Sleep and mental health in children and adolescents

Chapter 32

Sleep and mental health in children and adolescents Michelle A. Shorta, Kate Bartela, Mary A. Carskadonb a

School of Psychology, Flinders University, Adelaide, SA, Australia, bE.P. Bradley Hospital, Brown University, Providence, RI, United States

INTRODUCTION Mental illness poses one of the largest disease burdens of all conditions [1]. While the burden of diseases is felt most acutely among older adults, such psychiatry illnesses as depression and anxiety are prevalent across much of the human lifespan. Indeed, late childhood and adolescence are important developmental periods in terms of mental health, with a notable acceleration of the incidence of mood disorders, anxiety disorders, eating disorders, and psychosis occurring during this time [2]. Furthermore, these illnesses are frequently chronic and recurrent, and earlier age of onset is associated with a more severe and unremitting course, substantial impairments to educational and social functioning, and reduced quality of life [2]. Anxiety is the most common psychiatric disorder of childhood, affecting between 3.9% and 17.5% of children and adolescents, while depression affects between 2% and 8% [3, 4]. Depression and anxiety disorders are frequently comorbid, with anxiety typically preceding depression [2]. Another affliction that often cooccurs with both conditions is sleep problems, including insufficient sleep, trouble falling asleep, and unrefreshing sleep, among others. As many as 90% of children with anxiety and/or depression report problems with their sleep [5]. As reviewed below, strong evidence indicates that sleep causally impacts a range of factors relating to mental health, including mood, emotion dysregulation, depression, anxiety, and suicide [6–8]. The importance of prevention and early intervention for mental health in youth is indisputable. Identifying sleep disturbances as a factor that contributes to deleterious alteration in mood, emotion regulation, and psychopathology is key because sleep is a target amenable to change. The amount of sleep children and adolescents obtain and the quality of sleep, affect their mood and mental health [7, 9–11]. This chapter focuses on the evidence linking sleep and mental health with the aim to (a) review and Sleep and Health. https://doi.org/10.1016/B978-0-12-815373-4.00032-0 © 2019 Elsevier Inc. All rights reserved.

s­ ummarize the literature regarding the impact of sleep duration and sleep quality in healthy school-age children and adolescents, and those with depression and anxiety and (b) identify approaches for families, school leaders, clinicians, and policy makers to improve child and adolescent sleep for optimal mental health functioning. It is important to note that this chapter focuses on the spectrum of mental health and not solely on mental illness. This is to acknowledge that mental health occurs on a spectrum that is much broader than simply the presence or absence of a diagnosable mental conditions. Thus, the included literature includes both healthy and clinical populations, and mood outcome measures include positive and negative mood states, emotion regulation, symptoms of depression and anxiety, and diagnoses of depression and anxiety. Another important distinction to make at the outset is regarding the measures used to characterize sleep, which are varied across studies. Most studies use subjective selfor parent-reports of sleep, which are often included as items within a larger survey. These have the advantage of being time- and cost-effective and can be used for larger, epidemiological studies. The limitations of subjective survey measures of sleep include inaccuracy—especially when the reporter is a parent [12]—and reporting biases. Sleep diaries have widespread clinical use and involve recording sleep patterns each day. While this also relies upon self- or parentreport, sleep diaries are not as susceptible to the reporting inaccuracies and biases as survey measures, as the reporting is anchored to the sleep of the previous night. To overcome some of the limitations of subjective reports, objective measures of sleep are also used, often actigraphy (using activity monitors) or polysomnography. Activity monitors are usually worn on the wrist like a wristwatch uses contain an accelerometer to measure movement. Algorithms are then applied to these movement data to estimate sleep and wake. While this is an objective method, limitations include the

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reliance of concurrent sleep diaries to identify the time in bed period and any times that the device was not worn. In addition, there have been concerns regarding the accuracy of actigraphic algorithms when used with adolescents [13]. The gold standard of sleep measurement is polysomnography. Polysomnography uses electrodes applied to the scalp to directly measure brain activity and thus identify either wake or stage of sleep. While this method is the most accurate, it is time- and cost-intensive and is not often not feasible for many studies. As such, few studies routinely include polysomnography to measure sleep.

