THE RELATIONSHIP BETWEEN SLEEP TIME, SLEEPINESS, AND PSYCHOLOGICAL FUNCTIONING IN ADOLESCENTS MELISA MOORE. For the degree of Doctor of Philosophy

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1 THE RELATIONSHIP BETWEEN SLEEP TIME, SLEEPINESS, AND PSYCHOLOGICAL FUNCTIONING IN ADOLESCENTS by MELISA MOORE Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Department of Psychology CASE WESTERN RESERVE UNIVERSITY August, 2007

2 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of candidate for the Ph.D. degree *. (signed) (chair of the committee) (date) *We also certify that written approval has been obtained for any proprietary material contained therein.

3 TABLE OF CONTENTS Page Introduction..1 Methods...23 Results 32 Discussion..38 Tables...46 Figures...50 Appendix A 56 References..59 iii

4 LIST OF TABLES Page Table 1: Sample characteristics...46 Table 2: Descriptive statistics for sleep variables..47 Table 3: Descriptive statistics for psychological variables 47 Table 4: Results from final regression models predicting sleep variables by subject characteristics.48 Table 5: Parameter Estimates of path models for sleep and psychological variables...49 iv

5 LIST OF FIGURES Page Figure 1: Conceptual model of sleep time, sleepiness, and psychological functioning...21 Figure 2: Hypothesized model of subject characteristics related to sleep time, night to night variability, and sleepiness.34 Figure 3: Sleep and psychological variables included in hypothesized models 36 Figure 4: Final model of total sleep time and externalizing behavior (CBCL).50 Figure 5: Final model of coefficient of variation (CV) and externalizing behavior (CBCL)..51 Figure 6: Final model of coefficient of variation (CV) and parent perception of teen s health (CHQ-pf).52 Figure 7: Final model of sleepiness and depressive symptoms (CDI)...53 Figure 8: Final model of sleepiness and anxiety symptoms (MASC)...54 Figure 9: Final model of sleepiness and perceived health (CHQ-cf).55 v

6 The Relationship Between Sleep Time, Sleepiness, and Psychological Functioning in Adolescents Abstract by MELISA MOORE Normative biological, psychological, and social changes that occur during adolescence contribute to insufficient sleep time, irregular sleep schedules, and sleepiness in teenagers. Such negative changes in sleep may lead to psychosocial consequences such as depressed mood and behavior problems, and in fact this has been demonstrated in adults and in school age children. Although there are few empirical studies of the effects of poor sleep or sleepiness on psychological functioning in adolescents; the number of teens reporting sleep problems and the potential impact of those problems suggest that research is warranted. The current study investigated whether an association between sleep time, sleepiness, and specific aspects of psychological functioning was present in adolescents. This study had several methodological advantages over previous investigations of adolescent sleep including the use of actigraphy (an objective measure of sleep time), multiple measures and reporters of adolescent psychological functioning, the use of Tanner staging to determine pubertal status, and the use of path analysis. The 208 study participants were part of a larger population-based cohort study of sleep and health, the Cleveland Children s Sleep and Health Study (CCSHS), and were between the vi

7 ages of Based on prior research, it was hypothesized that pubertal status, minority status, sex, body mass index (BMI), preterm status, parent income, and parent education would relate to mean total sleep time, variability in sleep time, and sleepiness. It was also hypothesized that less mean total sleep time, more variability in sleep time, and more sleepiness would be associated with higher scores on measures of anxiety, depression, externalizing behaviors, and perceptions of poor health. Results were that higher BMI (p<.001), minority status (p<.05), and male sex (p<.005) predicted less total sleep time. Higher BMI (p<.001), minority status (p<.005), and older age (p<.001) predicted more variability in sleep time and higher BMI (p<.01) and minority status (p<.001) also predicted more sleepiness. Higher self-reported sleepiness scores predicted higher scores on measures of anxiety (p<.001), depression (p<.01), and perceived health (p<.001); however other relationships between sleep variables and psychological variables were not found. vii

8 THE RELATIONSHIP BETWEEN SLEEP TIME, SLEEPINESS, AND PSYCHOLOGICAL FUNCTIONING IN ADOLESCENTS The current study examined the association between sleep time, sleepiness, and psychological functioning in adolescents. The introduction is organized as follows: first changes in sleep quantity and quality occurring in adolescence will be discussed, then the relationship to of sleep to psychological functioning will be reviewed, and finally limitations of previous studies as well as the benefits of this study will be presented. Based on the use of terms in the sleep literature, sleep difficulties and sleep problems are defined as both clinical and sub-clinical reports of trouble sleeping which can include a range of conditions from difficulty falling asleep to obstructive sleep apnea syndrome (OSAS). Sleep disorders encompass only the clinical subpopulation of sleep problems. Insufficient sleep is defined as one or more nights where the recommended total sleep time is not obtained and sleep deprivation is chronic insufficient sleep. Insufficient Sleep During Adolescence Normative biological, psychological, and social changes occur during adolescence that predispose teenagers to insufficient sleep, and not surprisingly sleep difficulties are widely reported by adolescents. In non-clinical samples, reports of sleep problems by teenagers have ranged from 18-31% (Andrade & Menna-Barreto, 2002; Dahl et al., 1996; Roberts, Roberts, & Chen, 2002) and similarly, other studies have demonstrated that 63-87% of adolescents report that they do not get enough sleep (Mercer, Merritt, & Cowell, 1998; Wolfson & Carskadon, 1998). Although the need for sleep does not decrease during the teenage years, adolescents typically obtain less than the 9.2 hours of sleep that is recommended (Carskadon, 1982, 1990; Dahl & Carskadon, 1995; Dahl & Lewin, 1

