Sleeping 5 hours per night instead of 8 would win us a full year and 91 days of active life every decade. Who could imagine that it could be so astoundingly easy deceive the time and ‘lengthen’ our lives?
The question is whether it is possible for humans to reduce their sleep so radically without any devastating effects on their health. There have not been too many studies looking at long-term effects of sleep reduction. However, certain pieces of information challenge the common belief that everybody needs 8 hours of sleep per night in order to stay healthy and function properly.
First, there have been recorded cases of famous people sleeping 4 hours a night or less on regular basis. Leonardo da Vinci is one of them. He was known to sleep 15 minutes every 4 hours, in total 1.5 hours per day – at least during a certain period of his life. No one can argue that Leonardo's productivity was impaired because of not getting the 'normal' eight hours of sleep every night. After all, he is commonly considered one of the most talented artists of all time.
A case of extreme short sleeps from the present time, is the one of a retired lady who would sleep only one hour per day on regular days and not at all "if she had something interesting to do" (Meddis, 1977, pp. 42-44, cited in Pinel, 2002).
Second, when humans stay awake longer than usual, the following sleep time is shorter and not longer. Humans as most animals have sleep-wake cycles of approximately 24 hours; therefore, the longer they are awake, the less time there is left for sleep (Pinel, 2002).
Third, if ‘enough’ sleep is necessary for our well-being, how is it possible that sleep-deprivation can be beneficial for people suffering from depression? Sleep deprivation has antidepressant effects, causing an increase in serotonin levels during the sleep deprivation day (Lopez-Rodriguez, F., Wilson, C., Maidment, N., Poland, R. & Engel Jr., J., 2003). The effect is short-term, but it cannot be accomplished by any antidepressants available to us right now, which take around 3 weeks to get to the same effect.
Fourth, the disabling effects that sleep deprivation is supposed to have on functioning are not always as clear-cut as they are believed to be. Learning in the serial reaction task suffers from total sleep deprivation. Experiments by both Heuer and Klein (2003) and Cajochen, Knoblauch, Wirz-Justice, Kräuchi, Graw & Wallach (2004) found that sleep deprivation impairs learning of new sequences but not the expression of the sequences already learned.
Function Of Sleep
There are two types of theories of sleep. Recuperation theories state that being awake disrupts the internal physiological stability (homeostasis) of the body and sleep is needed to restore it.
Opposing to the recuperation theories are circadian theories, stating that sleep is caused by an internal timing mechanism. According to these theories, humans, as the rest of the animals, stay awake as much as they have to in order to meet their survival needs and sleep as much as they have to in order to avoid the dangers carried by the darkness. One extreme version of a circadian theory proposes that sleep plays no role in the efficient physiological functioning of the body. Accordingly to it sleep is a behaviour highly motivating for humans but not at all necessary for their health.
Sleep must have quite an important physiological function since all mammals and birds sleep no matter the danger they are under while sleeping (Pinel, 2002). However, the species that need to stay awake longer in order to survive sleep very little. For example, zebras and deers, who can be easily attacked by a predator when they sleep, sleep only 2 or 3 hours per day. Certain sparrows, during their migration season, sleep only a third of their regular sleeping time, not changing their performance on tests of learning in the lab (Milius, 2004).
Species that do not need to put long hours of effort into their survival tend to sleep longer. Koalas sleep 18 hours per day while even though they spend most of their awake time on a tree eating. I have personally had a privilege of watching a pug for the past six months, and I can say it with full confidence that there is nothing that these dogs do during the day, which would justify the amount of time they sleep. Energy expenses of animals like koalas or pug dogs are minimal and the amount of time they sleep does not match. African lions, after they have satisfied themselves on a kill, sleep more or less continuously for two or three days (Pinel, 2002). Who would endanger them while they are sleeping?
Circadian theories seem to make a better prediction of how much an organism needs to sleep, based on how much time it needs to invest to meet its survival requirements.
Impairment caused by sleep deprivation
There are many studies showing the impairment of performance caused either by sleep reduction or sleep deprivation. Skipping a night’s sleep, for example, affects our psychomotor performance, impairs our mood, and increases subjective feeling of sleepiness (Howard, 2003). Engle-Friedman, Riela, Golan, Ventuneac, Davis, Jefferson & Major (2003) found that sleep loss causes people to choose behaviour requiring lower effort.
