Eur Child Adolesc Psychiatry DOI 10.1007/s00787-013-0502-y
ORIGINAL CONTRIBUTION
Sleep problems and depression in adolescence: results from a large population-based study of Norwegian adolescents aged 16–18 years Børge Sivertsen • Allison G. Harvey Astri J. Lundervold • Mari Hysing
•
Received: 24 July 2013 / Accepted: 19 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Both sleep problems and depression are common problems in adolescence, but well-defined large epidemiological studies on the relationship are missing in this age group. The aim of this study was to examine the association between depression and several sleep parameters, including insomnia, in a population-based study of adolescents aged 16–18 years, and to explore potential gender differences. A large population-based study in Hordaland County in Norway conducted in 2012, the ung@hordaland study, surveyed 10,220 adolescents aged 16–18 years (54 % girls) about sleep and depression. The sleep assessment included measures of the basic sleep
B. Sivertsen (&) Division of Mental Health, Norwegian Institute of Public Health, Bergen, Norway e-mail: [email protected] B. Sivertsen Uni Health, Uni Research, Bergen, Norway B. Sivertsen Department of Psychiatry, Helse Fonna HF, Haugesund, Norway A. G. Harvey Department of Psychology, University of California, Berkeley, USA A. J. Lundervold M. Hysing Regional Centre for Child and Youth Mental Health and Child Welfare, Uni Health, Uni Research, Bergen, Norway A. J. Lundervold Department of Biological and Medical Psychology, University of Bergen, Bergen, Norway A. J. Lundervold K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Bergen, Norway
parameters for weekdays and weekends. Depression was defined as scoring above the 90th percentile on the total score of Short Moods and Feelings Questionnaire (SMFQ). There was a large overlap between insomnia and depression in both genders and across depressive symptoms. Depressed adolescents exhibited significantly shorter sleep duration and time in bed as well as significantly longer sleep onset latency (SOL) and wake after sleep onset (WASO). Adolescents with insomnia had a 4- to 5-fold increased odds of depression compared to good sleepers. There was also a significant interaction between insomnia, sleep duration and depression, with a more than eightfold increase in odds of depression for those who met criteria for insomnia and who slept \6 h. These associations held for both genders, but were stronger in boys. To the best of our knowledge, this is the first population-based study to investigate sleep and insomnia in relation to depression among adolescents. The findings call for increased awareness of sleep problems and depression as a major public health issue. Keywords Insomnia Sleep Depression Epidemiology
Introduction Sleep problems have historically been regarded as an epiphenomenon of depression, with sleep problems being included as a core symptom of depression in both major diagnostic classification systems [2, 39]. There has been a paradigm shift driven by the mounting data pointing to a reciprocal relationship between insomnia and depression in both adolescence and adults [5, 24, 28, 32] and strengthened by intervention studies documenting sleep as a
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residual symptom after treatment of depression [6].This change in our understanding of the association between sleep and depression is also reflected in the new diagnostic criteria. Whereas the DSM-IV had separate diagnoses for insomnia with and without a co-existing mental disorder, this distinction is not included in the new DSM-V diagnostic criteria; the mood disturbances are listed as one of the functional impairment criteria for insomnia disorder, and insomnia symptoms are still mentioned in the criteria for depression. Whereas most investigations of the link between sleep problems and depression have been conducted in adult samples, sleep problems are among the most frequent symptoms of depression in adolescents. In a large community sample of adolescents with major depressive disorder, nine out of ten reported co-occurring sleep disturbances [27], and a high rate of insomnia in depressed adolescents has also been reported [21]. Similarly, a Finnish study of adolescents with major depressive disorder (MDD) found that sleep disturbances were both frequent and significantly related to the severity of the depression, with insomnia being the most frequent sleep disturbance [37]. Clinical studies of sleep measured by polysomnography (PSG) have demonstrated both prolonged sleep onset latency (SOL) and wake after sleep onset (WASO) in depressed compared to healthy adolescents [10, 14]. In an overview of the literature on the relation between sleep and depression, half of the studies on children and adolescents demonstrated that depression had an effect on sleep continuity based on PSG, while sleep onset problems and early morning awakenings were seldom found [3]. However, more recent studies have not confirmed this association between depression and disturbed sleep using PSG [4, 13]. Further, most studies on sleep in depression are small, clinical studies with welldefined samples and strong methodology. It is thus not certain if these results can be generalized to adolescents with depression in the general population. However, using an epidemiological approach, where brief instruments assessing self-rated mood commonly are the only and best assessment method, may not capture the diversity and severity of depressive disorders [1]. Most epidemiological studies also tend to include limited sleep assessments and few studies have used stringent definitions based on diagnostic criteria. Crude measures of time in bed are typically included, leaving actual sleep duration and other sleep parameters most relevant to insomnia, such as SOL and WASO, unexplored. The high rate of long SOL and decreasing sleep duration in adolescence over the last decade [16, 25] underscore the importance of understanding such parameters in relation to depression in adolescence. Insomnia is also highly prevalent in the general population, and while varying across
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definitions [16], few epidemiological studies have gone beyond a more general assessment of sleep problems in relation to depression. The high rate of both depression [23] and insomnia [16] during adolescence, with similar developmental patterns such as an increase during puberty and a female preponderance, suggest that co-occurrence may be likely. Together, these data chime well with the emerging evidence that a key function of sleep is emotion regulation [40]. Indeed, sleep problems or sleep loss may be especially detrimental during adolescence due to the vulnerable period of brain development [9], affecting both body restoration [30], learning and memory [19], decisionmaking [18, 33] and brain maturation [12]. Based on the above considerations, the main objective of the current study was to examine the relationship between depression and a range of sleep parameters using data from a large population-based study. The first aim was to establish the extent of the overlap between depression and insomnia. The hypothesis tested was that insomnia and depression would be strongly interrelated. The second aim was to investigate the relationship between depression and other specific sleep parameters. Based on the research reviewed, we hypothesized that depressed teens would report prolonged SOL and WASO. The third aim was to investigate the relationship between specific symptoms of depression and sleep parameters. The fourth aim was to investigate the independent contribution of insomnia and short sleep duration on depression. This has been a topic of considerable interest in the adult literature [38], but has yet to be explored among adolescence. Hence, this aim was included on an exploratory basis. Finally, Hudziak et al. [15] highlight the importance of studying gender differences in adolescence, given the difference between girls and boys in the manifestation and prevalence of various psychiatric disorders in youth with girls being diagnosed at higher rates than boys. Accordingly, the impact of gender was examined across all aims. To the best of our knowledge, there is no prior literature to guide a hypothesis about gender differences regarding the association between sleep and depression. Hence, this additional aim was included on an exploratory basis.
