Background
Sleep is recognized as a crucial factor for children’s and adolescents’ health and wellbeing [
1]. Sleep recommendation vary with age and according to the US National Sleep Foundation teenagers are recommended 8–10 h of sleep [
2]. However, when Gariepy and colleagues examined sleep patterns in 24 European and North American Countries, including 165,793 adolescents, findings revealed that insufficient sleep is prevalent in many countries [
3]. Insufficient sleep impacts the daytime functioning in adolescents, leading to various negative consequences in their lives [
4]. Extensive research evidence has reported that insufficient sleep among adolescents increases the risk of physical, psychosocial, and behavioral problems, and is associated with worse health outcomes [
4‐
9].
When examining sleep duration in adolescents, research evidence refers to both the time in bed (TIB) and the sleep onset time (SOT) until wakening as estimates of sleep duration. It is suggested that TIB might overestimate the sleep duration in adolescence [
10], as adolescents don’t immediately fall asleep when they go to bed. The latency time from going to bed to SOT was reported to be on average around 17 min for older adolescents in 2002 [
11]. However, considering the commonality of screen time use before bedtime nowadays, it is presumed that this average time has increased [
12,
13]. A recent Norwegian sleep study reported the average time between going to bed and SOT was over one hour, revealing that eight in ten adolescents in upper secondary school actually failed to obtain the minimum recommended amount of sleep (8 h) on school days [
10].
Research evidence points to several causes of insufficient sleep in adolescence, which are commonly categorized into internal- and external factors. External factors may include reduced parental involvement, excessive homework or activities, perceived stress, and screen time usage, whereas internal factors refer to puberty and biological processes such as a shift in the circadian rhythm [
4,
14‐
18]. Regardless of its causes, insufficient sleep is reported to impact all aspects of adolescents’ daily life and wellbeing [
4‐
7,
9,
14,
16,
17,
19‐
21]. A well-known indicator of subjective well-being is Life Satisfaction measure, which serves as a useful complement for comparing data across ages and countries, and is assessed to evaluate their life as a whole rather than their current feelings [
22]. Satisfaction with life is therefore a well-known measure to indicate happiness across countries and time [
22]. According to Diener, the measure reflects the cognitive judgment of one´s satisfaction with life [
23]. It has been reported that girls tend to report lower satisfaction with life compared to boys during adolescence, along with a general decrease in satisfaction with life throughout this period [
24].
Since most Norwegian adolescents do not meet the recommended 8 h of sleep [
10], it is crucial to investigate potential consequences for this age group. Since life satisfactions is a good indicator of adolescent’s well-being, and a proxy for happiness it would be interesting to investigate the relationship between sleep duration and satisfaction with life using large dataset with high response rate. Such research can provide substantial insights for both practice and policy development, potentially emphasizing the significance of adhering to the sleep recommendations in Norway. The main aims of the present study were (1) to describe sleep duration, factors impacting sleep, consequences of insufficient sleep and satisfaction with life in Norwegian adolescents, stratified by sex and by adherence to the 8-hour sleep recommendation, and (2) to examine potential association between adherence to the 8-hours of sleep recommendation and satisfaction with life in Norwegian adolescents.
We hypothesized that adolescents adhering to the 8-hour sleep recommendation would have a more positive association to satisfaction with life compared to adolescents sleeping seven hours or less.
Discussion
In this study, we aimed to describe sleep duration, factors impacting sleep, consequences of insufficient sleep and satisfaction with life in Norwegian adolescents and examine possible associations between adherence to the 8-hours of sleep recommendation and satisfaction with life. Findings revealed that 73% of adolescents did not meet the recommended sleep duration of at least 8 h per night, with similar results for girls and boys. 64% reported that they felt tired at school or in activities, however more prevalent in girls than boys. Screen time had a negative impact for getting enough sleep in 62% and was more prevalent among girls than boys. Gaming disturbed sleep in 23% and was more prevalent among boys. Satisfaction with life score was 7 out of 10 for the total study sample, with somewhat higher scores for boys than girls. Adhering to the 8-hours sleep recommendation was positively associated with satisfaction with life, and there were similar findings in girls and boys. All findings remained statistically significant after adjusting for SES, perceived stress, physical activity level and OTCA use.
