Are we at our most alert in the morning? In the case of young adults the answer is no, says Russell Foster, a fact that may have a detrimental impact on their ability to learn

We spend about 30 per cent of our lives asleep. A prodigious amount of time engaged in what Thomas Edison regarded as a criminal waste of time. The persistent failure to appreciate the nature of sleep is perhaps the main reason why our 24/7 society has such little regard for it.

At best we tolerate the obvious need for sleep, and at worst we think of sleep as an illness that needs a cure. This attitude is beautifully portrayed by Jonathan Coe in his book House of Sleep . One of the central characters, the deranged Dr Dudden, describes sleep as a plague that shortens life by a third and regards insomnia as the cure for this awful disease. We laugh at this portrayal, but it is frighteningly close to the attitude held by many of our leaders and policymakers. How often do we hear that "sleep is for wimps and the lazy"? We are obliged to squeeze more and more into an already overcrowded day - and sleep is invariably the first victim. When we were ruled by sunrise and sunset, rather than the alarm clock and electric light, we intuitively appreciated the benefit of sleep. Shakespeare often mentions sleep: in Julius Caesar , we are told to "Enjoy the honey-heavy dew of slumber". And John Keats in his poem What Is More Gentle than a Wind in Summer? provides a moving eulogy to sleep.

Our more recent marginalisation of sleep is harmful to all - but young adults may be particularly vulnerable. New studies allow us to appreciate some of the fundamental functions of sleep. For example, a fascinating paper published by neuroscientist Jan Born's group at the University of Lubeck in Germany examines the relationship between creativity and sleep.

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His group studied "insight" - the process of mental restructuring in the brain that leads to sudden understanding or explicit knowledge. Their subjects were asked to perform a mathematical task that could be completed in a straightforward linear sequence. However, it was also possible to complete the assignment more quickly by appreciating that there was a hidden rule to it. The participants were familiarised with the task and either tested later in the same day, allowed to sleep overnight and tested the next morning, or kept awake and tested the next morning. Yet another group was not given a period of familiarisation with the task but was tested fresh after either a night of sleep or being kept awake. With these various combinations, the researchers were able to control for the effects of fatigue, and the results were striking. The chance of gaining insight and completing the task quickly was almost three times higher if the individual had been allowed to sleep overnight.

This elegant study demonstrates that sleep allows the restructuring of a new memory. In short, sleep seems to allow insight and hence the expression of a critical aspect of our creativity. Perhaps, therefore, it is no coincidence that Albert Einstein required eight to ten hours of sleep every night and that many artists and scientists have woken from sleep with a long-standing problem solved, including Friedrich Kekule, who came up with the chemical ring structure of benzene - the famous image of a snake biting its tail. In the arts, Robert Louis Stevenson had his inspiration for The Strange Case of Dr Jekyll and Mr Hyde after sleep; Jules Massenet claimed that several of his opera compositions came from his sleep and dreams; and Paul McCartney awoke from sleep and found the music to Yesterday firmly lodged in his head.

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On average, adults sleep 7.2 hours a night, and evidence from the historical literature and from experiments on individuals who are allowed to sleep as much as they want suggests that we slept significantly longer in the recent past. But the introduction of electricity and artificial light in the 19th century and the restructuring of work times have progressively detached our species from the 24-hour cycles of light and dark. In general terms, sustained periods of reduced sleep will result in poor performance ranging from increased errors, impaired vigilance, poor memory, reduced mental and physical reaction times, reduced motivation, increased risk-taking and depression.

Sleep loss and disruption is most dramatic in night-shift workers, and a series of recent studies on American medical students by researchers led by Charles Czeisler, professor of sleep medicine at Harvard University, demonstrates the alarming consequences of overtime. These students had schedules of about 70-80 hours a week, and often had to work a single shift as long as 32 hours four times a month. Czeisler's findings showed that these medical students had a 16 per cent increased risk of having a car crash during their commute from work to home and a 32 per cent increased risk of committing a serious medical error while working overnight on the wards. Reducing the total time at work to 63 hours a week and allowing shifts of no longer than 16 hours a day made mistakes less than half as likely. Sleep deprivation is also associated with a range of metabolic abnormalities, with glucose metabolism being particularly sensitive to sleep loss. In a study by Eva Van Cauter and her team at the University of Chicago's department of medicine, young men were allowed only four hours of sleep for six consecutive nights before they were given a high-carbohydrate meal. It took these individuals 40 per cent longer to regulate their blood-glucose levels and insulin fell to levels seen in the early stages of diabetes. Allied studies have shown that sleep loss elevates the hunger hormone ghrelin and depresses the hormone leptin, which gives us our sense of feeling full. The authors of these studies suggest that long-term sleep deprivation might contribute to chronic conditions such as diabetes, obesity and hypertension - which are now alarmingly common in the young.

But it gets worse. One night without sleep has been shown to lower the activity of one type of immune cell, called a natural killer cell, by as much as 28 per cent. Sleep disruption also increases the level of the stress hormone cortisol. Just one lost night can raise cortisol levels by nearly 50 per cent by the following evening, and a side-effect of cortisol is to suppress the immune system. Small wonder that sleep-deprived individuals are more susceptible to colds, flu and other infections.