Methods Procedure In this population-based study, we used data from the ung@hordaland-survey of adolescents in the county of Hordaland in western Norway. All adolescents born between 1993 and 1995 and all students attending secondary education during spring 2012 were invited. The main aim of the survey was to assess prevalence of mental
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health problems and service use in adolescents. Data were collected during spring 2012. Adolescents in upper secondary education received information via e-mail, and one classroom school hour was allocated for them to complete the questionnaire. Those not in school received information by postal mail to their home addresses. The questionnaire was web-based and covered a broad range of mental health issues, daily life functioning, use of health care and social services, demographics, as well as a request for permission to obtain school data, and to link the information with national health registries and parental reports on a corresponding questionnaire. Uni Health collaborated with Hordaland County Council to conduct the study. The study was approved by The Regional Committee for Medical and Health Research Ethics in Western Norway. After complete description of the study to the subjects, written informed consent was obtained. Sample All adolescents born between 1993 and 1995 were invited (n = 19,430) to participate in the current study during the first months of 2012, of which 10,220 agreed, yielding a participation rate of 53 %. All sleep variables were manually checked for validity with subjects providing obvious invalid responses being omitted for further analyses. Invalid responses included (1) SOL or WASO [ 12 h, (2) SOL ? WASO [ time in bed (TIB), (3) negative values of sleep duration and sleep efficiency. This resulted in 374 subjects being omitted. Thus, the total sample size in the current study was 9,875, of which 5.3 % were defined as immigrants as they had at least one parent born outside Norway. Instruments Depression Depression was assessed using the short version of the Mood and Feelings Questionnaire (SMFQ) [35]. The SMFQ comprises 13 items assessing depressive symptoms rated on a three-point Likert scale. The wordings of the response categories in the Norwegian translation equals the original categories of ‘‘not true’’, ‘‘sometimes true’’ and ‘‘true’’. High internal consistency between the items and a strong unidimensionality have been shown in populationbased studies [31], and was recently confirmed in a study based on the sample included in the present study [23]. For the purposes of the current study, depression was defined as a score above the 90th percentile of the total SMFQ-score. It should be noted that term depression as used in the current study does not imply existence of a clinical diagnosis, such as MDD. Also, being a relatively brief self-
report questionnaire, the SFMQ does not differentiate between different types of depressive disorders/conditions. The Cronbach’s alpha of the SMFQ in the current study was 0.91. Sleep parameters Difficulties initiating and maintaining sleep (DIMS) were rated on a three-point Likert scale with response options ‘‘not true’’, ‘‘somewhat true’’ and ‘‘certainly true’’. Given a positive response (‘‘somewhat true’’ or ‘‘certainly true’’), participants were then asked how many days per week they experienced problems either initiating or maintaining sleep. Duration of DIMS of at least three times per week was rated in weeks (up to 3 weeks), months (up to 12 months) and a last category over a year. A joint question on tiredness/sleepiness was rated on a three-point Likert scale with response options ‘‘not true’’, ‘‘somewhat true’’ and ‘‘certainly true’’. If confirmed (‘‘somewhat true’’ or ‘‘certainly true’’) participants reported the number of days per week they experienced sleepiness and tiredness, respectively. Insomnia was operationalized in accordance with Lichstein et al.’s quantitative criteria for insomnia [20]: self-reported DIMS at least three times a week, with a duration of 6 months or more, in addition to reporting SOL and/or WASO of more than 30 min, as well as tiredness or sleepiness at least 3 days per week. No attempts were made to differentiate between primary or comorbid insomnia. Self-reported bedtime and rise time were indicated in hours and minutes using a scroll down menu with 5 min intervals and were reported separately for weekend and weekdays. Time in bed (TIB) was calculated by subtracting bedtime from rise time. SOL and WASO were indicated in hours and minutes using a scroll down menu with 5 min intervals, and sleep duration was defined as TIB - SOL and WASO. Sleep efficiency was calculated as sleep duration divided by TIB multiplied by 100 (reported as percentage). Subjective sleep need was reported in hours and minutes, and sleep deficiency was calculated separately for weekends and weekdays, subtracting total sleep duration from subjective sleep need. For the purpose of the present study, sleep duration was also split into ten categories (\4, 4–5, 5–6, 6–7, 7–8, 8–9, 9–10, 10–11, 11–12, and [12 h). Data analysis IBM SPSS Statistics 21 for Mac (SPSS Inc., Chicago, IL) was used for all analyses. Independent sample t tests (for means) and v2 tests (for proportions) were used to examine differences in sleep parameters in adolescents with and without depression. v2 tests were also used to explore potential gender differences in the overlap between
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Fig. 1 Overlap between insomnia and depression stratified by gender in the ung@hordaland study (n = 9,846). Error bars represent 95 % confidence intervals
insomnia and depression. 95 % confidence intervals were calculated manually for proportions in Microsoft Excel 2010, and statistics with non-overlapping confidence intervals were interpreted as statistically different. Pearson correlation coefficients were calculated to investigate the associations between sleep parameters (SOL, WASO, sleep duration) and each of the 13 SMFQ items. Logistic regression analyses were used to further explore the association between depression and the sleep parameters. All tests were two-tailed.
Results Sample characteristics In all, 9,846 adolescents provided valid responses on the relevant questionnaire on sleep and depression. The mean age was 17 years, and the sample included more girls (53.5 %/n = 5,252) than boys (46.5 %/n = 4,594). The majority (97.9 %/n = 9,219) were high school students. Prevalence and overlap of depression and insomnia Depression and insomnia were more prevalent in girls than boys. The prevalence of insomnia among girls was 17 % (n = 874), compared to 9.6 % (n = 424) among boys; whereas, a score on SMFQ indicating depression was more than three times as prevalent among girls (13.5 %/ n = 683) than boys (4.0 %/n = 173). There was a significant overlap between insomnia and depression. As depicted in Fig. 1, the prevalence of insomnia in depressed adolescents was 33.5 % (n = 58) and 38.7 % (n = 264) for boys and girls, respectively, compared to 8.8 % (n = 360) and 13.5 % (n = 591) for
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non-depressed adolescents. Similarly, the prevalence of depression among boys and girls with insomnia was 13.9 % (n = 58) and 31 % (n = 264), compared to 3.0 % (n = 115) and 10.0 % (n = 419) among good sleeping boys and girls, respectively. Logistic regression analyses were conducted to further examine the association between insomnia and depression. Meeting the criteria for insomnia was associated with 4- to 5-fold increased odds of reporting depression. As detailed in Table 2, report of combined difficulties initiating and maintaining sleep was a stronger predictor of depression than reporting just either one of these problems. The effect was particularly strong for boys (OR = 9.4) compared to girls (OR = 5.9). However, the duration of insomnia was not significantly related to depression. Depression and other sleep parameters Both sleep duration and time in bed was significantly shorter among adolescents with depression compared to those without depression (Table 1). This pattern was evident both during the weekdays and in the weekends, and for both genders. For example, as detailed in Fig. 2, 32 % (n = 51) of the boys with depression slept \4 h, compared to only 6 % (n = 251) among boys without depression. A similar but weaker effect was found for girls. Adolescents with depression also reported significantly longer SOL, WASO, and had significantly lower sleep efficiency compared to adolescents without depression. For example, 30.5 % (n = 261) of the depressed adolescents reported a SOL of more than 2 h, while the corresponding figure for this was 10.3 % (n = 878) in adolescents without depression. These findings were evident in both girls and boys. We found a dose–response relationship between both SOL and WASO, and depression; the longer SOL and
Eur Child Adolesc Psychiatry Table 1 Depression and sleep parameters among girls and boys in the ung@hordaland study (n = 9,846) Girls
P level
Non-depressed
Depressed
Mean
SD
Mean
SD
23:08
0:54
23:24
1:10
Risetime Time in bed
6:42 7:34
0:38 0:58
6:41 7:18
Sleep duration
6:32
1:34
Bedtime
1:15
Risetime
Boys
P level
Non-depressed
Depressed
Mean
SD
Mean
SD
\0.001
23:26
0:59
23:44
1:25
\0.001
0:51 1:15
0.510 \0.001
6:52 7:26
0:39 1:01
6:55 7:10
1:06 1:18
0.353 0.001
5:22
1:55
\0.001
6:31
1:33
5:02
2:11
\0.001
1:20
1:34
1:31
\0.001
1:51
1:33
2:08
1:42
0.021 0.692
Week days Bedtime
Weekends 11:03
1:23
11:21
1:31
\0.001
11:26
1:37
11:30
1:54
Time in bed
9:48
1:18
9:47
1:31
0.759
9:35
1:24
9:19
1:41
0.020
Sleep duration
8:46
1:44
7:51
2:12
\0.001
8:39
1:48
7:11
2:31
\0.001
Week days/weekends Sleep onset latency
0:47
0:55
1:20
1:07
\0.001
0:43
0:56
1:25
1:11
\0.001
Wake after sleep onset
0:14
0:35
0:35
0:52
\0.001
0:11
0:38
0:40
1:05
\0.001
Sleep efficiency
86.0
16.5
73.0
22.3
\0.001
87.3
16.4
69.3
26.0
\0.001
Sleep deficiency
2:05
2:15
3:52
2:51
\0.001
1:55
2:30
3:25
3:27
\0.001
Subjective sleep need
8:39
1:37
9:12
2:12
\0.001
8:26
2:00
8:31
2:57
0.639
Fig. 2 Sleep duration among non-depressed and depressed girls and boys in the ung@hordaland study (n = 9,846). Error bars represent 95 % confidence intervals, with non-overlapping confidence intervals being statistically significant
WASO, the stronger the association with depression. A dose–response effect was also found for sleep duration; compared to sleeping 7–9 h, sleeping 5–6 h was associated with threefold increased risk of depression, while sleeping \5 h yielded ORs between 6 and 9 (see Table 2 for details). The correlations between each of the SMFQ items and SOL, WASO and sleep duration were all similar in magnitude (ranging from 0.11 to 0.32); we found no specific domain of depressive symptoms that was more strongly associated with sleep problems.
