Poor sleep has been linked to mental health issues such as mood problems, anxiety, and suicidality (1, 2). The recommended amount of sleep for young people is 8-10 hours, however research shows that sleep duration among young people is often much less than this. The number of young people reporting less than 7 hours of sleep per night has increased over the last decade (3, 4). Access to and use of a media device (e.g. a portable device such as smartphone or tablet) at bedtime has been associated with poor sleep quality, inadequate sleep quantity, and daytime sleepiness in young people (5). Studies have also shown that extended periods of screen time can displace positive activities (e.g. outdoor physical activity) that are beneficial for sleep outcomes and mental health (6, 7).
There is also increasing evidence of an association between mobile screen use and adverse mental health and wellbeing outcomes in young people (7, 8). A systematic map of reviews on this topic highlighted the increase in studies exploring the relationship between screen-based activities and mental health outcomes, and in particular, depression (7). Another review published in 2018 found that frequent mobile phone use was associated with depression and problems with sleep in young people (8).
A recent UK survey showed that among 5-19 year olds, 12.8% had at least one mental health disorder and the prevalence increased with age (9). The effects of inadequate and poor-quality sleep in adolescence can be serious and wide-ranging and there is increasing evidence of a bidirectional association between sleep disturbance and depression in young people (10). Poor sleep can lead to depressive symptoms while depression and anxiety are predictors of poor sleep (10) creating a negative feedback loop. The Royal College of Paediatrics and Child Health consulted 104 young people, age 11-24 years, across the UK about their views on screen time use and found that 88% felt that screen time negatively affected their sleep and 35% felt that screen time negatively affected their mood and mental health (11).
Despite the above research, the literature reviews that underpin the most recent advice on screen time and screen-based activities were focused only on television viewing (12). Yet, screen time now includes tablet and mobile phone use. Furthermore, the above systematic and literature reviews were primarily composed of cross-sectional studies (5-8, 10), which cannot answer questions of temporality or causal effects, including the potential mediating role of sleep on screen use and mental health outcomes. There are numerous calls for longitudinal studies that can clarify relationships between sleep, screen time, and mental health (7, 8, 10) and as these studies are being published with increasing frequency, a systematic literature review on the most recent experimental and longitudinal evidence is needed.
The Scottish Government released a report in 2019 titled: 'Exploring the reported worsening of mental wellbeing among adolescent girls in Scotland' (13). The report highlighted interrelated factors that could be influencing worsening mental wellbeing in Scottish adolescents, including inadequate sleep and social media use.
This systematic review follows on from the existing Scottish Government report, addresses the identified gap in the literature, and adds to the existing evidence reviews as the focus of investigation is the impact of: (i) time spent on mobile devices typically used by young people of the 21st century, and (ii) the type of mobile device activities or uses on sleep outcomes, and how this is affecting young people's mental health.
Review aim and Research Questions
The aim of this systematic review is to answer the following Research Questions (RQ):
1. To what extent does adolescents' mobile device screen time impact on sleep outcomes?
2. What are the potential causal mechanisms through which mobile device screen time affects sleep outcomes amongst adolescents?
3. What are the implications of the potential impact of mobile device screen time on sleep for adolescents' mental health and wellbeing?
4. To what extent might girls' and boys' differential mobile device screen time, and its relationship with sleep, contribute to inequalities in mental health and wellbeing by gender?
5. What existing evidence is there on adolescents' views of how mobile device screen time affects their sleep, and following on from this, their mental health and wellbeing?
Figure 1 illustrates the different pathways and directions of associations considered for this systematic review in relation to the Research Questions above.
Figure 1. Pathways and direction of associations underpinning Research Questions 1-5. (Yellow=Research Question 1, blue=Research Question 2, red=Research Questions 3-5)