Among the most deprived are teenagers, and an increasing body of evidence from sleep researchers suggests that relatively minor changes in the way we time educational activities could have major benefits. Work by professor of chronobiology Till Roenneberg and colleagues at the University of Munich has shown that sleep timing changes markedly as we age. By puberty, bed times and wake times drift to later and later hours. This tendency to get up later continues until about the age of 19.5 years in women and 20.9 years in men. At this point, there is a reversal and a drift towards earlier sleep and wake times. By the age of 55 we are getting up as early as we did when we were ten. These and allied results demonstrate that young adults really do have a problem getting up in the morning. Roenneberg stresses that this is due to our biology and is not an artefact of our society and that this delayed sleep and wake time may be part of the reason why young adults are so chronically sleep deprived.

Mary Carskadon, a researcher in the biology of sleep, has shown that, on average, US teenagers sleep about 7.5 hours a night during the week, but as many as 25 per cent get fewer than six and a half hours a night. She estimates that to be optimally alert teenagers need about nine hours of sleep. Carskadon's work shows as untrue the long-held assumption that, as children develop into young adults, they need less sleep.

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Teenagers show both delayed sleep and high levels of sleep deprivation, and these problems have been largely ignored in terms of the time structure imposed on teenagers at school. Studies by psychologists Lynn Hasher and David Goldstein at the University of Toronto and Carskadon have shown that a later starting time for school would greatly improve alertness and the mental abilities of teenagers during their morning lessons. So why do our schools have to start so early? Hasher and Goldstein point out that there is a longstanding Western cultural belief that we should be active in the morning - as illustrated by aphorisms such as "early to bed, early to rise, makes a man healthy, wealthy and wise" or "the early bird gets the worm".

But this simply ignores the absence of morning activity preferences in most adolescents and young adults. Hasher and Goldstein also make the point that there is a widespread belief that subjects such as English and mathematics should be taught early in the school day while other, possibly less analytical topics, such as physical education, art and music, should be taught later in the day. The assumption is that teenagers are, or should be, more alert in the morning and that is when the intellectually demanding subjects should naturally be taught. But the work of Carskadon, Hasher, Goldstein and others has shown that although children and adults prefer mornings, teenagers and young adults prefer afternoons or evenings for both intellectual and physical activities. It is ironic that the performance of young adults tends to improve across the day, while their older teachers will show a decline in performance over the same period. Young adults are sleep deprived and forced, like shift workers, to function at a time of day that is suboptimal for their performance. A cursory glance at the online advice given to students by university student health centres shows that "tiredness and sleep problems" feature large. My guess is that the incidence of such problems has increased in the past few years. Why? Because many students now work long hours to help finance their degrees.

Time formerly spent sleeping is now spent earning the rent. The only certainty about any reorganisation is that it will produce unintended consequences. Many predicted that the loss of student grants would cause financial hardship, but to my knowledge nobody articulated the view that this withdrawal of funding might generate numbed brains.

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Perhaps it is not too surprising that teenagers and young adults turn repeatedly to stimulants to compensate for their sleep loss. At the relatively benign end of the stimulant spectrum are caffeinated and sugar-rich drinks. The effects of caffeine act within 15-30 minutes and increase performance, learning and memory and muscular strength and, overall, caffeine reduces sleepiness. There is considerable individual variation in how quickly caffeine is metabolised, but it can stay in the body for many hours. So an afternoon or evening cup of coffee can result in significant amounts of caffeine at bedtime - and this has been shown to delay sleep. The results of a shortened sleep are felt the next day, and are reversed by repeated doses of caffeine. Caffeine, of course, is not the only stimulant used by teenagers. Nicotine improves alertness, hand-eye co-ordination, concentration, reaction times and short-term memory compared with non-smokers after sleep deprivation. The developing teenage brain may be particularly sensitive to the addictive effect of smoking. Edward Levin, professor of psychiatry and psychological and brain sciences at Duke University, suggests that teenagers are more likely to become seriously hooked on cigarettes than those who take up the habit as adults.

After a day of caffeine and nicotine consumption, sleep can be difficult. And this is where sleeping pills and alcohol, with their sedative effects, are often used. But although alcohol can promote sleep it also shortens sleep, particularly the amount of rapid eye movement sleep - that part of sleep so important to our reasoning and mental processing. And so a vicious cycle can develop where alcohol is used to induce sleep at night in the overstimulated brain, and increasingly higher levels of stimulants, such as caffeine and nicotine, are used during the day.

It is time we stopped ignoring the sleep patterns of young adults. Sleep provides all of us with our sense of wellbeing and the faculty that helps make us human - our extraordinary capacity for creativity and innovation. It is cruel to impose a cultural pattern on teenagers that makes them underachieve. Most school regimes force teenagers to function at a time of day that is suboptimal, and many university students are exposed to considerable dangers from sleep deprivation. This imposition may trigger a cascade of events that at best amplify the problems of adolescents and at worst may precipitate a crisis for the developing brain.

Russell Foster is professor of circadian neuroscience at Oxford University. His research considers how the brain generates our 24-hour rhythms of activity and rest and how light regulates these rhythms. He will speak at the conference Creativity or Conformity: Building Cultures of Creativity in ÖйúAƬ at the University of Wales Institute, Cardiff, January 8-10.

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