Interaction between insomnia, sleep duration and depression There was a significant interaction between insomnia, sleep duration and depression (P \ 0.001). Adolescents without insomnia but sleeping \6 h had an odds ratio of 3.1 (95 % CI 2.6–3.8) of reporting depression compared with noninsomniacs with a sleep duration of 6–8 h. Adolescents with insomnia sleeping 6 h or more had an OR of 4–5 of reporting depression, whereas adolescents with insomnia sleeping \6 h had more than eightfold increased odds of
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Eur Child Adolesc Psychiatry Table 2 Associations between sleep parameters and depression among girls and boys in the ung@hordaland study (n = 9,846) Girls OR
Boys 95 % CI
OR
95 % CI
Difficulties initiating and maintaining sleep (DIMS) None
Reference
Initiating only (3? nights)
3.69
2.88–4.73
Reference 4.09
2.47–6.75
Maintaining only (3? nights)
4.00
2.87–5.59
2.90
1.14–7.36
Both (3? nights)
5.94
4.85–7.28
9.38
6.36–13.83
\3 3–12
Reference 1.18
0.84–1.65
Reference 2.90
1.39–6.04
[12
1.30
0.97–1.73
1.61
0.83–3.13
Duration of DIMS (months)
Insomnia No insomnia
Reference
Insomnia
4.03
Reference 3.38–4.81
5.25
3.76–7.33
Sleep onset latency (SOL) (min) \15
Reference
15–29
0.99
0.69–1.43
0.42
0.18–0.98
30–59
1.56
1.16–2.12
1.21
0.70–2.11
60–119
2.85
2.13–3.80
3.15
1.93–5.15
120?
5.59
4.15–7.52
6.52
3.96–10.74
Reference
Wake after sleep onset (WASO) (min) \15
Reference
15–29
2.08
1.51–2.87
2.39
1.18–4.84
30–59 60–119
3.33 3.67
2.56–4.34 2.86–4.71
1.23 5.71
0.53–2.84 3.70–8.82
120?
4.65
3.50–6.18
6.82
4.35–10.72
Reference
Sleep duration (h) 7–9
Reference
6–7
1.99
1.56–2.54
1.78
5–6
3.39
2.58–4.44
2.56
1.43–4.57
\5
6.27
4.99–7.89
8.92
5.80–13.70
depression. These interactions were more evident among boys than girls: whereas the odds for depression among girls with both insomnia and short sleep duration was OR = 6.9 (95 % CI 5.5–8.7), the corresponding odds among boys was OR = 10.9 (95 % CI 7.0–16.8).
Discussion The overall objective of this large population-based study was to examine the relation between depression and sleep parameters in adolescence. In short, we found a large overlap between insomnia and depression, evident across the different depression items in the SFMQ-scale. Adolescents with depression exhibited significantly shorter sleep duration, and spent more time both trying to fall asleep and time awake during the night. While girls
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Reference 1.09–2.91
reported more insomnia and depression, the associations between these conditions were somewhat stronger among boys, although significant in both genders. The hypothesis that depression and insomnia would be strongly interrelated was supported by the prevalence of insomnia 3–4 times higher among depressed adolescents compared to their non-depressed peers. The overlap between insomnia and depression is comparable to similar epidemiological studies among adults [32]. The general pattern of overlap between the two disorders was confirmed. Still, the magnitude of overlaps was not large (ranging from 14 to 39 %), demonstrating that insomnia and depression should be regarded as distinct entities in line with the amendments in DSM-V. Depression was clearly related to sleep duration, SOL and WASO. The average sleep duration was 1–1.5 h shorter among adolescents with depression compared to
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their non-depressed peers. The prolonged SOL and WASO contributed to the short sleep duration in line with our predictions, in addition to later bedtimes. These findings are in accordance with some previous clinical studies using PSG [10, 14], while others have failed to demonstrate this relation. Depression or high rates of depressive symptomatology may have an impact on the report style of the adolescents, and thus the subjectively perceived sleep may differ from what is assessed by PSG. However, our findings are strengthened by the demonstrated dose–response relationship in most sleep parameters. At the extreme end, SOL or WASO over 2 h was associated with a sixfold increased risk of also reporting depression, and similarly, sleeping \5 h was associated with a 6- to 9-fold increased risk of depression. This is in line with sleep being related to the severity of the depression in clinical studies [37]. The depressed adolescents in the current study reported getting less sleep than themselves deem necessary, with a sleep deficiency between 3 and 4 h on weekdays. While the sleep duration is much shorter than experts’ recommendations, a small part of this effect in girls seems to be driven by an increased perceived sleep need with an average of over 9 h, which is significantly higher than reported by their nondepressed peers. The adult literature suggests that the impact of insomnia and short sleep duration both contribute independently to depression. The results from the present study indicate that this may also hold true for adolescents. We found a significant interaction between insomnia, sleep duration and depression, with adolescents reporting both insomnia and \6 h of sleep being eight times more likely to report depression, which was significantly more than having either just insomnia or short sleep duration. This finding emphasizes the importance of taking on a broad approach when assessing sleep in adolescents with depression, including both measurements of insomnia and other sleep parameters. In an adult depression treatment trial, short sleep duration and prolonged SOL independently or in conjunction with insomnia predicted non-remission [36]. Investigating if the interaction between insomnia and short sleep duration on depression may also exert the same influence on treatment outcome in adolescent warrants attention. While both insomnia and other sleep parameters increase the risk of depression, it seems that the effect is a general effect, and not related to a specific depressive symptom. This is in line with the unidimensionality of the SFMQ, and the underlying depression construct, rendering the possibility that artifact findings from specific items are less likely. The female preponderance in both insomnia and depression in late adolescence was as expected. However, the relative rate of overlap between insomnia and
depression was not gender specific, and when boys exhibited these problems over the threshold, the rate of cooccurrence was even higher. The mechanisms leading to these gender differences are not yet known. The results could be interpreted in light of the ‘‘gender’’ paradox of comorbidities that suggest that the gender with the lowest prevalence rate of the comorbidity will be more severely affected [22]. A similar pattern was demonstrated in a study of adolescents demonstrating gender as a moderator between depression and psychological correlates and functional impairment, concluding that boys functioning were more impaired than girls [11]. Insomnia is one of the functional impairment requirements of a diagnosis of depression, and thus the study supports that insomnia, short sleep duration, long SOL and frequent WASO are frequently co-occurring functional impairments. As depression and insomnia are frequently reported to co-occur in adolescents, further studies of how this co-occurrence may lead to functional consequences, e.g., for later academic and occupational success, is warranted. There are some methodological limitations of the present study. First, depression was assessed by a self-report instrument, the SMFQ. As no validated cut-off exists for Norwegian adolescents, the 90th percentile on the total SFMQ score was chosen as en operationalization of depression. Clearly, this does not imply existence of a clinical diagnosis, such as MDD, and the lack of clinical interview in confirming a clinical diagnosis of depression is a limitation of the present study. In relation to this, the absence of sleep items, or any other vegetative items in the SMFQ is both a limitation and an asset for the purpose of this study. A conventional depression rating scale, including sleep problems as a symptom, would by definition increase circularity, and make the interpretation of the results more ambiguous. Tiredness was included in the SMFQ, but the association to several sleep parameters was not higher for this item than for other depressive symptoms. Second, while the overlap between depression and insomnia was demonstrated, conclusions regarding causal directionality warrant longitudinal studies with multiple measurements. Third, while the definition of insomnia was based on published quantitative criteria, it was not based on a structured interview, which of course is difficult to employ in a population-based study. Fourth, the sample was relatively ethnically homogeneous. Future research is needed to establish if the reported patterns hold among other ethnic and racial groups. The use of both SOL and WASO to estimate exact sleep duration was a significant strength of the current study, as most population-based studies on sleep rarely provide such accurate measures. It should, however, be mentioned that no data on time awake in bed prior to putting the light out, and lying awake prior