SLEEP DURATION AND MENTAL HEALTH Much of the research on sleep and mental health has focused on how much sleep children and adolescents obtain. The recommended sleep duration in children ages 6–13 years is 9–11 h, while adolescents are recommended to sleep 8–10 h per night [14, 15]. Recent studies with mood symptoms as an outcome have estimated that adolescents require between 7.5 and 9.5 h sleep per night for optimal mood [16, 17]; however, many—if not most—teens sleep less [18]. A recent metaanalysis pooled data regarding normative sleep estimates from studies that included actigraphic estimates of sleep on school nights. Pooled results showed that most children and adolescents typically obtain sleep below these recommended amounts [19]. Much of the extant research linking sleep and mental health in children is cross-sectional [20–22], with short sleep linked to increased emotional lability [23]. For example, short sleep duration, objectively measured by actigraphy in a sample of 7-year old children, was associated with heightened emotional reactivity [24]. Similarly, among 8–12-year old children, shorter sleep durations were associated with heightened affective responses in domains including sadness, anger, fear and disgust [25]. Of interest, sleep duration was not correlated with positive affective responses [25]. Sleep duration has also been linked to mental health symptomology and disorders such as anxiety and depression [20]. A telephone survey of parents of children aged 6–17 years revealed that as the number of nights per week of inadequate sleep increased, so did symptoms of depression. However, depression and anxiety diagnoses were not related to the number of nights of inadequate sleep [26]. Another study reported that, according to sleep diary measures, children with anxiety slept less than those without anxiety [27]. Sleep complaints, including insufficient sleep, also appear to feature highly among children with high levels of depression symptoms or a diagnosis of depression [28]. On the other hand, findings about the association of objectively measured sleep to childhood depression are less consistent [20, 28].

Experimental studies have shown a causal relation between sleep duration and a wide range of mood outcomes in children and adolescents [6, 8, 18, 25, 29–33], though experimental studies involving children are less abundant [21, 22]. Nonetheless, these studies provide evidence that children with sufficient sleep experience better mood and are able to regulate their emotions better than those who are sleep restricted [34]. Metaanalytic data from studies of children aged 5 to 12 years indicate that sleep restriction is related to increased internalizing behavior problems, especially when experimentally shortened for 2 or more nights [22]. This association was demonstrated by Gruber and colleagues [32], who after a baseline of 5 days of habitual sleep (as measured via actigraphy), assigned 34 children, aged 7–11 years, to either 1 week of 1 h less time in bed per night or 1 week of 1 h more time in bed per night. When sleep was extended (by an average of 27 min per night), teacher ratings of the children’s emotional lability decreased, whereas restriction of sleep (by an average of 54 min per night) led to increased teacher-reported emotional lability [32]. Another experimental study investigated the impact of sleep duration on teacher ratings of internalizing symptoms (e.g., anxious/sad affect and emotional lability) in children aged 6–12 years. Three sleep conditions were compared: 1 week of typical sleep (average 9.5 h’ time in bed), 1 week of optimized sleep (minimum 10 h’ time in bed), and 1 week of restricted sleep (8 h’ time in bed for first and second graders; 6.5 h’ time in bed for children in third grade or older) [33]. While attention and academic problems were negatively affected by restricting sleep, internalizing symptoms remained similar across the 3 weeks [33]. Vriend and colleagues used a similar experimental protocol to restrict and extend sleep in 32 children aged 8–12 years [25]. In this study reports of emotion regulation were obtained from parents and children, rather than teachers. All children experienced sleep restriction and sleep extension conditions in a counterbalanced order after 1 week of baseline sleep. Sleep period was extended by going to bed 1 h earlier and restricted by going to bed 1 h later, each condition for 4 consecutive nights; a 3-night “washout” period occurred in between conditions [35]. Children slept an average of 74 min longer during the extended sleep condition compared to the short sleep condition. Positive affective in response to positive emotional images and parent-reported emotion regulation decreased following nights of short sleep. By contrast, negative affective response to negatively valenced images and child-reported emotion regulation did not differ between conditions [35]. While these experimental studies including children were all home-based studies, many studies of adolescents have been laboratory based, thus enabling better adherence to study protocol regarding sleep and avoidance of countermeasures, such as caffeine. Measures of positive and negative affect are often used among adolescent ­studies.

