Download Longitudinal Course and Outcome of Chronic Insomnia in Hong

CHRONIC INSOMNIA IN HONG KONG CHINESE CHILDREN
doi: 10.5665/sleep.1286
Longitudinal Course and Outcome of Chronic Insomnia in Hong Kong Chinese
Children: A 5-Year Follow-Up Study of a Community-Based Cohort
Jihui Zhang, MD1; Siu Ping Lam, MRCPsych, FHKAM (Psych)1; Shirley Xin Li, MA1; Albert Martin Li, MD, FHKAM (Paed)2;
Kelly Y.C. Lai, MRCPsych, FHKAM (Psych)1; Yun-Kwok Wing, FRCPsych, FHKAM (Psych)1
1
Department of Psychiatry, 2Department of Pediatrics, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong SAR
Objectives: There are limited data on the long-term outcome of childhood insomnia. We explored the longitudinal course, predictors, and impact
of childhood insomnia in a community-based cohort.
Design: 5-year prospective follow-up.
Setting: Community-based.
Participants: 1611 children (49% boys) aged 9.0 ± 1.8 years at baseline; 13.7 ± 1.8 years at follow-up.
Intervention: NA.
Main Exposures: Chronic insomnia was defined as difficulty initiating sleep, difficulty maintaining sleep and/or early morning awakening ≥ 3 times/
week in the past 12 months.
Outcome Measures: General health, upper airway inflammatory diseases, and behavioral problems in recent one year were assessed at both time
points, while mental health and lifestyle practice were assessed at follow-up study. The questionnaires at baseline and follow-up were reported by
parents/caretakers and adolescents themselves, respectively.
Results: The prevalence of chronic insomnia was 4.2% and 6.6% for baseline and follow-up, respectively. The incidence and persistence rates
of chronic insomnia were 6.2% and 14.9%, respectively. New incidence of insomnia was associated with lower paternal education level, baseline
factors of frequent temper outbursts and daytime fatigue as well as alcohol use and poor mental health at follow-up. Baseline chronic medical disorders, frequent temper outbursts, and poor mental health at follow-up were associated with the persistence of insomnia in adolescents. Baseline
insomnia was associated with frequent episodes of laryngopharyngitis and lifestyle practice (coffee and smoking) at follow-up.
Conclusions: Chronic insomnia is a common problem with moderate persistent rate in children. The associations of adverse physical and mental
health consequences with maladaptive lifestyle coping (smoking and alcohol) argue for rigorous intervention of childhood insomnia.
Keywords: Childhood insomnia, longitudinal study, lifestyle, upper airway inflammatory diseases, behavioral problems
Citation: Zhang J; Lam SP; Li SX; Li AM; Lai KYC; Wing YK. Longitudinal course and outcome of chronic insomnia in Hong Kong Chinese children:
a 5-year follow-up study of a community-based cohort. SLEEP 2011;34 (10):1395-1402.
INTRODUCTION
Insomnia is commonly found in childhood general population with a prevalence rate of 4% to 9% (by restrictive diagnostic criteria of 3 times/week or often).1-3 Most of the
epidemiologic studies on childhood insomnia are, however,
of cross-sectional design.1-3 Among the few available prospective studies of the long-term course of insomnia in children
and adolescents, insomnia or sleep disturbances tend to run
a persistent course, at least for a proportion of individuals.4-11
Nonetheless, most of these studies,5-8,11,12 especially the earlier ones, used nonspecific terms such as “sleep disturbances” or “sleep problems” rather than operational definition of
insomnia. Overall, these prospective studies revealed certain
longitudinal patterns of childhood insomnia. First, the usage of
stricter criteria leads to lower persistence and incidence rate of
insomnia.4 Second, persistence of insomnia seems to be agedependent. Persistence of sleep difficulty is not found between
infants and young children12 but becomes significant in older
children and adolescents.6
The clinical significance of childhood insomnia is reflected
by its correlation with medical conditions,2,13 mental dysfunction, and poor academic performance.14 However, the crosssectional nature of most studies could not disentangle the
interactive relationship between insomnia and various dysfunctions.14 A few prospective studies suggest that insomnia
or sleep problems at baseline might be associated with poor
somatic health,13 substance use15 and behavioral problems in
adolescents.8,15,16
In brief, previous studies have found that childhood insomnia could be a persistent sleep problem with adverse health
consequences. However, several aspects are still unclear.
First, all longitudinal studies were conducted in western
countries. Little is known about the long-term course of insomnia in non-western populations. Second, adolescents experience significant developmental changes both physically
and psychologically,17 but little is known about the changes
of insomnia symptoms of children when they are entering
adolescence. Finally, the long-term association of insomnia
with physical and mental problems is still inadequately investigated. In this community-based cohort, we aimed to: (1)
determine the longitudinal course of chronic insomnia and its
correlates in Hong Kong Chinese children; (2) examine the
long-term association of childhood chronic insomnia with
physical and mental health in adolescents.
A commentary on this article appears in this issue on page 1289.
Submitted for publication November, 2010
Submitted in final revised form April, 2011
Accepted for publication May, 2011
Address correspondence to: Dr. Yun-Kwok Wing, Professor, Director of
Sleep Assessment Unit, Department of Psychiatry, Shatin hospital, The
Chinese University of Hong Kong, Shatin, Hong Kong SAR; Tel: 85226367748; Fax: 852-26475321; E-mail: [email protected]
SLEEP, Vol. 34, No. 10, 2011
1395
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
Finally, a total of 1611 adolescents out of 3416 contactable
children (47.2%) returned their packages of questionnaires at
the follow-up study.
6447 children at baseline
Measurements
The measures were mainly reported by parents at baseline
but were answered by adolescents themselves at follow-up.
