The objective of this systematic review was to summarise the published literature on experimental and longitudinal evidence on adolescent mobile device screen time or use, sleep and mental health and wellbeing. Five Research Questions guided this systematic review which includes evidence from both quantitative and qualitative studies.
Only 11 studies (quantitative=9, qualitative=2) met the inclusion criteria and were therefore the primary sources for answering the five Research Questions. As per the eligibility criteria, the included studies were conducted in Western high-income countries comparable to the UK context (USA, Canada, Australia, New Zealand, European countries). Therefore, findings are more likely to be transferrable to Scotland. Overall, the methodological quality of quantitative studies was poor and some studies lacked a detailed description of methodology which made assessing the risk of bias difficult. There were limited numbers of studies that assessed the same mobile screen device exposure and sleep or mental health outcome. In other words, there were various exposures (e.g. time spent using a mobile device, social media use) and various outcomes (e.g. sleep duration, sleep quality), and only one or two studies that assessed each exposure/outcome relationship, indicating an incomplete and inadequate body of evidence. The limitations in the quality of studies and/or incomplete evidence means that the observed associations must be interpreted with caution as there is a high risk of bias. With this in mind, the key findings were:
RQ1 (9 quantitative studies)
- Mobile phone use around bedtime and cybervictimisation, but not the overall time spent engaging in mobile phone activities per se (at any time of the day), was linked to lower sleep duration.
- Sleep quality was negatively influenced by mobile phone use in general and social media use in particular.
- Experiencing pressure to engage socially using a mobile phone was associated with poor sleep hygiene.
- Stopping phone use one hour before bedtime was not linked to earlier sleep.
- One pilot study (a small scale, preliminary study) showed that use of a smartphone app (under development) that teaches about the importance of consistent sleep and wake times, and recommended bedtimes was associated with a potential improvement in sleep duration, sleep quality and earlier sleep onset.
RQ2 (1 quantitative study)
- Experiences of cybervictimisation were indirectly associated with sleeping less than the recommended 8 hours per night. The factor linking cybervictimisation with shorter sleep was repetitively thinking and obsessing about distressing thoughts, emotions, and memories
- Other potential mechanisms (that have not been evidenced in longitudinal research) through which mobile device screen time or use affect sleep outcomes are sleep displacement (i.e. using the phone instead of sleeping), delaying sleep time, increased alertness through blue light exposure, psychological arousal which can result in bodily responses (e.g. faster heart beat) through binge watching and/or watching violent or upsetting content.
RQ3 (3 quantitative studies)
- Night-time mobile use and problematic social media use were linked to depressed mood through experiences of poor-quality sleep. Poor sleep quality also affected the link between night-time mobile phone use and low self-esteem, poor coping skills and higher externalising behaviour (e.g. disobeying rules, physical aggression).
- In a pilot study, the use of a smartphone app that teaches healthy sleep habits was associated with lower depressive symptoms. The app was also associated with reduced anxiety.
RQ4 (no studies identified)
- None of the included quantitative studies reported separate data for boys' and girls' mobile device screen time or use and its relationship with sleep that in turn might contribute to inequalities in mental health and wellbeing for boys and girls differently.
- In August 2019, a new eligible study was published which we did not include in our evidence synthesis because of its availability after we had completed our literature search.
- The study found that using social media multiple times daily when aged 13-15 predicted lower life satisfaction, lower happiness, and higher anxiety among girls 1- to 2-years later but not among boys.
- It also found that sleeping less than 8 hours per night, not being physically active most days, and experiencing cyberbullying play a detrimental role in the association between social media use and lower wellbeing in girls only.
RQ5 (2 qualitative studies)
- In the qualitative studies both adolescent boys and girls reported using smartphones in bed and recognised that it may negatively affect their sleep.
- Adolescents felt that sleep issues were connected to the content in video games rather than their use.
- Boys were more likely to report trying to follow guidelines (e.g. putting electronics away one-hour pre bedtime) whilst girls suggested they specifically used their mobile screen devices as a tool to aid sleep (e.g. listening to music).
- No study asked young people directly about their perception of the relationship between sleep and mental health but thinking of the importance of sleep revealed the 'energising, relaxing, stress-reducing and restorative qualities of sleep'.
- Young people reported the influence of mental health (e.g. anxiety, worries or fear of nightmares) on sleep.
- No study asked young people explicitly about the connections between screen use, sleep and mental health and wellbeing.
