Use of digital screens by adolescents and association on sleep quality: a systematic review

This study aimed to analyze the influence of digital screen use on adolescents’ quality of sleep. This systematic review was recorded on PROSPERO (CRD42020203403) and conducted according to PRISMA guidelines. Studies covering adolescents from 10 to 19 years were included without language or publication restrictions which answered the following guiding question: “Does the use of digital screen influence adolescents’ quality sleep?”. Article search included the following databases: (MEDLINE/PubMed), LILACS, SciELO, Scopus, EMBASE, Web of Science, IBECS, Cochrane Library, ClinicalTrials. gov, and Open Gray. The following descriptors were used: “Sleep Quality”, “Screen Time”, and “Adolescent”. The Newcastle-Ottawa Scale (NOS) assessed the methodological quality of the cohort studies, and a modified NOS was used to assess the cross-sectional ones. In total, 2,268 articles were re-trieved, of which 2,059 were selected for title and abstract reading, after du-plicates were deleted. After this stage, 47 articles were selected for full reading, resulting in the 23 articles which compose this review. Excessive use of digital screens was associated with worse and shorter sleep, showing, as its main consequences, night awakenings, long sleep latency, and daytime sleepiness. The use of mobile phones before bedtime was associated with poor quality of sleep among adolescents. Our evaluation of the methodological quality of the chosen studies found seven to be poor and 16, moderate.


Introduction
In adolescence, the period between 10 and 19 years of age 1 , important changes take place in individuals' sleep/wake cycle patterns, including a delay in the sleep phase, characterized by later sleeping and waking times. Sleep acts as an important component of physical growth and biological and mental development, considered a source of revitalization of organic functions associated with health indicators 2 . Moreover, proper sleep stimulates the immune system, helping it to fight infections and can thus reduce the risk of diseases 3,4,5 .
According to the National Sleep Foundation (NSF; United States) 6 , sleep should last for nine hours per night for adolescents to have optimal good health and development. However, research indicates that many teenagers sleep for less hours than appropriate. A study conducted in Brazil with 177 adolescents aged 12 to 19 years showed an average duration of 7.7 hours during the week 7 . Another, conducted with 524 Lebanese students, found an average sleep duration of 6.9 hours on weekdays 8 . In South Korea, 1,796 adolescents reported sleeping only 6.4 hours on school days 9 .
Among adolescents, digital screen viewing is common. These activities can take up more than 14 hours a day 3 . Increasing the time spent viewing television sets, computers, mobile phones, and various types of portable digital screens can damage adolescents' health, causing, for example, poor quality of sleep 10,11,12,13,14 .
In recent decades, the use of digital screens has changed how young people interact and acquire knowledge. As with cell phones, 75% of adolescents use them to access social media, online games, streaming services, and applications 15,16,17 . Therefore, it is important to highlight that screen time is their most common sedentary behavior, consisting of the time spent playing video games, using cell phones, tablets, computers, and/or watching television 15 .
Excessive use of digital screens can both impair sleep and reduce physical well-being among adolescents due to headaches, tinnitus, stomach pain, musculoskeletal pain, or high body mass index, among others 16,17 . Similarly, increased use of these digital screens is associated with a higher likelihood of social isolation, suicidal thoughts, self-mutilation, peer victimization, and mental health problems among adolescents 18 .
Therefore, this systematic review aimed to verify the relation between the use of digital screens and adolescents' sleep quality.

Methodology
This systematic review was registered on PROSPERO (protocol n. CRD42020203403) and was conducted according to PRISMA guidelines. Our clinical issue consisted of the question: "Does the time spent on digital screens influence the quality of adolescent sleep?" (P = adolescents; I = excessive use of digital displays; C = low use of digital displays; O = poor quality of sleep).

Eligibility criteria
Studies which evaluated screen usage time and sleep duration and quality among adolescents were included in this review. No restriction to date of publication, language, and study design were set but adolescents from 10 to 19 years of age were included, according to the World Health Organization (WHO) classification 1 . Case reports or series, letters to editors, literature reviews, theses, and dissertations were excluded.

Search strategy
The available articles from the following databases were included: MEDLINE/PubMed, LILACS, SciELO, Scopus, EMBASE, Web of Science, IBECS, Cochrane Library, ClinicalTrials.gov, and Open Gray.
The following descriptors were used in our advanced search: "Sleep Quality", "Screen Time", and "Adolescent" and their synonyms recognized by the Medical Subject Headings (MeSH) and Health