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For example, adolescents consistently report feeling reduced positive affect following sleep restriction [18, 29, 30, 36], suggesting that sleep loss diminishes their ability to feel positive affective states such as enthusiasm and excitement. The effects of restricted sleep on negative affect, however, are less consistent, with only one study showing significantly increased negative affect [36]. When considering discrete mood states, results from adolescent total sleep deprivation and chronic sleep restriction paradigms have shown reports of significantly increased anxiety, anger, confusion, and fatigue following sleep loss [6, 8]. As well as affecting mood states, sleep loss modifies the ability to regulate mood and emotion. Emotion regulation refers to the ability of an individual to monitor, evaluate, and modulate emotional reactions in a way that helps individuals to achieve goals and function effectively across different contexts [37, 38]. One hypothesis as to why emotions are affected by sleep duration proposes that short sleep disrupts the limbic system, which helps maintain emotion regulation [22]. Thus, impaired sleep renders a child vulnerable to emotional instability at a physiological level. This is clinically relevant, as emotion dysregulation is an important transdiagnostic factor that heightens the risk of a wide range of psychopathology outcomes [37]. Sleep loss is also implicated in suicidal ideation and suicide attempts, with one study finding a threefold increased risk of suicide attempt in adolescents who slept less than 8 h per night [22]. Experimental studies have found that adolescents’ abilities to regulate their emotions is worsened with sleep loss [8, 35, 39]. For example, one study exposed adolescents aged 10–16 years to two night of sleep restriction (6.5 h on the first night and 2 h on the second night) and two nights with 7–8 h sleep per night. Conditions were separated by 1 week and the order was counterbalanced [39]. Following each sleep condition, participants completed an affective measurement battery. Adolescents reported increased anxiety during a catastrophizing task and rated the likelihood of potential catastrophes as higher following two night of restricted sleep when compared to when they had longer sleep opportunities. Furthermore, the younger adolescents, aged 10–13 years, found their main worry as more threatening when they were sleep deprived. While experimental studies have been invaluable in demonstrating a causal relationship between sleep loss and many aspects of mood and emotion regulation, such brief sleep manipulations have not consistently shown direct effects of sleep loss on either depressed mood or anxiety symptoms. For example, although self-reported depressed mood symptoms increased with total sleep deprivation, sleep restriction in two studies with adolescent participants did not show the same response [6, 8]. Among intervention studies, adolescents randomly allocated to sleep extension, as well as adolescents who extended their sleep by 45 min following a delay to school start times,

r­eported ­significantly fewer depressed mood symptoms [31, 40], but not reduced anxiety [41]. While experimental studies have the advantage of experimental control, they often include highly screened, healthy participants without elevated depressed mood or anxiety symptoms, who are exposed to long sleep opportunities prior to sleep restriction, and their sleep is restricted over relatively short periods. Ecologically, children and adolescents typically restrict their sleep over multiple weeks and months during the school term. Thus, short-term in laboratory studies may not be able to capture effects of sleep that may appear only when sleep is chronically restricted over long periods. As a result, longitudinal studies are instrumental to indicating whether chronically restricted sleep is related to subsequent long-term deficits in mood and/or psychopathology and more effective for elucidating relationships between sleep, depression, and anxiety that are difficult to elicit in time-limited experimental studies. This approach often has the advantage of greater ecological validity by including a broader cross-section of participants. Among healthy adolescents, for example, evidence for a longitudinal association between sleep and subsequent depressed mood is reported in most [42, 43], but not all [44], studies. One study of 12- to 15-year old Dutch adolescents found that less time in bed at baseline was associated with greater severity of symptoms of depression/anxiety at follow-up, but not vice-versa [10]. Similarly, a study of 2259 US adolescents aged 12–15 years reported both concurrent and longitudinal associations between short sleep duration and lower self-esteem and higher depressive symptoms [43]. Another approach taken by recent studies is to examine the temporal relationship between sleep duration and next day mood in healthy samples and in adolescents with anxiety and depression disorders [16, 45, 46]. Fuligni and colleagues [16], for example, collected data on nightly sleep and daily mood over a 2-week period from 419 adolescents in grades 9 and 10. The analysis of nightly sleep and nextday depressed mood and anxiety symptoms determined the duration of sleep required for optimal next-day mood. This optimal sleep duration was estimated at 9.03 h (SD = 0.86) of sleep per night, similar to estimates of sleep need required for optimal daytime alertness and sustained attention [15, 47]. The association between sleep duration and mood was U-shaped, with both long and short sleep associated with worse anxiety and depressed mood. These findings may explain why some studies do not find significant linear associations between sleep duration and mood, as nonlinear relationships are not always tested. In addition, Fuligni and colleagues found that the relation of sleep duration to subsequent mood was not uniform but varied depending on sex and mental health status. Indeed, this study estimated that girls require more sleep than boys for optimal mood, and adolescents experiencing clinically significant internalizing symptoms require more sleep than adolescents below

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the clinical range [16]. These findings indicate differential vulnerability to the effect of short sleep in some populations and may explain why such associations are stronger in clinical groups compared to healthy controls [45]. A relationship between sleep duration and anxiety and depression symptoms has similarly been found in children and adolescents, aged 5–18 years (M age = 10.5 years), diagnosed with various psychiatric disorders. Among these clinical groups, parent-reported shorter sleep was associated with increased anxiety and depression symptoms [48].

