Sleep deprivation is like being mildly intoxicated. When the brain habituates to sleeplessness to maintain function it slows down. People are often unaware of it. Major causes of sleep deprivation are the electric light bulb, the complexity of daily life, the increase in its pace and the shortage of time. Sleep is the most expendable activity in comparison with other priorities. The main symptom of sleep loss is sleepiness, which has become an endemic condition in a 24-hour society where light bulbs and television sets prompt people to postpone bedtimes and assign alarm clocks to rouse them each morning. With each foreshortened night, they add to their sleep debt until they reach a point where they can no longer voluntarily stay awake. Although mild sleep deprivation is of little concern, people are less productive, ill-humoured and dissatisfied with life if they fail to get a full complement of sleep each night. When sleep deprivation becomes chronic and extensive, it can lead to impaired judgement and accident proneness.
Boredom unmasks sleep debt. If you get sleepy when bored, or while trying to read or listen to a lecture, you have probably been deprived of enough sleep. Normal biological rhythms induce sleepiness between 1 p.m. and 4 p.m. and between 2 a.m. and 6 a.m.
Under natural circumstances, humans go to sleep soon after nightfall and arise as the dawn breaks. At the Equator (where humans evolved) this means people would sleep about nine hours a night. Studies in sleep laboratories, where people live without reference to day and night and artificial time, most adults need eight to ten and a half hours of sleep a night. The need for sleep does vary somewhat with the individual. Some people need only 6 hours a night, while others need 10.
An increase in daytime sleepiness can be detected for sleep debts as low as 1 hour. Those most likely to be sleepy during the day are those who are unmarried and work full-time, snorers, and those with a history of clinical depression.
Resting does not substitute for sleep.
Surveys indicate that the majority of people in industrialized countries (who normally sleep 6.5 hours) are sleeping at least 60 to 90 minutes less than required to overcome daytime sleepiness. One third of the adults surveyed in a 1998 study got 6 hours of sleep or less during the work week.
A recent British study suggested that over the five year period between 1992 and 1997, the average person has lost 12 minutes sleep a night; it is estimated that two-thirds of Europeans now sleep less than seven hour a night (most experts recommend at least 7.5 hours).
Only 5% of the Americans experiencing sleep-related problems consult a doctor about them, although admitting that their daytime sleepiness interfered with their daytime activities.
It is reported that sleepiness is second only to drunkenness as a cause of traffic accidents. In the USA in 1998 100,000 road accidents a year were sleep-related, including 1,500 vehicular deaths and 71,000 injuries. More than 20% of drivers report having fallen asleep more than once while driving. In Canada, traffic accidents increased by 7 percent on the day after summer time was introduced (one hour lost sleep) and decreased by 7 percent on the day after winter time was introduced (one hour more sleep).
The most sleep-deprived group may be high school and college students. From the ages of 17 to 25, sleep needs are greater than at any other time of life after early childhood, but the pressures to postpone or even skip sleep are also greatly increased. The average student sleeps only six hours, but needs about 10 hours, accumulating a sleep debt of 4 hours a night. The average American now probably accumulates a sleep debt of 500 hours a year.
Young children who miss naps and lack sleep may be more prone to accidental injury. Sleeping less than 10 hours a day (including naps) put children at an 86% higher risk of injuries caused by accidents such as slipping, tripping or falling. Especially vulnerable are children aged 3 to 5. The injury risk for boys increased by up to four times if they have been awake for at least 8 hours straight. Research based on hospital admissions shows that only a small difference in sleep - about 20 minutes a day - may distinguish a well-rested period two days before an injury and a "sleep-deprived" period just prior to visiting the emergency department.