Social media use raises children’s risk of mental health problems by up to half, a major study has found.
Almost 10,000 youths aged 13 to 16 were observed over three years in England between 2013-2015 in the study published by The Lancet Child & Adolescent Health journal.
The study suggested efforts should be made to reduce young people's exposure to harmful content online.
Very frequent use of social media may compromise teenage girls' mental health by increasing exposure to bullying and reducing sleep and physical exercise, the study found.
The impact on boys' mental health appeared to mainly be due to other factors not revealed by this study, researchers said.
"Very frequent" social media use was defined by researchers as using social networks, instant messaging or photo-sharing services such as Facebook, Instagram, Twitter, Snapchat and WhatsApp three or more times daily.
Scientists analysed data from three sets of interviews with teenagers from about 1,000 schools across England, as they progressed from Year 9 in 2013 to Year 11 in 2015.
The teenagers were also asked about their experiences of cyber bullying, sleep and physical activity.
In both sexes, researchers found very frequent social media use was associated with greater psychological distress.
In girls, the more often they accessed or checked social media, the greater their psychological distress.
In 2014, 28 per cent of girls who very frequently used social media reported psychological distress on the general health questionnaire, compared with 20 per cent of those using it weekly or less.
But the effect was not as clear in boys.
Researchers also found that persistent, very frequent social media use across 2013 and 2014 lowered well-being in girls.
Girls who regularly used social media very frequently reported lower life satisfaction and happiness, and greater anxiety in 2015.
No significant associations were identified by the survey in boys.
The authors found that almost all of the effect on girls' well-being in 2015 was down to cyber bullying, reduced sleep and less physical activity.
They also found that nearly 60 per cent of the effect on psychological distress in girls in 2014 could be accounted for by their sleep being disrupted and by greater exposure to cyber bullying.
Reduced physical activity also played a lesser role.
But cyber bullying, sleep and physical activity appeared to explain only 12 per cent of the effects of very frequent social media use on psychological distress in boys.
That suggested there were other factors at play.
"Our results suggest that social media itself doesn't cause harm but that frequent use may disrupt activities that have a positive impact on mental health, such as sleeping and exercising, while increasing exposure of young people to harmful content, particularly the negative experience of cyber bullying," said Prof Russell Viner, who led the research.
His co-author, Dr Dasha Nicholls from Imperial College London, said: "The clear sex differences we discovered could simply be attributed to girls accessing social media more frequently than boys, or to the fact that girls had higher levels of anxiety to begin with.
“Cyber bullying may be more prevalent among girls, or it may be more closely associated with stress in girls than in boys.
"However, as other reports have also found clear sex differences, the results of our study make it all the more important to undertake further detailed studies of the mechanisms of social media effects by gender."