9 2002; Fredriksen, Rhodes, Reddy, & Way, 2004). Lack of adequate sleep can lead to chronic patterns of sleep deprivation and attempts at catch-up sleep (Mindell, Owens, & Carskadon, 1999). Such lack of sleep and irregular sleep patterns may lead to negative psychosocial consequences such as depressed mood and behavior problems, and in fact these have been demonstrated in adults and in school age children (Pilcher & Walters, 1997). It has been hypothesized that sleep deprivation may contribute to such problems as suicide and motor vehicle accidents, which are two of the leading causes of death in teenagers (Carskadon & Acebo, 2002). Sleep deprivation may also contribute to problems such as increased reports of pain and reports of poor overall health (Lewin & Dahl, 1999; Moffitt, Kalucy, Kalucy, Baum, & Cook, 1991) as well as poor functioning at school and work. There are relatively few empirical studies of the relationship between sleep and psychological functioning in adolescents. Moreover, the number of teens reporting sleep problems and the potential impact of those problems underscore the importance of additional research (Dahl & Lewin, 2002; Fredriksen et al., 2004; Roberts et al., 2002). Why do adolescents tend to experience problematic changes in the amount and regularity of their sleep? Developmental changes in physiology that occur with the onset of puberty as well as social and psychological changes that occur with adolescence contribute to difficulties in obtaining sufficient sleep. The interaction of these physiological, psychological, and social factors cause adolescence to be a period of development associated with poor sleep. 2

10 Changes in Amount and Regularity of Sleep Related to Adolescence Studies have shown that when adolescents and children sleep for the same number of hours per night, adolescents report higher rates of sleepiness during the day. These findings suggest that the onset of adolescence does not result in a decreased need for sleep. A seminal longitudinal study conducted by Carskadon and various collaborators described sleep patterns in children and adolescents at a summer camp over ten years beginning in 1976 (Carskadon & Acebo, 2002; Carskadon et al., 1980). Findings from this study were that sleep need did not change from ages and that at mid-puberty, there was an increased tendency to sleep during the day. In addition to the importance of the results of this study, it was also unique in its methodology in several respects. First, it utilized an objective sleep measure, polysomnography, to determine sleep time, regularity, and sleepiness. Second, this study evaluated sleep based on a fixed schedule during the assessment nights and also for one week before each evaluation, rather than examining subjects usual sleep schedules. This reduced the potential variance associated with different bedtimes. Third, it used Tanner staging to determine pubertal status, which is more relevant in studies with adolescent populations because it is thought that physiological changes in sleep relate to changes in puberty not to chronological age (Knutson, 2005). Physiological Influences on Amount and Regularity of Sleep and the Potential Impact on Psychological Outcomes Although research has shown that adolescents do not have a decreased need for sleep, there may be physiologically based reasons that adolescents obtain less sleep. One of the most widely reported physiological changes in adolescents is the circadian shift to 3

11 later bedtimes and wake times, which is also described as a preference for eveningness. It has been shown that from school age through later adolescence, sleep schedules change with bedtimes becoming later and wake times staying the same, and consequently, total sleep time declines (Carskadon, Viera, & Acebo, 1993). A retrospective self-report study of 6631 adolescents ages (Giannotti, Cortesi, Sebastiani, & Ottaviano, 2002) found two types of circadian phases in adolescents, evening type and morning type. Adolescents preferences for evening related to attention problems, poorer school achievement, and more emotional upset (i.e. depressed mood, anxiety). Adolescents with evening preference also reported more sleep problems (overall sleep onset problems and in older adolescents, increased night awakenings) when age and gender were considered. Other research has supported the idea that this evening type preference may change with age, and that there may be an increased preference for eveningness that is limited to adolescence (Carskadon et al., 1993; Valdez, Ramirez, & Garcia, 1996). It has been suggested that later melatonin release is one etiology for this shift toward eveningness. Melatonin, a hormone that is excreted nocturnally, usually precipitates sleepiness and continues to be released until just before waking. Delayed release of melatonin (as a result of puberty) may cause a later onset of sleepiness as well as a later natural wake time (Dahl & Lewin, 2002). Not only is less total sleep time associated with problematic psychological consequences (Carskadon & Acebo, 2002), but the discrepancy between weekday and weekend sleep times may also influence sleep deprivation and adolescent psychological functioning. For example, a teenager might sleep from 12am-6am on the weekdays and 2am-1pm on the weekends. This shift makes it more difficult to go to bed earlier on 4