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to rising were collected, and thus TIB - (SOL ? WASO) might also include such periods. This may potentially lead to the sleep efficiency being even lower than reported in the current study. Also, the criteria for daytime functional impairment in the present study were tiredness and sleepiness assessed by a joint variable. Although sleepiness is more commonly used as a symptom of obstructive sleep apnea, we have included both tiredness and sleepiness in the operationalization of insomnia due to a large overlap of these terms in the Norwegian language and due to limited ability in lay-persons to discriminate between the two constructs. Also, we did not assess the possible overlap between insomnia and delayed sleep phase. A delayed sleep phase along with a slower buildup of sleep pressure [17] often occurs in puberty as a consequence of a biological delay in the circadian rhythm [7]. Therefore, as previous studies have linked circadian phase with affective disorders, including depression [29], it is possible that a biologically driven phase delay might partly explain some of the associations found in the current study. Finally, it should be noted that all data in the present study were based on self-reports, which renders the results susceptible to influence from the common method bias [26]. The attrition from the study could affect generalizability, with a response rate of about 53 % and with adolescents in schools overrepresented. Based on previous research from the former waves of the Bergen Child Study, non-participants often have more psychological problems than participants [34]. Insomnia and depression are both highly prevalent and associated with considerable functional impairment. Both conditions warrant clinical attention, and should not merely be considered a secondary outcome or byproduct of the other. As such, treating both conditions concurrently seems warranted. Evidence-based treatment is available for depression and insomnia in youth, but how to treat these conditions when they co-occur is an important topic for future research. Given the apparent reciprocal relationship between insomnia and depression, interwoven approaches in which each session makes progress on both the depression and the sleep problems seem advantageous [8]. Conflict of interest
None.
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4. Bertocci MA, Dahl RE, Williamson DE, Iosif AM, Birmaher B, Axelson D, Ryan ND (2005) Subjective sleep complaints in pediatric depression: a controlled study and comparison with EEG measures of sleep and waking. J Am Acad Child Adolesc Psychiatry 44:1158–1166 5. Buysse DJ (2005) Insomnia state of the science: an evolutionary, evidence-based assessment. Sleep 28:1045–1046 6. Carney CE, Segal ZV, Edinger JD, Krystal AD (2007) A comparison of rates of residual insomnia symptoms following pharmacotherapy or cognitive-behavioral therapy for major depressive disorder. J Clin Psychiatry 68:254–260 7. Carskadon M, Vieria C, Acebo C (1993) Association between puberty and delayed phase preference. Sleep 16:258–262 8. Clarke G, Harvey A (2012) The complex role of sleep in adolescent depression. Child Adolesc Psychiatr Clin N Am 21:385–400 9. Dahl RE (2004) Adolescent brain development: a period of vulnerabilities and opportunities. Keynote address. Ann N Y Acad Sci 1021:1–22 10. Dahl RE, Ryan ND, Matty MK, Birmaher B, al-Shabbout M, Williamson DE, Kupfer DJ (1996) Sleep onset abnormalities in depressed adolescents. Biol Psychiatry 39:400–410 11. Derdikman-Eiron R, Indredavik MS, Bakken IJ, Bratberg GH, Hjemdal O, Colton M (2012) Gender differences in psychosocial functioning of adolescents with symptoms of anxiety and depression: longitudinal findings from the Nord-Trondelag Health Study. Soc Psychiatry Psychiatr Epidemiol 47:1855–1863 12. Feinberg I, Campbell IG (2013) Longitudinal sleep EEG trajectories indicate complex patterns of adolescent brain maturation. Am J Physiol Regul Integr Comp Physiol 304:R296–R303 13. Forbes EE, Bertocci MA, Gregory AM, Ryan ND, Axelson DA, Birmaher B, Dahl RE (2008) Objective sleep in pediatric anxiety disorders and major depressive disorder. J Am Acad Child Adolesc Psychiatry 47:148–155 14. Goetz RR, Puig-Antich J, Ryan N, Rabinovich H, Ambrosini PJ, Nelson B, Krawiec V (1987) Electroencephalographic sleep of adolescents with major depression and normal controls. Arch Gen Psychiatry 44:61–68 15. Hudziak JJ, Achenbach TM, Althoff RR, Pine DS (2007) A dimensional approach to developmental psychopathology. Int J Methods Psychiatr Res 16:S16–S23 16. Hysing M, Pallesen S, Stormark KM, Lundervold AJ, Sivertsen B (2013) Sleep patterns and insomnia among adolescents: a population-based study. J Sleep Res 22:549–556 17. Jenni OG, Achermann P, Carskadon MA (2005) Homeostatic sleep regulation in adolescents. Sleep 28:1446–1454 18. Kelley A, Schochet T, Landry C (2004) Risk taking and novelty seeking in adolescence. In: Dahl R, Spear L (eds) Adolescent brain development. Vulnerabilities and opportunities New York Academy of Sciences, New York, pp 27–32 19. Kopasz M, Loessl B, Hornyak M, Riemann D, Nissen C, Piosczyk H, Voderholzer U (2010) Sleep and memory in healthy children and adolescents—a critical review. Sleep Med Rev 14:167–177 20. Lichstein KL, Durrence HH, Taylor DJ, Bush AJ, Riedel BW (2003) Quantitative criteria for insomnia. Behav Res Ther 41:427–445 21. Liu X, Buysse DJ, Gentzler AL, Kiss E, Mayer L, Kapornai K, Vetro A, Kovacs M (2007) Insomnia and hypersomnia associated with depressive phenomenology and comorbidity in childhood depression. Sleep 30:83–90 22. Loeber R, Keenan K (1994) Interaction between conduct disorder and its comorbid—effects of age and gender. Clin Psychol Rev 14:497–523 23. Lundervold AJ, Posserud M, Stormark K, Breivik B, Hysing M (2013) Symptoms of depression as reported by Norwegian adolescents on the Short Mood and Feelings Questionnaire. Front Psychol 4:613
Eur Child Adolesc Psychiatry 24. National Institutes of H (2005) National Institutes of Health State of the Science Conference statement on manifestations and management of chronic insomnia in adults, June 13–15, 2005. Sleep 28:1049–1057 25. Pallesen S, Hetland J, Sivertsen B, Samdal O, Torsheim T, Nordhus IH (2008) Time trends in sleep-onset difficulties among Norwegian adolescents: 1983–2005. Scand J Public Health 36:889–895 26. Podsakoff PM, MacKenzie SB, Lee JY, Podsakoff NP (2003) Common method biases in behavioral research: a critical review of the literature and recommended remedies. J Appl Psychol 88:879–903 27. Roberts RE, Lewinsohn PM, Seeley JR (1995) Symptoms of DSM-III-R major depression in adolescence: evidence from an epidemiological survey. J Am Acad Child Adolesc Psychiatry 34:1608–1617 28. Roberts RE, Roberts CR, Chen IG (2002) Impact of insomnia on future functioning of adolescents. J Psychosom Res 53:561–569 29. Saxvig IW, Pallesen S, Wilhelmsen-Langeland A, Molde H, Bjorvatn B (2012) Prevalence and correlates of delayed sleep phase in high school students. Sleep Med 13:193–199 30. Shapiro CM, Flanigan MJ (1993) ABC of sleep disorders. Function of sleep. BMJ 306:383–385 31. Sharp C, Goodyer IM, Croudace TJ (2006) The Short Mood and Feelings Questionnaire (SMFQ): a unidimensional item response theory and categorical data factor analysis of self-report ratings from a community sample of 7-through 11-year-old children. J Abnorm Child Psychol 34:379–391 32. Sivertsen B, Salo P, Mykletun A, Hysing M, Pallesen S, Krokstad S, Nordhus IH, Overland S (2012) The bidirectional association between depression and insomnia: the HUNT study. Psychosom Med 74:758–765
