Although the biological function of sleep is still largely unknown, sleep is seen as an important part of the healing process and is considered essential to life in the physical, neurological, and emotional areas. There are short- and long-term effects on life in sleep deprivation. The short-term effects include poor attention and concentration, reduced quality of life, low productivity and an increased absence in class or work, while long-term effects include higher morbidity and mortality due to car accidents, coronary artery disease, heart failure, hypertension, obesity, type-2 diabetes, stroke, depression, memory loss, and decreased immune function¹⁾.

Sleep problems in children and adolescents cause serious conditions, medically and psychologically²⁾. Severe sleep breathing disorders may lead to left ventricular hypertrophy, arrhythmia, cardiac pulmonary syndrome, heart failure, growth failure, and death^3,4,5). Sleep apnea and other sleep disorders can lead to depression, attention deficit and hyperactivity disorder, cognitive disorders, learning disabilities, and emotional instability^6,7,8).

According to a recent study, the prevalence of sleep-related diseases in children and adolescents was determined to be approximately 43%, the rate of insomnia was determined to be 5%–20%, the rate of obstructive sleep apnea was determined to be 1%–3%, the frequency of snoring was determined to be 5%–27%, and the rate of parasomnias was determined to be 14%–37%⁹⁾. In Korea, snoring, bruxism, and enuresis have been reported to occur in 16.5%–26.7%, 13.2%, and 8.7%, respectively^10,11,12).

Despite the high incidence and considerable impact of sleep problems in the lives of children and adolescents, sleep problems are not of major concern among parents and doctors. Furthermore, there are only a few studies regarding the prevalence of sleep disorders in Korea^10,11,12).

In this study, we used the Pediatric Sleep Questionnaire (PSQ) to examine the prevalence of sleep disorders in Korean children and adolescents (Appendix). The PSQ focused on snoring and sleep disordered breathing (SDB). This questionnaire was employed to overcome the practical difficulties in asking patients about sleep problems in an outpatient setting^2,13,14).

This research investigated the frequency of sleep-related problems by surveying 936 patients under the age of 18, who had visited 1 of 6 different pediatric hospitals in the Seoul and Gyeonggi area. Results indicated that, among the patients, 13.2% had insomnia, 15.1% had sleep-related breathing disorders and 31.6% snored, of which 16.9% snored regularly (i.e., more than 3 times a week). In addition, other sleep related disorders, such as sleep walking, sleep terror, bruxism and enuresis, were also frequent, occurring in 1.6%, 19%, 21.1%, and 18% of subjects, respectively. Of the 5 relevant survey questions about insomnia, 13.2% replied “yes” to more than 2 questions, and a high rate (29.2%) replied “yes” to more than 1 question.

Archbold et al.²⁾ reported that 18% replied “yes” to more than two questions and 41.4% said “yes” to more than one question in a similar survey. Furthermore, Lozoff et al.¹⁵⁾ stated that the frequency of sleeping disorders in children was 31%. These studies, like this study, choose the study subjects and used surveys completed by children and parents who visited hospitals but did not have chronic illnesses.

The frequency of behavioral insomnia in children, including insomnia and night walking, was between 20% and 30% in early childhood, 15% in school-age children^16,17) and the prevalence of insomnia in adolescents between 16 and 18 years old was approximately 11%¹⁸⁾. As in previous studies, we can see that the prevalence of behavioral insomnia is high in infants.

Childhood insomnia can be classified as either behavioral insomnia or psychological-physiological insomnia. Behavioral insomnia is usually more frequent in younger children, and psychological-physiological insomnia is more common among older children and adolescents^14,19). Since the survey used in this study investigates the presence of behavioral insomnia, it is presumed that the prevalence of insomnia was higher in younger patients. Furthermore, younger children often sleep together with their parents so their parents would have more easily observed symptoms related to insomnia.

Sleep-related breathing disorders are conditions that present problems in breathing during sleep and are caused by increased resistance in the upper respiratory tract. This includes snoring, upper airway resistance syndrome and obstructive sleep apnea.