12 weekdays, thus contributing to the likelihood of chronic sleep deprivation. Irregular sleep patterns are thought to further disrupt both the body s drive for homeostasis and circadian rhythms in the body, both which affect sleep, thus creating a cycle of sleep problems (Carskadon & Acebo, 2002). Both total sleep time and regularity of sleep schedules are thought to be important contributing factors in the overall quality of sleep. Aside from sleep onset and morning waking difficulties, the nature and quality of sleep may be different in adolescents compared with school age children. Stages 3 and 4 of sleep generally take place during the first one to three hours of sleep and this is where slow wave, restorative sleep occurs. During early adolescence, the total time in slow wave sleep decreases by approximately 40% compared to school age children (Carskadon, et al., 1980; Dahl & Lewin, 2002; Mindell et al., 1999). This decrease continues throughout the lifespan, yet at a much more gradual rate. The onset of Rapid Eye Movement Sleep (REM) occurs following stage 4 sleep, and teenagers also show changes in time to first REM onset. In school age children, time from sleep onset to REM is approximately 3 hours and in early adolescents, the time to REM is minutes (Mindell et al., 1999). Normative developmental changes in amount of slow wave sleep and timing of REM sleep occur during adolescence, which may contribute to increased sleepiness during the day. Adults demonstrate significant individual variation in amount of sleep needed for optimal functioning (Fitchen, Libman, Creti, Bailes, & Sabourin, 2004; Monk, Buysse, Welsh, Kennedy, & Rose, 2001). Although there may be less individual variation in sleep need during adolescence than adulthood (Carskadon et al., 1980; Carskadon 1982), such variability remains an important consideration in adolescents (Thorleifsdottir, Bjornsson, 5

13 Benediktsdottir, Gislason, & Krisbjarnarson, 2002). Individual differences in teen sleep need are difficult to study as a result of methodological challenges. However, assuming that sleepiness is a consequence of inadequate sleep, the study of sleepiness may provide a window into such individual differences. For example, if two adolescents obtain the same total sleep time and one is less sleepy, it is possible that he/she needs less sleep to function at an equivalent level. Sleep Disorders Related to Adolescence In addition to normative physiological changes in sleep, sleep disorders that are common in adolescents or have a typical onset occurring in adolescence contribute to sleep deprivation in teenagers. These sleep disorders, which are thought to have a biological etiology (Mindell & Owens, 2003), include delayed sleep phase syndrome, insomnia, sleep disordered breathing, and narcolepsy. The consequences of each of these disorders may include increased daytime sleepiness, poor academic and social functioning, and emotional and behavioral problems (Mindell & Owens, 2003). Delayed sleep phase syndrome (DSPS) is the most common sleep disorder in adolescence and is estimated to occur in 5-10% of adolescents (Mindell & Owens, 2003; Mindell et al., 1999). DSPS is a large shift in sleep schedule, which is over and above normative adolescent changes in sleep time, with bed and wake times being least two hours later than usual. Although preference for staying up late may be a normal consequence of adolescence, a preference for staying up until 12am or later has been shown to be a strong risk factor for the development of DSPS (Mindell & Owens, 2003). Insomnia has also been widely reported by teenagers with estimates of insomnia symptoms ranging from 25-34% (Ohayon, Roberts, Zulley, Smirne, & Priest, 2000; 6

14 Roberts et al., 2002). Symptoms of insomnia include difficulty with sleep onset, staying asleep, or early morning wakening. Insomnia is often caused by maladaptive bedtime associations such as watching television to facilitate sleep onset (Mindell & Owens, 2003). A third sleep disorder is obstructive sleep apnea syndrome (OSAS). OSAS is most common in young children; however, there is also an increased likelihood of OSAS in middle adolescence that is associated with obesity (Mindell et al., 1999). During sleep the airway may be slightly obstructed or blocked, causing airflow to decrease or to stop, thus leading to repeated hypoxia and frequent wakings during sleep. Less common than DSPS, insomnia, or OSAS, narcolepsy is a sleep disorder with a typical age of diagnosis in late adolescence. Narcolepsy is characterized by excessive daytime sleepiness, loss of muscle tone following strong emotional experiences, spontaneous naps during the day, hallucinations during the transition from sleep to wakefulness, and sleep paralysis (Mindell & Owens, 2003). Psychological and Social Influences on Amount and Regularity of Sleep Psychological and cognitive changes during adolescence may also affect the amount and regularity of sleep obtained. Dahl et al. (1996) suggested that developmental changes in cognitions increase the impact of worrying on sleep. Younger children are less likely to have difficulty falling asleep as a result of worrying. Adolescent sleep on the other hand is more likely to be affected by rumination. This may reflect the increased ability for insight and self-reflection that comes with cognitive development and/ or may reflect the more complex peer relationships and increased family and peer conflicts emerging during the teen years. One example of the relationship between peer conflicts 7