33. Steinberg L (2004) Risk taking in adolescence. What changes, and why? In: Dahl R, Spear L (eds) Adolescent brain development. Vulnerabilities and opportunities. New York Academy of Sciences, New York, pp 51–58 34. Stormark KM, Heiervang E, Heimann M, Lundervold A, Gillberg C (2008) Predicting nonresponse bias from teacher ratings of mental health problems in primary school children. J Abnorm Child Psychol 36:411–419 35. Thapar A, McGuffin P (1998) Validity of the shortened Mood and Feelings Questionnaire in a community sample of children and adolescents: a preliminary research note. Psychiatry Res 81:259–268 36. Troxel WM, Kupfer DJ, Reynolds CF 3rd, Frank E, Thase ME, Miewald JM, Buysse DJ (2012) Insomnia and objectively measured sleep disturbances predict treatment outcome in depressed patients treated with psychotherapy or psychotherapy-pharmacotherapy combinations. J Clin Psychiatry 73:478–485 37. Urrila AS, Karlsson L, Kiviruusu O, Pelkonen M, Strandholm T, Marttunen M (2012) Sleep complaints among adolescent outpatients with major depressive disorder. Sleep Med 13:816–823 38. Vgontzas AN, Liao D, Pejovic S, Calhoun S, Karataraki M, Basta M, Fernandez-Mendoza J, Bixler EO (2010) Insomnia with short sleep duration and mortality: the Penn State cohort. Sleep 33:1159–1164 39. World Health Organization (1993) The ICD-10 classification of mental and behavioural disorders: diagnostic criteria for research. World Health Organization, Geneva 40. Yoo SS, Gujar N, Hu P, Jolesz FA, Walker MP (2007) The human emotional brain without sleep—a prefrontal amygdala disconnect. Curr Biol 17:R877–R878
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ORIGINAL CONTRIBUTION
Sleep problems and depression in adolescence: results from a large population-based study of Norwegian adolescents aged 16–18 years Børge Sivertsen • Allison G. Harvey Astri J. Lundervold • Mari Hysing
•
Received: 24 July 2013 / Accepted: 19 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Both sleep problems and depression are common problems in adolescence, but well-defined large epidemiological studies on the relationship are missing in this age group. The aim of this study was to examine the association between depression and several sleep parameters, including insomnia, in a population-based study of adolescents aged 16–18 years, and to explore potential gender differences. A large population-based study in Hordaland County in Norway conducted in 2012, the ung@hordaland study, surveyed 10,220 adolescents aged 16–18 years (54 % girls) about sleep and depression. The sleep assessment included measures of the basic sleep
B. Sivertsen (&) Division of Mental Health, Norwegian Institute of Public Health, Bergen, Norway e-mail: [email protected] B. Sivertsen Uni Health, Uni Research, Bergen, Norway B. Sivertsen Department of Psychiatry, Helse Fonna HF, Haugesund, Norway A. G. Harvey Department of Psychology, University of California, Berkeley, USA A. J. Lundervold M. Hysing Regional Centre for Child and Youth Mental Health and Child Welfare, Uni Health, Uni Research, Bergen, Norway A. J. Lundervold Department of Biological and Medical Psychology, University of Bergen, Bergen, Norway A. J. Lundervold K.G. Jebsen Centre for Research on Neuropsychiatric Disorders, University of Bergen, Bergen, Norway
parameters for weekdays and weekends. Depression was defined as scoring above the 90th percentile on the total score of Short Moods and Feelings Questionnaire (SMFQ). There was a large overlap between insomnia and depression in both genders and across depressive symptoms. Depressed adolescents exhibited significantly shorter sleep duration and time in bed as well as significantly longer sleep onset latency (SOL) and wake after sleep onset (WASO). Adolescents with insomnia had a 4- to 5-fold increased odds of depression compared to good sleepers. There was also a significant interaction between insomnia, sleep duration and depression, with a more than eightfold increase in odds of depression for those who met criteria for insomnia and who slept \6 h. These associations held for both genders, but were stronger in boys. To the best of our knowledge, this is the first population-based study to investigate sleep and insomnia in relation to depression among adolescents. The findings call for increased awareness of sleep problems and depression as a major public health issue. Keywords Insomnia Sleep Depression Epidemiology
Introduction Sleep problems have historically been regarded as an epiphenomenon of depression, with sleep problems being included as a core symptom of depression in both major diagnostic classification systems [2, 39]. There has been a paradigm shift driven by the mounting data pointing to a reciprocal relationship between insomnia and depression in both adolescence and adults [5, 24, 28, 32] and strengthened by intervention studies documenting sleep as a
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residual symptom after treatment of depression [6].This change in our understanding of the association between sleep and depression is also reflected in the new diagnostic criteria. Whereas the DSM-IV had separate diagnoses for insomnia with and without a co-existing mental disorder, this distinction is not included in the new DSM-V diagnostic criteria; the mood disturbances are listed as one of the functional impairment criteria for insomnia disorder, and insomnia symptoms are still mentioned in the criteria for depression. Whereas most investigations of the link between sleep problems and depression have been conducted in adult samples, sleep problems are among the most frequent symptoms of depression in adolescents. In a large community sample of adolescents with major depressive disorder, nine out of ten reported co-occurring sleep disturbances [27], and a high rate of insomnia in depressed adolescents has also been reported [21]. Similarly, a Finnish study of adolescents with major depressive disorder (MDD) found that sleep disturbances were both frequent and significantly related to the severity of the depression, with insomnia being the most frequent sleep disturbance [37]. Clinical studies of sleep measured by polysomnography (PSG) have demonstrated both prolonged sleep onset latency (SOL) and wake after sleep onset (WASO) in depressed compared to healthy adolescents [10, 14]. In an overview of the literature on the relation between sleep and depression, half of the studies on children and adolescents demonstrated that depression had an effect on sleep continuity based on PSG, while sleep onset problems and early morning awakenings were seldom found [3]. However, more recent studies have not confirmed this association between depression and disturbed sleep using PSG [4, 13]. Further, most studies on sleep in depression are small, clinical studies with welldefined samples and strong methodology. It is thus not certain if these results can be generalized to adolescents with depression in the general population. However, using an epidemiological approach, where brief instruments assessing self-rated mood commonly are the only and best assessment method, may not capture the diversity and severity of depressive disorders [1]. Most epidemiological studies also tend to include limited sleep assessments and few studies have used stringent definitions based on diagnostic criteria. Crude measures of time in bed are typically included, leaving actual sleep duration and other sleep parameters most relevant to insomnia, such as SOL and WASO, unexplored. The high rate of long SOL and decreasing sleep duration in adolescence over the last decade [16, 25] underscore the importance of understanding such parameters in relation to depression in adolescence. Insomnia is also highly prevalent in the general population, and while varying across