SLEEP QUALITY AND MENTAL HEALTH Sleep quality refers to a wide range of factors associated with the ease or difficulties with initiation and maintenance of sleep, as well as how subjectively refreshing or satisfying sleep is to the individual. A number of studies show that sleep quality and mental health are related, with longer sleep onset latencies, more frequent awakenings during the night, longer time spent awake after sleep onset, greater sleep disturbances, and poor subjective sleep quality predicting worse mood, poorer emotion regulation, and increased likelihood of mood disorders [9, 49–51]. Sleep complaints pertaining to the quality of sleep are also common in children with anxiety, including difficulty falling asleep or staying asleep, refusing to go to bed, nightmares and nighttime fears [52]. Similar to studies assessing sleep duration and mental health in children, those examining sleep quality are often cross-sectional [22]. Poor sleep quality has been shown to have a deleterious effect on mood beyond the effect that sleep quality variables may have on sleep duration [53]. Indeed, sleep quality shows unique associations with mental health functioning independent of sleep duration [54, 55]. For example, in a cross-sectional study of nearly 100,000 Japanese high school students, results indicated that difficulty falling asleep, difficulty staying asleep, and subjective sleep quality showed dose-dependent relationships to mental health status, with worse sleep predicting worse mental health [50]. A review of 10–13-year old children regarding sleep and anxiety demonstrated that subjective sleep complaints were common among children with anxiety, especially when parent report was used [27, 56]. Furthermore, based on self and parent report, children who reported sleeping difficulties were more likely to have a diagnosis of anxiety than children who did not report trouble sleeping. Moreover, sleep issues are more likely to persist as the child ages in those who experience anxiety [27]. Conversely, a recent metaanalysis found that decreased sleep efficiency was not associated with internalizing behavior problems [22]. Regarding specific components of sleep quality, children who experience anxiety may exhibit longer sleep latency. However, literature is inconsistent, as when objective measures of sleep are employed (actigraphy or

p­ olysomnography), some studies demonstrate this difference, whereas others find no difference between anxious children and controls [27, 56, 57]. Anxious children may have less slow wave sleep and more nightly awakenings than those with depression or no psychiatric diagnoses [28]. The type of anxiety disorder may also relate to the sleep issue, with increased sleep latency, as measured by polysomnography, among children with general anxiety compared to those without any diagnosis. Furthermore, nightmares may be exhibited more frequently among children with separation anxiety [28]. Regarding sleep efficiency, data from a week’s actigraphy measurements were not correlated with positive or negative affect [25]. In fact, anxious children may have higher objective sleep efficiency than controls [27]. Of note, when sleep is experimentally restricted, thus decreasing sleep fragmentation (i.e., improving sleep quality), the effects of shorted sleep are still evident—that is, despite improved sleep quality, emotional liability increased during a period of sleep restriction [32]. Overall, it appears that subjective sleep complaints are high among anxious children, yet objective sleep difficulties show less consistent evidence [56, 57]. In part, the study’s environment may play a role in different findings. That is, a comfortable home environment may facilitate sleep, compared to a novel laboratory environment exacerbating sleep issues in anxious children [27]. Moreover, some laboratory studies may not capture the home sleep environment, which enables difference in sleep patterns. For example, room sharing and changing beds during the night may occur at home in both anxious and nonanxious children, yet, these behaviors are not practiced in a laboratory [56]. Associations between aspects of sleep quality and mental health are also borne out longitudinally. Longitudinal studies demonstrate that sleep issues in childhood predict later anxiety and depression, in most, but not all studies [20]. In one study of 5-year-old children, sleep was measured at the age of 5 years using polysomnography and internalizing problems were measured 1 year later. Results showed that children who had poor sleep quality (indicated by sleep latency, sleep period time and number of awakenings after sleep onset), reported more internalizing problems in their child 1 year later, when compared to parents of children with good/normal baseline sleep [58]. Longitudinal studies also indicate that sleep disturbances in early childhood increase the likelihood of development of anxiety in adolescence and adulthood [28]. Stronger evidence suggests that sleep issues precede anxiety, however, the inverse relationship may also hold true [28, 59]. That is, sleep issues and emotional disturbances are interrelated, and may predispose a child to future anxiety. It is likely that sleep and emotional functioning hold a bi-directional relationship, thus those with poor sleep are more likely to exhibit symptoms of anxiety and depression, and v­ ice-versa, with each issue