15 and sleep problems can be found in a study from the Netherlands wherein children and early adolescents ages 9-12 who were being bullied reported 2.4 times more problems sleeping than children who did not report being bullied (Fekkes, Pijpers, & Verloove- Vanhorick, 2004). The relationship between sleep problems and peer relationships is an important demonstration of the impact of the interaction of physiological, social, and psychological factors on sleep. For example, teens may attempt to go to bed at an earlier time, but not be able to sleep because of circadian rhythm changes. Because they are not sleeping, they may lie in bed awake thinking distressing thoughts. This worrying may then lead to further difficulty falling asleep. An additional reason for the association between sleep time, sleepiness, and psychological functioning involves the impact of sleep on the quality of affect-regulation. Described as the ability to control or modulate negative emotions in the face of a higher cognitive goal (Dahl, 2002; Sroufe, 1996), problematic affect regulation has been linked to the development of psychopathology such as anxiety and depression (Bradley, 1990, 2000). According to Muraven and Baumeister (2000), the ability to self-regulate is similar to a muscle wherein it can be strengthened or depleted. Sleep deprivation disrupts affect regulation ability (Dahl, 2002). Thus, sleep deprivation may lead to reduced emotion regulation ability which may contribute the more serious problems such as anxiety or depression. Moreover, it has been hypothesized that rest can restore this ability (Baumeister, 2002). Dahl (2002), summarized several years of psychobiological studies, and reported that affect regulation requires a high level of cognitive and emotional processing, which is particularly sensitive to sleep deprivation during the adolescent period (Dahl, 2002). 8

16 Influence of Social Demands and Technology on Amount and Regularity of Sleep Social factors that change during adolescence also greatly influence sleep. First, school-related demands, including academic expectations and amounts of homework, increase for adolescents (Dahl & Lewin, 2002; Fredriksen et al., 2004). Additionally, many adolescents become more involved in social activities including sports and clubs that may have later practices, meetings, and games. Carskadon et al. (1989) found that nearly 20% of a sample of high school students reported spending 20 hours per week or more in extracurricular activities. Teens also begin to work and often have jobs that begin after school. In one study, 58.7% of adolescents reported having a part time job and 28.3% reported working 20 hours or more per week (Carskadon et al., 1989). Moreover, teens tend to have more freedom to spend time with peers and to stay out later. These peer relationships can be more stressful in the teenage years especially as dating begins and romantic relationships develop. Teens also have more control over their diets, which in turn may affect the quality and quantity of their sleep. For example, Giannotti, Cortesi, Sebastiani, and Ottaviano (2002) found that teenagers who preferred to stay up later ingested more caffeinated beverages. Adolescents increased use of technology may also be an important influence on sleep during adolescence. Many teenagers use computers and cell phones to communicate with friends without consistent regulation by adults. Such methods of communication can occur without parental knowledge, because there is no indicator (such as a phone ringing) that it is happening. Teens may access television, movies, and the web at any time of day or night, likely contributing to insufficient sleep. 9

17 Contextual, Socioeconomic, and Sex Influences on Amount and Regularity of Sleep One interesting but as yet poorly understood contextual influence on sleep is neighborhood. A study by Cooley-Quill and Lorion (1999) used self-reports of 64 adolescents ages to examine relationships between violence in the community, physiological arousal, and sleep difficulties. Teens completed a 29-item self- report questionnaire regarding lifetime exposure to violent situations against themselves or a person in their community and were also asked about how they were exposed (direct experience, witness, media, hearsay). The participants then filled out a five-item questionnaire about sleep habits over the past week. During the visit, teens had their blood pressure and pulse rate measure multiple times. Results demonstrated that high community violence was positively correlated with sleep problems, but not with elevated blood pressure or pulse rate. Even though teens may be physiologically adapting to violence in their neighborhoods, sleep may continue to be affected. Minority status, SES, and years of parental education have also been shown to be associated with amount of sleep obtained. A study by Spilsbury et al. (2004) showed that minority boys obtained significantly less sleep than all girls and than non-minority boys. Minority children were also more 4.8 times more likely than non-minority children to have bedtimes of 11 pm or later. Roberts, Roberts, and Chen (2000) also found differences in sleep problems based on minority status; however, the direction and magnitude of the effect depended on the ethnic group, with Chinese-American youths at lower risk for insomnia and Mexican youth at higher risk for insomnia. Fredriksen et al. (2004) found that teens that were more economically disadvantaged obtained less sleep than those who were not. A related finding is that greater education has been associated 10

18 with better sleep quality and with higher income (Moore, Adler, Williams, & Jackson, 2002). This study of adults found that when controlling for age, gender, ethnicity, and health status, education was related to sleep quality, but not sleep quantity and that more education was associated with higher income. Sex has been shown to relate to both amount of sleep and frequency of sleep disturbances, though the etiology of this effect is unknown. Results of various studies report contradictory findings about whether boys or girls obtain more sleep. For example, one study found that girls got less sleep than boys and reported greater sleep disturbances (Giannotti, Cortesi, Sebastiani, & Ottaviano, 2002). Another study showed that boys woke up later than girls on weekdays and hypothesized that this was a result of girls having more lengthy morning grooming routines (Lee, McEnany, & Weekes, 1999). Alternatively, at least one other study has found that boys obtain less sleep than girls (Spilsbury et al., 2004). It is possible that inconsistencies in the results of existing studies may in fact reflect differences in the measurement of sleep time (e.g. parent report, selfreport, sleep diary, actigraphy). Sleep Time and Psychological Functioning There are multiple factors that contribute to insufficient sleep in adolescents. The outcomes of such sleep loss may include academic difficulties, problems with attention and concentration, and mood disturbances as well as more severe outcomes such as motor vehicle accidents (Carskadon, 1990). The current study focused on the potential psychological consequences of insufficient sleep. In particular, this study investigated whether in a population predisposed to insufficient sleep (e.g. adolescents); less total sleep time, more variability in sleep time, and sleepiness were related to lower levels of 11

