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* From the Department of Paediatrics (Dr. Ng, Mr. Kwok, Ms. Cheung, Ms. Leung; Mr. Chow, Mr. Chan, and Dr. Ho), Kwong Wah Hospital; and Department of Paediatrics and Adolescent Medicine (Ms. Wong), Queen Mary Hospital, The University of Hong Kong, Hong Kong, ROC.
Correspondence to: Daniel K. Ng, FRCP, Department of Paediatrics, Kwong Wah Hospital, Waterloo Rd, Hong Kong SAR, ROC; e-mail: dkkng{at}ha.org.hk
| Abstract |
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Design: Cross-sectional telephone questionnaire survey in a community.
Participants: A total of 3,047 6- to 12-year-old apparently healthy children.
Intervention: Those who agreed to the study were contacted by telephone. Survey questions were asked about the symptoms of the different sleep disorders, and the frequency of each positive symptom was noted for the preceding 1 week.
Outcome measures: Prevalence and risk factors of sleep disorders in Hong Kong primary school children.
Results: The prevalence of the following sleep symptoms was listed as follows: habitual snoring (10.9%), witnessed sleep apnea (1.5%), nocturnal enuresis (5.1%), and sleep teeth grinding (20.5%). Significant risk factors for habitual snoring included witnessed sleep apnea, mouth breathing during sleep, snoring in first-degree relatives, headache on rising, male gender, allergic rhinitis, and sleep teeth grinding. Significant risk factors for witnessed sleep apnea included habitual snoring, allergic rhinitis, tiredness on rising, and excessive daytime sleepiness. Poor academic results were associated with present of witnessed sleep apnea and absence of sleep teeth grinding. None of the sleep problem was associated with poor conduct results. The mean sleep duration was 8.79 h (SD 0.96).
Conclusions: This study provides epidemiologic data of sleep-disordered breathing, enuresis, sleep teeth grinding, and duration of sleep in Chinese primary school children in Hong Kong.
Key Words: child enuresis epidemiology sleep apnea, obstructive snoring
| Introduction |
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6 years old from different studies from Europe and the United States.1 Prevalence rates for obstructive sleep apnea syndrome (OSAS) were estimated at 0.7% in the preschool age group2 and 1.6% in the 2- to 18-year age group.3 As the prevalence of OSAS and other sleep-related health problems is related to the ethnic origin of the population,4 its prevalence in individual ethnic groups needs to be ascertained. One study on sleep-related health problems in Chinese children was reported by Liu et al,5 who found sleep walking to be the most common sleep problem (14.2%). In the same study, excessive daytime sleepiness (EDS), ie, sleep in class, was found in 9.4% and nocturnal enuresis (NE) was found in 4.5%. The prevalence of snoring and witnessed sleep apnea was not addressed in that study. NE was found to occur in 3.5% of Hong Kong children aged 4 to 12 years.6 We report here a community-based, structured telephone interview to estimate the prevalence of snoring, witnessed sleep apnea, teeth grinding, EDS, primary and secondary NE, and sleep duration in a group of randomly selected primary school Chinese students in Hong Kong. | Materials and Methods |
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Parents who had impaired hearing or a speech impediment were excluded. The occurrence of symptoms of different sleep disorders was asked with the reference period being the preceding 1 week or 1 day, depending on the question. If the parents were not sure of the answers, they received an explanation of the different symptoms, and were contacted 1 week later.
Habitual snoring was defined as snoring for 6 to 7 nights a week. EDS was defined as the coexistence of two or more daytime sleepiness symptoms (ie, falling asleep while watching television, falling asleep during a lesson, falling asleep while doing homework, and falling asleep in a vehicle). Primary NE was defined as nocturnal bed-wetting beyond the age of 5 years and never having a period of dryness. Secondary NE was defined as bed-wetting after a period of at least 6 months of dryness. Parents were asked about the overall examination and conduct results in the preceding school term. Academic results were ranked as good (grade A/B), fair (grade C/D), or poor (grade E). Conduct was graded by the class teacher in charge, with the scores from A to F. Those who scored E or F were classified as bad conduct. The protocol of this study was approved by the ethic committee of Kwong Wah Hospital.
