Pre-Bed Screen Time and its Effect on Adolescent Sleep: A Systematic Review

Introduction

Poor sleep quality is a growing issue among adolescents. A UK survey with a sample size of 18,642 students found 46.4% of high school students older than 10 experience poor sleep quality¹. Sleep is pivotal for crucial areas in a person’s life, such as their physical and mental health. Biologically, sleep plays a role in the growth and development of one’s body and directly affects many different body systems including the cardiovascular, immune, endocrine, and neurologic systems². Poor sleep quality can lead to several issues among adolescents such as increased risk of cardiovascular disease, obesity, and even lower self-esteem³. One factor known to impact sleep quality is pre-bed screen time ⁴. This systematic review aims to examine the impact of pre-bed screen time on sleep quality among adolescents.

Literature Review

Sleep, although difficult to define, is a state characterized by a posture in which the body is lying down with closed eyes, the reduction of activity and responsiveness to stimuli, and its ability to be reversed with ease⁵. Scientists also define it by physiological changes, such as lowered body temperature and brain wave activity patterns⁵. The brain wave activity patterns observed during sleep are what help to differentiate the sleep stages. The various stages are classified as being either rapid-eye movement (REM) sleep or non-REM (NREM) sleep. REM sleep is a stage of sleep in which the eyes move rapidly under the eyelids while dreams occur, and the brain activity closely resembles the activity while awake. An entire sleep cycle consists of three NREM sleep stages first, followed by REM sleep which takes between 90 and 120 minutes to complete and occurs four to five times in one night’s sleep⁶.

The processes that regulate sleep are the body’s circadian rhythm and sleep/wake homeostasis. The circadian rhythm, often referred to as a biological clock, functions on a 24-hour cycle to maintain homeostasis in harmony with environmental factors such as sunlight⁷. Its goal is to control levels of alertness throughout the day, which eventually influences amounts of sleepiness and wakefulness⁸.

Circadian rhythms themselves are regulated by a brain structure called the suprachiasmatic nucleus, which responds to light and dark signals⁹. This is the reason that circadian rhythms generally follow sun patterns and can be disrupted by artificial light at night¹⁰. Sleep/wake homeostasis, another sleep- regulating process, is responsible for the balance between sleep need and wakefulness based on the amount of time spent awake⁸.

Good sleep quality is often discussed as the ability to fall asleep within half an hour of getting into bed, sleeping through the night for the recommended age-dependent duration with minimal disturbances, being able to fall back asleep within 20 minutes if awakening occurs, and the feeling of being rested the next day¹¹. Sleep quality is most widely measured by the use of full night polysomnography (PSG) which measures sleep physiologically using factors such as body position, electrocardiograms (EEG), respiratory movement, and other physiological indicators¹². This form of objective sleep measurement has also been done on a smaller scale by some researchers with the use of tools such as the Fitbit smartwatches¹³. Another common method of measuring sleep quality that requires much less equipment is through the use of self-report indexes that focus on self-satisfaction as a way of assessing sleep quality¹². One index that has been used extensively since its development is the Pittsburgh Sleep Quality Index (PSQI). The PSQI is a tool that evaluates sleep quality in clinical populations over one month in the form of a self-report questionnaire. It consists of 19 questions that generate seven individual scores assessing subjective sleep quality, sleep duration, daytime dysfunction, sleep latency, sleep disturbances, sleep efficiency, and use of sleeping medication. The scores are then added to form a global score, and a score of greater than five indicates poor sleep quality¹⁴.

There are several lifestyle factors that affect the sleep quality in the lives of adolescents. Some of the most pertinent factors that have been researched include their diet, caffeine consumption, levels of physical activity, relationship with their family, and daily screen time.

Diet

Diet is a significant factor that researchers focus on concerning sleep quality among adolescents.