In both studies, the informants (parents or adolescents) were
encouraged to talk with relevant family members while completing the questionnaires. At baseline study, the parents/
caretakers were chosen as informants, as there was information that would need the input from the parents, for example,
presence of specific medical disorders of their young children.
Furthermore, the rate of insomnia in children under 12 years
old as reported by parents would be more precise when evaluating a longer term course of insomnia, such as the current
study about sleep problems over 12 months.9,21 At follow-up
study, the subjects were asked to complete the questionnaires
themselves, as we believed that the adolescents would be able
to give a more reliable account of their own sleep and medical
problems, especially over some sensitive questions on lifestyle
habits (such as smoking and drinking).
575 children
without phone
number excluded
5872 children left phone
numbers
2456 children
were not
contactable
3416 children were
contactable
55 children
refused
3361 sets of questionnaires
sent
1750 children did
not return
Environmental and Sociodemographic Risk Factors
Assessment of socioeconomic status included several binary
or ordinal questions,2 such as parental educational level (< 12
years or ≥ 12 years), parental employment (employed vs. unemployed), housing type (private vs. public), parental marital status (married or cohabited vs. devoiced or separated), and family
income (≤ HK$15,000/month vs. more than HK$15,000/month;
HK$7.8 = US$1).
1611 children (47.2% of
contactable) returned
Figure 1—Flow diagram in the recruitments of subjects
METHOD
Sleep Questionnaire for Children
Our baseline questionnaire consisted of 54 items on demographics, sleep environment, sleep habits and problems, and
family information.2,19,20 In brief, there were 25 items about
childhood sleep problems. The psychometric property of the
questionnaire was found to be satisfactory, with Cronbach α
coefficient of 0.868 and 5-factor structure corresponding to
major childhood sleep problems by factor analysis.2 The questionnaire in the follow-up study was slightly modified, but the
items about insomnia were the same as previous one. Difficulty
initiating sleep (DIS), difficulty maintaining sleep (DMS), and
early morning awakening (EMA) were assessed by the following question: “during the past 12 months, how often has
your child (or “you,” in follow-up questionnaire) had: (1) difficulty initiating sleep? (2) sudden awakening during sleep and
difficulty in returning to sleep? (3) early morning awakening,
and could not fall asleep again?” respectively. Subjects were
instructed to respond on a 5-point Likert scale (0 = never, 1
= less than once per month, 2 = 1-3 times per month, 3 = 1-2
times per week, 4 = ≥ 3 times per week). Subjects reporting any
subtype of insomnia ≥ 3 times/week over the past 12 months
were defined as suffering from chronic insomnia. As the major
aim of our study was to explore the long-term course and consequences of sleep problems including chronic insomnia, a period
of 12 months was chosen. The report of sleep symptoms over
the past year could allow the estimation of insomnia problem at
the conservative end.
Subject Selection
The study was conducted and reported as according to the
recommendations of the STROBE guideline.18 This study is
part of an ongoing epidemiologic study about sleep problems
among Hong Kong Chinese children and their parents, which
started since 2003-2004 (baseline).2,19,20 Follow-up was conducted during the period of 2008-2010. The protocols of this
study at both baseline and follow-up were approved by the
institutional ethics review committee. Parent (s) or caregiver
(s) of the subjects gave written consents to participate this
study, and the adolescents gave written assents to the study.
Figure 1 delineates the recruitment of the subjects. A total of
6447 children were recruited at baseline. Among 5872 families
who left their telephone numbers, a total of 3416 were contactable at the time of follow-up. While 55 of them refused to
participate, 3361 (98.4%) gave verbal consents and agreed to
complete the study questionnaires. The package of questionnaires for adolescents, fathers and mothers as well as their sibling (s) aged > 6 years old (if any) was mailed to the address
provided. The data about the adolescents was analyzed in the
current study. The families were reminded at 2-4 week intervals about returning the questionnaires. If the questionnaires
were not returned after 2 months, a reminder phone call was
made again to the families. If the questionnaires were not returned after another 2 months, a final reminder letter was sent.
SLEEP, Vol. 34, No. 10, 2011
1396
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
Daytime Symptoms
Different daytime symptoms in the past 12 months, including difficulty getting up in the morning, feeling unrefreshed
in the morning, morning headache, and daytime fatigue were
also asked.22 We did not incorporate these daytime symptoms to
define insomnia disorder,23-26 but instead we treated these daytime symptoms as correlates of insomnia symptoms in the current study. Studying insomnia symptoms rather than syndrome
(symptoms plus impairment) would allow us to estimate the
repercussion of insomnia at the conservative end.
nia at follow-up, while those subjects with insomnia at baseline
would be analyzed for the persistent rate of insomnia at followup. The exposures (risk factors) for the course of insomnia were
based on the baseline information, including sociodemographics,
behavioral problems, and medical conditions. Another series of
major outcomes included general health condition, 5 common
upper airway inflammatory diseases, behavioral problems, and
lifestyle practice at follow-up. Their exposures were the courses
of chronic insomnia (i.e., baseline, incident, and persistent
insomnia). The covariates for these major outcomes included age,
gender, parental educational level, and family income.
General Health, Chronic Medical Diseases, and Upper Airway
Inflammatory Diseases (Baseline and Follow-Up)
To measure subjects’ general health, the following questions
were asked: “how is your child’s (your) general health condition in recent one year?” The responses could be: (1 = very
poor; 2 = poor; 3 = fair; 4 = good; 5 = very good. Those with responses of 1 to 2 and 3 to 5 were grouped together. “Does (Do)
your child (you) need to take medication regularly?” The responses could be: “yes” or “no.” They were also asked whether
they had any chronic medical disorders that were diagnosed and
required treatment (altogether 14 disorders, including hypertension, eye diseases, hypercholesterolemia, arthritis, epilepsy,
cardiovascular disorders, diabetes mellitus, lung disorders, psychiatric/mood disorders, renal disorders, chronic pain, eczema,
gastroesophageal reflux disease [GERD], and others). However, due to limited number of cases for each disorder, they were
not analyzed individually.