Adenotonsillar hypertrophy is the most common cause of SDB in children and tends to occur in nasal obstruction (e.g., rhinitis, sinusitis, nasal septum deviation). Other risk factors include obesity, gastroesophageal reflux disorder, laryngomalacia, central facial hypoplasia syndrome (e.g., Pierre Robin sequence, Treacher Collins, Crouzon syndrome), lingual hypertrophy (e.g., 21 trisomy, Beckwith Wiedeman syndrome), and neuromuscular diseases^20,21).

There are a few major differences in SDB between children and adults. In children, the symptoms are more diverse and difficult to diagnose individually. In addition, excessive daytime sleepiness is common in adults while it is only seen in approximately 7% of children²²⁾. Conversely, hyperactivity is commonly seen among children. Lastly, symptoms of SDB vary in children depending on their age. In young cases, snoring, apnea, frequent arousal, sweating, dry mouth, and stunted growth are frequently seen. In contrast, cases in older patients frequently included symptoms of night terrors, sleep-talking, sleep-walking, enuresis, hyperactivity, and depression²³⁾. SDB can be diagnosed on the basis of patient history, physical examination, and polysomnography²⁴⁾.

In this study, the prevalence of snoring was 31.6%, of which habitual snoring (more than 3 days per week) was 16.9%. Preschool children (39%) and school age children (34%) showed a higher rate of snoring than did the other age groups. A previous study done in Korea by Cho et al.¹¹⁾ indicated that 15.5% of children snore at least once a week and 4.3% of children snore almost every day. In another study which investigated elementary school children¹⁰⁾, 26.7% children were observed to snore and 7.1% of children snored more than 3 days a week. These 2 studies^10,11), which showed lower resulting numbers than does the current study, differed from this study in the recruitment of research subjects. The 2 studies gathered research subjects from elementary schools, whereas this study recruited outpatients. The diseases that the outpatients may have had at the time (e.g., upper respiratory infection, sinusitis, rhinitis, tonsillitis, etc.) could have had an influence on snoring, thereby increasing the frequencies shown in the study. In addition, since the subjects were children who visited hospitals, results might have shown higher snoring rates than an average child of similar age.

Particularly notable in this study was the frequency of habitual snoring in children younger than 24 months (9%) and in children between ages 2–5 (18%). Furthermore, this study is the first in our country to document the frequency of snoring in young children. Recently, it was shown that 60% of facial bones develop in children during the first 4 years of life²⁵⁾. Animal studies have shown changes in facial structure after induced nasal congestion²⁶⁾, and persistency of SDB with long-term follow-up²⁷⁾ suggest that persistent oral breathing caused by factors such as nasal congestion may structurally cause chronic development of SDB. This in turn highlights the necessity for early treatment during infancy and early childhood. Early detection and treatment of snoring and oral breathing may prevent the development of sleep apnea. However, the nature of this period has not yet been explored in our country. It can be said that the high incidence of 9%–18% shown in this study expresses the need for a more active diagnosis and treatment by pediatricians.

Research outside of Korea has demonstrated no difference in snoring between the sexes. However, this study showed a significantly higher incidence of snoring in boys. This was also the case in the two other studies^10,11) that were conducted in Korea. More research should be conducted to see if it this is due to unique characteristics of children in Korea.

Snoring children showed a significantly higher incidence of SDB, night terrors, and bruxism (Table 6). Logistic regression analysis showed the risk of SDB to be 4 times higher in children with habitual snoring (Table 7). Snoring is one aspect of SDB and the correlations between SDB and night terrors or bruxism has been demonstrated in previous studies^28,29). Parasomnia is regarded as a symptom of SDB in children, which is supported by the observation that treating SDB also relieves parasomnia and by its higher incidence in children who have a family history of SDB²⁹⁾. Therefore, in children with night terror or bruxism, it is recommended to primarily determine whether SDB is present and to treat it first.

In general, the prevalence of enuresis is higher in cases of snoring. The relationship between enuresis and snoring is believed to be due to an increase in plasma brain natriuretic peptide and a decrease in antidiuretic hormone concentration during sleep in SDB, thereby causing increased urine production, which is then aggravated by increased abdominal pressure due to the strong respiratory effort exerted by patients with SDB. Together, these events lead to urination.