One cross-sectional study¹⁵ found that there was a significant correlation between eating habits and sleep quality in adolescents. Specifically, it found that frequent consumption of breakfast and fruits and vegetables is negatively correlated with sleep problems, and soft drink and sweet consumption is positively correlated with sleep problems. Another cross-sectional study¹⁶ found that there was a correlation between the level of processing food goes through and sleep quality. Higher energy intake from fresh or minimally processed foods was linked to a lower occurrence of poor sleep quality, while higher energy intake from ultra-processed foods was linked to a higher occurrence of poor sleep quality, as per the PSQI¹⁶.

This can be explained biologically when examining how the consumption of certain macronutrients and micronutrients in food affect various aspects of sleep. Macronutrients include components such as fat, carbohydrates, tryptophan, and proteins, whereas micronutrients include components such as folate, iron, magnesium, and vitamin D¹⁷. One laboratory based intervention study¹⁸ found that a diet with high carbohydrate and low fat levels in comparison to one with low carbohydrate and high fat levels resulted in decreased slow wave sleep. Another cross-sectional study¹⁹ focusing on fats found an association between fat consumption and shorter sleep duration. Additionally, one study²⁰ found that eating highly saturated fat, sugar, and low amounts of fiber as opposed to being on a fixed diet resulted in reduced slow wave sleep and increased arousals at night. As for micronutrients, a cross- sectional study²¹ found that a deficiency in folate, zinc, magnesium, vitamin D, phosphorus, iron, and selenium was associated with decreased sleep duration. Furthermore, a randomized control trial²² found that foods with high zinc content were associated with decreased sleep onset latency and better sleep efficiency. Overall, nutritional choices seem to have a biological impact on the quality of sleep due to the presence or absence of specific macro and micronutrients in one’s diet.

Caffeine Use

Caffeine is a subset of diet that a few researchers have specifically studied in relation to adolescent sleep quality. One study²³ surveyed U.S. students’ consumption of caffeine in the form of coffee and soft drinks and found that high levels of caffeine intake were correlated with morning tiredness and trouble sleeping. Another American study²⁴ found that high levels of caffeine consumption were significantly correlated with longer wake time after sleep onset, decreased sleep duration, and higher daytime sleep. These studies exhibit that higher levels of caffeine consumption among adolescents may impact multiple aspects of their overall sleep quality. This is explained by the fact that caffeine is a stimulant and when consumed, it is a competitive antagonist to the hormone responsible for sleep-wake cycle regulation: adenosine. In other words, it competes with adenosine to bind to its receptor and therefore prevents the receptor from being activated by blocking adenosine, affecting sleep-wake cycle regulation¹⁷. This is the suggested biological reason behind why caffeine has a major effect on sleep quality.

Physical Activity

Physical activity and its impact on sleep quality among adolescents is another major area of research. One cross-sectional study²⁵ found that there was a positive relationship between moderate to vigorous physical activity (MVPA) levels and sleep efficiency the following night for females.

Additionally, males who partook in a minimum of 60 minutes of MVPA had shorter sleep onset latencies. Sleep quality was measured using an accelerometer on the wrist. Another cross-sectional study²⁶ that used both the PSQI and an accelerometer to measure sleep quality found a significant correlation between adolescents who did more physical activity and shorter sleep onset latency, which is the time it takes to fall asleep. These studies both illustrate that the amount of physical activity adolescents integrate into their lives may influence their sleep quality.

Biologically, this has been attributed to the various effects exercise has on the central nervous system and mood, which in turn impacts sleep quality²⁷. In a study investigating central nervous system sleep²⁸, it has been found that exercise in the afternoon leads to substantially increased amounts of stage 3 and 4 slow-wave sleep. In terms of mood, exercise has been found to be a potential therapy option for depression by a couple of studies,^29,30 and since depression is a potential cause of sleep disturbance, the rationale is that exercise may indirectly improve sleep quality because of how it improves the symptoms of depression²⁷. These are both indirect ways through which exercise can be linked to better sleep.