The participants were also asked whether they had the following 5 common upper airway inflammatory diseases in
recent one year: allergic rhinitis, nasosinusitis, asthma, adenotonsillitis, and laryngopharyngitis. The responses could be: 1 =
never; 2 = sometimes; 3 = frequently). Those with “frequent”
upper airway diseases were considered abnormal.
Statistics
Descriptive statistics were presented as percentages for discrete variables and as means (standard deviation) for continuous
variables. The differences in sample characteristics were tested
by independent t-test or χ2 to explore the potential sample attrition
between recruited and drop-out subjects whenever appropriate.
Long-Term Course of Chronic Insomnia and Its Predictors
Chi-square statistic was used to compare the prevalence of
chronic insomnia at baseline and that of follow-up in the study
cohort. As the response rate (47.2%) was less than ideal, the
prevalence, persistence, and incidence rate of insomnia at follow-up were further weighted for sociodemographic variables
(parental education level, family income and housing type)
which differed between those recruited and drop-out subjects.
The incidence and persistence rate of chronic insomnia and
their predictors were analyzed. The risk factors were extracted
from baseline data. Logistic regression (enter method) analysis
was used to determine the association between chronic insomnia (incidence and persistence) and risk factors after adjusting
for age and gender. Those independent variables found to be
significantly associated with the progress of chronic insomnia
were further tested by multivariate logistic regression with forward likelihood method.
Behavioral Problems and Academic Performance during the
Past 12 Months (Baseline and Follow-Up)
Hyperactivity and frequent temper outbursts of children (adolescents) were rated as “yes” or “no.” Academic performance
was rated as poor if the subjects rated “very worst or worst than
past one year.”
Consequences of Chronic Insomnia
Chi-square statistic or Fisher exact test was used to explore
the potential association between the progress of chronic insomnia and various consequences. Multiple logistic regression
(enter method) was used to examine the strength of these associations after controlling for age, gender, parental education
level, family income, and corresponding consequences at baseline. For example, the strength of association between hyperactivity at follow-up and chronic insomnia was explored after
controlling for age, gender, parental education level, family
income, and hyperactivity at baseline. As GHQ and lifestyle
practice were only assessed at follow-up, these dependent variables were only adjusted for age, gender, parental education
level and family income. P-values < 0.05 were considered statistically significant. SPSS 16.0 for Windows (SPSS Inc, Chicago, IL) was used for all statistical tests.
Mental Health Assessment during Past One Month
(Follow-Up Only)
The Chinese version of General Health Questionnaire
(GHQ-12) was employed to evaluate mental health status of the
adolescents at follow-up. A GHQ-12 score ≥ 4 was considered
poor mental health.27
Lifestyle Assessments during Past 12 Months (Follow-Up Only)
Four types of lifestyle habits, including regular tea, coffee, alcohol, and smoking were asked at follow-up. All of the
questions about lifestyle were rated as 0 = never/seldom or 1 =
sometimes/often.
RESULTS
Outcomes, Exposures, and Covariates
All subjects were divided into 2 groups on the basis of their
insomniac status at baseline. Those subjects without chronic
insomnia at baseline were analyzed for the incidence rate of insomSLEEP, Vol. 34, No. 10, 2011
Sample Characteristics
Table 1 delineates the characteristics of subjects at baseline
and follow-up. The mean age of study subjects (n = 1611) was
1397
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
Table 3 presents the factors associated with the incidence and
persistence rate of insomnia. Several baseline risk factors were associated with new incidence of insomnia in adolescents, including
lower paternal education level (OR[95%CI] = 2.49[1.13-5.51]),
frequent temper outbursts (OR[ (95%CI] = 1.85[1.16-2.97])
and daytime fatigue (OR[95%CI] = 2.17 ([1.24-3.77]). Other
daytime symptoms, including difficulty getting up, dry mouth,
morning headache, and feeling unrefreshed in the morning, were
not associated with either persistence or incidence of insomnia
in the final models. Chronic medical conditions (OR[95%CI] =
10.2[1.99-52.54]) at baseline were significantly associated with
persistence of chronic insomnia in adolescents. Upper airway
inflammatory diseases and parent-reported poor health condition at baseline could not predict the course of chronic insomnia
(data not shown, P > 0.05).
9.0 ± 1.8 years old at baseline and 13.7 ± 1.8 at follow-up, with
a mean follow-up duration of 4.7 years. Those children who
participated in the follow-up study had slightly higher socioeconomic status (higher parental education, housing type, and
family income, P < 0.05) and were slightly younger (9.0 ± 1.8
vs. 9.2 ± 1.8 years, P < 0.05), but had similar prevalence of
chronic insomnia when compared to the dropouts. Similar boy/
girl ratios were found between those recruited (boys 49.1%)
and drop-out subjects (50.6%) (P > 0.05).
Course of Chronic Insomnia and Its Predictors
Table 2 reports the 5-year progress of chronic insomnia in our
study cohort. The prevalence of chronic insomnia was slightly higher at follow-up than that of baseline (6.6% vs 4.2%, P = 0.001). The
incidence and persistence rates of chronic insomnia were 6.2% and
14.9%, respectively. DIS had the highest persistence rate (19.0%),
followed by DMS (5.3%). Subjects with EMA at baseline all remitted at follow-up, which indicated that EMA was a rather unstable condition in children. When using a looser criterion of sleep
symptoms (≥ once per week), the incidence and persistence rates
of chronic insomnia increased to 18.0% and 27.4%, respectively.