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definitions [16], few epidemiological studies have gone beyond a more general assessment of sleep problems in relation to depression. The high rate of both depression [23] and insomnia [16] during adolescence, with similar developmental patterns such as an increase during puberty and a female preponderance, suggest that co-occurrence may be likely. Together, these data chime well with the emerging evidence that a key function of sleep is emotion regulation [40]. Indeed, sleep problems or sleep loss may be especially detrimental during adolescence due to the vulnerable period of brain development [9], affecting both body restoration [30], learning and memory [19], decisionmaking [18, 33] and brain maturation [12]. Based on the above considerations, the main objective of the current study was to examine the relationship between depression and a range of sleep parameters using data from a large population-based study. The first aim was to establish the extent of the overlap between depression and insomnia. The hypothesis tested was that insomnia and depression would be strongly interrelated. The second aim was to investigate the relationship between depression and other specific sleep parameters. Based on the research reviewed, we hypothesized that depressed teens would report prolonged SOL and WASO. The third aim was to investigate the relationship between specific symptoms of depression and sleep parameters. The fourth aim was to investigate the independent contribution of insomnia and short sleep duration on depression. This has been a topic of considerable interest in the adult literature [38], but has yet to be explored among adolescence. Hence, this aim was included on an exploratory basis. Finally, Hudziak et al. [15] highlight the importance of studying gender differences in adolescence, given the difference between girls and boys in the manifestation and prevalence of various psychiatric disorders in youth with girls being diagnosed at higher rates than boys. Accordingly, the impact of gender was examined across all aims. To the best of our knowledge, there is no prior literature to guide a hypothesis about gender differences regarding the association between sleep and depression. Hence, this additional aim was included on an exploratory basis.
Methods Procedure In this population-based study, we used data from the ung@hordaland-survey of adolescents in the county of Hordaland in western Norway. All adolescents born between 1993 and 1995 and all students attending secondary education during spring 2012 were invited. The main aim of the survey was to assess prevalence of mental
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health problems and service use in adolescents. Data were collected during spring 2012. Adolescents in upper secondary education received information via e-mail, and one classroom school hour was allocated for them to complete the questionnaire. Those not in school received information by postal mail to their home addresses. The questionnaire was web-based and covered a broad range of mental health issues, daily life functioning, use of health care and social services, demographics, as well as a request for permission to obtain school data, and to link the information with national health registries and parental reports on a corresponding questionnaire. Uni Health collaborated with Hordaland County Council to conduct the study. The study was approved by The Regional Committee for Medical and Health Research Ethics in Western Norway. After complete description of the study to the subjects, written informed consent was obtained. Sample All adolescents born between 1993 and 1995 were invited (n = 19,430) to participate in the current study during the first months of 2012, of which 10,220 agreed, yielding a participation rate of 53 %. All sleep variables were manually checked for validity with subjects providing obvious invalid responses being omitted for further analyses. Invalid responses included (1) SOL or WASO [ 12 h, (2) SOL ? WASO [ time in bed (TIB), (3) negative values of sleep duration and sleep efficiency. This resulted in 374 subjects being omitted. Thus, the total sample size in the current study was 9,875, of which 5.3 % were defined as immigrants as they had at least one parent born outside Norway. Instruments Depression Depression was assessed using the short version of the Mood and Feelings Questionnaire (SMFQ) [35]. The SMFQ comprises 13 items assessing depressive symptoms rated on a three-point Likert scale. The wordings of the response categories in the Norwegian translation equals the original categories of ‘‘not true’’, ‘‘sometimes true’’ and ‘‘true’’. High internal consistency between the items and a strong unidimensionality have been shown in populationbased studies [31], and was recently confirmed in a study based on the sample included in the present study [23]. For the purposes of the current study, depression was defined as a score above the 90th percentile of the total SMFQ-score. It should be noted that term depression as used in the current study does not imply existence of a clinical diagnosis, such as MDD. Also, being a relatively brief self-
report questionnaire, the SFMQ does not differentiate between different types of depressive disorders/conditions. The Cronbach’s alpha of the SMFQ in the current study was 0.91. Sleep parameters Difficulties initiating and maintaining sleep (DIMS) were rated on a three-point Likert scale with response options ‘‘not true’’, ‘‘somewhat true’’ and ‘‘certainly true’’. Given a positive response (‘‘somewhat true’’ or ‘‘certainly true’’), participants were then asked how many days per week they experienced problems either initiating or maintaining sleep. Duration of DIMS of at least three times per week was rated in weeks (up to 3 weeks), months (up to 12 months) and a last category over a year. A joint question on tiredness/sleepiness was rated on a three-point Likert scale with response options ‘‘not true’’, ‘‘somewhat true’’ and ‘‘certainly true’’. If confirmed (‘‘somewhat true’’ or ‘‘certainly true’’) participants reported the number of days per week they experienced sleepiness and tiredness, respectively. Insomnia was operationalized in accordance with Lichstein et al.’s quantitative criteria for insomnia [20]: self-reported DIMS at least three times a week, with a duration of 6 months or more, in addition to reporting SOL and/or WASO of more than 30 min, as well as tiredness or sleepiness at least 3 days per week. No attempts were made to differentiate between primary or comorbid insomnia. Self-reported bedtime and rise time were indicated in hours and minutes using a scroll down menu with 5 min intervals and were reported separately for weekend and weekdays. Time in bed (TIB) was calculated by subtracting bedtime from rise time. SOL and WASO were indicated in hours and minutes using a scroll down menu with 5 min intervals, and sleep duration was defined as TIB - SOL and WASO. Sleep efficiency was calculated as sleep duration divided by TIB multiplied by 100 (reported as percentage). Subjective sleep need was reported in hours and minutes, and sleep deficiency was calculated separately for weekends and weekdays, subtracting total sleep duration from subjective sleep need. For the purpose of the present study, sleep duration was also split into ten categories (\4, 4–5, 5–6, 6–7, 7–8, 8–9, 9–10, 10–11, 11–12, and [12 h). Data analysis IBM SPSS Statistics 21 for Mac (SPSS Inc., Chicago, IL) was used for all analyses. Independent sample t tests (for means) and v2 tests (for proportions) were used to examine differences in sleep parameters in adolescents with and without depression. v2 tests were also used to explore potential gender differences in the overlap between
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Fig. 1 Overlap between insomnia and depression stratified by gender in the ung@hordaland study (n = 9,846). Error bars represent 95 % confidence intervals
insomnia and depression. 95 % confidence intervals were calculated manually for proportions in Microsoft Excel 2010, and statistics with non-overlapping confidence intervals were interpreted as statistically different. Pearson correlation coefficients were calculated to investigate the associations between sleep parameters (SOL, WASO, sleep duration) and each of the 13 SMFQ items. Logistic regression analyses were used to further explore the association between depression and the sleep parameters. All tests were two-tailed.
