A "steep increase" in the use of computers, phones and other devices was putting the health of young UK citizens at risk, according to a World Health Organisation report.
According to data for England, Wales and Scotland over three-quarters of children aged 11 to 15 spent two or more hours using electronic devices on weekdays.
According to experts, this was reducing the amount of time children took to exercise each day, increasing the risk of ill health.
Use of gadgets had more than tripled for girls aged 15 and above between 2002 and 2014, with increasing use of social media.
Of 42 countries that WHO studied, Scotland reported the highest computer use by girls.
According to lead author Dr Jo Inchley from the University of St Andrews, risks posed by the increased use of social media included cyberbullying and sleep deprivation.
She added that inactivity also posed the long-term risk of cardiovascular disease, obesity and Type 2 diabetes.
Dr Inchley said, "One of the main challenges for us is that this kind of activity (social media and computer use) is so much part of young people's lives these days, how do we manage this and the health risks associated with it?'', Sky News reported.
In England in 2014, for children aged 11 to 15, 74.6 per cent of girls and 76.5 per cent of boys used a computer, tablet or phone for two or more hours on a weekday that was not for playing games.
The corresponding figures for Scotland were 79.9 per cent of girls and 83.6 per cent of boys, and in Wales there were 76.4 per cent of girls and 84.6 per cent of boys – all greater than 50 per cent rise on 2002 figures.
Dr Inchley 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.''