The most important finding was that degree of sleepiness, but not objectively determined estimates of sleep duration or variability in sleep duration, was correlated with adolescents’ report of symptoms of depression and anxiety as well as with their perceived health. It has been argued that the ability to self regulate (and thus modulate emotions) may depend in part on having adequate personal resources, including sufficient sleep (Baumeister, 2002
). This study indicated that it may be level of sleepiness (rather than absolute sleep duration) that is associated with affect. A subjective feeling of sleepiness might cause a general negative mood as well as a decreased ability to regulate emotions, thus contributing to depressed and anxious feelings and somatic symptoms.
Conversely, it is also possible that adolescents, who are more anxious, depressed, or feel less healthy may feel sleepier. Research has found that depressed children report disturbed sleep despite normal architecture measured by electroencephalography (Bertocci et al., 2005
). These findings are consistent with the current study wherein the subjective report of sleepiness related to findings on measures of depression, anxiety, and perceived health while objectively measured sleep duration and variability in sleep duration by actigraphy did not. There are several potential explanations for this finding, each of which might play a role in the relationship between sleepiness and psychological functioning. First, adolescents who are anxious, depressed, or feel less healthy may in fact, need more sleep than those with better psychological functioning. The challenges of getting through an ordinary day may require increased energy for these adolescents. It is also possible that adolescents who are anxious, depressed, or less healthy may have more negative perceptions of their sleep and sleepiness.
Additionally, it may be that relationships between sleep duration and psychological functioning are impacted by individual sleep need. At this time, there is no way to measure these individual differences; however, as technology advances, this is an important area of research. It may also be that selective deficits in certain sleep stages (e.g., slow wave or REM sleep) rather than modest deficits in sleep duration, may mediate the relationship between sleepiness and psychological functioning. On the other hand, because there may be individual differences in sleep need, a subjective measure of sleepiness may in fact, be more sensitive than an objective measure of sleep duration. Although we chose to use an objective measure of sleep duration (actigraphy), even this measure is subject to misclassification, and may have biased the findings to the null.
Despite previous studies that have found associations between sleep duration and externalizing behavior (Chervin et al., 2003
; Smedje et al., 2001
), in this study sleepiness, sleep duration, and sleep duration variability were not associated with parent and teacher reports of externalizing behavior. It is possible that the inability to detect an association was due to our use of a broad externalizing score that may not have been as sensitive to the effects of sleep problems as more specific externalizing behavior subscales, such as those that measure symptoms of inattention or aggression.
Our finding showing an association between self perceived sleepiness and psychological symptoms is consistent with two studies which demonstrate the relationship between subjective reports of depression and subjective reports of sleep quality (Bertocci et al., 2005
; Tang et al., 2004
). Future work utilizing objective measures of sleepiness such as the Multiple Sleep Latency Test may help to further assess whether the associations between psychological functioning and self reported sleepiness reflect a greater sensitivity of subjective measures compared to objective measures, or whether sleepiness per se, as a more proximate mediator for behavior than sleep duration, is the stronger predictor.
Another important finding in this study was that despite increasing research supporting the importance of sleep for adolescents, adolescents in this sample generally did not get enough sleep and nearly one quarter had elevated sleepiness scores. The mean sleep duration of just under 8 h was less than the 9.2 h recommended for adolescents (Carskadon, 1982
), but is consistent with previous literature (Carskadon & Acebo, 2002
Limitations and Future Directions
The methodological limitations of the current study affect the interpretation of results and at the same time, suggest avenues for future research. First the cross-sectional study design limited the ability to attribute causality to the relationship between the sleep variables and the psychological variables. For example, while it was hypothesized that sleepiness would contribute to poorer perceptions of health; it is possible that poorer perceptions of health result in being sleepier. As previously mentioned, it is likely that many of the relationships between sleep and psychological functioning are bidirectional, and longitudinal studies with large samples are needed in order to investigate the causality.
Second, the use of adolescent self-reported measures of sleepiness, adolescent depression, anxiety, and perceived health may have influenced the results. For example, it is possible that correlations were inflated as a result of method variance. On the other hand, prior studies (Angold et al., 1987
) have found that adolescents may be the best reporters of their own internal states. The use of objective measurements of sleepiness, such as the MSLT or the Maintenance of Wakefulness Test (MWT) might reduce measurement error and better clarify the relationships between sleepiness and psychological symptoms.
The variables investigated in this study explained only a small amount of the variance in the regression models, as may be expected in studies of a generally healthy community based cohort. While this study found an association between sleepiness and perceived health, studies exploring the effect of sleepiness on physiological or clinical measures of health and illness would also be valuable. Research could be expanded to various populations including adolescents with chronic illnesses or in the intensive care unit. Such studies are needed in order to further examine functional outcomes of sleepiness in a variety of vulnerable populations.
Empirical evidence, including findings from this study, continues to highlight the relationship between sleep and psychological functioning. One clinical implication of such findings is that adolescents and their parents should be educated concerning the natural predisposition to poor sleep in adolescents and the relationship of sleepiness to psychological functioning. Moreover, when adolescents present with psychological symptoms such as anxiety, depression, and somatic complaints, they should be offered guidance about monitoring sleepiness and developing healthy sleep habits in addition to more traditional psychological interventions.
Second, although assessments of psychological functioning often include brief questions about total sleep duration and quality, clinicians should also ask about sleepiness. As suggested by this study, sleepiness may be a more sensitive predictor of psychological symptoms than are objective estimates of sleep duration. Informed clinical assessment should include questions about sleepiness and its functional consequences.
Moreover, interventions to reduce sleepiness need to be developed and tested. Such interventions could be delivered in multiple ways including in schools (for example: via health class, the school counselor or nurse, to parents at PTA meetings, and to teachers) and through mental health services such as psychiatry, psychology, and social work. Additionally, practitioners who develop psychological treatment manuals for conditions such as anxiety and depression should consider including modules that address the potential consequences of sleepiness.
National Institutes of Health, National Heart Lung Blood Institute: (HL07567; HL60957; K23 HL04426; M01 RR00080; 1U54CA116 867; NIMH 100830; AG08415).
Conflict of interest: Dr. Ancoli Israel is a consultant to or on the advisory board of: Arena, Ferring Pharmaceuticals, Inc., Orphagen Pharmaceuticals, Respironics, sanofi-aventis, Sepracor, Inc., Schering-Plough, and Somaxon. She has grants from and contracts with Sepracor, Inc., Takeda Pharmaceuticals North America, Inc., and Litebook, Inc.