Results Sample characteristics In all, 9,846 adolescents provided valid responses on the relevant questionnaire on sleep and depression. The mean age was 17 years, and the sample included more girls (53.5 %/n = 5,252) than boys (46.5 %/n = 4,594). The majority (97.9 %/n = 9,219) were high school students. Prevalence and overlap of depression and insomnia Depression and insomnia were more prevalent in girls than boys. The prevalence of insomnia among girls was 17 % (n = 874), compared to 9.6 % (n = 424) among boys; whereas, a score on SMFQ indicating depression was more than three times as prevalent among girls (13.5 %/ n = 683) than boys (4.0 %/n = 173). There was a significant overlap between insomnia and depression. As depicted in Fig. 1, the prevalence of insomnia in depressed adolescents was 33.5 % (n = 58) and 38.7 % (n = 264) for boys and girls, respectively, compared to 8.8 % (n = 360) and 13.5 % (n = 591) for
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non-depressed adolescents. Similarly, the prevalence of depression among boys and girls with insomnia was 13.9 % (n = 58) and 31 % (n = 264), compared to 3.0 % (n = 115) and 10.0 % (n = 419) among good sleeping boys and girls, respectively. Logistic regression analyses were conducted to further examine the association between insomnia and depression. Meeting the criteria for insomnia was associated with 4- to 5-fold increased odds of reporting depression. As detailed in Table 2, report of combined difficulties initiating and maintaining sleep was a stronger predictor of depression than reporting just either one of these problems. The effect was particularly strong for boys (OR = 9.4) compared to girls (OR = 5.9). However, the duration of insomnia was not significantly related to depression. Depression and other sleep parameters Both sleep duration and time in bed was significantly shorter among adolescents with depression compared to those without depression (Table 1). This pattern was evident both during the weekdays and in the weekends, and for both genders. For example, as detailed in Fig. 2, 32 % (n = 51) of the boys with depression slept \4 h, compared to only 6 % (n = 251) among boys without depression. A similar but weaker effect was found for girls. Adolescents with depression also reported significantly longer SOL, WASO, and had significantly lower sleep efficiency compared to adolescents without depression. For example, 30.5 % (n = 261) of the depressed adolescents reported a SOL of more than 2 h, while the corresponding figure for this was 10.3 % (n = 878) in adolescents without depression. These findings were evident in both girls and boys. We found a dose–response relationship between both SOL and WASO, and depression; the longer SOL and
Eur Child Adolesc Psychiatry Table 1 Depression and sleep parameters among girls and boys in the ung@hordaland study (n = 9,846) Girls
P level
Non-depressed
Depressed
Mean
SD
Mean
SD
23:08
0:54
23:24
1:10
Risetime Time in bed
6:42 7:34
0:38 0:58
6:41 7:18
Sleep duration
6:32
1:34
Bedtime
1:15
Risetime
Boys
P level
Non-depressed
Depressed
Mean
SD
Mean
SD
\0.001
23:26
0:59
23:44
1:25
\0.001
0:51 1:15
0.510 \0.001
6:52 7:26
0:39 1:01
6:55 7:10
1:06 1:18
0.353 0.001
5:22
1:55
\0.001
6:31
1:33
5:02
2:11
\0.001
1:20
1:34
1:31
\0.001
1:51
1:33
2:08
1:42
0.021 0.692
Week days Bedtime
Weekends 11:03
1:23
11:21
1:31
\0.001
11:26
1:37
11:30
1:54
Time in bed
9:48
1:18
9:47
1:31
0.759
9:35
1:24
9:19
1:41
0.020
Sleep duration
8:46
1:44
7:51
2:12
\0.001
8:39
1:48
7:11
2:31
\0.001
Week days/weekends Sleep onset latency
0:47
0:55
1:20
1:07
\0.001
0:43
0:56
1:25
1:11
\0.001
Wake after sleep onset
0:14
0:35
0:35
0:52
\0.001
0:11
0:38
0:40
1:05
\0.001
Sleep efficiency
86.0
16.5
73.0
22.3
\0.001
87.3
16.4
69.3
26.0
\0.001
Sleep deficiency
2:05
2:15
3:52
2:51
\0.001
1:55
2:30
3:25
3:27
\0.001
Subjective sleep need
8:39
1:37
9:12
2:12
\0.001
8:26
2:00
8:31
2:57
0.639
Fig. 2 Sleep duration among non-depressed and depressed girls and boys in the ung@hordaland study (n = 9,846). Error bars represent 95 % confidence intervals, with non-overlapping confidence intervals being statistically significant
WASO, the stronger the association with depression. A dose–response effect was also found for sleep duration; compared to sleeping 7–9 h, sleeping 5–6 h was associated with threefold increased risk of depression, while sleeping \5 h yielded ORs between 6 and 9 (see Table 2 for details). The correlations between each of the SMFQ items and SOL, WASO and sleep duration were all similar in magnitude (ranging from 0.11 to 0.32); we found no specific domain of depressive symptoms that was more strongly associated with sleep problems.
Interaction between insomnia, sleep duration and depression There was a significant interaction between insomnia, sleep duration and depression (P \ 0.001). Adolescents without insomnia but sleeping \6 h had an odds ratio of 3.1 (95 % CI 2.6–3.8) of reporting depression compared with noninsomniacs with a sleep duration of 6–8 h. Adolescents with insomnia sleeping 6 h or more had an OR of 4–5 of reporting depression, whereas adolescents with insomnia sleeping \6 h had more than eightfold increased odds of
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Eur Child Adolesc Psychiatry Table 2 Associations between sleep parameters and depression among girls and boys in the ung@hordaland study (n = 9,846) Girls OR
Boys 95 % CI
OR
95 % CI
Difficulties initiating and maintaining sleep (DIMS) None
Reference
Initiating only (3? nights)
3.69
2.88–4.73
Reference 4.09
2.47–6.75
Maintaining only (3? nights)
4.00
2.87–5.59
2.90
1.14–7.36
Both (3? nights)
5.94
4.85–7.28
9.38
6.36–13.83
\3 3–12
Reference 1.18
0.84–1.65
Reference 2.90
1.39–6.04
[12
1.30
0.97–1.73
1.61
0.83–3.13
Duration of DIMS (months)
Insomnia No insomnia
Reference
Insomnia
4.03
Reference 3.38–4.81
5.25
3.76–7.33
Sleep onset latency (SOL) (min) \15
Reference
15–29
0.99
0.69–1.43
0.42
0.18–0.98
30–59
1.56
1.16–2.12
1.21
0.70–2.11
60–119
2.85
2.13–3.80
3.15
1.93–5.15
120?
5.59
4.15–7.52
6.52
3.96–10.74
Reference
Wake after sleep onset (WASO) (min) \15
Reference
15–29
2.08
1.51–2.87
2.39
1.18–4.84
30–59 60–119
3.33 3.67
2.56–4.34 2.86–4.71
1.23 5.71
0.53–2.84 3.70–8.82
120?
