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Eight hours they give to sleep.

Sir Thomas More, Utopia (1551)

The evidence that chronic sleep deprivation is a common feature of contemporary life comes in several interlinked strands. We will start with perhaps the most obvious one of all: the observation that many people feel sleepy when they are awake.

Assessing the extent of daytime tiredness in society is tricky, not least because so many people have come to regard feeling tired as normal. Nonetheless, numerous scientific studies have unearthed evidence that the problem is real and widespread. For example, a 2001 poll of Americans’ sleeping habits found that 22 per cent of adults felt so sleepy during the day that it interfered with their activities. A 1994 survey found that 5 per cent of the British population were experiencing severe daytime sleepiness, while a further 15 per cent felt moderately sleepy during the day. It also found that the people suffering from daytime sleepiness were twice as likely to have a vehicle accident.

A similar picture has emerged from other countries. For instance, a recent study discovered that 10 per cent of middle-aged Finns were excessively tired and tended to fall asleep unintentionally during the day. Their sleepiness was statistically associated with an array of nasty things, including a heightened risk of traffic accidents, premature retirement, depression and anxiety. In Sweden, 9 per cent of adults were found to be suffering from daytime sleepiness, while a survey in Warsaw recorded that 21 per cent of adults felt moderately sleepy during the day. Australian researchers detected excessive daytime sleepiness in 11 per cent of adults. You get the picture. Not even the youngest and healthiest are immune. A French investigation of 58,000 army conscripts discovered that 5 per cent of these fit young men were affected by excessive daytime sleepiness and 14 per cent of them were sufficiently tired to sleep during the day.

Overall, it is safe to conclude that at least one in ten adults in the general population (you, me and the people next door) are currently affected by moderate or severe daytime sleepiness. Some scientists believe the situation is much worse, with up to one in three adults suffering from significant sleepiness. A major review undertaken by the US National Commission on Sleep Disorders Research estimated that as many as 70 million Americans – more than a quarter of the population – were suffering from sleep deprivation or some form of sleep problem, at a direct cost to the national health care bill of about 16 billion dollars a year. The Commission’s report concluded that:

A convincing body of scientific evidence and witness testimony indicates that many Americans are severely sleep-deprived and, therefore, dangerously sleepy during the day … By any measuring stick, the deaths, illness, and damage due to sleep deprivation and sleep disorders represents a substantial problem for American society.

The problem appears to have deepened over time. Objective evidence about historical changes in sleepiness is hard to find, but there is some. A standard psychological test of personality, which has been regularly administered to large numbers of Americans since the 1930s, revealed that the proportion of men who felt tired during the day was significantly higher in the 1980s than it had been in the 1930s. And the average amount of sleep American students get has fallen by more than one hour over the past three decades. We seem to be a generally wearier bunch than our forebears.

Tired people are certainly common enough in the doctor’s waiting room. Physicians frequently encounter patients complaining of feeling tired all the time. The condition even has its own acronym, TATT. Of course not everyone who feels tired all the time is suffering from a lack of sleep. Chronic fatigue can result from anaemia, diabetes, cancer, depression and a whole host of other medical disorders. The distressing condition known as chronic fatigue syndrome (CFS), also referred to as myalgic encephalomyelitis (ME), is characterised by debilitating fatigue, pain in the muscles and joints, impairments in thinking and a general, horrible malaise. CFS is a distinct medical condition that cannot be attributed simply to lack of sleep. The origins of CFS remain controversial, but current theories focus on a combination of malfunctioning immune reactions and psychological factors.

CFS and other medical conditions undoubtedly account for some of the tiredness in society, but not much. The fact is that most people who feel tired during the day are just that – tired. They are tired because they have not been getting enough sleep. This explanation is so simple and so blindingly obvious that it is frequently overlooked.

Ordinary, everyday tiredness does not always require a medical explanation, but one is often sought nonetheless. ‘Exhaustion’ has become a voguish affliction of actors, pop stars and other celebrities. From time to time, a distraught and haggard celeb will flee to a clinic feeling, well, exhausted. The clinic duly subjects them to a battery of medical tests to establish whether they have diabetes, anaemia, ME or a thyroid disorder, while the media throb with stories about personal relationship problems, nervous breakdowns, exotic diets, exotic drugs, professional insecurities and emotional crises – just about everything, in fact, apart from plain tiredness. But given the long hours they are sometimes expected to work, plus the jet lag-inducing international travelling, it would be surprising if our stars of stage and screen did not occasionally feel very tired.