Statistical Analysis
All analyses were done using statistical software (SPSS, Release 10.1 for Windows; SPSS; Chicago, IL). Distribution of data was assessed by one-sample Kolmogorov-Smirnov test. Comparisons of continuous variables were conducted with unpaired Student t test or one-way analysis of variance. A Pearson
2 test was used for categorical variables.
Risk factors for snoring, witnessed sleep apnea, EDS, NE, poor academic results, and poor conduct were analyzed by logistic regression. Significant risk factors were defined as a Wald statistic gave a p value < 0.05. The adjusted odds ratio (OR) of each significant factor was reported.
| Results |
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9 years old (n = 1,638, 53.8%). The male/female ratio was 1.32:1. The gender distribution in the two age groups was similar (Table 1 ) There was significantly more boys than girls in the study population when compared to the general population of the same age (male/female ratio, 1.07:1) [p < 0.001].
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NE
NE was found in 159 children (5.2%; 95% CI, 4 to 6%) Primary NE was found in 113 children (3.7%; 95% CI, 3 to 4%), whereas secondary NE was reported in 46 children (1.5%; 95% CI, 1 to 2%). The mean age for primary NE was 8.1 years (SD, 1.51). Mean age for secondary NE was 8.04 years (SD, 1.41). There was a marked male predominance in both enuretic groups (male/female ratio, 115:44;
2 = 15.651; df = 2; p < 0.001; OR, 2.05; 95% CI, 1.44 to 2.93). For primary NE, the only significant risk factor identified by logistics model was witnessed sleep apnea (p = 0.033; adjusted OR, 3.18; 95% CI, 1.23 to 8.19). For secondary NE, no significant risk factor was identified.
| Discussion |
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Witnessed sleep apnea was reported to occur in 1.5% (95% CI, 1 to 2%) of the studied population. This prevalence was similar to that in white children found by Goodwin et al,7 who reported the prevalence of witnessed apnea to be 1.9% in white children and 4.7% in Hispanic children with similar age groups as the current study. Assuming most of these children would have OSAS, the prevalence would be similar to the 1.6% reported by Redline et al3 in a similar age group. Allergic rhinitis was found to be a significant risk factor for witnessed sleep apnea in the present study. This was similar to the findings by Redline et al.3 Hence, it would not be surprising that treatment of allergic rhinitis helped control OSAS as demonstrated by Brouillette et al.12
Lower academic performance was shown by the current study to be associated with the presence of witnessed sleep apnea, which was a cardinal symptom of OSAS. This finding was similar to that of Gozal,13 who reported that children with features of OSAS had better academic results after tonsillectomy and adenoidectomy than a similar group without tonsillectomy and adenoidectomy. Further studies are warranted to shed light on the relationship between OSAS and academic performance. It was interesting to note, in the current study, that sleep teeth grinding was associated with good academic performance in the current study. This was exactly the opposite of that reported by Agargun et al,14 who suggested that bruxism might be associated with learning difficulties. We noted that teeth grinding was closely associated with habitual snoring in the current study and habitual snoring was a common symptom of OSAS that was associated with a learning problem.13 The current study suggests that the two closely associated conditions, ie, habitual snoring and sleep teeth grinding, had an opposite effect on academic results. This probably explained why Urschitz et al15 found no association between habitual snoring and academic results in primary school children, as the confounding effect of sleep teeth grinding was not investigated. Similar to Urschitz et al,15 we also found no association between habitual snoring and academic performance (
2 test, p = 0.406; data not shown here). Thus, habitual snoring was not entered into the logistic regression model of academic results (Table 5). Stress may be involved in the development of nocturnal bruxism.161718 Cheung and Leung-Ngai19 found that primary school students in Hong Kong spent 1.5 to 2 h daily doing homework, which was longer than that reported from America and Asia.20 In addition, anxiety symptoms and depression symptoms were significantly associated with homework hours in Hong Kong students.19 The better academic results of those with teeth grinding in the current study could be mediated through the longer homework hours and, hence, stress in those higher achievers. Further studies to examine this relationship are warranted. The significant association between academic results and sleepiness during class or homework was similar to that found by Goodwin et al,7 who found daytime sleepiness to be associated with learning problems.
