Most of us will spend approximately one third of our lives asleep, therefore it must play a very important role in our body. Although scientists are still trying to learn exactly why people need sleep, studies on animals have shown that sleep is necessary for our survival. For example, while rats normally live for two to three years, those deprived of rapid eye movement sleep will only survive for about five weeks, and rats deprived of all sleep will only live for about three weeks. Some studies have indicated that sleep deprivation can produce changes in the body that mimic the effects of adult onset diabetes and other studies suggest that sleep deprivation can impair the immune system, thus making us more susceptible to disease and infection.
Sleep also appears to be necessary for our nervous system to work properly. Too little sleep leaves us drowsy and unable to concentrate the next day. It also leads to impaired memory and physical performance and reduced ability to carry out calculations. If the sleep deprivation continues, hallucinations and mood swings may develop. Some researchers believe sleep gives nerves used while we are awake a chance to shut down and repair themselves. Without sleep, nerves may become so depleted in energy or so polluted with by-products of normal activities that they begin to malfunction. Sleep may also give the brain a chance to exercise important nerve connections that might otherwise deteriorate from lack of activity.
Deep sleep coincides with the release of growth hormone in children and young adults, and is therefore a very important component of growth. Many of the body's cells also increase production and reduce breakdown of proteins during deep sleep. Since proteins are the building blocks needed for cell growth and for repair of damage from factors like stress and ultra-violet rays, deep sleep may truly be 'beauty sleep'. Activity in parts of the brain that control emotions, decision-making processes and social interactions is drastically reduced during deep sleep. This suggests that this type of sleep may help maintain optimal emotional and social functioning while they are awake. A study in rats also showed that certain nerve signalling patterns, which the rats generated during the day were repeated during deep sleep. This pattern repetition may help encourage memories and improve learning.