Why Do We Sleep?

All animals, including humans, sleep. When animals are prevented from sleeping they eventually die. Despite the thousands of experiments that have been done to study sleep, none has been able to declare with assurance the reason why all animals sleep. It is possible that in different species sleep serves a different function. For instance, most animals spend their time looking for food when they are awake and then find a safe place to sleep and hide from predators. Animals near the top of their food chain, such as lions, seem to sleep when and where they want.

We do not know why we sleep, just as we don't know why we are awake.
Reasons typically given for why we sleep include conservation of energy, the restoration of important bodily functions, and the repair of damaged tissues.

For example, some hormones are secreted mainly during sleep. Such theories are attractive, but all of these functions could be met by simply resting and having whatever hormones are secreted during sleep secreted during rest, not necessarily having the brain go into an unconscious state. We do know this for sure: if people do not sleep the right amount, they feel rotten the next day, their brains do not work properly, and they might be quite mentally impaired and unable to perform complex tasks. You certainly do not want a sleepdeprived pilot to be flying you across the Pacific. Even the medical profession now admits that sleep-deprived doctors might be a hazard to their patients.

We can conclude that sleep serves many important functions, and that the different types of sleep fulfill different needs. For instance, stages three and four, "slow-wave sleep," are believed to be the type required to feel refreshed upon awakening. Many scientists believe that REM sleep is the time when memories are saved in our nervous system. The right amount of sleep really does contribute to making you feel vigorous and in a great mood. Shakespeare was probably correct when he wrote in Macbeth that sleep was "Chief nourisher in life's feast."

How Much Sleep Do We Need?

How much we sleep, when we sleep, and how much deep sleep and dreaming sleep we need varies with age. Thus, seven to nine hours of sleep, which is adequate for most adults, would leave the average nine-year-old extremely sleepy during the daytime. Figure 1.3 shows sleep requirements for different ages. As you can see, there are ranges for each age group. The amount of sleep a woman needs is an individual characteristic just like her height. Each person needs his or her own unique amount of sleep. The amount of sleep needed is that which makes you wide awake and alert. Research has also shown a link between sleep time and health: women who sleep much more or much less

Data obtained from several sources, including sleepfoundation.org