Chervin et al21 reported that inattention and hyperactivity were more common in habitual snorers (OR, 2.2; 95% CI, 1.4 to 3.6), and they showed that boys < 8 years old accounted for most of the association between hyperactivity and habitual snoring (but not sleepiness). A similar association was not identified by the current study using poor conduct as a marker for inattention and hyperactivity. This is most probably due to the difference in the study population, as 53.8% of the current study population is
8 year old (Fig 1), compared to 35% in the study by Chervin et al.21 Variations in conduct scores could be attributed to different factors; in other words, personality traits, peer pressure, and assessment criteria of teachers and conduct scores might not be appropriate surrogate markers of inattention and hyperactivity.
In the current study, EDS, defined as the presence of more than two daytime sleep symptoms, was found to be 6.7%. This was similar to that reported by Goodwin et al,7 who found EDS in 5.8% of white children and 9.6% of Hispanic children. In the current study, significant risk factors for EDS were similar to the clinical features of OSAS, ie, witnessed sleep apnea, habitual snoring, headache on rising, allergic rhinitis. This was similar to the findings of Gottlieb et al,22 who found a strong association between symptoms of OSAS and EDS, defined as overly sleepy during the daytime at least once a week, in a group of 5-year-old children.
Hong Kong is a modern city with around-the-clock activities. It is common for both parents to work, and they often come home late for dinner. This results in a routine that encourages children to sleep late but wake up early for school because of heavy traffic. Hence, it is not surprising that the parent-reported sleep duration of 8.79 h (SD, 0.96) in our study is much shorter than the parent-reported sleep duration in American children in 1981.8 It is also similar to the shortest sleep duration reported in the literature, that of the Israeli pupils.23 Acute sleep restriction to 5 h of sleep for 1 night has been shown to impair higher cognitive functions, eg, verbal creativity and abstract thinking.24 Sadeh et al25 reported no correlation between total sleep duration and neurobehavioral functioning in 135 7- to 13-year-old Israeli children, although they did show a significant adverse impact of decreased sleep percentage, ie, percentage of true sleep time over total sleep period, on neurobehavioral functioning in the 7- to 9-year-age group. Gau and Soong26 also reported nighttime sleep duration on school days was significantly related to alertness in the morning. These reported findings might well explain the finding in the current study that those scored poorly in the academic results had a shorter duration of sleep, an average reduction of 13.76 min. This result echoes the findings by Epstein et al,27 that a 24-min reduction in sleep duration resulted in "increased prevalence of difficulties in concentrating and paying attention during classes." In the current study, sleepiness during class and homework, which might be an indirect marker for sleep inadequacy, were shown to be significant risk factors for poor academic results.
In the current study population, primary school boys slept significantly more than girls. This was exactly opposite to that reported for American children8 and Israeli children.26 The Hong Kong girls slept less than their American and Israeli counterparts, and this may be attributed to the heavier academic workload in Hong Kong.19
The prevalence of NE was similar to that reported previously in Hong Kong6 and China.5 Similar to a previous report,6 boys were found to be twice as likely to be enuretic as girls. As previously reported by Brooks and Topol,28 we found witnessed sleep apnea to be a significant risk factor that approached significance for primary NE. Hence, OSAS should be actively looked for in enuretic children.
The prevalence of sleep teeth grinding was higher than that reported previously from students in Turkey with similar age groups.14 However, the prevalence in the current study was similar to that reported in Canadian children (aged 3 to 10 years)18 and American college students.2930 The sleep teeth grinding was found to be associated with habitual snoring in the current study. This was similar to that reported previously.3031 Further study into the mechanism underlying this association is warranted.
The main limitation of the current study was the rather low participation rate, as only 68.8% of those approached agreed to the study, and this might invoke a degree of selection bias in favor of recruiting those who had sleep symptoms. This was reflected by significantly more boys than girls in the studied population. This would result in an overestimation of the snoring symptom as allergic rhinitis; a main risk factor for snoring was more likely to occur in boys.11 Nonetheless, the prevalence of doctor-diagnosed asthma and allergic rhinitis were comparable with that obtained previously in Hong Kong children. Hence, the population selection might not be significantly different from the general population. This leads us to believe that our survey return rate of 68.8% was a good representation of the general primary school population in Hong Kong.
