London - Social media could be wreaking havoc on the quality of sleep of millions of teenagers, affecting their academic achievement and emotional development.
Teenagers who spend more than three hours a day on sites such as Twitter or Facebook have poor sleeping patterns, according to research led by the University of Glasgow.
They are more likely to wake up in the middle of the night and struggle to get back to sleep, more likely to still be awake after midnight and more likely to struggle to wake up in the morning, the scientists found.
Alarmingly, this applies to 33% of teenagers, putting them in the "heavy use" risk category.
Researchers who tracked 12 000 Britons aged 13 to 15 found 21% spent more than five hours a day using the websites, making them "very heavy users" and more than twice as likely to fall asleep late on school nights as "average users", who spent between one and three hours on social media.
The increased likelihood for "heavy users" was 23%. Heavy users were also 56% more likely to sleep past 8am on school days, while very heavy users were 97% more likely.
Furthermore, very heavy users were 36% more likely to wake up throughout the night and have trouble getting back to sleep, while heavy users were 8% more likely.
A similar pattern occurred at weekends and during holidays, with heavy and very heavy users more likely to stay up late and sleep in. "Low users" – who spent less than an hour a day on social media – were the least likely to fall asleep late.
Writing in the BMJ Open medical journal, the researchers said going to sleep late on school days was of "particular concern" because it led to poorer academic achievement and emotional development.
Dr Bernadka Dubicka, chairperson of the child and adolescent faculty at the Royal College of Psychiatrists, said: "Lack of sleep can be hugely damaging and is often related to poor mental health and academic achievement. Children and young people should avoid using screens in the last hour before bed as this will help them sleep better at night."