19 psychological functioning. The prevalence and impact of insufficient sleep on adolescents underscores the need to study clinically relevant domains of psychological functioning including externalizing behaviors, depression, anxiety, and perceived health that may be affected by insufficient sleep. These outcomes are reviewed in the following section. Relationship of Insufficient Sleep to Depression One very well-supported association in the literature is between sleep problems and depression in children and adolescents. It should be noted that it is likely that a bidirectional relationship exists whereby depressive symptoms disrupt sleep (in fact, sleep disturbance is one of the DSM-IV criteria for major depressive disorder) and sleep problems increase depressive symptoms. Studies of depressive symptoms have consistently found associations with sleep problems. For example, self-reported sleep problems are common in children and adolescents diagnosed with major depressive disorder, with insomnia being more common (75% of cases) than hypersomnia (25% of cases) (Ryan et al., 1997). Tiredness has been reported in both children and adults with suicidal ideation (Choquet, Kovess, & Poutignat, 1993; Choquet & Menke, 1987; Liu, 2004; Vignau et al., 1997). Adolescents diagnosed with major depression and suicidal ideation have also been found to have increased sleep latency (i.e. time to fall asleep) (Dahl et al., 1990). Conversely, studies of sleep problems among adolescents have also identified elevated rates of depressive symptoms. One study found that the strongest correlates of insomnia in adolescents were unhappiness, mood disturbance, substance use, and suicidal ideation (Roberts, Roberts, & Chen 2001). In Morrison, McGee, and Stanton s (1992) 12

20 study of a group of 943 adolescents via clinical interview, those who reported sleep problems also reported more depressive, anxious, inattentive, and conduct disordered symptoms than those who reported occasional or no sleep problems. Wolfson and Carskadon (1998) showed that teenagers who obtained less than 6 hours of sleep per night or reported a discrepancy between school night and weekend bedtimes of greater than two hours, reported significantly more depressive symptoms. Roberts et al. (2001) found that on a questionnaire of depressive symptoms, teenagers with insomnia were 5.9 times more likely to report symptoms of mood disturbances and 3.4 times more likely to report suicidal ideation than those who did not report symptoms of insomnia. The same study showed that odds ratios of reports of mood disturbance (OR=3.5) and suicidal ideation (OR=2.8) were also elevated in teenagers who reported symptoms of hypersomnia compared with controls. This finding indicates that self-report of mood disturbances may be related to self-report of sleep problems in general, regardless of whether such disturbances cause too much or too little sleep. Another study utilized growth curve modeling to study the relationship between amount of sleep, depressive symptoms, and self esteem in 2,259 middle school children ages (Fredriksen et al., 2004). Teens filled out a questionnaire about depressive symptoms and a questionnaire about self-esteem. As part of a larger survey, they were also asked one question about how much sleep they typically obtained on a school night. Consistent with previous research, the investigators found that older children reported less total sleep time than younger children (both girls and boys), and that overall girls obtained less sleep than boys. The investigators also found that self-report of sleep time was positively related to self-report of both depressive symptoms and lower self esteem. 13

21 A study by Gregory and O Connor (2002) followed 490 children from ages Parents filled out a behavioral screening measure that included scales for various emotional and behavior problems as well as sleep problems. It was found that parent report of sleep problems at age four predicted behavioral and emotional problems on the same parent questionnaire at age fifteen. Additionally, parent report of sleep problems decreased from ages four to fifteen. It is possible that this finding reflects an actual decrease in sleep problems or alternatively, it may be a result of parents being less aware of their child s sleep habits during adolescence as compared with childhood. Relationship of Insufficient Sleep to Anxiety Much more empirical research examining the relationship between depression and sleep deprivation has been conducted than with anxiety disorders and sleep deprivation (Owens & Mindell, 2003). However, sleep disturbances have been associated with anxiety disorders in the clinical literature (Hill, 1994; Simonds & Parraga, 1984) and are part of the diagnostic criteria for such disorders (American Psychiatric Association, 2000). Again the causal direction of the association is not known. Consistent with the clinical literature, a study by Morrison, McGee, and Stanton (1992) found that during a clinical interview adolescents who reported symptoms of insomnia also reported symptoms of anxiety. Relationship of Insufficient Sleep to Perceived Health Sleep problems have also been found to relate to teenagers perceptions of their health. A cross-sectional study by Roberts, Roberts, and Chen (2002) found that sleep problems related to somatic complaints in adolescents. Further longitudinal analysis of these data, however, did not support the effect of insomnia on future somatic complaints, 14

22 indicating that the association between insomnia and somatic complaints may be time limited. Mahon (1995) also found an association between perceived health and sleep in adolescents. A sample of 106 teens divided into early adolescence (12-14), mid adolescence (15-17) and late adolescence (18-21) were given a 15-item measure of sleep where responses were scored using a visual analog scale. They were also given a 22-item questionnaire of perceived health status. This correlational study examined the relationship between sleep disturbance and perceived health status as well as between total sleep time per day and perceived health status. In the group of year olds (middle adolescents), positive correlations were found between perceived health and sleep efficiency (amount of time actually sleeping while in bed) and between perceived health and total sleep time. However, no relationships were found between the sleep variables and perceived health status in early or late adolescents. Relationship of Insufficient Sleep to Externalizing Behavior Problems Sleep problems have been shown to relate to externalizing behavior problems in children and adolescents. Morrison, McGee, and Stanton (1992) found that adolescent report of symptoms of insomnia during a clinical interview positively related to parent report of their children s inattention and general behavior problems on a questionnaire. A study of 113 children and adolescents ages 2-18 by Smedje, Broamn, & Hetta (2001) of parent report of sleep and behavioral difficulties indicated that 36% of children with sleep problems had behavior problems and that 15% of those with behavior problems had sleep problems. The wide age range of the subjects in this study encompassed a variety of 15

