Elsevier

Sleep Medicine

Volume 13, Issue 2, February 2012, Pages 193-199
Sleep Medicine

Original Article
Prevalence and correlates of delayed sleep phase in high school students

https://doi.org/10.1016/j.sleep.2011.10.024Get rights and content

Abstract

Purpose

To investigate prevalence and correlates of delayed sleep phase, characterized by problems falling asleep in the evening and rising at adequate times in the morning, in a large sample of Norwegian high school students.

Methods

A randomized sample of 1285 high school students (aged 16–19 years) participated in an internet based study answering questions about sleep habits, height, weight, smoking, alcohol use, school grades, and anxiety and depression symptoms. Delayed sleep phase was operationalized as difficulties falling asleep before 2 a.m. at least three nights per week together with much or very much difficulty waking up in the morning.

Results

The results show a prevalence of delayed sleep phase of 8.4%. In all, 68% of these students (5.7% of the total sample) also reported problems advancing their sleep period as well as one daytime consequence (oversleeping at least two days a week or experiencing much/very much sleepiness at school). Delayed sleep phase was associated with lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.

Conclusions

Delayed sleep phase appears to be common amongst Norwegian adolescents and is associated with negative outcomes such as lower average school grades, smoking, alcohol usage, and elevated anxiety and depression scores.

Introduction

During adolescence a delay in the sleep/wake cycle normally occurs [1]. Researchers have consistently reported delayed bed times, delayed weekend wake-up times, increased daytime sleepiness, and increased evening preference during the course of the pubertal transition [2], [3], [4]. Psychosocial factors are believed to contribute to this phase delay, such as increased norm pressure from peers to stay up late and a co-occurring reduction of parental influence on their children’s sleep pattern. However, since adolescent sleep phase delay is present both across cultures and across mammalian species, and since it seems to be related to pubertal stage rather than age, it is clear that biological mechanisms are heavily involved [3], [5]. According to the two-process model of sleep regulation [6], sleep is regulated in an interplay between a homeostatic drive for sleep accumulating during wake (process S) and intrinsic circadian oscillations in sleep propensity (process C). Endogenous alterations in both processes appear to contribute to the sleep phase delay, both by delaying the internal time keeping system and by a slowing of homeostatic build up, shifting the major sleep period to a later phase of the circadian rhythm [5], [7].

The misalignment between adolescents’ sleep/wake rhythm and the demands from their society (e.g., school start times) forces adolescents with a delayed sleep phase to perform under conditions where both homeostatic (process S) and circadian (process C) factors promote sleep. Many adolescents rise in the morning before they have obtained their recommended amount of sleep [8]. Chronic sleep curtailment causes sleepiness and may have widespread implications on both physiological and neurobehavioral functioning [9], with the neurobiological effects of sleep debt seemingly accumulating over time [10]. In line with this, several studies have shown an association between poor sleep habits and reduced academic performance in adolescents [8], [11], [12]. Poor sleep habits also appear to be linked to being overweight, depressive mood, smoking, and alcohol usage [13], [14], [15], [16], [17], [18]. Rising at times when the biological clocks are set for sleep, adolescents with a delayed sleep phase may experience problems performing optimally during school hours due to circadian fluctuations in bodily functions such as subjective sleepiness, cognition, attention, and physical performance [19]. Yet another common consequence of a delayed sleep phase is oversleeping. Oversleeping affects school attendance and may consequently contribute to poor school performance. Adding to the problem, oversleeping and compensating behavior such as napping or sleeping in on weekends may further contribute to the sleep/wake rhythm delay, making it difficult to fall asleep at appropriate times. By this, some adolescents conceive themselves as being trapped in a vicious cycle/positive feedback loop.

Eveningness is a chronotype characterized by a preference for mental and physical activity at relative late times during the day. Such circadian preference is closely connected to irregular and delayed sleep patterns [20] and appears to be a risk factor for both poor mental and physical health [21]. Homeostatic and circadian factors may be involved, but it is possible that eveningness affects daytime functioning in ways not mediated through sleep regulatory processes. Several studies have linked eveningness to personality features such as neuroticism and conscientiousness, and in particular, low self-control [22], [23]. Low self-control may explain some of the associations between eveningness and low school attendance, reduced school performance, higher levels of depressive symptoms, risk-taking, and bad health behavior (e.g., use of tobacco and alcohol as well as inadequate dietary habits, see [24] for review).

At the most extreme, a delayed sleep phase may reflect delayed sleep phase syndrome (DSPS), a circadian rhythm sleep disorder characterized by a stable delay in the sleep/wake rhythm [25]. It is not clear whether DSPS represents the quantitative extreme of adolescent sleep phase delay or a qualitatively distinct clinical entity. According to the latter view, patients with DSPS are characterized by rigidity in the circadian rhythms, whereas normal adolescents seem to have a more flexible circadian rhythm that is fairly easily adjusted [26]. DSPS is associated with problems such as daytime sleepiness, inability to work or attend school, and depressed mood [4]. The prevalence of DSPS is not clear, although it is believed to be particularly common in young people. Prevalence rates between 7% and 16% are commonly assumed [1], [25], although rates as low as 0.5% [27], [28] have been reported. The diagnosis of DSPS cannot be confirmed in absence of sleep logs or actigraphy monitoring instruments which are not easily applicable in population studies. Hence, most studies have used different survey methods and operationalizations to assess the prevalence of the collection of symptoms resembling the disorder [1].

The main objective of the present study was to estimate the prevalence of delayed sleep phase, operationalized as difficulties falling asleep before 2 a.m. at least three nights a week together with much/very much difficulty awakening in the morning, in a large sample of Norwegian high school students. We also wanted to identify correlates of delayed sleep phase (smoking, alcohol use, weight, height, school grades, and anxiety and depression scores).

Section snippets

Methods

The survey was conducted amongst high school students in Hordaland County in Western Norway. E-mails explaining the purpose and procedure of the study were sent to every student included in our sample. Students participated by logging onto a given internet address where they could answer the survey questionnaire. This was done while the students were at school. The procedure secured anonymous data collection. Participation was voluntary with a passive consent procedure in which completion of

Results

A total of 216 students (17.2%, CI: 15.1–19.2) reported difficulties falling asleep before 2 a.m. at least three nights a week whereas 345 students (27.3%, CI: 24.9–29.7) reported problems awakening at the desired time (much or very much difficulties waking up in the morning). The number of students reporting both these symptoms and, hence, a DSP according to our operationalized criteria, was 105 (8.4%, CI: 6.9–10.0). Table 1 displays the prevalence of each of the different sleep habits

Discussion

We operationalized DSP as problems falling asleep before 2 a.m. at least three nights a week together with many/very many difficulties waking up in the morning. The prevalence of students reporting DSP was 8.4% in the present study. Logistic regression analyses showed that average school grade was negatively, whereas smoking, alcohol use, and scores on anxiety and depression were positively associated with DSP.

With less than 7 and 8 h estimated average TST in the DSP and non-DSP groups,

Conflicts of Interest

The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: doi:10.1016/j.sleep.2011.10.024.

. ICMJE Form for Disclosure of Potential Conflicts of Interest form.

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