Similar results were found upon further weighted analysis with adjustment to sociodemographic variables.
Association of Medical, Behavioral, Mental, and Lifestyle
Problems at 5-Year Follow-Up with Chronic Insomnia
Table 4 shows the association between the longitudinal
course of chronic insomnia and various outcome measures (i.e.,
general health, upper airway inflammatory diseases, mental
health, behavioral problems, and lifestyle practice) at followup. Baseline insomnia was associated with frequent episodes of
laryngopharyngitis and lifestyle practice
(coffee drinking and smoking) but not
Table 1—Sample characteristics of subjects at baseline and follow-up
mental health and behavioral problems at
5-year follow-up. Although baseline inBaseline
Baseline
Follow-up
sample
cohort
cohort
somnia was associated with poor health
N = 6447
N = 1611
N = 1611
condition and chronic medical conditions
Children’s age (years)*, mean ± SD
9.2 ± 1.8
9.0 ± 1.8
13.7 ± 1.8
at follow-up initially, these associations
Gender, male %
50.6
49.1
49.1
did not persist after controlling for the
potential confounding factors and corInsomnia rate, %
4.0
4.2
6.6
responding problems. New incidence of
Paternal occupation (employed),%
96.2
97.5
97.3
insomnia was associated with poor health
Paternal educational level, tertiary or above, %*
15.8
19.3
19.3
condition, frequent episodes of asthma
Maternal occupation (employed), %
41.4
40.8
50.2
and laryngopharyngitis, frequent alcohol
Maternal educational level, tertiary or above, %*
10.0
12.7
12.7
and smoking, behavioral problems, and
Housing type (public), %*
59.9
54.2
53.9
poor academic performance at followFamily income > HK$15,000/month, %*
46.9
56.4
67.5
up (P < 0.05). Persistence of chronic
Parental marital status (married or cohabited), %
92.5
93.3
91.2
insomnia was associated with presence of
chronic medical disorders at baseline and
Wave 1 sample (W1 sample) included all recruited subjects at baseline; Wave 1 cohort (W1 cohort)
poor mental health, frequent temper outand Wave 2 cohort (W2 cohort) only included recruited subjects at both baseline and follow-up study.
bursts, and coffee drinking at follow-up.
*P < 0.05 between recruited and drop-out subjects at follow-up. HK $7.8 = US $1.
Poor mental health as defined by GHQTable 2—Insomnia symptoms of the study cohort at baseline and follow-up
Prevalence Rates
Children
DIS (%)
DMS (%)
EMA (%)
Overall insomnia (%)
Insomnia ≥ 1 time/week (%)
Cohort Change
Baseline sample Baseline cohort Follow-up cohort
N = 6447
N = 1611
N = 1611
2.5
2.6
5.6 (5.5)
1.3
1.2
0.8 (0.7)
1.2
0.9
1.4 (1.5)
4.0
4.2
6.6 (6.6)
11.1
12.9
19.2 (19.4)
Incidence
5.2 (5.2)
0.7 (0.6)
1.4 (1.5)
6.2 (6.2)
18.0 (18.1)
Persistence
19.0 (17.8)
5.3 (5.0)
0 (0)
14.9 (14.1)
27.4 (28.1)
Remission
81.0 (82.2)
94.7 (95.0)
100 (100)
85.1 (85.9)
72.6 (71.9)
DIS, Difficulty initiating sleep; DMS, Difficulty maintaining sleep; EMA, Early morning awakening; Overall insomnia was defined as any subtype of insomnia ≥
3 times/week. Values in the bracket were weighted for paternal education level, maternal education level, family income, and housing type.
SLEEP, Vol. 34, No. 10, 2011
1398
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
Table 3—Baseline factors associated with the progress of insomnia in the study cohort
Incidence vs Non-Insomnia
Baseline Information
Gender, female vs male
Persistence vs Remission
Crude OR
(95%CI)
1.09 (0.72-1.65)
Adjusted OR
(95%CI)
—
Crude OR
(95%CI)
0.51 (0.12-2.20)
Adjusted OR†
(95%CI)
—
1.00 (0.66-1.54)
—
1.61 (0.67-3.89)
—
2.56 (1.24-5.41)*
2.49 (1.13-5.51)*
0.63 (0.10-4.05)
—
1.57 (0.75-3.31)
—
3.50 (0.58-21.08)
—
1.89 (1.15-3.11)
1.81 (1.17-2.80)*
1.42 (0.83-2.41)
2.18 (1.25-3.79)*
1.15 (0.41-2.24)
0.99 (0.99-1.00)
1.84 (1.18-2.85)*
1.01 (0.36-2.83)
—
1.85 (1.16-2.97)*
—
2.17 (1.24-3.77)*
—
—
—
—
0.83 (0.17-4.21)
3.45 (0.81-14.74)
6.53 (1.49-28.23)*
1.90 (0.49-7.37)
4.56 (0.97-21.43)
2.60 (0.43-15.7
2.58 (0.61-10.90)
1.97 (0.43-8.97)
—
—
10.2 (1.99-52.5)*
—
—
—
—
—
†
Family income (monthly)
≤ 15,000 vs > 15,000 (HK$)
Paternal education
Non-tertiary level vs tertiary level
Maternal education
Non-tertiary level vs tertiary level
Children’s Information
Hyperactivity
Frequent temper outbursts
Chronic medical disorders
Feeling tired during daytime, ≥ 3 times/week
Feeling unrefreshed after waking up, ≥ 3 times/week
Feeling headache after waking up, ≥ 3 times/week
Difficulty getting up in the morning, ≥ 3 times/week
Moring dry mouth, ≥ 3 times/week
†
Adjusted for age, gender, parental education, and family income. — Without significance in adjusted model. *P < 0.05.