Results
Initially, we found 2,268 articles, of which we excluded 209 as duplicates, totaling 2,059 articles for title and abstract reading. After this phase, we chose 47 articles for a complete textual analysis. We excluded 24 studies since they failed to meet our inclusion criteria, leaving the 23 studies we included in this systematic review ( Figure 1).
As for temporal distribution, 21.73% of studies took place between 2010-2015; 33.43%, in 2017; 8.69%, in 2018; 26.08%, in 2019; and 13.04%, in 2020. We found no studies for 2016. As for their geographical distribution, 39,13% of the studies was conducted in Europe; 34.78%, in Asia; 13.04%, in South America; 8.69%, in North America; and 4.34%, in Oceania. Regarding their study design, 20 were transversal, and three, cohort. We found no randomized clinical or case-control trials. Table 1 summarizes the chosen studies on the use of digital screens and sleep quality, highlighting their authors, year, country of origin, type of study, sample, screen use duration, sleep quality, association between screen time and sleep quality, and the consequences of excessive screen use. Tables 2 and 3 show our bias risk assessment according to the cohort-specific NOS score and its version adapted for cross-sectional studies, respectively. Of the 23 studies included, we considered seven as poor (three cohort and four cross-sectional studies) and 16, as moderate (all crosssectional studies).

Figure 1
Identification of the final sample.

Discussion
This systematic review aimed to verify the relation between digital screen use and adolescents' sleep quality. Our results indicates that digital screen use at bedtime was associated with poor sleep quality, shorter sleep duration, and greater daytime sleepiness 5,7,11,21,22 . Our findings support recommendations suggesting that interventions be developed and evaluated to reduce access to digital screens at bedtime 5,7,11,14,21,22,23 .
We considered the three cohort studies evaluated by the NOS (Table 2) as poor 24,25,26 due to their incomplete sample data description and absent cohort monitoring, showing more than 20% of loss or incomplete description thereof. Moreover, it we found selection and information biases, confounding factors, and undescribed result importance and its applicability in clinical practice.
We considered the quality of the studies included in the modified NOS as moderate 3,5,7,9,10,11,12,13,14,21,22,23,27,28,29 (Table 3). Their limitations include non-validated measurement instruments 28 Table 2 Evaluation of the quality of cohort studies on the relation between sleep quality and use of digital screens in adolescents, based on the