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exacerbating the other [27, 59, 60]. More research employing objective measures is needed to clarify the strength and direction of associations [59]. When examining bidirectional relationships between sleep quality and anxiety disorders, one review found support for the role of sleep problems predicting anxiety disorders, but limited support for the role of anxiety as a predictor of sleep problems [11]. For example, Gregory and O’Connor assessed sleep problems and behavioral/emotional problems in a sample of 490 young people, assessed at age 4 years and again at m ­ id-adolescence [9]. Sleep problems at age 4 predicted more attention problems, aggression, and depression/anxiety during mid-adolescence. Of note, the reverse relationship was not supported, as behavioral/emotional problems in early childhood did not predict sleep problems during adolescence. The authors also found that the concurrent association between sleep problems and anxiety/depression grew significantly stronger across this developmental period, increasing from r = 0.39 at 4 years to r = 0.52 during mid-adolescence [9]. This may be due to the greater prevalence of sleep problems among 4-year-olds, with sleep problems scores decreasing by approximately 50% between early childhood and mid-adolescence. As sleep problems are highly prevalent in young children, the presence of sleep problems may be less sensitive as a predictor of mental health in the very young. In a study of 516 Japanese adolescents, Kaneita and colleagues assessed sleep and mental health at age 13 years and again after 2 years [51]. Concurrent with the reduction in sleep quality over this time was a reduction in mental health status. A new onset of poor sleep quality and chronically poor sleep quality both significantly predicted the development of poor mental health. Similar findings were reported from a longitudinal study of 3134 US adolescents, aged 11 to 18 years, who were assessed at baseline and approximately 1-year later [61]. Poor quality sleep was highly prevalent, with 60% experiencing nonrestorative sleep, 17% reporting difficulty falling asleep and 12% waking frequently during the night either often or almost every day. After controlling for covariates, there was a dose-response relationship between insomnia symptoms at time 1 and depression at time 2. Specifically, greater insomnia symptom severity at baseline predicted worse mental health 1 year later [61]. One limitation in this literature is the reliance upon subjective self-report measures of sleep and mood. These associations may be inflated due to rater biases, whereby an adolescent who reports poor sleep may be more likely to report poor mood and vice versa. Objective measures of sleep are needed to mitigate against this and to determine whether subjectively short or poor-quality sleep is paralleled by objectively short or poor-quality sleep, or alternatively, whether youth with poorer mental health misperceive their sleep as being worse than it objectively is. Among the limited literature that has examined sleep and mental health using polysomnography, one study a­ ssessed

objective sleep over two consecutive nights in youth aged 7–17 years with either anxiety disorders (N = 24), major depressive disorder without comorbid anxiety disorders (N = 128), or no history of psychiatric disorder (N = 101) [62]. Youth with anxiety disorders took longer to fall asleep on the second night than controls or youth with depression (longer sleep onset latencies are common on the first night of polysomnography, however, this typically resolves on subsequent nights among most individuals), and they experienced more awakenings than the depressed group [62]. Overall, it appears that sleep disturbances are related to childhood anxiety, possibly in a reciprocal fashion [63]. Similarly, children who experience depression symptoms to a large extent also experience sleep disturbances, such as insomnia [20, 28]. However, this association is likely to be stronger in adolescents and adults [20, 63]. A similar pattern of results was reported in a recent metaanalysis examining bidirectional relationships between sleep and adolescent depression. Specifically, they found that adolescents with depression took longer to fall asleep, had more frequent and longer awakenings during the night, had objectively lighter sleep (more stage 1 sleep) and reported worse sleep quality [7]. When examining prospective relationships over time, poor sleep quality was a predictor of subsequent major depression and suicide attempts, but not vice versa [7]. Among the various subjective and objective sleep predictors of concurrent and future depression, those variables associated with wakefulness in bed were most consistent in predicting depression. The authors propose a model of the relationship between sleep disturbances and depression. They suggest that increased time spent awake in bed due to long sleep onset latencies and wake periods during the night, coupled with poor subjective sleep quality leads to increased night time rumination, where adolescents lie in quiet wakefulness in bed and engage in negative repetitive thoughts focused on the symptoms, causes and consequences of their distress. This focus may be on their distress about their sleep, as is commonly witnessed among individuals with insomnia, or it may be about more general factors, such as relationships with others, issues related to school, mood and tiredness [64]. This model is supported by research showing that such negative thoughts are associated with poor sleep quality in both healthy adolescents, sleep-disordered adolescents, and children and adolescents with mood disorders [64–66]. Taken together, these findings highlight that the presence of sleep problems during adolescence are a “red flag” that teens are at heightened risk of psychopathology [36].

IMPROVING SLEEP AND MENTAL HEALTH IN CHILDREN AND ADOLESCENTS While insufficient and poor-quality sleep are extremely common among children and adolescents, the opportunities for change are many. Given the contribution of sleep

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to mental health, simple interventions to target sleep are likely to have broad beneficial impacts on how they experience and regulate mood and emotion, as well as the likelihood of developing mood and/or anxiety disorders. Bronfenbrenner’s ecological systems theory [67] posits that children’s development occurs in the context of several interacting ecosystems that include the self, the family, peers, school, community and public policy. The sleep of children and adolescents is nested among, and impacted by, these different ecological systems. Thus, suggestions and strategies on how to improve sleep in children and adolescents are provided across four levels: families, schools, clinicians and public policy makers.