Symptoms in children were reported by parents without any independent verification (eg, overnight polysomnography, nocturnal home pulse oximetry, and actigraphy) in the current study. This was the intrinsic problem of all postal or telephonic questionnaires. Subjective reporting of symptoms by parents might underestimate the incidence and severity of sleep-disordered breathing.32 Moreover, overlapping of sleep time of parents and children decreased the likelihood of parental witnessing of sleep problems. Further similar study should be augmented with polysomnography or videotaping of sleep to verify the symptoms reported by parents. A drawback in the current study involved the lack of data on obesity, a well-known risk factor for sleep disordered breathing.33 Future epidemiologic study should address the issue of obesity and sleep problems.
In conclusion, the current study identified the prevalence of habitual snoring and witnessed apnea in Chinese children, and it was similar to the white population. Sleep deprivation is a common phenomenon in Hong Kong children. Daytime sleepiness and witnessed sleep apnea were associated with poor academic results.
| Appendix |
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I am the consultant pediatrician of the "Children Sleep Disorder Service" of Kwong Wah Hospital. I am inviting you to participate in a research program in our hospital. Approximately 10% of children are found to have snoring at night in many surveys. Among them, OSAS was diagnosed in 10%. In our Children Sleep Disorder Unit, we have seen 109 children with OSAS in 352 snoring children since 1997.
The aim of this sleep survey is to investigate the sleep problems of primary school children in Hong Kong. You need to observe your childs sleep habits for 1 week. Our researcher will call you and ask some questions. All the information provided is only for research purpose, and it will be kept strictly confidential. You have the right to reject this survey. In addition, you may withdraw at any time during the survey. Thank you for your participation.
Yours faithfully,
Dr. Daniel Ng Kwok Keung
Reply
I agree/disagree that my child to join the "Hong Kong Children Sleep Survey Questionnaire." If you agree to join the survey, please kindly leave your contact number and choose a convenient time for the telephone questionnaire.
Telephone No.
Time to call
1. Monday to Friday 9 AM to 5 PM
2. Monday to Friday 6 PM to 9 PM
Hong Kong Children Sleep Survey Questionnaire (English Translation)
Age of child:
Gender of child:
1. In the preceding week, how often has your child snored (snoring is audible)? (no/12 nights/35 nights/67 nights)
2. In the preceding week, has your child been grinding his/her teeth while asleep? (yes/no)
3. In the preceding week, has your child wet the bed? (yes/no)
An additional question for enuretic children: Has your child ever been dry (absence of bed-wetting) for 6 months? (yes/no)
4. In the preceding week, have you observed your child to have apnea while asleep (apnea means to stop breathing for few seconds, as evidenced by movement of rib cage without any sound of breathing; additional evidence includes a struggle to breathe)? (yes/no)
5. In the preceding week, have you observed your child to have mouth breathing while sleeping? (yes/no)
6. In the preceding week, has your child complained of restless sleep (restless sleep means tiredness on rising or unrefreshed sleep)? (yes/no)
7. In the preceding week, has your child complained of morning headaches? (yes/no)
8. Has allergic rhinitis been diagnosed in your child by a doctor? (yes/no)
9. Has asthma been diagnosed in your child by a doctor? (yes/no)
10. In the preceding week, has your child fallen asleep while watching television? (yes/no)
11. In the preceding week, has your child fallen asleep while doing homework? (yes/no)
12. In the preceding week, has you child fallen asleep in a vehicle? (yes/no)
13. In the preceding week, have any teachers complained that your child has fallen asleep during a lesson? (yes/no)
14. What was your childs academic result in the last academic year (good = grades AB, fair = grades CD, and poor = grades EF)? (good/fair/poor)
15. What is the conduct assessment of your child in the last academic year (good = grades AB, fair = grades CD, poor = grades EF)? (good/fair/poor)
16. What time did your child go to bed last night?
17. When did your child wake up this morning?
18. Are there any family members who snore at night? (yes [which member: father, mother, siblings, other]/no)
19. Are there any family members who have diagnosed sleep apnea? (yes [which member: father, mother, siblings, other]/no)
| Footnotes |
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This project was supported by a research grant from the Board of Directors, Tung Wah Group of Hospitals, Hong Kong SAR, who had no involvement in the study design; collection, analysis, and interpretation of data; writing of the report; and the decision to submit the report for publication.
Received for publication November 9, 2004. Accepted for publication January 19, 2005.
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