Selection
Sample representativeness a  a  a  Sample selection c c c

Outcome
Outcome evaluation c c c    31  the fact that only three studies performed inferential analyses 12,24,26 , and lack of adjustment analysis for confounding factors 8,11,22,27,32 . We observed differences in the results of the analyzed studies. We believed that the low and moderate quality of their scientific evidence is due to disparities in their methodological and sampling criteria. Moreover, studies proved to be heterogeneous due to factors related to socioeconomic status 3,27 ; local cultural issues 5,11,12,23 ; questionnaire type, associated to different digital screen types 5,8,9,32 ; and time analysis of answers 3,14,21 .
Only four studies (out of 23) found sufficient sleep duration in their samples 5,22,32,33 . The literature reports that inadequate sleep duration leads to lower performance in social and school activities and greater daytime sleepiness in adolescents 8,28,33 . These findings indicate that access to and use of digital screens at bedtime damages individuals' health, causing low immunity, heart diseases, and reduced longevity, among others 22 . Moreover, we also found, in the study by McManus et al. 24 , an association of poor sleep quality with symptoms of depression.
The studies by Hisler et al. 25 and Jun et al. 27 showed a 4h30 and 4h40 daily use of digital screens (TV, mobile phones, video games, and computers), respectively. Scott et al. 13 verified a daily use of digital screens greater than 5h per day. Mak et al. 3 highlighted that adolescents spent 5h54min/day on digital screens. Among the limitations of the mentioned studies is their lack of description of the time of day at which individuals used screens.
Many factors lead to poor sleep quality in adolescents, ranging from biological factors (such as maturation changes) to environmental factors (such as family life, caffeine consumption, and use of electronic devices) 13 . Among young people, poor quality of sleep may be associated with its insufficient duration 10,14,25,26,28,31 which, in turn, may be related to biological and maturational factors, behavioral and social changes, increased school obligations, social activities, and excessive use of electronic equipment 14,25,26,28,31 . Note that bedtime changes appear to be greater in adolescents than in other age groups 25 . The literature has suggested that stressful (and sometimes annoying) media content may be an underlying factor of how mobile phone use can affect sleep 14 .
A large proportion of adolescents ignore the adverse effects of the use of digital screens, such as mobile phones, in bed 5 . They mistakenly believe that these media can help them sleep since they associate digital screens with their personal routine. However, using digital screens at bedtime can delay the onset of sleep. Some adolescents report finding it hard to turn off social media to sleep 13 .
Among all the digital screens the studies evaluated, cell phones are the most associated with poor sleep quality 3,5,7,9,11,12,21,27,30,31 due to their ease of access and practicality. The study by Munezawa et al. 21 pointed out that using a mobile phone after switching off the lights (> 2h a night) to make calls or send text messages is associated with poor quality of sleep among adolescents. It is important to highlight how school schedules influence adolescents' sleep duration and the conflict with the use of screens at night 34 since the excessive use of screens compromises school routine and sleep duration 26,31 .
Melatonin is a hormone produced by our body which regulates the circadian rhythm. The study by Cabré-Riera et al. 12 describes that refraining from using digital screens at least one hour before going to sleep is ideal for good sleep, as the light from the screen reduces the production of melatonin and gives the brain a false sensation that it is still day. Moreover, time spent on digital screens can replace time which might be devoted to study, which, together with worse sleep, can result in lower academic performance 8,28,33 . For a good sleep regimen, individuals need to stipulate an hour to sleep and wake and promote a silent environment with low light and away from electronic devices 5,20 .
Smith et al. 26 identified interventions to limit the use of screens to improve sleep in adolescents. Silent mode, turning theme off, time restrictions, no screens in bedrooms, screenless nights, and parent-set bedtime effectively restricted screen usage and improved sleep quality in adolescents, especially younger ones.
Mobile phone use and online browsing increase physical and emotional arousal, which could interfere with sleep quality 23 . Note that, besides cell phones, television is one of the digital screens adolescents most use 5,23,26,31,32 , especially at night, followed by electronic games, which are more used by boys 8,33 .
We also point out that the use of cell phones can cause musculoskeletal pain in adolescents' thoracolumbar region and back, caused by incorrect posture, inadequate furniture or prolonged use of screens while sitting 3,35 . Adolescents may experience neck pain due to overload by head tilt during device use 35 .
Poor sleep, associated with the excessive use of digital screens, has been closely related to adverse effects on the cognitive processes of the prefrontal cortex, which can negatively influence operational memory and the executive function of the brain 33 . Moreover, poor sleep reduces daytime alertness, the ability to learn new information in school, and hinder sports, driving, and working which, in turn, can affect attention and lead to adolescents' lower performance on social activities 8,24,28,33 .
Due to the evolution of technology and the replacement of textbooks by media devices in schools, the access and use of digital screens increased, especially due to the COVID-19 pandemic. We are unable to ignore the impacts of the COVID-19 pandemic, which emerged in China in late 2019 and spread rapidly around the world 36 .
Changes in the pattern of daily activity (as due to the COVID-19 pandemic), have further increased time spent with digital screens. This new condition caused several changes in lifestyle, physical and mental health, and relationships 37 . Measures of social isolation, school closing, linked to stress and anxiety made adolescents more vulnerable to excessive exposure to screens 38 . A Polish study found that the percentage of children and adolescents who spend more than six hours a day watching TV and using the Internet increased from 1.3% to 5.1%, influencing the quality of how they spend their hours 39 .
Another study conducted with immunosuppressed and healthy adolescents aged 10-18 years confirmed the increased use of meshes by both groups during the pandemic 40 , corroborating the findings of Zhou et al. 41 , who studied healthy adolescents and young adults aged 12-29 years old, who showed increased cell phone screen use and worse sleep quality, prolonged sleep latency, and shorter sleep duration.
We should emphasize that adolescents have a greater need for sleep than adults 25 , in addition to the occurrence of a natural delay in the time of sleep onset. Before the pandemic, adolescents followed a usual routine, with face-to-face classes and set times, which reduced the use of screens during school activities. After the pandemic, adolescents were able to make the schedule of their classes more flexible and adapt it to their sleep preferences. Online classes starting later, social distancing, changes in the class system (use of screens), and the pressure of confinement motivated a shift in sleep habits and quality 42 .
We found that the excessive use of digital screens has negatively affected these adolescents' lives. The increased use of these devices at bedtime negatively affects the relation between sleep and rest, stimulating physiological processes such as the suppression of melatonin release, a sleep-inducing hormone, and providing psychological changes, such as high levels of anxiety and depression 12 . Shorted sleep affects school and family routines. Thus, establishing a sleep regimen in adolescents' routines is essential to improve their quality of sleep and, consequently, their lives.

Limitations
The limitations of this study relate to most included studies showing cross-sectional designs, which precludes the assessment of cause-and-effect relations. Moreover, we observed some methodological limitations, such as undescribed sample losses and team calibration. Furthermore, the lack of standardization in the data collection methods of the chosen studies, such as sleep duration and screen use, hindered our comparisons.

Conclusion
This systematic review could verify that the use of digital screens influences sleep quality and can generate consequences which affect adolescents' quality of life. The analyzed studies showed that adolescents' show insufficient sleep duration (less than eight hours per day) and that the main digital screens used before sleeping are cell phones, televisions, computers, and video games. Excessive use of digital screens can bring some consequences, such as daytime sleepiness, night awakenings, difficulty waking, poor school performance, irritability, anxiety, depression, feelings of sadness, and sleep deprivation.

Contributors
S. S. Silva, M. A. C. Silveira, H. C. R. Almeida, M. C. P. Nascimento, and M. A. M. Santos contributed to the study design, data analysis and interpretation, and writing. M. V. Heimer contributed to the data analysis and interpretation and writing. All the authors approved the final version of the manuscript. S. S. Silva is also the guarantor of the study, responsible for its integrity as a whole, from its inception to its publication.