4.65
3.50–6.18
6.82
4.35–10.72
Reference
Sleep duration (h) 7–9
Reference
6–7
1.99
1.56–2.54
1.78
5–6
3.39
2.58–4.44
2.56
1.43–4.57
\5
6.27
4.99–7.89
8.92
5.80–13.70
depression. These interactions were more evident among boys than girls: whereas the odds for depression among girls with both insomnia and short sleep duration was OR = 6.9 (95 % CI 5.5–8.7), the corresponding odds among boys was OR = 10.9 (95 % CI 7.0–16.8).
Discussion The overall objective of this large population-based study was to examine the relation between depression and sleep parameters in adolescence. In short, we found a large overlap between insomnia and depression, evident across the different depression items in the SFMQ-scale. Adolescents with depression exhibited significantly shorter sleep duration, and spent more time both trying to fall asleep and time awake during the night. While girls
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Reference 1.09–2.91
reported more insomnia and depression, the associations between these conditions were somewhat stronger among boys, although significant in both genders. The hypothesis that depression and insomnia would be strongly interrelated was supported by the prevalence of insomnia 3–4 times higher among depressed adolescents compared to their non-depressed peers. The overlap between insomnia and depression is comparable to similar epidemiological studies among adults [32]. The general pattern of overlap between the two disorders was confirmed. Still, the magnitude of overlaps was not large (ranging from 14 to 39 %), demonstrating that insomnia and depression should be regarded as distinct entities in line with the amendments in DSM-V. Depression was clearly related to sleep duration, SOL and WASO. The average sleep duration was 1–1.5 h shorter among adolescents with depression compared to
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their non-depressed peers. The prolonged SOL and WASO contributed to the short sleep duration in line with our predictions, in addition to later bedtimes. These findings are in accordance with some previous clinical studies using PSG [10, 14], while others have failed to demonstrate this relation. Depression or high rates of depressive symptomatology may have an impact on the report style of the adolescents, and thus the subjectively perceived sleep may differ from what is assessed by PSG. However, our findings are strengthened by the demonstrated dose–response relationship in most sleep parameters. At the extreme end, SOL or WASO over 2 h was associated with a sixfold increased risk of also reporting depression, and similarly, sleeping \5 h was associated with a 6- to 9-fold increased risk of depression. This is in line with sleep being related to the severity of the depression in clinical studies [37]. The depressed adolescents in the current study reported getting less sleep than themselves deem necessary, with a sleep deficiency between 3 and 4 h on weekdays. While the sleep duration is much shorter than experts’ recommendations, a small part of this effect in girls seems to be driven by an increased perceived sleep need with an average of over 9 h, which is significantly higher than reported by their nondepressed peers. The adult literature suggests that the impact of insomnia and short sleep duration both contribute independently to depression. The results from the present study indicate that this may also hold true for adolescents. We found a significant interaction between insomnia, sleep duration and depression, with adolescents reporting both insomnia and \6 h of sleep being eight times more likely to report depression, which was significantly more than having either just insomnia or short sleep duration. This finding emphasizes the importance of taking on a broad approach when assessing sleep in adolescents with depression, including both measurements of insomnia and other sleep parameters. In an adult depression treatment trial, short sleep duration and prolonged SOL independently or in conjunction with insomnia predicted non-remission [36]. Investigating if the interaction between insomnia and short sleep duration on depression may also exert the same influence on treatment outcome in adolescent warrants attention. While both insomnia and other sleep parameters increase the risk of depression, it seems that the effect is a general effect, and not related to a specific depressive symptom. This is in line with the unidimensionality of the SFMQ, and the underlying depression construct, rendering the possibility that artifact findings from specific items are less likely. The female preponderance in both insomnia and depression in late adolescence was as expected. However, the relative rate of overlap between insomnia and
depression was not gender specific, and when boys exhibited these problems over the threshold, the rate of cooccurrence was even higher. The mechanisms leading to these gender differences are not yet known. The results could be interpreted in light of the ‘‘gender’’ paradox of comorbidities that suggest that the gender with the lowest prevalence rate of the comorbidity will be more severely affected [22]. A similar pattern was demonstrated in a study of adolescents demonstrating gender as a moderator between depression and psychological correlates and functional impairment, concluding that boys functioning were more impaired than girls [11]. Insomnia is one of the functional impairment requirements of a diagnosis of depression, and thus the study supports that insomnia, short sleep duration, long SOL and frequent WASO are frequently co-occurring functional impairments. As depression and insomnia are frequently reported to co-occur in adolescents, further studies of how this co-occurrence may lead to functional consequences, e.g., for later academic and occupational success, is warranted. There are some methodological limitations of the present study. First, depression was assessed by a self-report instrument, the SMFQ. As no validated cut-off exists for Norwegian adolescents, the 90th percentile on the total SFMQ score was chosen as en operationalization of depression. Clearly, this does not imply existence of a clinical diagnosis, such as MDD, and the lack of clinical interview in confirming a clinical diagnosis of depression is a limitation of the present study. In relation to this, the absence of sleep items, or any other vegetative items in the SMFQ is both a limitation and an asset for the purpose of this study. A conventional depression rating scale, including sleep problems as a symptom, would by definition increase circularity, and make the interpretation of the results more ambiguous. Tiredness was included in the SMFQ, but the association to several sleep parameters was not higher for this item than for other depressive symptoms. Second, while the overlap between depression and insomnia was demonstrated, conclusions regarding causal directionality warrant longitudinal studies with multiple measurements. Third, while the definition of insomnia was based on published quantitative criteria, it was not based on a structured interview, which of course is difficult to employ in a population-based study. Fourth, the sample was relatively ethnically homogeneous. Future research is needed to establish if the reported patterns hold among other ethnic and racial groups. The use of both SOL and WASO to estimate exact sleep duration was a significant strength of the current study, as most population-based studies on sleep rarely provide such accurate measures. It should, however, be mentioned that no data on time awake in bed prior to putting the light out, and lying awake prior
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to rising were collected, and thus TIB - (SOL ? WASO) might also include such periods. This may potentially lead to the sleep efficiency being even lower than reported in the current study. Also, the criteria for daytime functional impairment in the present study were tiredness and sleepiness assessed by a joint variable. Although sleepiness is more commonly used as a symptom of obstructive sleep apnea, we have included both tiredness and sleepiness in the operationalization of insomnia due to a large overlap of these terms in the Norwegian language and due to limited ability in lay-persons to discriminate between the two constructs. Also, we did not assess the possible overlap between insomnia and delayed sleep phase. A delayed sleep phase along with a slower buildup of sleep pressure [17] often occurs in puberty as a consequence of a biological delay in the circadian rhythm [7]. Therefore, as previous studies have linked circadian phase with affective disorders, including depression [29], it is possible that a biologically driven phase delay might partly explain some of the associations found in the current study. Finally, it should be noted that all data in the present study were based on self-reports, which renders the results susceptible to influence from the common method bias [26]. The attrition from the study could affect generalizability, with a response rate of about 53 % and with adolescents in schools overrepresented. Based on previous research from the former waves of the Bergen Child Study, non-participants often have more psychological problems than participants [34]. Insomnia and depression are both highly prevalent and associated with considerable functional impairment. Both conditions warrant clinical attention, and should not merely be considered a secondary outcome or byproduct of the other. As such, treating both conditions concurrently seems warranted. Evidence-based treatment is available for depression and insomnia in youth, but how to treat these conditions when they co-occur is an important topic for future research. Given the apparent reciprocal relationship between insomnia and depression, interwoven approaches in which each session makes progress on both the depression and the sleep problems seem advantageous [8]. Conflict of interest
None.
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