It is fair to say that many people’s lives are dominated by screens; far more than they were even ten years ago. For all of the benefits and convenience that screen-based technology can have, there are concerns about the potential impact on our health of excessive screen usage. The World Health Organization recently advised that screen time for children should be reduced as much as possible, to reduce the risk of adverse health effects (WHO, 2019). This led to perhaps unhelpful tabloid headlines such as “SWITCH OFF: Kids under two should never be allowed to watch ANY screens – or they’ll get fat” (The Sun, 2019).

Nevertheless, if there are genuine causes for concern regarding screen time, children and young people, who in many cases will have grown up as ‘digital natives’ with constant access to screens, are surely at highest risk. However, what do we actually know about the impact of screen use? If it is bad for you, how come? And if it is harmful to our health, what solid evidence is there to inform policies on safe and unsafe screen time.

A recent article in BMJ Open by Neza Stiglic and Russel Viner has taken on the challenge of pulling together everything we know from peer-reviewed evidence, in order to highlight what we know (and don’t know) so far about the effects of screen time on health. They focused on children and young people, given that they are understood to be most at risk due to their increased exposure to screens, in some cases from birth. Whilst they did find moderately strong links between screen time and some health issues, the evidence suggests that the potential impact is not quite as universal as you might expect. Furthermore, the scope and quality of the research available leaves many questions unanswered about what the dangers of screen time may or may not be.

They found that higher levels of screen time were related to some physical and mental health concerns, such as poor diet, obesity and depression. However, they found very little evidence to link screen time with other issues such as behavioural problems, anxiety and concentration. As discussed below, there may be more to it than meets the eye when it comes to interpreting these results.

Methods

The authors undertook a systematic ‘review of reviews’ to synthesise all of the evidence they could find relating to screen time and the health and wellbeing effects on children and adolescents. A standard ‘systematic review’ would scour the entire published literature for all papers relating to a chosen topic, the findings of all papers then being analysed to give an overall picture of the evidence. This is a well valued approach which gives the reader a quick grasp of what lots of research has found, without having to trawl through all the papers yourself.

In this review, the authors pulled together all of the systematic reviews that have already been carried out and made sense of the findings we have to date on this topic; hence it is a review of reviews.

The authors followed the PRISMA procedure which outlined the preferred method of reporting a review of this kind. A comprehensive search strategy was used and the quality of each review was assessed, i.e. looking at how well controlled the methods were, risk of bias, sample size, and so on. All of this gives us confidence that the authors were robust in their methods and that the findings are a good representation of what research is out there.

Results

In total, 13 reviews were found with evidence on screen time and the health and well-being of children and adolescents. The results were broken down into eight areas, each of which was investigated for its links with screen time. The areas were: body composition (including obesity), diet, mental health, cardiovascular risk, fitness, cognition and education, sleep, pain and asthma.

Body composition

The authors concluded that there was moderately strong evidence linking television screen time with obesity. This was based on finding correlations in a high proportion of studies which have tested this link. This association was only found for television screen time, but not for other forms of screen time such as computer and mobile phone. They did not find a specific amount or threshold of screen time required in order to be affected.

Diet

There was also moderate evidence for a link between screen time, particularly television, and a higher energy intake and less healthy diet. In one review, this link was found even in the absence of food advertising. Also, the effects were stronger for children with obesity, suggesting they are more susceptible to environmental cues.

Mental health

There were a number of reviews analysed covering different areas relating to mental health.

• There was some moderately strong evidence linking depressive symptoms with screen time, but very limited evidence for this being social media screen time.
• In some cases, it was found that spending more than two hours daily on screens was the threshold for problems to develop.
• Similarly, there was a moderately strong relationship between reported quality of life and screen time.
• However, there was no strong evidence linking screen time to other difficulties, such as anxiety, behavioural problems, hyperactivity and inattention, and poor self-esteem.

Cardiovascular risk

The only high-quality review found within the literature search concluded that there was no evidence to link any form of screen time with metabolic syndrome (MetS); a cluster of conditions which, occurring together, increase the risk of heart disease, or with individual cardiovascular risk factors.

Fitness

Four separate reviews examined the relationship between screen time and fitness levels. There was a weak and inconsistent association between the two, with some studies even reporting higher physical activity levels in those spending longer on screens. The authors concluded that there was no strong evidence for these links either way.

Cognition and education

Some reviews looked at whether screen time was linked to poorer cognitive development in children. There was some evidence that it was linked in infants, but overall the evidence was sparse. Furthermore, screen time was not found to affect educational attainment.