The above two studies, however, deal only with short-term sleep reduction.
People who sleep little or irregularly in real life situations do so because they are under stress. Stress might contribute to or be responsible for some of the negative effects of the loss of sleep (Pinel, 2002).
Changes In Slow Wave Sleep Due To Sleep Pattern Changes
Human body, however, seems to be able to adjust the quality of sleep in case if the person’s sleeping pattern changes. Pinel (2002) states that people who get less sleep, sleep more efficiently. After a time of sleep deprivation people regain only a small part of their total lost sleep and most of the lost slow-wave sleep.
Short sleepers normally get as much slow-wave sleep as long sleepers do. In people who gradually reduce their usual sleep time the duration of slow-wave sleep remains about the same as before.
Personal Case Study
“Only when people are sleeping at their maximal efficiency is it possible to determine how much sleep they really need” (Pinel, 2002). I was intrigued by this statement and decided to carry out my own sleep reduction case study.
My personal, regular, so called “need” for sleep is between 8.5 and 9 hours per night. If I have to study for an exam, I wake up early and can sleep only a few hours per night, but then I feel tired and exhausted for most of the day. On 'regular', i.e. 'no special pressure' days the factors that determine how much sleep I will get are how interesting the things that I did late in the evening and how interesting the things I would do early the next morning are.
My experiment did not go too far, as I had a few stressful events happen in my life then, and decided not to deal with both the stress and the sleep reduction at the same time. In other words, I decided to sleep as long as it was possible to reduce the amount of time spent in the stressful situation around me. However, I still managed to shake my belief of how much sleep I actually needed, even during this short experiment (around 4 weeks).
I did not have the faith in myself in order to radically reduce my sleep as Dr. Pinel did. Instead, I tried to reduce my sleep continuously.
My first step was 7 hours per night, as my regular sleep is in general quite long. By the time I stopped the experiment, I was able to sleep only 6.5 hours a night. This meant at least 2 hours less sleep per day without disturbance of functioning.
Conclusion
It seems that humans need much less sleep than we are presently accustomed to getting. No species stay awake longer than it is necessary for their well-being and humans are not an exception. For animals other than humans their primary task of the day is providing for survival. The difference between us and giant sloths is that we can choose to do something that would be more interesting to us than sleep presently is. Nobody will happily choose to stay awake longer in order to do work the person does not enjoy for a few hours more.
In order to reduce their sleep patterns people need to meet two conditions. First, understanding that sleeping less than 8 hours is by itself not at all debilitating for the people’s physical and mental health. Second, deciding on a few highly motivating activities that can be carried out during the time taken away from sleep. Otherwise, we can all be compared to giant sloths.
References
Cajochen, C., Knoblauch, V., Wirz-Justice, A., Kräuchi, K., Graw, P., & Wallach, D. (2004). Circadian Modulation of Sequence Learning under High and Low Sleep Pressure Conditions. Behavioural Brain Research, 151, 167–176.
Engle-Friedman, M., Riela, S., Golan, R., Ventuneac, A., Davis, C., Jefferson, A., & Major, D. (2003). The effect of sleep loss on next day effort. Journal of Sleep Research, 12, 113-125.
Heuer, H., Klein. W. (2003). One Night of Total Sleep Deprivation Impairs Implicit Learning in the Serial Reaction Task, but not the Behavioral Expression of Knowledge. Neuropsychology, 17, 507-516.
Howard, S. (2003). Simulation Study of Rested Versus Sleep-deprived Anesthesiologists. Anesthesiology, 98, 1345-1356.
Lopez-Rodriguez, F., Wilson, C., Maidment, N., Poland, R., & Engel Jr., J. (2003). Total Sleep Deprivation Increases Extracellular Serotonin in the Rat Hippocampus. Neuroscience, 121, 523-531.
Meddis, R. (1977). The Sleep Instinct. London: Routledge & Kegan Paul.
Milius, S. (2004). Sparrows Cheat on Sleep. Science News, 166, 38.
Pinel, J. P. J. (2002). Biopsychology. (5th ed.) Boston: Allyn and Bacon.