23 behavior and sleep problems that change with developmental maturation, limiting the applicability of the results to any specific age group. A study by Chervin, Dillon, Archbold, & Ruzicka (2003) demonstrated that among 114 children ages 2-14, parent reports of bullying and aggressive behaviors were 2-3 times more likely among those at risk for sleep disordered breathing. The investigators also found that parent-reported conduct problems were associated with symptoms of restless leg syndrome, periodic limb movement disorder, and sleep disordered breathing. It is difficult to determine the applicability of these results to adolescents specifically, as a result of the wide age range of the sample. Another study of 13,831 adolescents ages used a self-report measure of mood and behavior to examine the relationship between sleep problems and substance use (Johnson & Breslau, 2001). The investigators found a significant association between sleep problems and cigarette, alcohol, and illicit drug use. They also found that these relationships became non-significant when internalizing and externalizing problems were included in the model, suggesting the importance of psychological functioning as a mediator in the relationship between sleep problems and substance use (Johnson & Breslau, 2001). Limitations of Previous Studies and the Specific Contribution of the Proposed Study Previous research has demonstrated that decreases in sleep quantity, irregular sleep patterns, and increased sleepiness occur with the onset of adolescence. However, there have been relatively few studies of the relationship between such sleep variables and adolescent psychological functioning. Moreover, the conclusions that can be drawn from existing studies have been affected by significant methodological limitations. 16

24 A primary limitation of previous research is inadequate measurement of both sleep and psychological functioning. Much of the research found in the current literature has relied on single item self-report or parent report of average total sleep time (i.e. how many hours do you/ does your child usually sleep at night ). Single item or few item questionnaires about total sleep time may not be adequate assessments of total sleep time. Teen report of how many hours they sleep may not be accurate and parents may not know how many hours their teen sleeps once they are in bed, thus limiting the internal validity of the measure of sleep time. Additionally, such short questionnaires have limited reliability, which decreases the likelihood of detecting a relationship if one is in fact present. Recent studies have also shown that perceptions of sleep time and quality may be distorted in certain populations, including anxious adults with higher levels of cognitive and physiological arousal (Tang & Harvey, 2004) and adolescents with major depressive disorder (Bertocci et al., 2005). The use of actigraphy, which is used in the present study as an objective measure of sleep time is a methodological strength, not only because of issues with adolescent and parent reported sleep time as described above, but for other reasons as well. Actigraphy allows for the measurement of sleep time over multiple nights in a subject s normal sleep environment, adhering to their own sleep schedule. Actigraphy is less intrusive than polysomnography (PSG) wherein a subject is required to sleep in a laboratory setting with multiple wires and leads attached to their head, face, and body. Studies that have used the same measure to determine both sleep deprivation and psychological outcomes (Gregory & O Connor, 2002; Morrison, McGee, & Stanton, 1992) may also have spurious findings owing to item overlap and shared symptoms on 17

25 sleep scales and scales of psychological symptoms. For example, a question on the CBCL internalizing problems subscale may have to do with insomnia, and this item will also be on the sleep problems subscale. Thus the correlations that are found are likely to be inflated as a result of the overlapping items. This study includes separate measures of sleep deprivation and psychological outcomes and sleep items were removed from psychological measures when such items were present. An additional problem with using the same measure for both the predictor and the outcome is informant variance. One can assume that part of the variance found between subjects is actually variance attributed to the reporter on a given measure. In the absence of corroborating measures from other sources, it may be difficult to determine whether the relationship between sleep and psychological symptoms is due to the reporter or to an actual relationship. To address the aforementioned limitation, multiple reporters of psychological functioning, including parent, teacher, and adolescent were employed. A general emotional and behavioral screening measure was used as well as specific instruments designed to assess symptoms of anxiety, depression, and perceived health. Past research has demonstrated generally low correlations between parent, teacher, and teen reports of internalizing and externalizing behavior ranging from (Achenbach, McConaughy, & Howell, 1987; De Los Reyes & Kazdin, 2004; Youngstrom, Loeber, & Stouthamer-Loeber, 2000). This may indicate that adolescents behavioral symptoms are not consistent across environments. A depressive symptom such as inattention might be more visible at school by a teacher while irritability might be more evident by a parent at home and loneliness might only be experienced by the adolescent. Also, given the 18

