smartphoneA combination of natural hormone changes and greater use of screen-based technology means more than half of all teenagers may be sleep deprived, according to experts.

Research has suggested teenagers need nine hours' sleep to function properly but Russell Foster from Oxford University says it is "largely ignored".

The Professor of Circadian Neuroscience said: "Sleep is fundamentally important but despite this it's been largely ignored as part of our biology."

"Within the context of teenagers, here we have a classic example where sleep could enhance enormously the quality of life and, indeed, the educational performance of our young people. Yet they're given no instruction about the importance of sleep and sleep is a victim to the many other demands that are being made of them."

Teens naturally veer towards later bedtimes
Research has shown that teenagers naturally veer towards later bedtimes and are later to rise in the morning, possibly because of the hormonal changes that occur during puberty.

However, Prof Foster believes electronic equipment accentuated this natural night-owl behaviour.

"The data that's emerging suggests that these computer screens and gaming devices may well have a big effect in increasing levels of alertness," he added.

"The great problem with teenagers is that you're not only biologically programmed to go to bed late and get up late, but there's also many attractions like gaming and Facebook and texting and many teenagers are doing this into the early hours of the morning and delaying sleep even further."

A recent pilot study by charity Sleep Scotland suggested 52% of teenagers were sleep deprived, and about 20% reported falling asleep in class at least once in the last two weeks.