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expert reaction to guidance on physical activity, sedentary behaviour and sleep for children under 5 years of age

Reactions to a study published by WHO on young people and sedentary behavior.

Dr Kathryn Hesketh, Sir Henry Wellcome Postdoctoral Fellow, UCL Great Ormond Street Institute of Child Health and Centre for Diet and Activity Research, Cambridge, said:

“The available evidence, drawing on a large number of experimental and observational studies conducted internationally, now allows recommendations to be made about elements such as tummy time in infants, screen time/ restraint, and inclusion of 60 minutes per day moderate-to-vigorous intensity activity for preschool-aged children.

“In infants, tummy time when awake is particularly important for development: starting from a few minutes at a time when babies are very young, building up to at least 30 minutes across the day strengthens muscles throughout the body. This helps babies meet motor milestones, which in turn form the building blocks for future physical activity.

“As with older children and adults, minimising the time young children spend sedentary or restrained is also likely to be beneficial for their health and development. This is particularly true if sedentary time can be swapped for higher intensity physical activity.

“Overall, although the evidence base has grown substantially for preschool-aged children and particular health outcomes such as adiposity, greater experimental evidence is required in infants and toddlers, and from Low and Middle income countries, to inform future recommendations. 

“It is hoped parents, care givers and practitioners will find recommendations useful about the amount of physical activity, sedentary time and sleep each day that will lead to optimal health and development. However, as anyone caring for young children knows, often no two days (or nights!) are the same. Children meeting all guidelines in a 24-hour period will therefore see the greatest health and developmental benefits, but meeting as many of the recommendations as possible each day is also likely to be of value, particularly compared to children who do not meet any.”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“This new document has high aims – to provide guidance for those responsible, in the governments of all countries and in NGOs, for developing plans for improving the health of young children. In the light of that worthy aim, it has a few surprising features. Perhaps the most surprising is that, under every one of its lists of recommendations, the report explicitly says ‘Strong recommendations, very low quality evidence’. I do rather wonder to what extent global guidelines on public health policy, affecting millions of families, should be based on ‘very low quality evidence’. Indeed it seems a little strange that the public health experts who produced the report should feel able to make ‘strong recommendations’ on the basis of such weak evidence.

“I do have some sympathy for the many researchers who have, over many years, tried to gather evidence about the health effects of low amounts of physical activity, high amounts of sedentary behaviour, or not enough sleep, in very young children. In most cases it’s not possible to do experiments on the children; instead you have to observe their levels of physical activity, amounts of sleep and so on, and see if they are associated in any way with measures of health. The trouble is that young children who, for example, are not very active physically, tend to differ from those who are more active in many ways, other than just their level of activity. There might be other differences between the children themselves, or their families and family circumstances, that are the real cause of any differences in health, and not the differences in physical activity after all. Sometimes statistical adjustments can be made to try to allow for these other differences, but they can’t allow for everything.

“Admirably, the report gives considerable detail on the sources of evidence that they used, and I do generally concur with the assessment of the report authors that the evidence is of low quality. Although a large number of previous research studies were found and considered, the great majority were observational, and indeed many were cross-sectional studies. These are usually regarded as providing relatively weak evidence, even for an observational study, because they do not follow the participants up over time, so there’s no way to check that a possible cause of ill health actually occurred before the ill health it was suspected of causing. Also, the hundreds of research studies were so varied in terms of exactly what they measured that it was generally not possible to pool their findings using the standard statistical method for pooling findings – meta-analysis. Only one very small meta-analysis turned out to be possible, involving just four studies of the health effects of overweight.

“The new report acknowledges that the evidence is poor overall, and makes many recommendations for research to fill the gaps. But in the light of that, should the authors really be making such strong recommendations, which appear in many cases to be based largely on consensus of expert judgement? Would it have been better to be less precise, rather than attaching such detailed numbers and times without decent evidence to support them?

“There’s something particularly strange about the way that the guidelines on sedentary behaviour are presented in the summary pages at the beginning of the report (pages viii-ix). For physical activity and sleep time, the graphics showing the guidelines clearly match what’s said in words above them. But for sedentary activity, the graphics mention only ‘sedentary screen time’ and don’t refer at all to the guideline that children at every age under 5 should not be restrained (e.g. in a stroller) for more than 1 hour at a time. Why such prominence for screen time? What exactly is ‘sedentary screen time’ anyway? The glossary says that it excludes ‘active screen-based games where physical activity or movement is required’, but that’s not very clear in my view. How much movement is required to stop it being ‘sedentary’? What’s available for very young children in terms of screen-based games and activities continues to change a lot, and the available evidence, such as it is, will to some extent have been gathered about screen use that’s different from today’s. Maybe the lack of clarity here reflects what’s said in the section (page 9) giving the rationale for the recommendations on sedentary time. This recognises that some sedentary activities (at least, some that do not involve screens) are likely to be beneficial in terms of development and health, though the authors refrain from commenting on this in their guidelines because ‘An attempt to comment on all possible beneficial sedentary activities would risk leaving out an activity that is important in a particular setting.’ But it’s the guidelines that will get publicity and affect policies, not comments in the rationale section. Couldn’t the authors at least have said in their recommendations that not all sedentary activity has to be bad?”