Our findings, revealing that 73% of the adolescents did not adhere to the 8-hours of sleep recommendation, are higher compared to international data, which shows that across countries, 32–86% of adolescents meet sleep recommendations [
3]. However, not adhering to the sleep recommendation appears to be common in Norway. In a Norwegian study by Saxvig and colleagues, it was revealed that 84.8% of adolescents aged 16–17 did not adhere to the recommendation of 8-hour sleep [
10]. These findings show a slightly higher prevalence compared to this current study, which may be due to several methodological differences in self-reporting. Saxvig and colleagues presents findings of sleep duration during schooldays, whereas the question provided by Ungdata refers to “how many hours did you sleep last night?”. Assuming that some Ungdata surveys were conducted on Mondays, the findings may be less comparable to data from schooldays, as adolescents commonly report a relatively large discrepancy between sleep duration on schooldays and weekends [
35]. A recent Norwegian study from 2023 reported that younger Norwegian adolescents tend to sleep one and a half hours longer on weekends compared to schooldays [
36]. Despite this, our findings point to the commonality of failing to obtain the recommendation of 8 h of sleep in the everyday life of Norwegian adolescents.
Estimating sleep duration by self-report in adolescence is challenging due to observed discrepancies between self-reported sleep and objectively measured sleep. However, research evidence suggests that adolescents aged 13–17 years may more precisely estimate their own sleep duration compared to when their parents report on their behalf, as parents tend to report an idealized version [
37]. Objective measures, including actigraphy and the currently considered gold standard, polysomnography, offer potential clinical advantages compared to self-reporting [
38]. However, these advantages are primarily related to pathological conditions, such as accurate diagnosis of sleep disorders and treatment monitoring. Lucas-Thompson and colleagues investigated the between- and within-person associations between self-reported and actigraph-measured nighttime sleep duration in adolescence [
39]. The findings indicated that adolescents reporting longer average nighttime sleep also exhibited longer average actigraph measured sleep duration [
39], suggesting that self-reporting in large samples of adolescence is likely to have high validity. Still, there are potential biases that should be discussed, which could be threating the validity of the study, such as self-report bias, including recall bias or social desirability bias. Despite the study is anonymous, there is no guarantee that adolescents´ didn’t under or overestimate their scores based on poor recollection or because of being afraid of observant classmates. Other relevant bias to mention is selection bias. Although the study includes the majority of Norwegian adolescents, findings may not accurately reflect the total target population.
Interestingly, our descriptive findings revealed similar sleep duration in girls and boys, which is in accordance with international data and other Norwegian sleep studies [
10,
36,
40]. However, our descriptive findings revealed some differences in terms of feeling tired (sleepiness). Only 29% of girls reported they never felt sleepy during school or in activities, whereof 44% of the boys reported the same. There might be underlying mechanisms related to sleep quality or productivity differences between girls and boys that might interfere, or it could be related to other aspects of adolescents’ life, such as difference in physical activity levels and gender preferences for activities provided at schools. Nevertheless, Forest and colleagues also reported gender differences in daytime sleepiness during school and social activities in adolescents, with girls perceiving more interference from poor sleep on daytime functioning compared to boys [
41]. Findings indicate other measures than sleep duration is needed for understanding daytime functioning in girls and boys. A meta-analytic review from a school setting, showed that sleepiness revealed the strongest association to school performance, followed by adolescents sleep quality and sleep duration [
42].
Another gender difference was that more girls than boys reported that screen time negatively impacted their ability to sleep. It is reported that time spent in front of a screen usually comes at the expense of sleep [
43]. The inability to sleep and screen time use at night are physiologically linked to the brightness and type of light, and such activity inhibit melatonin production, disrupt the circadian rhythm, and consequently affect adolescents´ feeling of sleepiness before bedtime [
44]. Therefore, the systematic review by Hale et al., explicitly advises to limit or reduce screen time exposure, especially before or during bedtime hours, to minimize any harmful effects of screen time on sleep and well-being [
13]. Moreover, Hale and colleagues reported that adolescents spend about 7 h per day in front of a screen [
13]. Gaming might also contribute to the total screen time in adolescence. In our study, more boys than girls reported that gaming affected their ability to sleep. Time spent on video gaming in adolescence is also reported to be negatively associated with sleep duration [
45].
It is interesting to link the differences in daytime sleepiness between girls and boys to the differences in satisfaction with life, as we suspect that there could be coinciding factors at play. Given that girls tend to experience more tiredness and sleepiness, it would presumably influence their subjective well-being and satisfaction with life, as sleepiness is strongly associated with adolescents’ overall quality of life [
46]. Extensive research evidence has reported gender differences in health-related quality of life (HRQOL) and satisfaction with life, wherein girls tend to report lower scores than boys [
24,
47‐
50]. Moreover, our findings of satisfaction with life align with the “Better Life index” score from the OECD, which reports 7.3 as an average score for Norwegians [
22]. Interestingly, in our study, both girls and those not adhering to the sleep recommendations had coinciding satisfaction with life scores below 7.0.
