Sleep scientists' wake-up call for later school starts
As they prepare a major study to test the idea, UK scientists have said that starting school at 10:00 could have huge benefits for teenagers.
Research suggests that society pays too little attention to our "body clock" - and adolescents in particular have a late-running biological rhythm.
This means insisting on an early start can cause sleep deprivation, which in turn can affect learning and health.
A sleep expert made the argument at the British Science Festival in Bradford.
Dr Paul Kelley said that adolescents effectively lose up to two hours of sleep per day, which is "a huge society issue".
He and colleagues from Oxford are leading a project called Teensleep, which is currently recruiting 100 schools from around the UK to take part in what Dr Kelley called "the world's largest randomised control trial", due to commence in 2016.
Ups and downs
Our body clock is a daily cycle which drives the regular rise and fall of certain genes as well as the ebb and flow of our cognitive performance, our metabolism and so on.
For much of our lives - and especially in adolescence - there is a mismatch between this rhythm and the typical working day.
In fact, Dr Kelley said, the body clock of most people between age 10 and 55 is not well suited to rising early.
"Most people wake up to alarms, because they don't naturally wake up at the time when they have to get up and go to work.
"So we've got a sleep deprived society - it's just that this age group, say 14-24 in particular, is more deprived than any other sector."
Dr Kelley and his colleagues, including well-known Oxford sleep researcher Prof Russell Foster, argue that school days should start at 10:00 and university at 11:00, to better match the circadian rhythms of adolescents and young adults.
"All the evidence points to the same thing," Dr Kelley told BBC News.
"There are no negative outcomes for moving [the school day] later, no positive outcomes for moving earlier."
The Teensleep experiment, which is funded by the Wellcome Trust and the Education Endowment Fund, will randomly assign its 100 schools into four groups.
One group of schools will shift their school days for 14- to 16-year-olds to a 10:00 start; another group will offer "sleep education" to their students.
This involves "helping students and staff realise sensible ways of making their sleep good sleep", Dr Kelley said, such as avoiding screen-based activity in the evening.
A third group of schools will introduce both a later start and sleep education, while a fourth, control group will make no such changes.
The interventions will commence in the 2016-17 academic year, and the researchers plan to report their results in 2018.
Derk-Jan Dijk is a professor of sleep and physiology at the University of Surrey. He cautioned that shifting the school day might be of limited use without changing other habits that affect our sleep, especially night-time light exposure - making the education part of the trial particularly important.
"It is clear that these adolescents tend to drift later. And many of them will probably prefer to start later," he told the BBC.
"But why do adolescents like to sleep in later and go to bed later? What is causing this?
"There is undoubtedly a biological component, but that interacts with our artificial light environment.
"And if we can't change that, then is delaying school times the best solution? Because that way you might not solve the problem - you might shift them even later."
Prof Dijk said the Teensleep experiment was an important one, which he would observe with interest.
"It will be very interesting to see the results."
What's stopping my slumber?
- A lack of sleep has been linked to weight gain, depression and reduced fertility.
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