In : The Dance of Sleeping and Eating Among Adolescents ISBN : 978-1-61209-710-7

Sleep-wake patterns undergo significant changes during adolescence. The most prominent changes are an increased delay in sleep phase and a reduction in nocturnal sleep time. These changes are caused by different psychosocial and physiological factors. In about ten percent of adolescents, these patterns may develop into a delayed sleep phase syndrome (DSPS), which is characterized by consistent reported sleep onset times and waking times that are considerably delayed relative to societal demands. Adolescents may suffer from other common sleep problems such as insomnia, which is shortly described in this chapter as well. Other potential medical sleep-related disorders (e.g., sleep disordered breathing, restless leg syndrome, Klein-Levine Syndrome), are not covered in this chapter. The second part of the chapter, describes the negative consequences of adolescents' chronic insufficient sleep. Sleepiness, poor academic performance and neurobehavioral functioning, emotional difficulties and increased risk taking behavior are all closely related to adolescents' typical sleep patterns (i.e. decreased nocturnal sleep, irregular sleep-wake schedule, late bedtime and rise time, poor perceived sleep quality). In the conclusion part we will describe among others the main methodological shortcomings of the research in this field with guidelines for healthy sleep in adolescents. * Correspondence: Liat Tikotzky, Ben-Gurion University of the Negev, Beer-Sheva, 84105 Israel, E-Mail: liatti@bgu.ac. il Liat Tikotzky and Avi Sadeh 110 CHARACTERISTICS OF ADOLESCENTS' SLEEP PATTERNS There is substantial evidence suggesting that the development of adolescents is accompanied by considerable changes in sleep and wakefulness patterns. The most extensive changes in sleep patterns manifest themselves in the timing and duration of sleep (i.e. sleep schedule patterns). [1-3] Carskadon [1], a central researcher in the domain of adolescents' sleep, and her colleagues, have documented the following main characteristics of adolescents' sleep: 1.During adolescence, there is a significant delay in sleep phase, manifested in markedly later bedtime and sleep onset time during the weekdays. Because sleep onset time is usually determined by school start time, adolescents show a significant shortening of nocturnal sleep duration. Whereas young adolescents (11-13 years old) sleep on average between 8.5 and 9.5 hours, during the high school years the average duration declines to around 7.5 hours [1-4]. 2. When allowed to sleep, adolescents will not only delay bedtime, but rise time will be shifted as well. As a result, there is an increasingly large discrepancy between sleep schedule during the weekdays and weekends. During weekends, the delay in sleep onset may be even more prominent, and many adolescents sleep into the late morning or noon hours as a way to compensate for the sleep deficit accumulated during the week. The gap in bedtime between school days and weekends averages between one and two hours and usually increases with age [1-4]. The difference in rise time is even larger and is estimated to be 1.5-3 hours in younger adolescents and 3-4 hours in high school students [2]. It is important to emphasize that the reduction in adolescents' sleep duration is not a result of decreased sleep needs. In fact, longitudinal studies carried out by Carskadon and colleagues demonstrated that when given the opportunity to sleep, adolescents would sleep approximately 9.2 hours across all pubertal stages and that optimal alertness in adolescents requires over 9 hours of nocturnal sleep [5, 6]. Different psychosocial and biological factors seem to be responsible for the profound changes in adolescents sleep patterns. Psychosocial factors include academic demands, social activities, sports, internet, television viewing, part-time employment, and use of mobile phone at night. In addition, parents are less involved in deciding about bedtime and social pressure may play a role as well[1-4, 7-9]. Moreover, increased emotional and sexual arousal accompanying adolescent development may lead to sleep onset difficulties and to delayed sleep [10,11]. Studies conducted by Carskadon and colleagues in the last 30 years highlighted the possibility that in addition to the well known influence of environmental factors, biological factors also play a role in delaying the timing of sleep during adolescent development[1,5,12-15]. In particular, Carskadon and colleagues proposed that during adolescent development the intrinsic circadian system changes in a way that contributes to the delay in sleep schedule. [13] The circadian clock is a physiological system that regulates, among other behaviors, sleep/wake behavior. Naturally, the circadian rhythms fluctuate with a period slightly greater than 24 hours. Therefore, under free running clock conditions, most individuals would fall asleep and awaken progressively later. However, the endogenous