RUSSELL Foster lives with three teenagers, and he's keen to defend the whole breed against accusations of laziness. The pale, pasty 15-year-old who prefers to stay up late and snooze long after dawn – ideally until lunchtime – is simply obeying biology.
The grandly-titled Professor of Circadian Neuroscience at Oxford University goes so far as to say that, rather than expecting teenagers to perform well in the mornings at school, it would be less cruel and more sensible to allow them a lie-in, conserving their efforts until later in the day when performance is at its natural peak.
Prof Foster studies body clocks or circadian rhythms. Watching his eldest, 17-year-old William, burning the midnight oil, then dragging himself out of bed for school early in the morning before crashing at weekends, is a pattern of sleep deficit followed by over-sleeping that neuroscientists the world over recognise.
"They're not just slobs, although that's how it appears to some people," says Prof Foster. "For reasons probably to do with hormonal and other changes in their bodies, including the release of the sleep-inducing melatonin hormone two hours later in teenagers than in adults, they don't feel like settling down in bed when the rest of us do."
Natural circadian rhythms in teenagers mean they are likely to underperform at school in the morning. They are more alert in the afternoons, and studies in the US and Germany have shown that in schools which switched to later start times, not only did test results improve but rates of truancy and depression fell.
Prof Foster goes so far as to say that, by imposing our traditional school hours on teenagers, we are forcing them into a pattern of under-achievement. However, unlike a few schools in Europe and America, the theoretical scheduling change that has found most favour in the UK is one that would start the school day even earlier.
"I know I've stuck a stick into a hornet's nest, but cognitive tests show that teenagers are more sparky in the afternoons. Yet teachers will tell you that they find young people more alert in the mornings."
It might be that they, the teachers, are more lively and cope better in the mornings, and find teenagers a bit too alert in the afternoons. Teachers' and students' biological clocks are almost certainly pulling against each other.
There's no suggestion that anyone is about to re-order the school day to suit the upside down body clock of the turbulent teenager, whose circadian rhythms will not calm down into something approaching an adult pattern until they are at least 20. Oversleeping at weekends, by the way, does little to address the "debt of sleep" accumulated by teenagers who get between five and seven hours a night all week.
Late-night activity, early mornings, the demands of study, hugely varied entertainment and sleep deprivation all combine to make young people vulnerable in terms of impaired mental development, poor performance and memory, reduced motivation and increased depression, says Prof Foster, who reckons society in general does not understand and value sleep enough.
The danger is, say the experts, that young people will resort to artificial stimulants more and more to keep them alert at the times of day in which we expect them to perform; they may also possibly use alcohol and drugs to relax them and induce sleep.
Mary Carskadon, a US expert in the biology of sleep, calculates that, to be really alert, teenagers need about nine hours' sleep. While society doesn't truly recognise the problems of teen sleep deficit, all that can be done is for young people and their families to be aware of the dangers of sleep debt and the need to rest for longer hours more consistently.
When our forebears were ruled by sunrise and sunset, rather than the alarm clock and light bulbs, they intuitively valued sleep, even if they didn't understand it. Albert Einstein didn't necessarily realise the relationship between adequate sleep and creativity, but sleep experts are not surprised that he snoozed for eight-to-10 hours a night.
The fields of the arts, sciences and innovation are littered with instances of great ideas or achievements arrived at on waking from a good long sleep, and scientifically-controlled tests underscore the relationship between peak creative performance, reactions, memory and problem-solving ability after sufficient sleep.
On average, adults sleep 7.2 hours a night, certainly longer than our grandparents. But the introduction of electricity and artificial light in the 19th century, together with the changing of working patterns, have gradually detached humans from the natural cycles of the 24-hour clock regulated by light and dark.
The effects of sleep loss are most dramatically highlighted in night shift workers, including medical students studied by Harvard University in the US. These students had 70-80 hour weekly schedules, and four times a month worked a single shift of 32 hours.
They were found to be 16 per cent more likely to have a road crash en route to or from work and 32 times more likely to commit a serious error while working overnight. In night shift workers at a metal plant, cardiovascular disease was up to 40 per cent higher than among their day shift colleagues.
Prof Foster says the burgeoning 24/7 society means we have demoted sleep even further in our scale of priorities. The body's natural response to light and dark (sleep in the dark, wake at daylight) does not switch off, even among long-term night shift workers.
Their circadian rhythms are not disrupted by artificial light at work, so the instinctive urge to slow down and sleep is constantly in conflict with the need to be alert and vigilant. Similarly, when they go home to sleep by day, their body's rhythm continues to tell them they should be awake.
Sleep deprivation has been linked with ill-effects to the body's metabolism, and research has identified a link between long-term lack of sleep and diabetes, obesity and high blood pressure – conditions which are growing alarmingly among the young.
Due to the relationship between sleep disruption and the increased levels of the stress hormone cortisol in the sleep-deprived, the human immune system is suppressed and we are more susceptible to colds, flu and infection. Just one lost night can raise cortisol levels by 50 per cent.
Drugs which increase alertness and super-high-intensity lights, mimicking daylight, are the focus of experiments in the quest to find an answer to conflict between the 24/7 society and man's natural propensity to sleep when it's dark. Drugs to beat jet lag and create "metabolically dominant soldiers", capable of fighting 24/7 without rest and without loss of judgment, are also in the pipeline.
The focus of worldwide scientific study is the relationship between the body's activity at different times and the effectiveness of drug treatments – including chemotherapy for cancer.
"Chemotherapy drugs don't distinguish between cancer cells and healthy cells that are actively going about their business and dividing," says Prof Foster. "We know a lot now about different bodily functions and their rhythm over 24 hours."
It makes sense, for instance, to give certain drugs during the night, when a major organ like the liver is "sleeping" and less likely to be damaged by the chemo. Adjusting the time of day of one childhood leukaemia treatment from morning to afternoon cut the risk of recurrence by two-and-a-half times.
"Changes might well mean, for instance, giving the drug at higher dosage during a shorter window of time," says Prof Foster. "So far the pharmaceutical industry isn't so keen on the idea, preferring the option of a higher dosage over a longer period. The fact that the industry is not actively interested has an effect on the dynamics of how such research is funded.
"Other studies are happening involving areas such as cardiac arrest and stroke, suggesting that anti-coagulant drugs need to be at peak effectiveness before you get up in the morning. The more we understand about the body clock and how functions are governed by night and day, the more we'll be able to improve treatments."
The bottom line is that the body clock is not trivial – and that sleep, far from being a waste of time, is at the heart of happiness and wellbeing.
sheena.hastings@ypn.co.uk

Rhythms of Life: The Biological Clocks That Control The Daily Lives of Every Living Thing by Russell Foster and Leon Kreitzman is published by Profile Books at £9.99. To order a copy call the Yorkshire Post Bookshop free on 0800 0153232 or order online at www.yorkshirepostbookshop.co.uk . Post and packing is £1.95.