26 discrepancy between informants, it is difficult to know whose report best predicts a given outcome. For example, a study by Paavonen, Solantaus, Almqvist, & Aronen (2003) found that children s report of their own sleep problems better predicted teacher report of psychiatric symptoms than parent report of the child s sleep problems. Because prior research has suggested that adolescents may be the best reporters of their own internalizing symptoms (Angold et al., 1987), in the current study, adolescent report was used for anxiety, depression, and perceived health. Parent report was used for both perceived health and externalizing symptoms and teacher report was also used for externalizing symptoms. Additionally, many studies have utilized a wide age range that encompasses both children and adolescents, which limits the conclusions that can be drawn about any particular age group. Moreover, chronological age may not be the most sensitive variable for defining adolescence, as physiological changes in sleep are thought to relate to physiological changes in puberty (Dahl & Lewin, 2002; Knutson, 2005). Thus, pubertal status is thought to be a more sensitive marker of physiological changes associated with adolescence. For this reason, Tanner staging was used to determine pubertal status in the current study. Finally, previous studies of the relationship between sleep problems and psychological functioning have relied primarily on correlational and regression analyses as data analytic methods. In addition to regression analyses, path analysis was used to test models of sleep and psychological functioning. Where significant relationships between total sleep time or variability in sleep time and a psychological variable were found, 19

27 sleepiness was then tested as a mediator of the relationship between the sleep variables (total sleep time or coefficient of variation) and the psychological variables. Moreover, most previous research on the relationship between sleep deprivation and psychological outcomes has not included reliability estimates of measures when testing the relationship between constructs. Unreliability of a particular measure may limit the detection of a relationship between variables. Consequently, the use of path analysis included an estimate of the unreliability of the measurement, allowing for a more accurate estimate of the relationship between the sleep variables and the psychological variables. Finally path analysis allowed the use of all data points, including those for subjects wherein certain data points were missing. This contributed to the precision of the analyses in this study. Specific Aims and Hypotheses The major aim of this study was to determine the associations between sleep time, variation in sleep time (coefficient of variation), sleepiness, and psychological functioning in adolescents. Previous research has demonstrated that adolescents are predisposed to problematic changes in amount and regularity of sleep (Carskadon & Acebo, 2002). Less total sleep time and inconsistent sleep patterns have been linked to more negative psychological outcomes. Thus it was hypothesized that less mean total sleep time, higher night to night variability (CV), and higher levels of self-reported sleepiness would be associated with increases in symptoms of anxiety, depression, and behavior problems as well as poorer perceptions of health (see Figure 1). It was hypothesized that pubertal status, sex, minority status, preterm status, body mass index, age, parental income, and parental education would predict total sleep time, variability in 20

28 sleep time, and sleepiness (see Figure 1). Finally, it was hypothesized that if a relationship between total sleep time or CV and any psychological variable was present, it would be mediated by sleepiness. Figure 1. Conceptual model of sleep time, sleepiness, and psychological functioning Pubertal status Sex Minority Status Preterm Status Body Mass Index Age Parent Income Parent Education Total sleep time Night to night variability Sleepiness Psychological Symptoms and Functioning Specific Hypotheses 1) Based on previous research investigating demographic characteristics which relate to sleep time, variability in sleep time, and sleepiness (Moore et al., 2002; Rhodes et al., 2004; Spilsbury et al., 2004), hypotheses were made about such characteristics. Age, pubertal status, minority status, and preterm status as well as body mass index (BMI), parent education, and parent income will relate to total sleep time and variability in sleep time with more advanced age and pubertal status, minority and preterm status, higher BMI, and less parent education and income correlating with less mean total sleep time and higher night to night variability. 21

29 2) Prior research has suggested that sleepiness is a consequence of sleep duration and quality (Carskadon et al., 1987). Thus, less total sleep time and more night to night variability will be associated with self-reported sleepiness. 3) Research has found an association between self-reported tiredness and depressive symptoms (Choquet et al., 1993; Vignau et al., 1997). Based on findings from these studies, it is hypothesized that self-reported sleepiness will be positively associated with self-report of depressive symptoms. It is also hypothesized that self-reported sleepiness will be positively related to parent and teacher report of externalizing behavior and self-reported symptoms of anxiety as well as negatively correlated with parent and self-report of perceived health. 4) Based on prior studies (Chervin et al., 2003; Mahon, 1995; Morrison et al., 1992) mean total sleep time will be positively associated with parent and teacher report of externalizing behavior and self-reported symptoms of anxiety and depression and negatively correlated with parent and self-report of perceived health. 5) Sleepiness is thought to be a functional outcome of insufficient sleep time (Carskadon et al., 1987) and may reflect individual differences in sleep need. Sleep deprivation may deplete affect regulation, potentially contributing to the development of psychopathology. Thus the relationship between mean total sleep time and psychological functioning (externalizing, anxiety, depression, and perceived health) will be mediated by sleepiness. 6) Though variability in sleep time (CV) has not been previously studied in adolescents, there is evidence that regularity of sleep patterns relates to depressive symptoms (Carskadon, 1998). Thus, it is hypothesized that the coefficient of 22

