Late for work again? Just blame it on 'social' jet-lag, say researchers

HALF the population are in a permanent state of jet-lag because their body clocks are so out of synch with the demands of modern life, sleep researchers claim.

A study of 500 people found huge variations in people's natural sleeping patterns, with some early risers getting up at the same time night owls were going to bed.

Professor Till Roenneberg, of Ludwig Maximilians University in Munich, said this meant that at least one person in two was "in effect, socially jet-lagged all the time" because their body clock did not conform with their working hours.

He suggested that the start times of schools and workplaces should be more flexible, to ensure pupils and staff were operating at their best.

Another sleep expert said the conclusions in the report, published in the journal Chronobiology International and reported by New Scientist were "absurd".

Prof Roenneberg said about half the people in his study were disadvantaged by work start and finish times, which he calls "external time" - particularly those whose internal clock meant they should still be asleep when they had to go to work.

"When you travel longitudinally, you suffer jet-lag because, when you arrive, the external time is different from your internal time," he said.

"External time in Germany [and other countries] has never changed since agricultural times and about half the population have to live with an internal and external time difference that is comparable to jet-lag."

And he said the problem was chronic. "Imagine you have to work on Moscow time, but you live in Edinburgh - that's what I'm talking about," he said

Prof Roenneberg said the problem was revealed at the weekends, when people reverted to more natural sleep patterns. Those worst affected by "social jet-lag" slept for about half their time off, simply to recover, he said.

Some people, he added, "are probably leaving work when they start to function well", while "in the first hours of the day they are not in a very good shape".

Sleep patterns tend to change as people get older; young children are usually early risers, adolescents gradually sleep later, a trend that peaks in the 20s and then reverses, with older people more likely to wake early.

Prof Roenneberg suggested altering school and work start times to fit better with this pattern would make a "huge difference" to exam results and productivity. He suggested more companies should start work at 10am rather than 9am because the biggest problem is with people who have not fully woken up in the morning.

Fellow sleep expert Professor Jim Horne, of Loughborough University, said the study was interesting, but he was critical of the conclusions.

"Most people like to have a lie-in, but you cannot say they are 'socially jet-lagged'," he said.

"If you ask most people if they want more sleep, most would say 'yes'."

"I'm not sure you can say there's something wrong with that - the idea your body clock is out of synch with life and you are suffering some kind of disorder like jet-lag seems absurd."

Prof Horne said about 20 per cent of the population were late risers, and about the same proportion early risers. And only about 10 per cent of the tendency to wake late or early was genetic. "The rest is social, lifestyle, the people around you," he said.