Teenagers who use their phones and computers in bed before sleep, are two and half times as likely to be sleep-deprived than those who don't.

It follows an Australian study of 11500 teenagers.

Sleep/Wake Centre research fellow Karyn O'Keefe says the problem isn't just using the phone.

"It's the blue lights in the bright light devices like cell phones and TVs and computers that tend to operate with our body clock the most so if you can take that out of the equation it should have some impact on sleep."