Strengths and limitations of the review process
This systematic review explored the body of knowledge on the link between use of different mobile device exposures and sleep, and the role of sleep in the association between mobile device exposures and mental health and wellbeing, taking adolescents' views and the most recent literature into consideration.
The strengths of this review were:
(i) Comprehensive search of literature published up to May 2019 in nine electronic databases,
(ii) Inclusion of longitudinal observational studies, experimental studies, and qualitative research studies,
(iii) Synthesis of the evidence for sleep and mental health and wellbeing outcomes by the different types of mobiles device screen time or use.
The nature of this work (turn-around time of 4 months) has inherent limitations which were as follows. Although a systematic search of the literature was applied, bias might have been introduced through the lack of independent duplicate screening of all articles at title/abstract and full-text stage, as well as independent duplicate data extraction and quality assessment of all included studies. Given the short timeframe for producing this evidence review no grey literature search was performed and, therefore, eligible studies and valuable evidence might have been missed, in particular on adolescents' views.
Implications for future research
There is a large body of literature on the cross-sectional association between mobile device screen time or use and sleep but the evidence regarding change over time is scarce both in amount and quality. Only two studies tested mobile device-related interventions for improving sleep outcomes but neither of these compared the intervention to a control group. This means that it is not possible to rule out that any observed change was due to other changes in adolescents' lives rather than the intervention itself. Therefore, to be able to understand the causal relationship between mobile device screen time or use and sleep outcomes, higher-quality prospective cohort studies and controlled intervention studies are needed. Furthermore, most potential mediating factors that might be at play in the causal pathway between mobile device screen time/use and sleep outcomes have been explored with cross-sectional data. However, to assess the mediating function of variables, longitudinal study designs with appropriate statistical modelling are required.
There is very little research available on the role of impaired sleep outcomes due to mobile device screen time or use and its subsequent effect on adolescent mental health and wellbeing. Verification of the observed associations in a large cohort of adolescents is warranted. Future research should also investigate the differential associations for boys and girls to inform the development of effective interventions and recommendations for mobile device screen time and use.
Finally, the voice of young people is not well represented in the literature with only two studies identified that explored links between mobile device use and sleep outcomes. It remains unknown to what extent young people perceive the negative consequences of mobile device screen time or use on sleep as a mechanism that affects their mental health and wellbeing. Future research should also explore interventions for improving mental health and wellbeing through strategies for better sleep. A co-production approach should be at the heart of future intervention development.
Given that mobile device technology has become such an integrated part of young people's lives, mobile digital technology could be part of the solutions for improved sleep outcome and subsequent mental health and wellbeing. Interventions could build on learning from Werner-Seidler et al's (23) pilot work with the Sleep Ninja app. Automatic reminders (through machine learning technology) of when it is time to stop using the smartphone (e.g. one hour before bedtime) might be another approach worth exploring.
Implications for policy and practice
Policy and practice initiatives could target all or a combination of the identified modifiable factors within the causal pathway between mobile device screen exposures and impaired sleep, but the current evidence severely limits the recommendations that can be made. Only one study (18) provided suitable data to explore potential causal mechanisms through which mobile device exposure influences sleep outcomes. It suggests:
- Young people should be protected from cybervictimisation and mandatory requirements of social media platforms to develop algorithms that block aggressive and upsetting content could be put in place. Education on the impact of cybervictimisation and how to avoid it (e.g. adequate privacy settings) could be embedded in the school curriculum.
- Ruminative coping as a consequence of cybervictimisation could potentially be targeted by initiatives that strengthen resilience in adolescents, in particular teaching young people and their parents healthy coping strategies (e.g. help seeking and sharing thoughts/emotions, mindfulness).
Other potential mechanisms through which mobile device screen time or use affect sleep outcomes are displacement of sleep time, increased alertness through blue light exposure, psychophysiological arousal through binge watching and/or watching violent or upsetting content, but further research is required before policy and practice recommendations for these can be made.
The current Mental Health Strategy 2017-2027 of the Scottish Government does not explicitly state an action point that relates to the exposure of mobile device screen use (12). However, the findings of this systematic review have potential to inform Scottish Government's future mental health and wellbeing improvement activities. In 2018, the Royal College of Paediatrics and Child Health published "The health impacts of screen time: a guide for clinicians and parents" which included a recommendation based on expert opinion (rather than research evidence) that "screens are avoided for an hour before the planned bedtime" (page 8; (11). Further guidance on reducing mobile device use before bedtime and avoidance of mobile device use during bedtime requires additional research.
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