This study provides objective and subjective sleep data from a large sample of children and adolescents with depression and/or anxiety disorders and healthy controls, all studied in the same environment under the same conditions. Overall, young people with anxiety disorders showed more evidence of objective sleep problems compared to healthy controls or those with MDD, even when those with comorbid MDD were excluded from the anxiety group. In contrast, the objective sleep measures in the children and adolescents with MDD were similar to those of the control group.
Sleep problems in the anxiety group were more evident in polysomnography-based than in subjective sleep measures. For example, despite having more awakenings and more minutes awake by these objective measures, young people with anxiety did not report experiencing these any more than did young people with MDD or healthy young people. The only variable for which both objective and subjective differences for anxiety disorders (and anxiety symptoms) emerged was sleep latency. Thus, a noteworthy associated finding is that young people with anxiety generally appear to be less aware of, or perhaps underreport, their sleep problems. For sleep latency, however, it appeared that young people without anxiety disorders tend to estimate their sleep more correctly.
Strikingly, youths with anxiety disorders showed greater objective sleep latencies than those of the control or MDD group on night 2 only. In the “first-night effect,” sleep latency typically decreases with adjustment to the sleep laboratory environment, with youths falling asleep more quickly on the second night.30
The first-night effect was not evident in the anxiety group, which suggests that anxiety interferes with the processes of adjusting to sleeping in the laboratory. Our findings may thus be related to first-night effects in the other two groups. Furthermore, the anxiety group was more likely to be missing night 2 EEG data, which suggests that the first-night experience may have influenced willingness to participate in a second night of recordings.
Consistent with our earlier findings, young people with MDD did not show evidence of objective sleep disturbances as measured by polysomnography. In fact, during the first night, the MDD group had significantly less time awake than did the control group. However, contrary to our hypotheses and our recent findings,11
young people with MDD also did not differ from control participants in subjective sleep. Depressive symptoms (rather than MDD) were associated with sleep problems to a limited extent, but this could be attributable to co-morbid depression in the anxiety group. Previous studies have also reported that, in contrast to the adult literature, there is not a consistent link between objectively assessed sleep problems and depression in children or adolescents. A meta-analysis revealed that the sleep of depressed youths was largely indistinguishable from that of controls.31
Furthermore, in contrast to previous findings that reduced REM latency predicts the recurrence of depression in depressed adults,32
findings about predictive value of REM latency in children and adolescents have been less strong.33
The maturity of the CNS could be implicated, and investigations of the microarchitecture of sleep have argued that depression × sex interactions may indicate alterations in neurodevelopment in some individuals.34
Our findings suggest that the anxiety group experienced heightened anxiety or “stress” during the night. Sleep problems in young people with anxiety disorders could reflect the vigilance processes and biased information processing postulated to characterize early-onset anxiety.35
Because vigilance interferes with the feelings of safety that are critical to the onset and maintenance of sleep,36
especially slow-wave sleep, it may contribute to the longer sleep latency and reduced deep sleep in young people with anxiety. Of note, we reported a similar pattern of findings with perisleep-onset cortisol, which was unusually high in children with anxiety disorders but not those with depression.37
Thus, it may be that anxiety in childhood is particularly associated with a set of disruptions in sleep-related physiology.
The apparent lack of awareness of sleep problems in the anxiety group was a surprising finding. Because people are believed to have unreliable memories concerning sleep, it is possible that young people with anxiety use other cues, such as daytime arousal, to interpret or make inferences about their sleep. An anxious child who interacts with responsive, caring staff at a sleep laboratory and is temporarily relieved of managing worries about school may be less aware of sleep difficulties. Alternatively, some young people with anxiety may be aware of their sleep problems but simply fail to report them. Methodologically, the magnitude of discrepancy between objective and subjective sleep measures in this clinical sample underscores the importance of considering how these domains of sleep measures can yield very different results.38
From a developmental perspective, we found the typical pattern of sleep changes associated with the pubertal transition. The fairly wide age range, including both children and adolescents, allowed us to examine both developmental effects and interactions of development with diagnostic group. There were not significant interactions between development and diagnosis in objective or subjective sleep measures, and the inclusion of age as a covariate did not appear to influence the results.
The limitations of the study include the methodological complexities of comparing objective and subjective measures of sleep, the diagnostic overlap between affective disorders and sleep problems, and the shared method variance of symptom reports and subjective sleep problems. The advantages of assessing sleep in a uniform environment are accompanied by the drawbacks of being unable to assess sleep in a typical environment and having missing data for some participants (which may influence night-specific findings). The cross-sectional design of the study limited our ability to understand the interplay of sleep problems, anxiety, and depression over time. Also, the relatively small anxiety group made it difficult to compare “pure” MDD, “pure” anxiety, and comorbid depression and anxiety. However, the strength of the findings, which generally did not change when the comorbid subgroup was excluded, suggests that anxiety has an association with sleep independently of depression. Although we did not find that sex moderated the relation between depression and sleep, it is still possible that it exerted an undetected influence. An important next step will be to use multiple measures to examine the mechanisms by which anxiety and sleep problems may be related. For example, it is difficult to determine without actigraphy data whether the notably long sleep latency that we observed in the anxiety group reflects typical sleep or anxiety associated with sleeping in the laboratory.
The psychiatric characteristics of the sample created additional limitations. First, the co-occurrence of depressive and anxiety symptoms in both clinical groups, although not atypical, presents challenges to separating the unique contributions of depression and anxiety to sleep problems. We hypothesize, based on findings when the comorbid group was excluded, that clinically and functionally meaningful anxiety is a key factor in objective sleep difficulties, so that anxiety symptom levels alone are not sufficient to disrupt sleep. Second, our exclusion criteria created limitations in the generalizability of findings to the larger population of young people with affective disorders. In particular, exclusion based on drug or alcohol use could have attenuated the relationship between MDD and sleep problems, given the high co-occurrence of MDD and substance use disorders.39
Given the comorbidity of depression and anxiety in young people,17
the different patterns of sleep disturbance in the MDD and anxiety groups raise compelling questions about ways in which these disorders may differ and about new opportunities for early intervention. For instance, a psychosocial treatment for anxiety may be more effective if it is augmented with an intervention to target specific symptoms such as vigilance and worry at bedtime. Targeting sleep problems that are especially responsive to treatment may have particular value for reducing anxiety. Similarly, specific treatments for anxiety may improve sleep quality in young people. Given that MDD was not associated with objective sleep problems, it could be useful to educate young people with depression about perceived sleep quality and to address their cognitive distortions about the consequences of poor sleep. Finally, given the sharply increased rate of onset of depressive disorders during adolescence40
and the tendency for anxiety to precede depression in young people,41
it may be especially critical to intervene at an earlier point in childhood, before anxiety and sleep problems have a chance to develop into more serious pathology.