Relationship with Family and Mental Health

A couple of studies investigated sleep quality as a mediator between various family-related issues and mental health problems among adolescents. For instance, one study³¹ found that adolescent sleep quality played a mediating role in the relationship investigating the impact of family chaos and disorder on depression and anxiety symptoms. This was accredited to the effect that family chaos had on adolescent sleep hygiene, which ultimately impacted sleep quality. Additionally, a longitudinal study³² conducted in China found that sleep quality mediated the association between intra-family conflict and mental health issues among adolescents. The researchers found that this may be because, based on other research^33,34, for a sleeping environment to be ideal, it should be free from external threats. Family conflict can be considered an external threat because it prevents adolescents from feeling secure. There seems to be a trend in the research that demonstrates sleep quality may mediate family issues and adolescent mental health.

Additionally, there needs to be further research on the directionality of the relationship between sleep and stress. Previous research³⁵ suggests a bidirectional relationship, where sleep and stress impact each other, known as the sleep-stress spiral. Yet another study³⁶ further investigated the directionality using repeated measures designed to explore this relationship within adolescents. Using this temporal approach, they found that sleep quality impacted stress in a unidirectional relationship, contrary to previous bidirectional results. Furthermore, they also found a unidirectional relationship where stress impacted sleep quality when comparing results in a between-subjects design. They also found an indirect impact of self-coping mechanisms, such that when individuals had better quality sleep, they had better self-coping mechanisms, which could also help reduce stress. This illustrates the pertinence of supporting adolescents in their ability to handle hardships as it directly affects sleep, which then affects mental health.

Day Screen Time

The use of screens throughout the day and their impact on sleep quality is a newer, growing area of research. A cross-sectional study³⁷ focusing mainly on mobile devices found that the problematic use of cellphones during the day was linked to poorer sleep quality as per the PSQI. Another longitudinal study³⁸ that also used the PSQI to assess sleep quality found that the use of screens during the day for social media and television was associated with poor sleep quality. A third study³⁹ found that use of cellphones had a negative impact on sleep duration, quality, and daytime sleepiness. All these studies were able to come up with possible reasons that screen time at night would affect sleep such as mental arousal or the suppression of melatonin through blue light but were not able to sufficiently explain its effect when used in the daytime.

Originality and Research Question

Other reviews have assessed the impact of screen time and sleep quality^40–42, but none were found to the best of the author’s knowledge specifically focusing on pre-bed screen time. Furthermore, this area has received an increase in interest recently, so this study will help to update the field with studies that were published over the last few years. The goal of this systematic review is to examine the influence that pre- bed screen time has on sleep quality among adolescents.

Methods

This systematic review used the PICO Cochrane⁴³ model to determine the inclusion and exclusion criteria and guide the search strategy. Inclusion criteria consisted of studies where the population included adolescents around the world aged approximately 13-18, the majority of which were in high school. This was based on the personal insights of the author and the generally high prevalence of screen usage by individuals in this age group⁴⁴. The exposure was the usage of any type of screen before bedtime such as smartphones, laptops, television, etc. This was done to have a more comprehensive review and to start to understand if the type of screen used has an impact. The outcome was any effects on sleep quality, including effects on aspects of sleep such as sleep onset latency and sleep duration, to best assess the research question. Studies from all over the world were included to offer a more comprehensive review due to similar electronics being used globally. Further, regardless of location, all humans go through the same stages of sleep and circadian rhythms⁴⁵. Studies from only over the past 10 years were included due to the large amount of this technology usage in teens that occurred over this time frame⁴⁶, as well as to focus on the most recent literature in the field.

Exclusion criteria included populations that focused on adults over the age of 19 as sleep physiology changes as individuals age⁴⁷ and daytime screen usage as theoretically screen time right before bed should have a larger and more consistent effect due to how light stimulation right before bed impacts circadian rhythm⁴⁸. Articles not in English were excluded as the author is an English speaker.

The databases used for the search were PubMed, OMNI, and Google Scholar. Keywords used to search the databases were “screen time”, “sleep quality”, and “adolescents” and the search was conducted between June and July of 2024. Results were also filtered by date of publication between 2014-2024 to focus on recent literature and coincide with the increased use of screens by adolescents as technology has become more available, peer-reviewed articles, and articles written in English. A search of PubMed and OMNI with these keywords and filters yielded a total of 537 results, out of which 128 were identified by Covidence (an online tool that aids in conducting systematic reviews) as duplicates. The remaining 409 articles were then manually screened by their titles and abstracts for relevancy to the research question.

