Turning out the light is key to stopping teenagers sleeping late, research says

It has been said that teenagers are programmed to wake up late, but new research suggests that simply turning down the lights at night could help them get to sleep - and make it easier to get up in the morning.

Delaying school start times - which has been suggested as a way to fit in with young people's sleep patterns - will not help youngsters get enough rest, the study suggests.

The research, by academics at Surrey University and Harvard Medical School, uses mathematical modelling to predict the impact of delaying school start times. The analysis, which used existing data, took into account factors such as whether someone is naturally a morning or evening person, the effects of natural and artificial light on body clocks and the typical time of an alarm clock.

It is accepted that teenagers like to sleep late and struggle to get up for school, the study notes, and a common explanation for this is that their biological clocks are delayed.

There have been suggestions that delaying lessons would allow youngsters to stay in tune with their sleep needs, it says.

While lessons in some US schools begin at 7am, most UK school start times are between 8.30am and 9am.

But the mathematical modelling found that delaying school start time in the UK would not help reduce sleep deprivation. Most teenagers' internal clocks would just drift later, and in a matter of weeks they would find it just as hard to get out of bed.

Instead, the research suggests the problem is teenagers' exposure to light. Getting up late in the morning leads to them leaving the lights on later at night, which delays their biological clock, in turn making it harder to get up.

The biological clocks of young people are particularly sensitive to light, it says.

Instead of moving UK school times, the modelling, published in Scientific Reports, suggests that young people should be exposed to bright light during the day, with the lights turned down in the evening and off at night.

Lead author Dr Anne Skeldon said: "What comes out of the maths is that teenagers are more sensitive to light, so there are physiological differences for teenagers. But if you were to look at teens who were hunter gatherers they wouldn't have had a problem getting up in the morning. Modern lifestyles make it harder for people to get up."

Turning off the lights includes switching off devices such as tablets and smartphones.

"There's been quite a lot about devices, and that's all consistent with what comes out of the modelling - light in the evening delays sleep," Dr Skeldon said.

She added that mathematics allows researcher to use existing knowledge about how light interacts with the biological clock to make predictions about what can help someone to get more sleep.

"It highlights that adolescents are not 'programmed' to wake up late and that by increasing exposure to bright light during the day, turning lights down in the evening and off at night should enable most to get up in time for work or school without too much effort and without changing school timetables."