Table 4—Association between the longitudinal course of insomnia and major outcome measures in the study cohort
Baseline Insomnia vs Non-Insomnia
Overall Health
Poor health condition (5.3%)
Chronic use of medication (4.7%)
Incidence vs Non-Insomnia
Persistence vs Remission
Crude
OR (95%CI)
Adjusted OR
(95%CI)
Crude
OR (95%CI)
Adjusted OR
(95%CI)
2.55 (1.18-5.52)*
–
2.65 (1.35-5.19**)
2.37 (1.12-5.01)*
2.04 (0.35-11.9)
–
2.53 (1.12-5.75)*
–
1.20 (0.47-3.05)
–
2.50 (0.41-15.1)
–
1.36 (0.79-2.34)
–
1.68 (1.08-2.62)*
–
1.78 (0.44-7.19)
–
7.55 (0.68-84.0)
–
†
†
Crude
OR (95%CI)
Adjusted OR†
(95%CI)
Upper Airway Diseases
Frequent allergic rhinitis (22.8%)
Frequent nasosinusitis (0.2%)
—
—
–
—
Frequent asthma (0.6%)
6.76 (1.38-33.2)*
–
6.09 (1.17-31.8)*
14.5 (2.02-104.2)**
—
—
Frequent adeno-tonsillitis (0.5%)
3.33 (0.40-27.4)
–
6.09 (1.17-31.8)*
–
—
—
Frequent laryngopharyngitis (1.8%)
3.86 (1.30-11.4)**
3.41 (1.11-10.57)**
4.98 (1.94-12.8)**
4.25 (1.50-12.0)**
23.1 (2.11-254)**
–
Behavioral Problems
Hyperactivity (8.5%)
0.86 (0.34-2.18)
–
3.59 (2.15-5.99)**
3.63 (2.09-6.32)**
1.42 (0.14-14.2)
–
Frequent temper outburst (22.5%)
1.61 (0.95-2.74)
–
2.45 (1.60-3.76)*
2.27 (1.42-3.63)**
12.9 (2.43-68.6)*
15.8 (2.25-111.6)**
Poor academic performance (12.3%)
1.25 (0.67-2.33)
–
2.81 (1.80-4.40)*
2.71 (1.68-4.37)**
—
—
1.32 (0.66-2.63)
–
3.86 (2.44-6.12)**
4.11 (2.51-6.74)**
5.33 (1.16-24.5)*
5.00 (1.09-22.1)*
Mental Health Condition
GHQ-12 score ≥ 4 (12.5%)
LIfestyle Practice
Tea drinking ≥ 3 times/week (43.9%)
1.11 (0.68-1.81)
Coffee drinking ≥ 3 times/week (11.1%) 2.43 (1.34-4.41)**
Alcohol ≥ 3 times/week (2.4%)
1.25 (0.30-5.31)
Smoking ≥ 3 times/week (1.1%)
5.12 (1.44-18.3)**
–
1.35 (0.89-2.04)
–
1.12 (0.29-4.29)
5.04 (1.63-15.6)**
1.47 (0.81-2.65)
–
7.67 (1.80-32.8)**
–
41.1 (3.68-460)*
–
3.69 (1.58-8.63)**
2.77 (1.02-7.57)*
6.00 (0.34-104)
–
4.24 (1.14-15.8)*
4.18 (1.15-15.2)**
3.97 (1.04-15.2)*
2.94 (0.24-2.41)
–
Adjusted for age, gender, parental education, family income, and parent-reported poor health condition at baseline. *P < 0.05; **P < 0.01. — Could not be
analyzed due to a lack of cases; – Without statistical significance in adjusted model. The percentages in the bracket of outcomes were rates of positive cases
of outcomes in overall sample.
†
SLEEP, Vol. 34, No. 10, 2011
1399
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
health and frequent episodes of asthma and laryngopharyngitis over the course of 5 years, while the presence of chronic
medical conditions could predict the persistence of insomnia.
In other words, there is an interactive relationship between insomnia and physical health. While chronic medical disorders
predisposed and perpetuated chronic insomnia, some medical
conditions were also the outcomes of insomnia.13
In addition, insomniac adolescents had increased predisposition towards frequent upper airway inflammatory diseases.
In particular, both baseline and new incidence of insomnia
could predict frequent attacks of laryngopharyngitis, while
new incident insomnia was associated with frequent asthmatic attacks in adolescents. The temporal association between
chronic insomnia and upper airway inflammatory diseases was
consistent with findings of the middle-aged adults cohort.34 In
other words, the predisposition to upper airway inflammatory
diseases suggested that alteration of immune functioning is
a possible distinct consequence of insomnia. It has been increasingly recognized that sleep plays a vital role in immune
functioning.35 Subjects with primary insomnia were reported
to have lower levels of CD3+, CD4+, CD8+ cells, and natural
killer cell responses than good sleepers.36,37 A recent experimental study found that subjects with poor sleep over past 2
weeks were 5.5 times more likely to develop a common cold
than good sleepers when they both received a nasal drop containing rhinovirus.38 Thus, immune dysfunction might play a
critical role in the relationship between chronic insomnia and
upper airway inflammatory diseases.
12 score ≥ 4 was associated with incidence and persistence of
chronic insomnia, with OR (95%CI) of 4.11 (2.51-6.74) and
5.0 (1.09-22.1) respectively, but not baseline chronic insomnia.