Families There are many ways that families can support better sleep. Limiting technology use, especially in the hour before bed, and removing access to technology overnight, helps to limit exposure to blue light, and allows the opportunity for sleep that is not broken by incoming calls and/or messages [68, 69]. Reducing evening light and limiting or eliminating caffeine can help to ensure that children and adolescents are not being unnecessarily alerted by these exogenous alerting factors [69]. Exercising during the daytime can help children and adolescents to get to sleep faster and have more consolidated and refreshing sleep [70], as can maintaining a comfortable sleeping environment that is dark, cool, and quiet [69]. While adolescents can implement some of these behavioral changes, family involvement to implement, support, and model positive sleep habits to children and adolescents is beneficial [71, 72]. Across the pediatric age range, families have an important role in supporting or harming sleep health. For example, setting limits around bedtime is associated with better sleep, better daytime functioning, and less depression and suicidal ideation [69, 72, 73]. Despite the numerous benefits to regulated bedtimes, research indicates that, even though many parents set limits around the bedtimes of their young children, they relinquish limit-setting at a very early age [72, 74]. A study of North American children and adolescents found that less than 1 in 5 children have a parent-set bed time at age 10 years, while less than 1 in 20 had a parent-set bedtime at age 13 [74]. Of note, however, this developmental shift did not reflect less parental involvement in regulating sleep patterns, overall. Rather, the focus of parental involvement shifted, with the reduction in parent-set bedtimes associated with a concurrent increase in the proportion of parents waking their children up for school in the morning [74]. While a small proportion of children and adolescents have a parent-set bedtime on school nights, this is largely not maintained across weekends. Thus, in older children and adolescents, even less regulation of bedtimes on weekends,

coupled with sleep debt accrued across the school week and a delayed body clock, result in a pattern of even later bedtimes on weekends and wake times. Regular bedtimes and waketimes across school nights and weekends are important for good sleep and for entrainment of circadian rhythms, or the body clock [75]. Children and adolescents who obtain sufficient sleep across the school week do not show the same pattern of “sleeping in” on weekends [76]. This catch up sleep extends weekend wake time until later in the morning, or, for some, even into the afternoon. This pattern makes it very difficult for children and adolescents to then fit back into a healthy sleep pattern for school, as their body clocks are shifted later with this weekend catch-up sleep [75]. Maintaining a regular sleep pattern that allows for sufficient sleep across the week avoids these problems. In addition to sleep-focused behaviors, general environmental factors impact sleep among families. As sleep requires the individual to disengage vigilance to the outside environment, it is important for children and adolescents to feel secure and safe at bedtime. Families can support sleep by maintaining a warm, supportive, and predictable family environment [71, 77]. One study of adolescents found that adolescents who self-reported their families as being more disorganized had worse sleep hygiene, took longer to fall asleep, obtained less sleep and were more sleepy during the day [71]. Conversely, among younger children, increased parental warmth was associated with more sleep [77]. These findings highlight the invaluable role of families in providing a home environment and family culture that supports good sleep.

Schools Where schools are able to determine their start time, ensuring that the school day does not start before 8:30 a.m. is likely to have wide-ranging benefits to students in terms of enabling them to obtain more sleep, maintain alertness during the day, perform better in the classroom, have fewer motor vehicle accidents, and have improved mood and less psychopathology [40, 77, 78]. A cross-cultural comparison between US adolescents, whose school days began at approximately 7:45 a.m., and Australian adolescents, whose school days started around 8:30 a.m., found that Australian adolescents obtained an average of 47 min more sleep per night sleep [79]. While several factors predicted this crosscultural difference, the largest predictor was school start time. The American Medical Association and the American Academy of Pediatrics both recommend that schools start no earlier than 8:30 a.m. [80]. The RAND Corporation estimated that if all US schools were to delay school start time until 8:30 a.m., this would add $US83 billion to the economy over the next decade due to higher high school graduation rates and thus better jobs, fewer costs associated with sleep-related car crashes, reduced obesity, and improved mental health [78].

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While school start times receive most public attention, any school-related activities that require children and adolescents to wake earlier or stay up later can impinge on their ability to obtain sufficient sleep. Resultingly, school sport and school activities should not be scheduled before 8:30 a.m. Similarly, high academic workloads with large homework volumes and/or attending night school, and high levels of academic pressure can push bedtimes later and negatively impact sleep and mental health [77, 81]. Thus, schools are urged to consider their policies regarding homework, and to question the assumption that homework quantity is important for academic achievement. Indeed, recent PISA (Programme for International Student Assessment) results show that, while many of the countries ranked highest in academic performance are countries in which students start school early and have high academic workloads, such as Singapore, Japan, and Taiwan, countries like Finland, who consistently rank among the top academically performing countries, provide evidence that early start times and high volumes of homework are not necessary for academic success. Finnish schools do not start early, their students do not typically attend night school, nor do they have large homework volumes, yet their students rank among the highest in the world when it comes to academic achievement. Most tellingly, students from high achieving countries with early start times and high academic workloads reported among the highest levels of school-work related anxiety, while Finnish students reported very low levels of school-work related anxiety [81]. Thus, high volumes of homework and night school are not necessary for high academic achievement and may come at a high cost to the children in those systems.