However, in this study of the frequency of enuresis in ages greater than 5, there was no significant difference in its incidence across the 23% (14 of 60) of patients with habitual snoring, the 15% (8 of 52) of patients with occasional snoring, and the 17% (33 of 191) of patients who do not snore. Even when compared to habitual snoring and otherwise, the prevalence of enuresis showed no significant difference. The different results from existing studies is thought to be due to the simplistic classification of patients by their “yes” answer to the Korean version of question “Does your child wet the bed?” This level of detail is not sufficient to indicate enuresis, which requires that patients wet the bed at least twice a week for at least 3 months in children ages 5 or more and many parents misunderstood the questionnaire.

The risk factors of habitual snoring are similar to those of SDB. In a study targeting elementary school children in China³⁰⁾, risk factors, such as low family income, lack of higher education in the father, breastfeeding for less than 6 months, smoking during pregnancy, obesity, overweight, respiratory problems (rhinitis, asthma, adenoids hypertrophy, chronic otitis media), and a family history of habitual snoring were investigated. In this study, however, such risks were not examined.

The prevalence of night terrors was 19% and showed a significant difference by age. Night terrors occurred in 27% of infants aged 0–1 years old and in 19% of preschool children. In a study of twins, similar results to this study were obtained. A higher incidence of night terrors was observed in younger children, with a prevalence of 36.9% in children 18 months old and 19.7% in children 30 months old³¹⁾. However, night terrors usually occur in ages 2–4 years and are known to appear in 6% of children, regardless of sex. The reason this study resulted in a high prevalence of night terrors is because all patients that answered “yes” to the question asking “awake in a panic or frightened” were classified as having night terrors, even though this question includes children who have either awaken while crying and those experiencing nightmares. This is a limitation of the survey since the patients may not have fully understood the meaning of night terrors.

Although there are many sleep-related problems in children and adolescents, parents and medical staff do not provide sufficient attention to this problem.

Meltzer et al.⁹⁾ reported that the prevalence of sleep problems according to the ICD-9 (International Classification of Diseases, 9th revision) is 3.7%, which was lower than the results of previous studies. Low prevalence is thought to be a result of the study having been conducted retrospectively based on medical records. Given the lack of interest in sleep problems, most issues relevant to our study were not recorded.

The lack of interest in addressing sleep problems has been studied in previous research³²⁾ that indicated that while 24.6% of patients suffer from sleep problems, only 4.1% of parents discussed the problems and only 7.9% of parents consulted a doctor.

Other causes of sleep problems that were not covered in this study, include family suffering from illness or accidents, sleeping with a parent, the absence of the mother during the day, depression of the mother, and maternal ambivalence toward their children. Nevertheless, a previous study had shown that sex, age, birth order, family size, breastfeeding, parental education, occupation, paternal presence¹⁵⁾.

Furthermore, children waking up in a panic were shown to have more stress in the family and the mothers exhibited more psychiatric disorders³³⁾.

In another study, the prevalence of sleep problems was higher in children of low income families and in infants younger than 1 year of age with a head circumference less than 2SD, in children older than 1 year of age with a body mass index greater than 2SD⁹⁾.

There are some limitations to this study. A diagnosis using the PSQ does not replace the clinical diagnosis of an experienced physician. However, using a survey consisting of verified items associated with sleep problems has been shown to be similar to a physician in achieving a diagnosis. Despite this, diagnosing parasomnias in particular is nonspecific compared to the sensitivity of the survey because it is diagnosed using only 1 question. In addition, the subjects of the study do not represent all children and adolescents of our country. As the survey was completed by outpatients, and not by members of the public, the prevalence shown in the results may be higher than that of the community. Further research related to sleep problems using a representative sample group would be necessary.

Moreover, because the participants conducted the survey after having visited the hospital because of an illness, there is a possibility that the disease was affecting sleep and thus the answer was affected. Additionally, while socio-economic status which we did not asked in this study may have affected the sleep in children. Finally, the age of the subject may affect survey responses. Young children are mostly observed by the parents while sleeping, whereas older children who sleep alone may have had difficulties recognizing their sleep problems, which may have affected their answers to the survey.

Despite these limitations, this study is meaningful given the prevalence of SDB, insomnia, and snoring among Korean children and adolescents. Pediatric clinics of primary medical care centers report a relatively high prevalence of these conditions. Furthermore, our results show a higher incidence of snoring in infants with a higher frequency in boys. These snoring children had a four times higher risk of SDB.