30 variation (CV) will be positively associated with parent and teacher report of externalizing behavior and self-reported symptoms of anxiety and depression and negatively correlated with parent and self-report of perceived health. 7) Because regularity of sleep patterns has demonstrated importance in adolescent functioning (Carskadon, 1998), it can be argued that regularity of sleep time may contribute to sleepiness and to psychological functioning. It is hypothesized that the relationship between CV and psychological functioning (externalizing, anxiety, depression, and perceived health) will be mediated by sleepiness. Methods Participants This study was part of a larger population-based cohort study of sleep and health, the Cleveland Children s Sleep and Health Study (CCSHS). Information about consent, recruitment, and the study cohort from the previous phase of the study, has been described in detail elsewhere (Rosen et al., 2003). The original cohort was comprised of a stratified random sample of 907 full term and preterm (< 37 weeks gestational age at birth) children born between at one of three major Midwestern urban hospitals. Because minorities were underrepresented, additional minority recruitment for the previous study was undertaken. A stratified random sample based on race, sex, and preterm status was identified from the previous study (Rosen et al., 2003) yielding a sampling frame of 371 adolescents ages Of those 371, 75.5% agreed to participate, 14.8% refused, 8.9% could not be located, and <1% were ineligible due to illness (e.g., kidney failure, oral surgery, and mental illness). Of the families who refused to participate, the most common reasons 23

31 were passive refusal (e.g., agreed to participate but did not respond to calls) (16.4%), too busy (20%), did not like blood work, needles, or hospitals (14.5%), or miscellaneous reasons (49.1%). Of the 280 who agreed to participate, 251 were eligible at the time of data analysis for this study. Comparisons with regard to age, minority status, sex, preterm status, and sleep disordered breathing revealed no significant differences between those who agreed to participate and those who did not. Of the 251 who agreed to participate, teens with diagnosed obstructive sleep apnea (an obstructive apnea hypopnea 3 index>5, n=28) were excluded as previous studies have shown that actigraphy may systematically underestimate sleep time in those with sleep apnea (Ancoli-Israel et al., 2003; Johnson, 2006). Teens whose actigraphy did not include at least two weekdays and one weekend day were also excluded (n=15), as one of the primary predictors was night to night variability. This brought the total sample to 208 (see Table 2 for characteristics of the sample). Procedures The Institutional Review Board approved this study, and written informed consent was obtained from all parents/ guardians as well as the adolescents, and assent was also obtained from all adolescents. The larger study, the CCSHS, utilized an extensive protocol that included home visits, in-home overnight cardio-respiratory studies (polysomnography and actigraphy), and questionnaires about sleep, general health, behavior, and emotional functioning. After informed consent was obtained, a research assistant visited the participant s home and provided instructions on actigraphy. The parent and child were taught how to use the actigraph and how to fill out the sleep diary. The actigraph was either returned to the investigators at a later clinic visit or was picked 24

32 up by the research assistant. Parents and children were also asked to fill out information about their child s/ their own sleeping patterns, medical history, and behavior. A behavioral questionnaire was also mailed to the child s primary teacher. Within two weeks of the home visit, the child came to the hospital wherein a general history and physical exam were obtained including height, weight, body mass index, and pubertal status. Further sleep studies were then conducted in the sleep laboratory. Measures Demographics Demographic information was collected from a parent questionnaire which included information about the teen s age, birth date, ethnicity, birth weight, sex, and parent income and education. Vacation status was defined as yes if the date of the actigraphy was over the summer or winter break of the Cleveland public schools. Body mass index (BMI) was calculated using the current height and weight and was defined as weight in kilograms divided by height in meters squared (kg/m 2 ). Sleep-related measures Actigraphy. Actigraphy, a non-invasive measure of sleep and wake times, determines amount of sleep obtained based on movement. An actigraph is a watch-like device worn on the wrist from bedtime to wake time. In this study, 5-7 day wrist actigraphy was used to determine mean total sleep time (MTST) as well as variability in sleep time across the week and weekend. The coefficient of variation of total sleep time (CV) was used to represent variability in sleep and wake times from night to night. CV was calculated as the standard deviation of total sleep time divided by the mean sleep 25

33 duration, expressed as a percentage. For total sleep time, studies with healthy adults have found rates of agreement with polysomnography (PSG), the gold standard of sleep measurement, to be 78-90% (Ancoli-Israel et al., 2003). A study by Johnson et al. (2006) showed intraclass correlation coefficients (ICCs) between actigraphy and PSG for total sleep time in adolescents to be 0.64 for those without sleep disordered breathing. ICCs were calculated on a subset of the current sample who also completed one night of both actigraphy and PSG in the sleep lab (N=115). The ICC for girls (N=59) was 0.72 and the ICC for boys (N=56) was Epworth Sleepiness Scale (ESS; Johns, 1991). The ESS was used to measure daytime sleepiness in this study. The ESS, a self-report questionnaire, consists of eight situations wherein subjects are asked to rate how likely they would be to fall asleep. The response possibilities are would never doze, slight chance of dozing, moderate chance of dozing, and high chance of dozing. Though this questionnaire was initially designed for adults, it has been used in several studies with children and adolescents (Bootzin & Stevens, 2005; Melendres, Lutz, Rubin, & Marcus, 2004). For this study, the last item in a car while stopped for a few minutes in traffic was replaced with doing homework or taking a test as has been done in previous studies with adolescents (Melendres et al., 2004). The ESS has demonstrated good five-month test-retest reliability, with ESS scores not significantly changing when sleepiness was not expected to change. In one study with 87 young adults, the correlation between the two time periods was 0.82, and Cronbach s alpha ranged from (Johns, 1992). In the current study, Cronbach s alpha was Additionally, a previous factor analysis was performed and only one factor emerged 26