Vicious cycle causes tiredness

TEENAGERS who sleep in are not lazy, they are just not getting enough sunlight in the morning, scientists claimed yesterday.

Light in the morning is essential to kick start a teen's body clock because it delays release of sleep hormone melatonin.

So a lack of morning light makes them go to bed later, as they don't recognise it's night time and this makes it harder for them to get up the following morning.

The disturbance to sleeping patterns affects concentration.

The study was conducted by America's Rensselaer Polytechnic Institute's Lighting Research Centre.

Dr Mariana Figueiro, who led the study, said: "These light-deprived teenagers are going to bed later, getting less sleep and possibly under-performing on tests. We are starting to call this the teenage night-owl syndrome."