DISCUSSION
Longitudinal Course of Chronic Insomnia from
Childhood to Adolescence
Although insomnia has been generally suggested to be
chronic and persistent in adults, limited information is known
about the long-term course of insomnia in children and adolescents. Our study found that the prevalence of chronic insomnia
was 4.2% and 6.6% at baseline and 5-year follow-up respectively. The lack of gender difference in the prevalence of insomnia in this study was consistent with our baseline data3 and
a previous adolescent study.4 However, it differed sharply from
adult insomnia, for which there is a definite female predisposition.28,29 Perhaps, the young age of our adolescent cohort could
not capture the emerging gender difference of insomnia in the
older adolescents and young adults.3,28,29
The persistence rate of chronic insomnia symptoms was
14.9%, which was slightly lower than the figures (21% to
60%) reported in previous studies.4-10 The slight disparity of
the persistence rate between ours and other studies might be
related to different study designs. The longitudinal follow-up
period (nearly 5 years) in our study was longer than previous
studies, which usually involved 1-2 years of follow-up.4-9,12
The second reason might be related to the use of relatively
more strict criteria in defining insomnia in our study (a frequency ≥ 3 times/week over past 12 months). When using
a looser criterion (i.e., once a week), the persistence rate of
chronic insomnia in the current study rose accordingly (from
14.9% to 27.4%). Another two studies similarly suggested
that stricter criteria, for example, insomnia symptom (s) plus
daytime fatigue or sleepiness, decreased the persistence rate
of insomnia from 45.8% to 22.8% and from 52% to 21%, respectively.4,6 As the insomnia symptoms were assessed over
the past 12 months, the current study could not differentiate
whether using a looser criterion with shorter period, such as
the past month, would lead to higher prevalence, incidence,
and persistence of insomnia. Further studies are warranted to
address the potential disparity in the prevalence and course of
insomnia across different criteria of insomnia.
Our logistic regression showed that lower paternal education level, frequent temper outbursts, and daytime fatigue in
children would predict the new incidence of insomnia during
adolescence. In other words, our data suggest that new onset of
insomnia may be related to baseline sociodemographic characteristics of the family and daytime functional impairments (fatigue and temper outbursts).
Association between the Course of Chronic Insomnia and
Behavioral, Mental, and Lifestyle Problems
Our baseline cross-sectional study found that both hyperactivity and frequent temper outbursts were correlated with
chronic insomnia.2 In the current follow-up study, the presence of frequent temper outbursts at baseline could predict new
incidence of insomnia (Table 3), while incidence of insomnia,
but not baseline insomnia, was associated with these two
behavioral problems at follow-up. Previous studies, however,
suggested that sleep problems were a risk factor for future
behavioral problems.8,15,16 A possible reason might be that
these studies measured sleep problems only at baseline and
treated sleep problems as exposures and behavioral problems
as outcomes. Hence, they could not analyze the effects of
behavioral problems on the development of chronic insomnia.
On the contrary, our study, by measuring both chronic insomnia and behavioral problems at baseline and follow-up, could
allow us to investigate the reciprocal association between
chronic insomnia and behavioral problems. These results, thus,
suggest that the associations between behavioral problems and
chronic insomnia are likely complex and reciprocal. Nonetheless, further studies with more detailed behavioral assessments
are warranted to disentangle the causal relationship between
chronic insomnia and behavioral problems in adolescents.
Although most studies suggest that chronic insomnia is an
important risk factor for future mental disorders in adults,26,39
little is known about the longitudinal association between
chronic insomnia and mental disorders in children and adolescents.40 In a cross-sectional study relying on retrospective
recall for the presence of lifetime insomnia and psychiatric
Course of Chronic Insomnia, Physical Health, and
Upper Airway Diseases
Previous cross-sectional studies suggested that insomnia
represents a common symptom of physical disorders and is
generally regarded as the distress or consequences of the medical conditions.30-33 However, our study indicates a reciprocal relationship between insomnia and medical conditions. We found
that presence of insomnia was associated with poor perceived
SLEEP, Vol. 34, No. 10, 2011
1400
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
disorders, Johnson et al. found that prior insomnia was significantly associated with the onset of depression but not anxiety
in adolescents.41 By employing a six-wave survey, Buysse
et al. reported that pure insomnia (without depression) was
prospectively inter-correlated with insomnia comorbid with
depression (insomnia + depression) but not pure depression
(without insomnia) in young adults.10 Altogether, these studies
suggest that insomnia might predict depression in adolescents,
especially those comorbid with insomnia. Our study found that
poor mental health (as measured by GHQ-12) at follow-up
was associated with the persistence and incidence of chronic
insomnia but not baseline chronic insomnia. This might suggest
that there is only state association between insomnia and poor
mental health in adolescents. Nonetheless, further prospective
study with structured interview for psychiatric disorders will
be needed to delineate the complex interactive relationship between chronic insomnia and mental disorders in our cohort.
The association between insomnia and substance misuse has
been increasingly recognized in adolescents.42 A previous study
found that smoking was a risk factor for future insomnia in
adolescents.6 On the other hand, our study found that childhood
insomnia predisposed to adolescents’ smoking behavior 5 years
later, which was consistent with a recent finding in children
having a strong family history of smoking.15 Thus, there was
likely a reciprocal association between insomnia and smoking
behaviors in adolescents. In addition, new incidence of insomnia was associated with enhanced risk of alcohol use. In other words, smoking and coffee consumption might be the two
major methods being employed by adolescents in coping with
daytime consequences (such as fatigue) of insomnia, while new
onset insomniac adolescents might consume alcohol to combat
their sleep problems.6,13
niac subjects with waxing and waning course within the 5-year
period. Fourthly, in view of the balance between enhancement
of valid response and that of over-detailing of the questionnaire in a large epidemiological survey, a parsimonious choice
of single item rather than detailed questionnaires (for example,
child behavioral checklist) to assess the perceived health and
behavioral problems was chosen at both baseline and followup. Fifthly, despite our intensive tracking of the subjects, the
response rate was rather suboptimal. Nonetheless, the sample
attrition in this study might not have prominently altered the
outcome, as similar results in the course of chronic insomnia
were found with a weighted analysis.