Sleep

The authors concluded that there was weak evidence from three reviews that screen time was related to sleep onset delay, total sleep and daytime tiredness. There was one low-quality review which was associated with poor sleep, for all forms of screen time. The evidence overall therefore is mixed.

Pain and asthma

Two reviews investigated pain and asthma respectively in relation to screen time. As such, the authors described the evidence as being insufficient for drawing firm conclusions either way.

Discussion

The aim of this paper was to conduct a systematic review of reviews, which compiled and analysed findings from all previous reviews investigating screen time, i.e. television, mobile, tablet etc., and various health and well-being factors in children.

The only moderately strong evidence suggested that children who spend longer watching television are more likely to be obese. The authors suggested that this link could be explained by the sedentary nature of watching TV. However, they also found that watching more TV was linked to having an unhealthy diet and eating energy-dense foods. Throughout the review, there is an issue of causality because there were no longitudinal or experimental studies available. This means that we cannot determine whether watching lots of TV leads to obesity, or whether obese children are more likely to watch TV, for example. The WHO guidance (2019), emphasises the need for non-sedentary behaviour in reducing health risks in children. This is undoubtedly sage advice, but based on this research it is not clear whether this needs to exclude the use of screens for everyone.

Aside from diet and body composition, the only other moderately strong evidence linked screen time to depression. One of the characterising features of depression is a lack of motivation and energy, which might help explain this association. Watching TV is a sedentary pastime, so it perhaps makes sense that those suffering with depression would engage more in this type of activity. Again, the issue of causality is at play here, without being able to say whether depression leads children to watch more TV, or vice versa. What is also not clear-cut is the role of other variables in this relationship. For example, is the type of TV programme watched important? The review complements previous elf posts such as this blog by Sarah Hetrick on a study of university students, which could not tell us whether negative social media experiences actually cause depression; simply that there was an interaction between these two factors.

 

The authors reflect on limitations of the study and raise several interesting points. Firstly, they discuss the generalisability of the review’s findings, because the studies within it are heavily weighted towards TV as the mode of screen time. This is clearly inadequate given that the methods via which young people are consuming digital information on screens is changing, as is the scope and type of content, including social media. To be able to advise appropriately, we need to know how much the effects of screen time relate to how long young people spend on screens, the content of what they are watching, and the context in which they are watching it. The authors suggest that the harmful effects of screen time could act via various means, such as:

• The act of screen time indirectly encouraging sedentary behaviour, i.e. displacing physical activity
• The content of screen time directly influencing young people, e.g. through advertising, desensitisation to violence or sexually explicit material, or exposure to bullying
• The act of screen time replacing socialising or learning time, which might lead to social isolation.

Perhaps the most striking finding of this review, is that the majority of health variables investigated were found not to be negatively affected by screen time. The authors suggest that those who argue strongly that digital media is having adverse effects on our health and social and cognitive development might be overestimating the potential for harm.

One of the major limitations identified was not of the methods used within the review, but of the lack of research in the wider literature on modern forms of digital media such as computer and mobile. Furthermore, the quality of evidence was generally low to moderate, with possible ethical considerations explaining the lack of longitudinal or experimental designs.

Overall, this was a well-conducted, highly relevant and valuable review. Over and above the actual findings, the review highlights a concerning lack of robust evidence for or against modern forms of screen usage among young people. The evidence base needs to be strengthened significantly in order to create the setting for a far more informed debate about the possible harm, and possible advantages, to young people by using screens.

Links

Primary paper

Stiglic, N., & Viner, R.M. (2018). Effects of screentime on the health and well-being of children and adolescents: a systematic review of reviews. BMJ Open, 9. e023191. doi:10.1136/bmjopen-2018-023191.

Other references

World Health Organization. (‎2019)‎. Guidelines on physical activity, sedentary behaviour and sleep for children under 5 years of age. World Health Organization.

McDermott, N. (2019, April 24). SWITCH OFF Kids under two should never be allowed to watch ANY screens – or they’ll get fat, WHO warns. The Sun. Retrieved from www.thesun.co.uk on July 27, 2019.

Photo credits

• Photo by Hal Gatewood on Unsplash
• Photo by Diego Passadori on Unsplash
• Photo by Noiseporn on Unsplash
• Photo by Boudewijn Huysmans on Unsplash
• Photo by Prateek Katyal on Unsplash