Children who are heavy users of social media are unhappier about their appearance than those who never use sites such as Facebook and Twitter, according to a leading study supported by the British Government.
The survey of 3,500 children, aged 10 to 15, found that only 53% who were on social networks for more than three hours a night said that they were happy with their appearance, compared to 82% for non-users.
Girls were twice as likely as boys to say that they used social networks for such long periods, according to the UK's Office for National Statistics (ONS).
Heavy users of social media are also more likely to argue with their parents. Some 44% who are online for more than three hours said that they quarrelled with their mum more than once a week.
The figure was nearly half that for light and non-users of social networks.
The figures are drawn from a survey of UK households being carried out over a number of years by the Institute of Social and Economic Research at Essex University and supported by a number of government departments.
They show that 17% of heavy social media users are bullied a lot or quite a lot, compared to just 11% of light users.
Truancy rates are higher for heavy users (14%) than light users (6%).
Heavy users were also twice as likely to say that they misbehaved in class.
Dissatisfaction with relationships was more prevalent in children who defined themselves as heavy social media users. They were less happy with friends, less happy with family and 5% said they did not feel supported by their family, compared to just 1% of youngsters who said that they were seldom on social sites.
The survey, entitled Understanding Society, involves 40,000 households across the UK and covers all ethnic groups. Respondents are asked to complete repeated questionnaires to track changing circumstances and attitudes. Alongside the adult surveys are questionnaires for children, aged 10 to 15, looking specifically at their well-being.
The one positive finding to emerge from the survey concerned children's educational aspirations after they reach 16.
Some 90% of heavy social media users said they wanted to go to university compared to 87% of the most modest users and 82% of those who avoided social networks altogether.