circadian system is synchronized to the 24-hour day through environmental time cues (i.e. the 24 hour light-dark cycle) [2]. Melatonin, a hormone secreted by the pineal gland, is responsible for transferring the light-dark information to brain centers that control the sleep wake cycle. Melatonin secretion rises in the evening hours, stays relatively constant during the night, declines in the early morning and is suppressed by light [15, 16]. The first study Sleep Problems during Adolescence 111 supporting the hypothesis that the circadian system changes during adolescence development, and that these changes are related to pubertal changes, demonstrated a significant link between self-assessed pubertal status and self-reported phase tendency (morning/evening preference) in sixth grade girls [13]. Girls with higher puberty scores had a tendency toward evening preference. A similar, though non-significant trend was found in boys. The authors suggested that the gender difference may be related to the fact that some of the girls achieved a higher degree of maturation than the boys [13]. The relation between the circadian phase delay and pubertal development was further confirmed by studies showing a correlation between physical measurements of puberty and the timing of melatonin secretion. More mature adolescents had a later start of melatonin secretion [14]. It has been speculated that a reduction in positive feedback of melatonin secretion to the circadian system during puberty could be responsible for changing the circadian signal to the sleep-wake system, thereby delaying sleep phase [17]. Later studies conducted by different research groups confirmed the findings regarding the changes in intrinsic circadian phase during adolescence [2, 6, 8, 18, 19]. However, it is important to emphasize that most of these studies are cross-sectional and correlation and rely on subjective reports, making it difficult to infer about developmental trends and impossible to draw conclusions about causality. A recent longitudinal study about sleep and puberty shed light on the developmental question regarding the direction of the relation between puberty and sleep[20]. The adolescents in this study were assessed at three different time points on both puberty and sleep measures. The findings demonstrated that changes in objective sleep measures (delayed sleep phase and lower sleep quality) at time 1 predicted an increase in pubertal ratings (more bodily changes) from Time 1 to Time 2. However, the predictive correlations from puberty at Time 1 to sleep at Time 2 were not significant. These findings suggest that the sleep changes during early adolescence were evident before the bodily changes of puberty [20]. In addition to the changes in the circadian system, the possibility exists that the homeostatic system responsible for accumulating sleep need with extended waking may change during adolescence as well. In a recent study by Jenni, Achermann and Carskadon [21], it was found that mature adolescents build up slower homeostatic sleep pressure than early pubertal adolescents. This process may also explain why older adolescents find it easier to stay awake longer than young adolescents [15]. In summary, in addition to psychosocial factors, biological changes in the sleep systems and in particular in the circadian system, are likely to contribute to the significant evening preference and sleep phase delay observed during adolescence. These changes seem to be associated with puberty development. However, more research is needed to explore the mechanisms underlying these relationships. It is important to note that the changes described in adolescents sleep patterns (e.g. delayed bedtime, delayed rising time on weekend, increasing discrepancies between school days and weekends in sleep duration and timing) seem to be widespread. Studies and surveys conducted in different developed countries around the world demonstrate similar trends with regard to these developmental changes[6-8, 19, 22-24]. Whereas most adolescents are likely to experience some phase delay and the associated characteristics of shorter sleep duration and weekday-weekend variations in sleep schedules, in a subgroup of adolescents, these characteristics may lead to the development of a delayed sleep phase disorder and to severe sleepiness and disturbed daytime performance. In the following sections, we will expand on these topics. Liat Tikotzky and Avi Sadeh 112 DELAYED SLEEP PHASE SYNDROME (DSPS) Phenomenology and Prevalence Delayed sleep phase disorder (DSPD) is a circadian rhythm disorder that usually appears during adolescence [25]. It is a disorder of the timing of sleep, characterized by consistent, reported sleep onset times and waking times that are significantly later than those common in our society [26]. The prevalence of the disorder is not well known but is estimated to be between 0.1-3.1% in the general population and between 7%-16% in the adolescents and young adult population [2,27-29]. There