, W.B., 2000. Sleep latency and duration estimates among sleep disorder patients: variability as a function of sleep disorder diagnosis, sleep history, and psychological characteristics. Sleep 23, 71–79. Vgontzas, A.N., Mastorakos, G., Bixler, E.O., Kales, A., Gold, P.W., Chrousos, G.P., 1999. Sleep deprivation effects on the activity of the hypothalamic-pituitary-adrenal and growth axes: potential clinical implications. Clinical Endocrinology 51, 205–215. Vignau, J., Bailly, D., Duhamel, A., Vervaecke, P., Beuscart, R., Collinet, C., 1997. Epidemiologc study of sleep quality and troubles in French secondary school adolescents. Journal of Adolescent Health 21, 343–350. Wolfson, A.R., Carskadon, M.A., 1998. Sleep schedules and daytime functioning in adolescents. Child Development 69, 875–887.