Clinical Implications and Conclusion
To our knowledge, this is the first study investigating the
long-term course of childhood insomnia and its long-term association with mental, behavioral, and physical problems in Chinese childhood general population. Several findings are worth
noting in our study. First, there was a moderate persistent rate
of insomnia in Chinese children over the course of five years.
Second, the findings of risk factors accounting for the persistence and incidence of chronic insomnia have important implications for the prevention and treatment of insomnia. Third,
the temporal relationship between insomnia and their correlates
shed light on their potential complex relationship. Finally, the
pervasive impairments in terms of medical, mental, behavioral,
and maladaptive lifestyle at 5-year follow-up argue for rigorous
intervention of childhood insomnia.
ACKNOWLEDGMENTS
This study was part of the epidemiological study funded by
Health and Health Services Research Fund (HHSRF) grant
(reference number 08090011) from Food and Health Bureau of
Hong Kong SAR, China.
Strengths and Limitations
The merit of this study builds on the longitudinal design in
a large community-based cohort. Secondly, a series of medical
and mental health, behavioral consequences, and lifestyle
habits were comprehensively investigated. Some of these
outcomes were assessed at both baseline and follow-up, which
could allow us to explore the reciprocal relationship between
chronic insomnia and various dysfunctions. However, there
were several limitations. Firstly, the current study was based
on self-reported data without further assessment by structured
interview and clinical examination. In this regard, some of the
potential comorbid sleep disorders such as OSA and PLMS
could not be completely excluded.43,44 Secondly, parents were
the key informants at baseline, which might lead to bias, as the
rates of insomnia were slightly higher when reported by children or adolescents themselves than by their parents or teachers.9,21 The higher rate of insomnia at follow-up than baseline
in our study might be related to the aging effect but the potential reporters’ bias (parents vs adolescents) could not be completely excluded. Although the adolescents were encouraged
to talk with relevant family members for higher accuracy of
their reports (for example, medical disorders), it remains unclear who did or did not consult their family members. Thirdly,
insomnia has been found to have relatively high remission
(around 40% in a period of 1 year) and relapse rates (e.g.,
around 30% in adults).45 Our study might miss those insomSLEEP, Vol. 34, No. 10, 2011
DISCLOSURE STATEMENT
This was not an industry supported study. The authors have
indicated no financial conflicts of interest.
REFERENCES
1. Ohayon MM, Roberts RE, Zulley J, Smirne S, Priest RG. Prevalence and
patterns of problematic sleep among older adolescents. J Am Acad Child
Adolesc Psychiatry 2000;39:1549-56.
2. Zhang J, Li AM, Kong AP, Lai KY, Tang NL, Wing YK. A communitybased study of insomnia in Hong Kong Chinese children: Prevalence, risk
factors and familial aggregation. Sleep Med 2009;10:1040-6.
3. Johnson EO, Roth T, Schultz L, Breslau N. Epidemiology of DSM-IV
insomnia in adolescence: lifetime prevalence, chronicity, and an emergent
gender difference. Pediatrics 2006;117:e247-56.
4. Roberts RE, Roberts CR, Chan W. Persistence and change in symptoms of
insomnia among adolescents. Sleep 2008;31:177-84.
5. Morrison DN, McGee R, Stanton WR. Sleep problems in adolescence. J
Am Acad Child Adolesc Psychiatry 1992;31:94-9.
6. Patten CA, Choi WS, Gillin JC, Pierce JP. Depressive symptoms and cigarette smoking predict development and persistence of sleep problems in
US adolescents. Pediatrics 2000;106:E23.
7. Clarkson S, Williams S, Silva PA. Sleep in middle childhood--a longitudinal study of sleep problems in a large sample of Dunedin children aged
5-9 years. Aust Paediatr J 1986;22:31-5.
8. Gregory AM, O’Connor TG. Sleep problems in childhood: a longitudinal
study of developmental change and association with behavioral problems.
J Am Acad Child Adolesc Psychiatry 2002;41:964-71.
9. Fricke-Oerkermann L, Pluck J, Schredl M, et al. Prevalence and course of
sleep problems in childhood. Sleep 2007;30:1371-7.
1401
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al
27. Chong MY, Wilkinson G. Validation of 30- and 12-item versions of the
Chinese Health Questionnaire (CHQ) in patients admitted for general
health screening. Psychol Med 1989;19:495-505.
28. Zhang B, Wing YK. Sex differences in insomnia: a meta-analysis. Sleep
2006;29:85-93.
29. Li RH, Wing YK, Ho SC, Fong SY. Gender differences in insomnia-a study in the Hong Kong Chinese population. J Psychosom Res
2002;53:601-9.
30. Taylor DJ, Mallory LJ, Lichstein KL, Durrence HH, Riedel BW, Bush
AJ. Comorbidity of chronic insomnia with medical problems. Sleep
2007;30:213-8.
31. Katz DA, McHorney CA. Clinical correlates of insomnia in patients with
chronic illness. Arch Intern Med 1998;158:1099-107.
32. Ancoli-Israel S. The impact and prevalence of chronic insomnia and other
sleep disturbances associated with chronic illness. Am J Manag Care
2006;12:S221-9.
