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.