Original ArticleNightmare and sleep paralysis among Japanese adolescents: A nationwide representative survey
Introduction
Various reports indicate that sleep disturbances increase the risk of various physical and mental problems [1], [2], [3], [4] and that one-fifth of Japanese adults suffer from some kind of sleep disturbance [2]. Sleep disturbances are prevalent not only among adults but also among 10–40% of adolescents [5], [6], [7]. The research team of Ohida et al. has performed large-scale epidemiological studies on the sleep status of Japanese adolescents [8], [9]. In a survey of approximately 106,300 Japanese junior high and high school students, 30.6% reported an average sleep duration of less than 6 h per night. Of these, 12.5% reported excessive daytime sleepiness (EDS), and 40% were not satisfied with their sleep quality [8]. Another survey reported that 23.5% of adolescents experienced symptoms of insomnia [9]. However, most studies of sleep disturbances among adolescents have focused on sleep deprivation and insomnia; other types of sleep disturbances have not been adequately addressed.
Parasomnias are a group of symptoms associated with problematic behavior or phenomena during sleep and can be divided into non-REM (rapid eye movement) and REM sleep parasomnias [10]. REM sleep parasomnias include REM sleep behavior disorder, nightmares, and sleep paralysis. Parasomnias disturb nighttime sleep [10]. Among these, the interrelated phenomena of nightmares and sleep paralysis are more important because their prevalence is higher than that of REM sleep behavior disorder [11]. The concepts of nightmares and sleep paralysis are well-known in Japanese culture; sleep paralysis is referred to as “kanashibari” [12].
A nightmare is the disruption of sleep by a dream associated with negative emotions (anxiety, fear, anger, etc.) during REM sleep, which results in frequent awakening [10]. The pathophysiological mechanisms of nightmares have not been clarified in detail. It has been reported that the heart and respiration rates increase during REM sleep, which is disturbed by nightmares [13]. Approximately 50–90% of the general population experience nightmares at some time [11], [14], [15]. Two surveys conducted on children aged 5–12 years revealed that 20–30% of the children had experienced nightmares at least once during the previous 6 months [16], [17], indicating that nightmares are common in childhood. In a study of adolescents, Nielsen et al. found that those who had experienced nightmares in the previous year accounted for 25% and 40% of 13-year-old boys and girls, respectively, and 20% and 40% of 16-year-old boys and girls, respectively [18]. In addition, some reports have indicated that the occurrence of nightmares increases in early adolescence and decreases from late adolescence to early adulthood [19], [20], [21], [22].
Sleep paralysis, a state in which the patient is unable to move the limbs and trunk although he/she is conscious, is often experienced by narcoleptic patients [11]. Hishikawa et al. reported that, in narcoleptic patients, sleep paralysis occurs during sleep onset REM (SOREM) [23]. However, it has been clarified that sleep paralysis affects normal individuals in addition to narcoleptic patients and tends to occur during SOREM in normal individuals too [24]. The lifetime prevalence of sleep paralysis was also found to be high (6–40%) [12], [25], [26], [27], [28]; although the range varied in different studies. The rate of onset of a first episode of sleep paralysis was reported to begin increasing at approximately 14 years of age and to peak at 17–19 years [12], [27].
On the basis of these findings, it is inferred that nightmares and sleep paralysis are experienced not only by adults but also by adolescents, and that the rates of onset of first episodes of these disturbances increase among adolescents. One of the reasons for this could be that developmental factors and lifestyle-related and environmental changes affect the occurrence of nightmares and sleep paralysis. To date, however, no nationwide study of nightmares and sleep paralysis has been conducted using large-scale samples of adolescents; in fact, little is known about the factors associated with these disturbances. Therefore, in the present study, we conducted a nationwide survey of Japanese junior high and high school students in order to examine the prevalence of nightmares and sleep paralysis and to examine other associated factors.
Section snippets
Subjects and sampling
We previously conducted three cross-sectional nationwide surveys (1996, 2000, and 2004) of lifestyle habits such as alcohol drinking, smoking, eating, and sleeping among Japanese adolescents. The present study was the fourth such survey.
For this study, of the 10,921 junior high schools and 4500 senior high schools registered in Japan in May 2006, 130 junior high schools (selection rate: 1.2%) and 109 senior high schools (selection rate: 2.4%) were sampled. We used a stratified, single-stage
Prevalence of nightmares and sleep paralysis
The prevalence (95% CI) of nightmares was 35.2% (34.9–35.5%) in the total sample: 30.3% (29.9–30.7%) among males, and 39.9% (39.4–40.4%) among females (Table 1). A statistically significant difference was observed between males and females (P < 0.001) and grades (P < 0.001). Among males, the prevalence of nightmares increased gradually from 10th to 12th grade. Among females, the prevalence of nightmares increased gradually from 7th to 9th grade, decreased in the 10th grade, and then gradually
Discussion
The results obtained from this study revealed that the prevalence of nightmares in adolescents was 35.2% (of the total sample); furthermore, the prevalence of nightmares among girls (39.9%) was found to be higher than that among boys (30.3%). To date, few studies have investigated the prevalence of nightmares in adolescents. Previous studies of the prevalence of nightmares in adults found that the range was 8–30% of the sample studied [34], [35], [36], [37]. The results of our study showed a
Conclusion
This study is a nationwide survey of nightmare and sleep paralysis among Japanese adolescents. The results of this study should be considered in the prevention of nightmares and sleep paralysis among Japanese adolescents. The findings of this study indicated a strong association between nightmares and sleep paralysis. These features are attributed to the pathophysiological background of REM sleep. Therefore, stable REM sleep seems to be important for the prevention of nightmares and sleep
Disclosure statement
This study was supported by a health science Research Grant from the Ministry of Health, Labor and Welfare of the Japanese Government. All of the authors have no potential conflicts of interest, including specific financial interests and relationships and affiliations relevant to the subject matter or materials discussed in the manuscript. There was no off-label or investigational use in this study.
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