Another reason for believing that sleep deprivation is a common problem is that many of us get less sleep than we want or need, and considerably less than the proverbial eight hours we all supposedly aspire to. The evidence on this point is clear. For example, research found that in the 1990s young American adults were sleeping for an average of 7.3 hours a night. However, even this modest figure was inflated by weekend lie-ins: on weekday nights, Americans slept for an average of only 6.7 hours. A more recent study, which assessed the sleep patterns of middle-aged adults, found an average of only 6.2 hours. Similar conclusions have emerged from other countries. To give just a few illustrations, a survey in Poland found that adults there slept for 7.1 hours on workday nights, while Korean university students averaged 6.7 hours. When the Japanese Ministry of Health conducted a large survey they discovered that almost two thirds normally slept less than seven hours a night, and more than a quarter slept less than six hours. Worse still, half of Japanese high school students reported sleeping six hours or less on weekdays.

The research leaves little doubt that most adults in the USA, UK and other industrialised nations get substantially less than eight hours’ sleep most nights of the week, and many get less than seven. But does that matter? How much should we sleep?

The mythical inhabitants of Sir Thomas More’s idyllic island state of Utopia accorded sleep the priority it truly deserves. They slept for eight solid hours each night. Of the remaining 16 hours, work accounted for only six. (Sensible people.) The Utopians worked for three hours before noon then ate lunch; after lunch they rested for two hours, worked for another three hours then ate supper. They went to bed at about eight in the evening and slept for eight hours. The rest of each day they did as they pleased. Not quite the urban chic lifestyle, perhaps, but a refreshingly different perspective on life.

Conventional wisdom still holds that we need about eight hours of sleep a night. For most of us, however, the reality falls far short of the Utopian ideal, except perhaps at weekends and when we are on holiday. But is an average of, say, six or seven hours a night enough? Obviously, we cannot use Thomas More’s sixteenth-century fantasy as a scientific yardstick. So how do we judge the adequacy of sleep?

One approach is to ask people whether they think they are getting enough sleep. A recent study of more than twelve thousand adults did just that, and found that 20 per cent of them felt they were not getting sufficient sleep. Unsurprisingly, one of the factors most strongly associated with insufficient sleep was working long hours. Further evidence came from the Planet Project, said to be the largest opinion poll ever carried out. In 2000, an Internet-based survey was conducted with 1.26 million people in 251 countries. When asked how much sleep they needed in order to feel rested, 47 per cent of people replied eight hours or more. But when asked how much sleep they actually got, only 15 per cent reported sleeping eight hours or more, while 8 per cent said they got less than five hours a night. Many respondents reported having gone without sleep for long periods, whereas a mere 6 per cent said they had never missed a night’s sleep.

Six or seven hours of sleep a night is probably not enough for many people on a long-term basis. The experimental evidence suggests that the underlying sleep tendency for a typical healthy adult – that is, the amount of sleep they would take if completely liberated from work schedules and other constraints – is more like eight or eight and a half hours a night. This implies a shortfall of around an hour and a half each night. A shortfall of this size almost certainly matters. Restricting someone’s sleep by an hour and a half for just one night will measurably reduce their daytime alertness. The cumulative effects, when sleep is short-changed night after night, are far more pervasive. We shall be looking at the psychological and physical consequences of chronic sleep deprivation in the next two chapters.

A substantial nightly shortfall in sleep is difficult to sustain for more than five or six days in succession without sleepiness seriously impairing daytime alertness, mood and performance. This aspect of human biology might conceivably have contributed to the establishment of the seven-day week, comprising five or six days of work followed by one or two days of legitimised rest, as a standard unit of time. Most humans have been following the seven-day pattern for thousands of years. The seven-day week dates back to the pre-Biblical Sumerian and Babylonian civilisations. Right from the outset, one day of the week was deemed to be a day of rest and recreation. The Babylonians originally named their seven days after the five visible planets plus the Sun and the Moon, but the choice of seven otherwise has no objective basis in astronomy or any obvious feature of the physical environment. The Romans later adopted the seven-day week, dabbled with eight, then reverted to seven. The seven-day week appeared in the Bible, again with the inherent concept of a day of rest. According to the Biblical account of the Creation, God laboured for six days and rested on the seventh. Nowadays, people who work long hours and sleep for only six or seven hours a night really do need that extra time in bed at weekends to stave off sleep deprivation.

The thesis that many people are chronically sleep-deprived is not without its sceptics, however. Yvonne Harrison and Jim Horne at Loughborough University have argued that we all have the capacity to sleep more than we usually do, but only in the way that we can carry on eating after our physiological need for food has been satisfied. In support of their sceptical position, Harrison and Horne have cited, for example, an experiment in which healthy young adults slept for up to ten hours a night for two weeks, getting an extra hour or so of sleep each night. This additional sleep produced some improvements in their reaction times and a slight reduction in daytime sleepiness. However, there were no significant improvements in the volunteers’ subjective ratings of their own mood or sleepiness.

Scientists are paid to be sceptical, and counterblasts are an essential part of scientific debate. Nonetheless, such arguments must be set against all the other strands of evidence showing that chronic sleep deprivation is a real and widespread phenomenon. We have considered some of that evidence and there is more to come. First, though, what about you?