By Gregg D. Jacobs, Ph.D.

One widely disseminated recommendation made by sleep specialists is that we need at least eight hours of sleep per night to stay healthy. This recommendation is based in large part on a single study, conducted by Dr. Thomas Wehr at the National Institutes of Health, in which young, healthy individuals were required to spend up to twelve hours per day in bed for almost a month. After a few days, their sleep duration stabilized at about eight and one quarter hours per night. Some sleep researchers have concluded from these findings that we are biologically programmed to sleep over eight hours per night. However, not all sleep researchers agree with this conclusion.

Dr. Wehr’s study involved young, healthy people who may require more sleep than middle-aged or older adults. In addition, Dr. Wehr's subjects spent twelve hours a day in bed, which may have led subjects to sleep more than usual due to the boredom of the experimental environment. Also, many people can not sleep eight hours per night even if they tried.

Some scientists have suggested that sleeping less than eight hours per night is a significant risk factor for increased sickness, and even death. The primary reason for this claim comes from research by Dr. Eve Van Cauter at the University of Chicago. She compared physiological functioning in healthy, young male sleepers who were allowed to sleep just under four hours a night, just over seven hours and just over nine hours over several weeks. She found that, compared to nine hours of sleep, four hours of sleep impaired the body's ability to process sugar (meaning that people could become more susceptible to diabetes or obesity).

However, these generalizations are premature. First of all, Van Cauter only found changes in physiological activity when four hours of sleep was compared to nine hours of sleep. This may be an unrealistic comparison since very few people can, or do, sleep nine hours per night. Furthermore, there were no changes in physiological activity when four hours of sleep was compared to a more realistic seven hours of sleep. In addition, only young, healthy sleepers were used (so the results may only apply to young people), and the same physiological changes have been observed in response to daily life stress. Also, insomniacs (who sleep less than six hours per night on average) do not have a greater incidence of diabetes or obesity. Other well-done studies have shown that sleep deprivation does not result in significant changes in metabolism or physiological functioning.

Other sleep deprivation studies have shown that when eight-hour sleepers are limited to four hours of sleep, their immune systems are compromised. However, these studies involved a severe reduction of sleep (50% loss of normal sleep) and therefore may not apply to the smaller reductions in sleep that we typically experience in daily life. Also, these findings on immune suppression may not be clinically meaningful since no one has shown that they actually cause disease. Stress has also been shown to have the same effects on immune functioning. In fact, it is possible that the stress of the experiment may be responsible for these effects instead of sleep loss itself.

A large-scale study conducted by Dr. Daniel Kripke and his colleagues at the University of California at San Diego casts significant doubt on the belief that we need to sleep eight hours per night to stay healthy. They studied over a million adults of all ages to determine the relationship between sleep duration and mortality. Their results (which have recently been replicated by researchers at Harvard Medical School) showed that people who slept seven hours per night had the lowest death rates over a six-year period, while people who slept eight or more hours had a greater risk of dying over the same period. In fact, the greater the sleep duration beyond eight hours per night, the greater the death rate and people who only slept five hours per night lived longer than those who slept eight or more. These findings suggest that seven hours of sleep may be the ideal sleep length in terms of longevity and that sleep may be like food: too little or too much is unhealthy, but the optimal amount may help us to live longer.

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