Professor John Reilly is the sole UK member of the group, composed of 14 researchers from 11 nations, which is assessing the amount of time children aged under five spend sitting, in front of a screen or sleeping. In particular, it will research the impact of lifestyle changes in developing countries – an area which has been comparatively under-researched in the past.

The Guideline Development Group for WHO Guidelines on Movement, Sleep and Sedentary Behavior in Children Under 5 Years of Age recently held its inaugural meeting and is to develop guidelines over the coming year, to inform global policy and practice.

Professor Reilly said: “Many of the lifestyle issues for children aged under five are now emerging in developing countries. There are many children who fail to get enough sleep, spend too much time in front of screens and spend too little time being physically active; time which might otherwise have been spent asleep or active is now often spent using a smartphone or tablet, even in young children.

“All of this is unfavourable to children’s development, not only in health but also in cognitive development and educational attainment. It is also leading to an increase among adults in illnesses and conditions which were once far less prevalent in developing countries, such as obesity, diabetes, heart disease, stroke, dementia and some forms of cancer.

“Lack of sleep in infancy and early childhood has emerged as an important risk factor for obesity yet this is not widely known among the public, policymakers, and researchers. Our research recently found that hardly any of the completed or ongoing childhood obesity prevention trials targeted children’s sleep behaviour.

“Most research in this area, however, has focused on developed countries and prevention is essential in developing countries, which have limited resources to treat these diseases. The first step towards successful prevention is monitoring of early childhood lifestyle but there are currently no guidelines for this. The WHO group will produce the first global recommendations in this area; our guidelines will prompt countries to start to monitor these behaviours in young children, and to develop policies to improve them.”

The group was established by WHO in response to the 2016 Ending Childhood Obesity Report. Prior to the report, Professor Reilly was one of only 17 members of an international working group reporting to WHO’s Director General on science and evidence for ending childhood obesity.