A dramatic rise in the use of computers and social media is wreaking havoc on the health of young people, a report from the World Health Organisation (WHO) has suggested.
Data for England, Wales and Scotland shows that children as young as 11 are spending increasing amounts of time on tablets, computers and smartphones.
Experts say this is leading to an increasing risk of ill health, with the vast majority of young people also failing to take the recommended level of exercise each day.
The study found a “continuous steep increase” between 2002 and 2014 in the proportion of children and young people using technology for two hours or more each weekday for things like social media, surfing the internet and homework.
While use increased for both sexes, it more than tripled for girls aged 15 and over during this period, with experts blaming the rise of social media.
In England in 2014, for children aged 11 to 15, 74.6% of girls and 76.5% of boys used a computer, tablet or phone for two or more hours on a weekday that was not for playing games.
In Scotland, the figure was 79.9% of girls and 83.6% boys, and in Wales there were 76.4% of girls and 84.6% of boys – all more than a 50% rise on 2002 figures.
Of 42 countries studied by the WHO, Scotland came top for computer use by girls, while Wales was fourth and England seventh.
For boys, Wales was second, Scotland third and England 15th.
The WHO, together with experts from the Health Behaviour in School-aged Children study, sent questionnaires to more than 200,000 children in schools in 42 countries, including 5,335 in England, 5,932 in Scotland and 5,154 in Wales.
A breakdown by age showed children as young as 11 spending a large chunk of time online.
In Wales, 53% of boys and 47% of girls aged 11 used a computer for two or more hours on a weekday that was not for playing games.
In Scotland, the figure was 42% of boys and 45% of girls, while in England it was 39% of boys and 43% of girls.
Out of 42 countries, Wales ranked third, Scotland was fourth and England was seventh.
When it came to using computers, tablets or smartphones just for games, between a third and two-thirds of children were spending two or more hours every weekday on them.
Lead author Dr Jo Inchley, from the University of St Andrews, said the rise in social media was having an impact on young people.
She told the Press Association: “We know that a positive impact of social media is social connectedness and the sense of interaction.
“But we also know there are risks, such as cyber bullying and impact on mental health, as well as things like missing out on sleep. Also, there are longer-term impacts on physical health from being sedentary.”
She said these risks included cardiovascular disease, obesity and Type 2 diabetes.
She added: “It’s about reducing time being spent sedentary, and ensuring that children still have opportunity to be active. We really need to start addressing these challenges now.”
The report is being presented at the European Congress on Obesity in Porto, Portugal.