Clinical review
The influence of sleep quality, sleep duration and sleepiness on school performance in children and adolescents: A meta-analytic review

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Summary

Insufficient sleep, poor sleep quality and sleepiness are common problems in children and adolescents being related to learning, memory and school performance. The associations between sleep quality (k = 16 studies, N = 13,631), sleep duration (k = 17 studies, N = 15,199), sleepiness (k = 17, N = 19,530) and school performance were examined in three separate meta-analyses including influential factors (e.g., gender, age, parameter assessment) as moderators. All three sleep variables were significantly but modestly related to school performance. Sleepiness showed the strongest relation to school performance (r = −0.133), followed by sleep quality (r = 0.096) and sleep duration (r = 0.069). Effect sizes were larger for studies including younger participants which can be explained by dramatic prefrontal cortex changes during (early) adolescence. Concerning the relationship between sleep duration and school performance age effects were even larger in studies that included more boys than in studies that included more girls, demonstrating the importance of differential pubertal development of boys and girls. Longitudinal and experimental studies are recommended in order to gain more insight into the different relationships and to develop programs that can improve school performance by changing individuals' sleep patterns.

Introduction

Sleep is crucial for children and adolescents' learning, memory processes and school performance.*1, *2, *3 Research shows that poor sleep, increased sleep fragmentation, late bedtimes and early awakenings seriously affect learning capacity, school performance, and neurobehavioral functioning.*1, *2, *3 Nevertheless, due to methodological differences between studies, it is difficult to draw generalizable conclusions about the relationship between sleep and school performance.

Previous research indicates an association between insufficient and poor sleep and school performance,*1, *2, *3 however, no systematic review, such as a meta-analysis, exists evaluating the empirical evidence. Meta-analysis is a statistical method combining different study results. It enables the discovery of consistencies in a set of seemingly inconsistent findings. By obtaining an effect size estimate of the true effect more accurate conclusions can be drawn than in a single study or a narrative review.4 The meta-analysis presented here aims at gaining more insight into the relationship between children and adolescents' sleep and school performance.

Problems with initiating and maintaining sleep are common in children and adolescents and can be seen as indicative of poor sleep quality. Reported prevalence of such problems varies from 11% to 47%.5, 6 Furthermore, although empirical evidence demonstrates that children and adolescents require an average sleep time of approximately 9 hours/night7 results revealed that 45% sleep less than 8 hours/night.7, 8 Insufficient sleep might be caused by an interaction of intrinsic (e.g., puberty, circadian or homeostatic changes) and extrinsic factors (e.g., early school start times, social pressure, academic workload) leading to later bedtimes while getting up times remain unchanged. Additionally, it is known that approximately 20–50% of children and adolescents report daytime sleepiness.9, 10

Sleep can be defined as an active, repetitive and reversible state of perceptual disengagement from and unresponsiveness to the environment.11 Empirical evidence demonstrates an association between sleep and the consolidation of cognitive performance, which is required for executive functioning including abstract reasoning, goal directed behavior, and creative processing.*1, 12 The sleep related overnight brain processes are thought to influence cognitive, physical and emotional performance throughout the day.*2, *13 A possible explanation for the association between sleep and cognitive- as well as school performance is based on the idea that shortness or disruptions of sleep reduces necessary overnight brain activity that is needed for neurocognitive functioning. Complex tasks requiring abstract thinking, creativity, integration, and planning are primarily influenced by sleep-related problems supporting this view.14 These tasks, representing higher order neurocognitive functioning, are all characterized by an involvement of the prefrontal cortex, which is known to be sensitive to sleep.*1, 15 Based on this evidence it can be suggested that insufficient or low quality sleep during (early) adolescence impairs the executive function of the prefrontal cortex16 and consequently the decline of learning abilities and school performance.17, *18

Sleep quality and sleep duration may be seen as two separate sleep domains. Although these sleep domains overlap to some extent, qualitative differences exist between them. Sleep quality refers to the subjective indices of how sleep is experienced including the feeling of being rested when waking up and satisfaction with sleep.19 Sleep duration, on the other hand, is a more objective sleep domain, namely the actual time during which the individual is asleep. Correlations between children and adolescents' sleep duration and sleep quality are low or not significant5, 20 supporting the idea that sleep quality and sleep duration represent two separate sleep domains. Theoretically it may be that sleep quality and sleep duration are not only different in their impact on measures of health and problem behavior but also on school performance.*1, 5, 19 Although both sleep domains are associated with sleepiness, emotional state, behavior and cognitive function,*13, *16 these associations are stronger for sleep quality than for sleep duration.19

The most common direct consequence of insufficient or disrupted sleep is increased daytime sleepiness.*2, *13 Increased daytime sleepiness may lead to reduced alertness and compromised daytime functioning of specific brain areas (e.g., the prefrontal cortex), causing impaired cognitive functioning.14, 21, 22 Daytime sleepiness results from either low sleep quality, reduced sleep duration or a combination of the two sleep domains.10 This might explain why studies demonstrated more consistently the negative consequences of daytime sleepiness on neurobehavioral functioning and school performance rather than of especially sleep duration.*2, 23

Section snippets

Study aim

The study aim of the present meta-analysis is twofold. First, it aims at investigating the effects of sleep quality, sleep duration and sleepiness on school performance by analyzing the effects of each sleep domain separately. Second, the study examines possible moderating influences of parameter assessment, including the assessment of sleep variables as well as the assessment of school performance, gender and age.

Description of identified moderators

A large variety of moderating or mediating factors (e.g., family, motivation, socio-economic status, race) can affect the proposed associations (e.g.,3). Although all of them might be relevant and influential, inclusion of moderators in a meta-analysis requires reports of their descriptive statistics in the majority of studies. As this was not the case for many variables, the moderator choice was reduced to parameter assessment, age and gender.

Description of studies

The majority of the studies was cross-sectional in design. One study was a longitudinal study.30 In this case it was decided to include only the first time of measurement in order to make results comparable to the other studies. In three cases more than one article was based on the same sample. Including all studies would violate the assumption of independence. Therefore, we decided to include the study that provided the most information about the effect sizes or which was the most recent

Discussion

With the present meta-analysis we get individual estimates of the different effects of sleep quality, sleep duration, and sleepiness on children and adolescents' school performance. Inspection of the three confidence intervals indicated the presence of statistically significant differences. As the confidence intervals of sleep quality, sleep duration and sleepiness hardly overlap it can be concluded that the association between sleep duration and school performance is significantly smaller than

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