Original ArticleA community-based study of insomnia in Hong Kong Chinese children: Prevalence, risk factors and familial aggregation
Introduction
Characterized by difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS) and early morning awakening (EMA) [1], [2], [3], insomnia is a common sleep disorder with a significant health care burden and morbidities [4], [5], [6], [7]. Insomnia has a prominent negative impact on the health and functioning of youths [4], a higher level of absenteeism from work [5], increased health care utilization [6] and predisposition to psychiatric morbidities [7]. Prospective studies also found that insomnia was a highly prevalent and persistent disorder among children and adults [8], [9]. The exact etiology of insomnia, however, is still unclear. A number of risk factors were considered to contribute to the development of insomnia such as age, female sex, lower socio-economic status, poor sleep hygiene and uncomfortable sleep environment, stressful life events and other comorbid psychiatric and medical conditions [7], [10], [11], [12], [13], [14], [15], [16].
Several twins and family studies suggested that insomnia was influenced by both environmental and genetic factors [17], [18], [19], [20], [21], [22], [23], [24], [25]. A family study can provide information for associations and interactions among genetic factors, environment and the disease, and thus plays a critical, pivotal role in genetic epidemiology [26]. To our knowledge, there were only limited family studies of insomnia, with the majority being carried out on Caucasian adults [17], [18], [19], [20], [21], [23], [27]. Similar to family studies of other sleep disorders (narcolepsy and restless legs syndrome) [28], [29], [30], the presence of a positive family history of insomnia was related to the earlier onset of insomnia in the probands [17], [21]. The other major finding was that the rate of family history was higher in the insomnia probands (current and past, primary and psychiatric insomnia) than the normal controls or self-defined good sleepers [18]. Although these existing studies suggested a familial aggregation phenomenon of insomnia, methodological problems such as small sample size, lack of adjustment for potential confounders and lack of a control comparison group limited their generalization [17], [18], [20], [21]. In addition, as suggested by the results in our family study on narcolepsy [31], the family history of a sleep problem that was solely reported by the probands themselves, without detailed assessments of the family members, might have led to potential reporting bias in the estimation of familial occurrence of the sleep problem.
As insomnia was suggested to have prominent negative consequences in childhood [4], [8], [10], [12], [32], [33], [34], the family study of childhood onset insomnia could shed light on familial aggregation and pave the way for finding the mechanism underlying the phenomenon of familial aggregation in insomnia, which might be contributed by the shared traits in the same family, such as socio-economic status, other environmental factors and probable genetic predisposition. Hence, we conducted the present study with a large community-based sample of family trios by using quantitative frequency criteria in the ascertainment of insomnia for both children and their parents.
Section snippets
Selection of children and their parents
This study was part of an ongoing epidemiologic study about sleep problems among Hong Kong Chinese children, which started in 2003 [35], [36]. The protocol was approved by the Institutional Ethics Review Committee. A total of 9172 questionnaires were distributed to children aged 6–13 years old (grade 1 to grade 6) from 13 randomly selected primary schools in both Shatin and Tai Po districts from October to December 2003. Please refer to our previous publications related to this study in more
Sleep questionnaire for children
The questionnaire consisted of 54 items on demography, sleep environment, family information, sleep habits and problems. More details about the items in this questionnaire for children could be found in Appendix 1 of our previous publication [35]. All the sleep information was based on the past 12 months. In this study, the items of insomnia were modified according to three basic subtypes of insomnia in the Manual of Mental Disorders, 4th edition (DSM-IV) and International Classification Of
Prevalence of insomnia in children and parents
Among 5695 available children, 2833 were girls (49.7%), with a mean age of 9.2 (SD = 1.8) years old. The mean age was 43.3 (SD = 5.5) years old and 38.9 (SD = 4.6) years old for fathers and mothers, respectively. Of the questionnaires for children 72.4% were reported by their mothers, 15.5% by fathers, 5.7% by both parents and 6.4% by others (other relatives or caretakers). The rates of insomnia in the past 12 months by definition of ⩾3 times/week among children, mothers and fathers were 4.0%, 12.8%
Prevalence of insomnia in children and parents
The prevalence of insomnia in children or adolescents varied widely from 4% to 31% based on varying frequency criteria [8], [9], [12], [23], [32], [33], [34], [38], [39], [40]. Our study indicated that insomnia in Hong Kong children was commonly reported by their parents, with a rate of 4.0% in the past 12 months. The prevalence of childhood insomnia in our study was similar to those studies using a more stringent frequency criteria of insomnia (⩾3 times/week or often), which reported the
Conclusions
A robust familial aggregation was found in childhood insomnia at this community-based epidemiological study even after adjustment of shared socio-demographic and environmental risk factors. The presence and frequency of parental insomniac symptoms had a dose–response effect on the rate of insomnia of their children and vice versa.
Conflict of interest
All the authors report no conflicts of interest.
Acknowledgements
This study was part of the epidemiological study funded by Grant (CUHK4161/02M) from the Research Grants Council of the Hong Kong SAR, China.
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