Clinicians Clinicians can work with children and families to improve both sleep and mental health. It is imperative that basic screening for sleep and mental health problems is routinely implemented. If children and adolescents are identified as having a sleep problem, the type of treatment used to improve sleep will depend largely on the sleep issue. Pharmacological interventions are not recommended as a first treatment approach [82], and are thus not reviewed here. Clinically, it is important to first assess the sleep issue. As well as a clinical interview, one means by which to do this is through a sleep diary, kept for at least 1 week [82]. Objective sleep measures, such as actigraphy, are desirable, but not always feasible [82, 83]. Review of both the clinical interview and sleep diary allow definition of the sleep issue (e.g., whether issues falling asleep are due to insomnia or a circadian phase delay) and the goals the client wishes to achieve, both of which inform treatment. Regardless of the specific treatment chosen, psychoeducation for the parent and child regarding sleep is valuable [82, 84]. Psychoeducation ­ typically includes

information about developmentally appropriate sleep duration recommendations, sleep hygiene, sleep pressure, sleep architecture, circadian rhythms, and the effects of light and darkness on the circadian rhythm. Children benefit from sleep hygiene techniques, such as a consistent bedtime routine, and a safe, comfortable sleep environment [83]. Children who have difficulty initiating or maintaining sleep, and negative daytime consequences, in the absence of medical conditions, may have insomnia [82]. As well as good sleep hygiene, insomnia interventions may involve further behavioral treatment, such as cognitive behavior therapy. Both night awakenings and sleep efficiency are improved through behavioral interventions [84]. Adjusting a child’s bedtime to a later time, to facilitate faster sleep initiation, may also be used. Once the child has associated bedtime with falling asleep, the bedtime is then moved earlier [82]. A list of resources for clinicians treating childhood insomnia can be found here [82] and here [85]. Concerning adolescents, there are two main psychological therapies which are implemented, again depending on the sleep disorder [82]. The first, bright light therapy, focuses on shifting the body clock of adolescents who have a delayed circadian rhythm. The adolescent is exposed to bright light for 30 min each morning, starting at the adolescents desired waking time, i.e., the time at which they would naturally wake up if they didn’t have to go to school. The timing of this light exposure is then shifted earlier by 30 min each day until the adolescent is waking at their desired time. Appropriately timed morning bright light is prescribed in the morning, and dim light is used in the evening, to shift the circadian rhythm. As the light advances each day, so too does the circadian phase [86, 87]. The other treatment widely used among adolescents is cognitive behavior therapy for insomnia, which is used to treat adolescents who experience insomnia. Cognitive behavior therapy for insomnia is a multimodal treatment, which aims to reduce difficulties initialing or maintaining sleep, and the clinical distress associated with such sleep difficulties [86]. It incorporates sleep hygiene, relaxation, stimulus control, sleep restriction and cognitive therapy, which all aim to reduced arousal associated with bedtime and sleep [86]. These treatments have effectively improved sleep latency, sleep duration and awakenings after sleep onset in adolescents. Both depression and anxiety symptoms may also be diminished through this therapy [86]. Many other low-intensity treatment options exist, to improve the sleep of adolescents, especially those who do not experience disordered sleep. These include brief mindfulness and relaxation, and prebed phone restriction [82, 88–90].

Policy makers While delaying school start times until at least 8:30 a.m. and implementation of lighter extra-curricular homework