33. Stewart R, Besset A, Bebbington P, et al. Insomnia comorbidity and impact and hypnotic use by age group in a national survey population aged
16 to 74 years. Sleep 2006;29:1391-7.
34. Zhang J, Lam SP, Li SX, et al. Long-term outcomes and predictors of
chronic insomnia: a prespective study in Hong Kong Chinese adults. Submitted.
35. Bryant PA, Trinder J, Curtis N. Sick and tired: Does sleep have a vital role
in the immune system? Nat Rev Immunol 2004;4:457-67.
36. Savard J, Laroche L, Simard S, Ivers H, Morin CM. Chronic insomnia
and immune functioning. Psychosom Med 2003;65:211-21.
37. Irwin M, Clark C, Kennedy B, Gillin CJ, Ziegler M. Nocturnal catecholamines and immune function in insomniacs, depressed patients, and control subjects. Brain Behav Immun 2003;17:365-72.
38. Cohen S, Doyle WJ, Alper CM, Janicki-Deverts D, Turner RB. Sleep habits and susceptibility to the common cold. Arch Intern Med 2009;169:62-7.
39. Fong SY, Wing YK. Longitudinal follow up of primary insomnia patients
in a psychiatric clinic. Aust N Z J Psychiatry 2007;41:611-7.
40. Ivanenko A, Johnson K. Sleep disturbances in children with psychiatric
disorders. Semin Pediatr Neurol 2008;15:70-8.
41. Johnson EO, Roth T, Breslau N. The association of insomnia with anxiety
disorders and depression: exploration of the direction of risk. J Psychiatr
Res 2006;40:700-8.
42. Johnson EO, Breslau N. Sleep problems and substance use in adolescence. Drug Alcohol Depend 2001;64:1-7.
43. Li AM, Au CT, Sung RY, et al. Ambulatory blood pressure in children with obstructive sleep apnoea: a community based study. Thorax
2008;63:803-9.
44. Wing YK, Zhang J, Ho CK, Au CT, Li AM. Periodic limb movement
during sleep is associated with nocturnal hypertension in children. Sleep
2010;33:759-65.
45. Morin CM, Belanger L, LeBlanc M, et al. The natural history of insomnia: a population-based 3-year longitudinal study. Arch Intern Med
2009;169:447-53.
10. Buysse DJ, Angst J, Gamma A, Ajdacic V, Eich D, Rossler W. Prevalence,
course, and comorbidity of insomnia and depression in young adults.
Sleep 2008;31:473-80.
11. Johnson EO, Chilcoat HD, Breslau N. Trouble sleeping and anxiety/depression in childhood. Psychiatry Res 2000;94:93-102.
12. Simard V, Nielsen TA, Tremblay RE, Boivin M, Montplaisir JY. Longitudinal study of preschool sleep disturbance: the predictive role of maladaptive parental behaviors, early sleep problems, and child/mother psychological factors. Arch Pediatr Adolesc Med 2008;162:360-7.
13. Roberts RE, Roberts CR, Duong HT. Chronic insomnia and its negative
consequences for health and functioning of adolescents: a 12-month prospective study. J Adolesc Health 2008;42:294-302.
14. Dewald JF, Meijer AM, Oort FJ, Kerkhof GA, Bogels SM. The influence of sleep quality, sleep duration and sleepiness on school performance in children and adolescents: a meta-analytic review. Sleep Med
Rev 2010;14:179-89.
15. Wong MM, Brower KJ, Zucker RA. Childhood sleep problems, early onset of substance use and behavioral problems in adolescence. Sleep Med
2009;10:787-96.
16. Gregory AM, Caspi A, Moffitt TE, Poulton R. Sleep problems in childhood predict neuropsychological functioning in adolescence. Pediatrics
2009;123:1171-6.
17. Christie D, Viner R. Adolescent development. BMJ 2005;330:301-4.
18. von Elm E, Altman DG, Egger M, Pocock SJ, Gotzsche PC, Vandenbroucke JP. The Strengthening the Reporting of Observational Studies in
Epidemiology (STROBE) statement: guidelines for reporting observational studies. Ann Intern Med 2007;147:573-7.
19. Li AM, So HK, Au CT, et al. Epidemiology of obstructive sleep apnoea
syndrome in Chinese children: a two-phase community study. Thorax
2010;65:991-7.
20. Li AM, Cheung A, Chan D, et al. Validation of a questionnaire instrument
for prediction of obstructive sleep apnea in Hong Kong Chinese children.
Pediatr Pulmonol 2006;41:1153-60.
21. Owens JA, Spirito A, McGuinn M, Nobile C. Sleep habits and sleep
disturbance in elementary school-aged children. J Dev Behav Pediatr
2000;21:27-36.
22. Li AM, Au CT, So HK, Lau J, Ng PC, Wing YK. Prevalence and risk
factors of habitual snoring in primary school children. Chest 2010;
138:519-27.
23. World Health Organization (WHO). International statistical classification
of diseases and related health problems: 10th revision (ICD-10). World
Health Organization , 2003.
24. American Psychiatric Association. Manual of mental disorders. 4th ed.
(DSM-IV). Washington, DC: American Psychiatric Association; 1994.
25. American Academy of Sleep Medicine. International classification of
sleep disorders: diagnostic and coding manual (1st ed). Rochester, MN:
American Academy of Sleep Medicine; 1990.
26. Ohayon MM. Epidemiology of insomnia: what we know and what we still
need to learn. Sleep Med Rev 2002;6:97-111.
SLEEP, Vol. 34, No. 10, 2011
1402
Longitudinal Course and Outcome of Insomnia in Children—Zhang et al