As hypothesized, the findings showed that adolescents adhering to the 8-hour sleep recommendation had higher life satisfaction compared to adolescents sleeping 7 h or less. Quite similar results were found in both girls and boys, despite a slightly lower
p-value was revealed among girls compared to boys, both associations remained significant after adjusting for relevant covariates. Indicating respective associations relevant for the total study sample. Interestingly, a Norwegian study by Ness and Saksvik-Lehouillier investigated the relationship between sleep and satisfaction with life in Norwegian university students. Their results indicated that all sleep parameters, such as sleep quality, less variability in rise time, less variability in sleep duration, longer mean sleep duration were associated with better satisfaction with life. However, less variability of sleep duration was identified as a significant predictor for life satisfaction and not mean sleep duration, indicating that less variability of sleep duration might be more relevant to well-being than sleep duration itself [
51]. Research evidence also reports higher risks of negative health outcomes with higher variability in sleep duration from weekdays to weekends in adolescents [
35,
52]. Further, a recent Norwegian study reported that sleep duration on weekdays was positively associated with all aspects of adolescents´ HRQOL, whereas sleep duration on weekends revealed mostly nonsignificant findings regarding aspects of HRQOL [
36]. These findings highlight the vulnerability of using only one general sleep duration measure to understand the complexity between sleep and satisfaction with life. Nevertheless, our findings reinforce the importance of the 8-hours sleep recommendation for Norwegian adolescents. Sleep is a multifaceted concept, including different measures such as sleep variability, sleep quality and sleepiness, all of which can have distinct impacts on adolescents’ satisfaction with life. Therefore, it is worth exploring the possibility of sleep recommendations that encompass not only sleep duration, but also explicitly address sleep variability and daytime sleepiness in adolescence in the future.
Strengths and limitations
The primary strength of this study lies in its large sample size, comprising adolescents from both urban and rural regions of Norway, collected within a school-based setting. Additionally, the high response rate (99%) regarding variables related to sleep and life satisfaction enhances the study’s reliability. These factors suggest that the findings could be generalizable for a broader population of Norwegian adolescents attending school. The question regarding sleep duration is based on SOT until awakening time, which is considered an accurate estimation of sleep duration [
10]. Further, Ungdata dataset is cleaned and they have several procedures for identifying unserious answers [
26]. Moreover, reporting according to STROBE guidelines [
25] should be considered a strength, as it provides transparency and accurate reporting of study method and results.
This study also has some limitations. The cross-sectional nature of the study hinders us from determining any causal inference between sleep duration and life satisfaction. Further, another limitation is the use of non-validated instruments regarding sleep as the respective questions in Ungdata derives from an unknown origin [
27]. Moreover, the sleep questions did not distinguish between weekdays and weekends, which might have affected the results. Another limitation is that the scope of this paper was focused on adhering to sleep recommendations or not, and as a result, the sleep duration variable was dichotomized. This dichotomization reduced variability in data and excluded other potential sleep-related variables that could have impacted adolescents’ satisfaction with life. Another limitation is due to study variables are measured over different time frames, as exposure is measured within last day and outcome over a few days. The predicting sleep variable would be more robust if data was provided over a longer period, which would convey a better understanding of sleep variability and average sleep duration. Moreover, we do not have any information on the non-responders, which increases the risk of selection bias. Finally, despite significant statistical associations, caution should be exercised when interpeting the findings for clinical relevance. Still, sensitivity analysis using 7 h of sleep as a cut-off shows a stronger association with lower life satisfaction than 8 h of sleep. This might indicate that less sleep is more strongly related to lower life satisfaction. This should be further explored in future studies investigating sleep as a continuous variable. However, we chose to dichotomize the variable according to sleep recommendations to make it clear and easy to interpret for adolescents, practitioners, and policymakers.
Perspectives
This study showed that the majority of adolescents did not adhere to the 8-hours of sleep recommendation, and many of them reported feeling tired at school or in activities. Screen time and gaming were identified as descriptive factors affecting adolescent’s ability to get enough sleep. Our study added new findings to the research literature by uncovering that sleep recommendations were positively associated with higher life satisfaction by controlling for several relevant covariates in a large sample of Norwegian adolescents, underpinning essential information for people working with adolescents and caregivers. Finally, practice and policy aiming at increasing health and satisfaction with life in adolescents should include and highlight sleep recommendations.
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