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loads are both discussed in greater detail in relation to how schools can improve sleep in children and adolescents, not all schools can act individually. Thus, public policy regarding these guidelines can have even wider benefit in supporting mental health of children and adolescents. Health promotion and education regarding child and adolescent sleep may also help to improve sleep and mental health [42]. Health promotion could include information about how much sleep children and adolescents need, indicators of good or problematic sleep, sleep hygiene, and tips on how to improve sleep and where to seek resources. While the present focus has been on how sleep impacts mental health, sleep also affects cognitive performance, risk-taking, drug use, road safety, and delinquency, and so the potential benefits of sleep promotion are widespread. Just as children sleep better in a safe home environment they also sleep better when they feel safe in their communities [91]. Children and adolescents who are exposed to community violence frequently experience sleep disturbances, nightmares and reduced mental health [92]. Even if children and adolescents are not victims of community violence, the perception of safety in their neighborhoods can impact sleep [91]. One study of 252 adolescents from a wide range of socioeconomic backgrounds in the Southeastern United States asked adolescents about their concern regarding community violence and measured their sleep using actigraphy and self-report. Adolescents who were more concerned about community violence had lower sleep efficiency, woke more during the night, and reported more sleep-wake problems and daytime sleepiness. This effect was stronger among adolescent girls [91]. Thus, policy targeting community safety, especially in areas containing a large proportion of families, is beneficial. Lastly, paid employment is a factor that can negatively impact the sleep of adolescents [74, 93]. High school students who work more than 20 h per week have later bedtimes and less sleep across the week. They also report more daytime sleepiness, are more likely to arrive late for school, have trouble staying awake at school, and are more likely to use caffeine, tobacco and alcohol [94]. These deficits of sleep and daytime functioning were even more pronounced among adolescents who coupled more than 20 h of paid work with more than 20 h of extra-curricular activity [94]. Australian research indicates that, while most adolescents are aware of their rights at work in terms of declining shifts, they often report feeling pressured to accept shifts, or believe that declining shifts will result in less work being offered to them in the future [95]. Thus, there is scope for policy regarding paid employment for school students. For example, by placing limits around the finishing time of shifts offered to high school workers during school term time. This would mitigate the problem of adolescents finishing shifts so late that they are unable to obtain sufficient

sleep before having to rise for school the next day to help support adolescent workloads, sleep and mental health.

CONCLUSION Summary Overall, these findings suggest that while estimates of sleep need for optimal mood functioning are between 9 and 11 h per night for children and 8–10 h per night for adolescents, many young people chronically obtain sleep that is below this amount. Studies examining the relationship between sleep duration and mood suggest that sleep loss produces reductions in positive mood states and affect and increases in negative mood states and negative affect. Longitudinal studies support bidirectional relationships between sleep duration and mood and mood disorders, however, the link from sleep to mood/mental health has been reported more consistently than link from mood/mental health to sleep. Studies focusing on sleep quality have found similar results, with multiple aspects of sleep quality found to impact mental health, including how long it takes to fall asleep, waking during the night, and subjective sleep quality all impacting mental health. Using Bronfenbrenner’s ecological systems theory as a guiding explanatory framework, suggestions and recommendations for improving sleep, and thus mental health, were provided. These recommendations targeted families, schools, clinicians and public policy makers, thus highlighting the importance of a multifaceted approach to support sleep and mental health in young people.

Limitations and future research directions Overall, the present chapter provides an overview of the relationship between sleep duration and sleep quality and how they either support or diminish mental health in children and adolescents. In addition, we provide suggestions for how sleep (and thus mental health) can be supported across multiple ecological levels. It is important to note, however, that this overview is not exhaustive, and other factors, such as sleep regularity and the timing of circadian rhythms (or the body clock) affect mental health both directly or indirectly, through their influence on sleep duration and sleep quality [54, 96]. While present findings support the importance of sleep for optimal mental health in children and adolescents, there remain gaps and limitations in the literature. First, multimodal assessment of sleep using both subjective and objective measures is needed to determine the degree to which subjectively reported insufficient or poor-quality sleep is also mirrored by objective data. While this is an important point across all developmental stages, it is particularly important among younger children, for whom research

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t­ypically relies upon parent reports of sleep. Second, while there is a sizeable body of work examining sleep quality and mental health outcomes, sleep quality is not unitary and the conceptual and operational definitions of sleep quality are often ill-defined. Research examining clearly defined and operationalized aspects of sleep quality, such as sleep onset latency, wake after sleep onset, number of night time awakenings, and subjective and objective sleep quality, is needed to determine how different facets of sleep quality affect mental health. Third, the literature consists largely of crosssectional studies which cannot address the significant issue of causation or causal direction. This is important given the relationship between sleep and mental health is likely bidirectional. Future research would profit from more experimental studies to determine causation and directionality. Several important areas remain underinvestigated. For example, studies to evaluate the efficacy of health promotion strategies aimed at sleep are needed to determine whether population-level interventions are effective. On a smaller scale, sleep intervention studies are urged to include mood and mental health outcomes to see how improving sleep on an individual level improves mental health. Finally, mood outcome measures need to include positive mood outcomes, such as happiness, as well as negative mood outcomes, such as depressed mood and anxiety. Emerging research suggests that positive emotion may be more sensitive to sleep loss and poor quality sleep than negative emotion [97]. While mood states relevant to mood disorders, such as depression and anxiety are important to measure, reduction in positive mood, or anhedonia, is also a clinically relevant.

Concluding remarks Sleep plays a crucial role in maintaining optimal mental health across the lifespan. Childhood and adolescence are critical developmental periods when the trajectories of many mental health conditions are begun and thus provides an optimal period for early intervention regarding sleep. Simple interventions to improve and safeguard sleep are thus important to benefit youth mental health and reduce the likelihood or severity of many mental health conditions.

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