Prof Andrew Przybylski, Associate Professor and Director of Research at the Oxford Internet Institute, University of Oxford, said:

“The guidance from WHO on sedentary activities is an interesting document. On the basis of common sense many of the recommendations make sense but in many ways the conclusions drawn about screens are out of step with scientific evidence of harm and many of the assumptions are not in line with recent guidance from the American Academy of Pediatricians and the Royal College of Paediatrics and Child Health.

“First, the advice is based on correlational evidence which is very low quality. The authors are overly optimistic when they conclude screen time and physical activity can be swapped on a 1:1 basis. This suggestion, and many others in the report are based on extremely small correlations and no evidence from intervention studies. The authors should have been much clearer that the advice is not evidence based. 

“Second, the authors fail to call for higher quality studies or the unlocking of industry data so that good scientific evidence can be collected. Both the need for high quality science and data from Facebook, Google, and video game makers has been identified by governments and health groups as necessary to increase our understanding of technology effects. The WHO report leaves this out.

“Third, the advice overly focuses on quantity of screen time and fails to consider the content and context of use. Both the American Academy of Pediatricians and the Royal College of Paediatrics and Child Health now emphasize that not all screen time is created equal.

“The context is key as screen time might have positive effects on the family system as a whole, for example freeing up parents to do necessary household tasks and provide young people benefits such as relaxation, low energy play, or communication with family.

“Taken together the report represents a missed opportunity for the WHO. The report doesn’t include information from other UNICEF research (e.g. and it is unfortunate the authors conclude screens are to blame on the basis of low quality evidence and tenuous correlations. None would contest the fact that increasing physical activity, sleep, and health are important goals and it is possible that screens impact young people in a wide range of ways but we won’t know that until good scientific studies are done.”

Dr Tim Smith, Reader in Cognitive Psychology, Centre for Brain and Cognitive Development, Birkbeck, University of London, said:

“In recent months UK parents of 0- to 5-year-olds and early-years practitioners have been bombarded with conflicting recommendations and guidelines about how and whether they should be managing their children’s screen time and sedentary behaviour, e.g. from the RCPCH and Chief Medical Officers. The release of new WHO guidelines does not help to clarify the situation, as its specific recommendations with regards to “sedentary screen time” and their negative impacts on physical, cognitive and psychosocial health are, by its own admission based on “moderate to very low-quality evidence”. There is currently no clear evidence for the specific duration limits proposed at this age range. While the report makes a potentially helpful step in distinguishing “sedentary screen time” from active screen based games, where physical activity is required, this remains an oversimplification of the many ways young children and their families engage with screen media.”

[In addition to the above comment from Dr Tim Smith] Dr Rachael Bedford, Research Fellow, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, said:

“During our research on infant and toddler touchscreen use – the Toddler Attentional Behaviours and LEarning with Touchscreens (TABLET) Project± – we have found that parents value a nuanced and personalised view of what “screen time” entails, as well as evidence-based duration limits and they are eager to know how to curate their child’s screen time to make it as educationally appropriate as possible. Unfortunately, empirical evidence of the causal impacts of different uses of screen media on developmental outcomes of very young children is currently lacking. Where there is consensus, is in the urgent need for such high-quality evidence to guide policy, particularly in the first few years of life where neural development is at its peak and potential impact of screen use, both positive and negative, may be at its greatest.”

±Dr Tim Smith and Dr Rachael Bedford Co-Lead the TABLET project

‘Guidelines on Physical Activity, Sedentary Behaviour and sleep for Children under 5 years of age’ was published by WHOat 14:30 UK time on Wednesday 24th April.

Declared interests

Dr Kathryn Hesketh: Dr Kathryn Hesketh is a member of the Expert Working Group revising UK Physical Activity guidelines for under 5s, which also used literature searches by the WHO to inform recommendations. 

Prof Kevin McConway: Kevin McConway is a trustee of the Science Media Centre, though these comments are made in a personal capacity and do not necessarily reflect SMC policy.

Prof Andrew Przybylski: I have no conflicts of interest to declare.

Dr Tim Smith: No conflicts of interest.

Dr Rachael Bedford: No conflicts of interest.

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