Teenagers in Britain may be putting their health and education at risk by spending too much time on social media at bedtime, according to a major study into adolescent sleep habits.

More than a third of teenagers spent at least three hours a day on social media, with a fifth devoting at least five hours to the activity, researchers found. Those who were on social media for three hours or more daily were most likely to get to sleep late.

Going to sleep late on school nights was a particular concern, researchers said, because it put teenagers at risk of “poorer academic and emotional outcomes”. Insufficient sleep in adolescence has been linked to a range of mental health problems, obesity and poor performance at school.

According to the study, the heaviest social media users also woke most in the night, a problem that may be driven, or exacerbated, by teenagers’ sleep being disturbed by notifications and the temptation to continue online conversations into the early hours.

Scientists at the University of Glasgow released the findings in a preliminary report that has yet to be peer reviewed and published in a journal. The report calls for support for young people to help them find a balance between social media and a good night’s rest, particularly on school nights.

“With the majority of adolescents reporting insufficient sleep to function properly or to meet recommended guidelines, there is growing concern that social media may be a contributing factor for today’s teenagers,” the researchers write.

Heather Woods, a psychologist at Glasgow, analysed data from the UK Millennium Cohort Study, a nationally representative survey that aims to explore the impact of home life on child and adolescent development. The study focused on data from nearly 12,000 children aged 13 to 15 from across the UK.

According to the report, the average teenager spent one to three hours on social media every day. A third, mostly boys, spent less than an hour a day on the sites. Social media use was classed as “high” for 14% who were on for three to five hours, and “very high” for 21% who were on for five or more hours. Girls were far more likely than boys to be heavy users, with 28% in the five hours plus group compared with only 14% of boys.

The study does not blame social media for sleep deprivation in teenagers, but those in the “high” and “very high” use categories were 17% and 68% respectively more likely to fall asleep after 11pm on school nights than similar teenagers in the “average” category. Both groups were more prone to rising late, after 8am, on school days.

Those who hardly used social media were least likely to fall asleep late or oversleep in the morning, suggesting that minimal use was best for a good night’s rest.

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Social media was also linked to poorer sleep quality, with the most avid users waking more in the night. Teenagers in the high and very high use groups were 7% and 28% more likely to report being awake at least “a good bit of the time” compared with average users. However, the study cannot rule out that broken sleep drives night-time social media use rather than the other way around.

Similarly, the trend for the heaviest social media users to go to sleep late may be down to teenagers who naturally fall asleep late using social media in bed until they feel tired. But the activity may also drive sleep loss, particularly on school nights, when it has to be crammed into night-time hours, and when routine tasks such as homework get done later because people are busy checking social media.

Holly Scott of the University of Glasgow, first author of the study, said: “We found that teenagers who spent more time using social media were more likely to fall asleep late on school nights. Although they also tended to wake up later, school start times meant they still were unlikely to get the hours of sleep they need on school nights.”

Other experts also raised concerns. “Given that on school days, young people tend to wake up by 8am, those who fall asleep later are more likely to have experienced fewer hours of sleep, and there is clear evidence that lack of sleep is related to physical and psychological issues,” said Bob Patton, a lecturer in clinical psychology at the University of Surrey. “The disturbed sleep experienced by those using social media for five or more hours a day will compound this further.”

But Andrew Przybylski, director of research at the Oxford Internet Institute, said the findings did not justify new restrictions on social media use. “The effects aren’t huge. A kid who is on Instagram for eight hours a day gets about half an hour less sleep than one who’s not using it,” he said. “This research is really good raw material for scientists to consider when we design studies, but it is not sufficient to change course.”