British teenagers are damaging their health by not getting enough sleep because they are distracted by electronic gadgets in their bedrooms, according to a survey on Tuesday.
Advice body The Sleep Council said "junk sleep" could rival the consumption of unhealthy junk food as a major lifestyle issue for parents of teenage children.
Its poll of 1,000 youngsters aged 12 to 16 found that 30 percent managed just 4 to 7 hours sleep as opposed to the recommended 8 or 9 hours.
Almost a quarter said they fell asleep more than once a week while watching TV, listening to music or using other electronic gadgets.
"This is an incredibly worrying trend," said Dr Chris Idzikowski of the Edinburgh Sleep Centre.
"What we are seeing is the emergence of Junk Sleep - that is sleep that is of neither the length nor quality that it should be in order to feed the brain with the rest it needs to perform properly at school."
Nearly all the teenagers had a phone, music system or TV in their bedroom, with around two-thirds possessing all three.
Almost one in five of the teenage boys said the quality of their sleep had been affected by leaving their TV or computer on. The survey also found that 40 percent of youngsters felt tired each day, with girls aged 15 to 16 faring the worst.
However just 11 percent said they were bothered by the lack or quality of sleep.
"I'm staggered that so few teenagers make the link between getting enough good quality sleep and how they feel during the day," Idzikowski said.
"Teenagers need to wake up to the fact that to feel well, perform well and look well, they need to do something about their sleep."