The 38 articles that remained after the title and abstract screening went through a full-text review to determine whether they fit the inclusion criteria of the study. Seven studies were selected from this systematic review. A topical search of Google Scholar using the same criteria was also performed. The goal of the topical search was to find approximately three additional articles to create a more comprehensive review. The results of the search were limited by filtering the date of publication to the last ten years and the first three articles that were found that fit the inclusion criteria upon a full text review were included in the study.

After all the articles were fully reviewed, a total of 10 articles were included in this review. The data that was extracted from these articles included the sample size of the study, the study design, the country, the specific intervention, the measurement tools used, the outcome concerning sleep quality, and any other variables that impacted sleep quality aside from screen time. The extracted data was put together and presented in a chart. Trends and results in the table were then assessed descriptively and qualitatively. It is noteworthy that many articles in this review are not open-access and were accessed through a university institution.

Results

Figure 1. PRISMA flow diagram

Table 1. Systematic Review Summary

Out of the 10 studies^13,49–57 that examined the relationship between pre-bed screen time and sleep quality among adolescents, 90% of the studies^{13,49–55,57} found a significant negative correlation. Eight of the studies^{13,49–53,55,57} used statistical correlations to establish a relationship, and all eight of those studies found statistically significant data. Only two studies^54,56 used descriptive percentages and out of those, one study⁵⁴ showed that 63.5% of adolescents who spent more than 60 minutes using devices before sleep were poor sleepers in comparison to 35.6% of others who spent 15 minutes or less.

Five studies^{57,54,50,55,56} used the PSQI to measure sleep quality and the other studies used different self-report questionnaires. All but one of the studies⁵⁶ using the PSQI found a statistically significant correlation between screen time and sleep quality. The five studies^13,49–52 performed in the Western region of the world including New Zealand, the United States, Norway, Italy, and France all found a statistically significant correlation between screen time and sleep quality. Out of the five, two studies^49,52 found correlations of p<0.01, and two^50,51 found correlations of p<0.001. The three studies^53–55 performed in the Middle Eastern region of the world including Turkey, Saudi Arabia, and the United Arab Emirates all showed strong correlational data between screen time and sleep quality with each study reporting statistical significances of p≤0.001. Out of the other two studies, including Brazil and India^56,57, only the Brazil study found a significant correlation of p<0.05 on weekdays and p<0.01 on weekends.

Two studies^50,55 found that the sleep quality of females was worse than that of males and both studies demonstrated this through a negative correlation with a statistically significant p-value of <0.001. Only one study⁵³ examined a potential mediator between screen time and sleep quality and found that the relationship is mediated by bedtime procrastination.

 Discussion

The influence that pre-bed screen time has on sleep quality has been attributed to a few different factors. The suprachiasmatic nucleus, which is responsible for regulating the circadian rhythm, does so by releasing a hormone called melatonin⁵⁸. Melatonin is produced in response to darkness and helps in falling asleep; however, it is suppressed by exposure to blue light⁴⁸. Since all screens emit blue light, this is a possible cause for longer sleep onset latency due to not feeling tired at night, which is a factor of poor sleep quality. This seems to be the primary issue, as it was attributed as a potential cause for poor sleep quality in all the reviewed articles. Another reason could be the possible psychological arousal caused by these devices, which also contributes to reduced tiredness at bedtime⁵⁹. Furthermore, the replacement of sleep time with screen time before bed is another possible cause of poorer sleep quality because of the reduction in hours of sleep, in other words, more time spent looking at screens ultimately creates less time for sleep itself⁶⁰. The finding that girls had poorer sleep quality in comparison to boys was common in two studies^50,55. Adolescent girls have been found to have poorer sleep hygiene, multitask frequently, and drink caffeine in the evening after eating, which has all been linked to possibly causing poor sleep quality⁶¹.

India was the only country in this review that showed no correlation between pre-bed screen time and sleep quality. The researchers attributed this to a few potential reasons. First, the authors established that, based on previous research, sleep disturbances may increase with age because older adolescents have more autonomy and academic stress. Specifically, one Mumbai study⁶² found that adolescents who are 15 and older have a higher chance of experiencing poor sleep quality. Because the eldest adolescents in this study were only 16, the researchers concluded that the lack of older adolescents in the study may be a reason why they were not able to find a significant correlation. Another reason they found was that most of the girls in the study had a short commute of less than 30 minutes to school, and this could be a reason why they get to sleep in longer and have an increased reported sleep duration.

In comparison to similar systematic reviews that assess the relationship between adolescent screen time and sleep quality, one review⁴⁰ that looked primarily at daytime screen time globally also found there to be a correlation between the two. Another review⁴¹ included adolescents and children in the Western world and assessed articles that looked at both daytime screen time and pre-bed screen time. Although it is noteworthy that for the adolescent group most of the studies did not specifically assess pre- bed screen time. In the adolescent age group of 13–15-year-olds, the researchers found that there was a correlation between spending more time on devices and shorter sleep duration. The reason for this link was not particularly addressed. They also found that interactive forms of media such as social media and mobile phones had a greater effect on sleep outcomes in comparison to passive forms such as television viewing. This was attributed to the psychological arousal that comes with these forms of media. A third review⁴² looked at both daytime and pre-bed screen time. Overall, it found that 90% of the studies showed a negative association between screen time and one of the sleep outcomes. Furthermore, it found a similar pattern to the last study where television had the least negative impact on sleep due to being passive instead of an interactive form of media. The study found that there were limitations similar to this review such as a lack of causality as a result of lack of experimental studies (the majority of the studies were cross-sectional).

Limitations and Future Directions

Although this review has many strengths, there are a few limitations that are important to address.

First, this review addresses the concept of screen time in a rather broad sense. Screen time in this study includes a large variety of devices that vary in functionality, such as smartphones, video games, and MP3 players. Because of the differing levels of active interaction involved across these devices, it may be beneficial for further research to focus on a specific type of device in isolation. Another limitation is the design of every study included in this review is a cross-sectional survey. Because of this, while correlations may be observed between screen time and sleep quality, establishing causality is difficult without the use of randomized control trials. No randomized control trials assessing the relationship between pre-bed screen time and sleep quality among adolescents were found to the best of the author’s knowledge, which suggests this is a study design that needs to be explored by researchers. Furthermore, the PSQI itself assesses sleep onset latency in a way that may lead to inaccurate results. This is because the PSQI only asks for the time it takes to fall asleep; however, this time may be longer due to the use of non-screen activities such as reading a book. Therefore, any non-screen activity performed in bed could falsely cause a higher PSQI score, which indicates poorer sleep quality.

It is also worth noting that none of the studies in this review address the relationship between screen time and sleep quality directionally. This implies that it is still uncertain whether screen time is affecting sleep quality or sleep quality is affecting screen time, or both (bidirectionality). To address this, there needs to be more research that establishes a temporal sequence. Furthermore, the field would benefit from more research looking specifically at gender differences and why the sleep quality of girls seems to be affected more than boys. Finally, since this review only focused on adolescents, future researchers should focus on different age groups such as pre-teens, adults, and seniors to see if similar results are found.

Conclusion

Overall, the majority of studies found that screen time had a negative impact on sleep quality. This may be attributed to the suppression of melatonin due to blue light from screens, psychological arousal, and the replacement of sleep time with screen time. Additional research needs to be done to better understand why girls have worse sleep quality than boys and more experimental studies need to be conducted to establish a causal relationship between pre-bed screen time and sleep quality.

These findings illustrate that there is an imperative need for screen time regulation before bedtime among adolescents. This could come in the form of practical measures such as screen time limits set on devices, enabling night modes, blue light filters, or even the promotion of non-screen activities before bed, such as reading. For screen time regulation among younger adolescents, parents should help implement these measures. Older adolescents would benefit more from being educated on the realities of poor sleep quality to learn to regulate themselves and make informed decisions regarding their health.

Public health educators should set out to create media campaigns targeting these adolescents to inform them of this critical issue.

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