Why do we need sleep?

As simple as the answer to this question might seem at first, there are many explanations as of why we actually have the need to sleep. We will now take look at different theories which try to explain our necessity to sleep. We will concentrate on those which are most widely accepted by experts.

Sleep- must or can?

Tests conducted on rats have shown that sleep deprivation over a few weeks (about four) lead to a strong drop of their body temperature, a drastic weight loss (although food consumption increased) and ultimately to death. (1) This shows that sleep is not only an important, but a vital contributor to a mammal’s biological equilibrium.

In the last 60 years sleep researchers have made more progress than in the thousands of years before that and they have come a great deal closer of "revealing the mysteries of sleep" in its details. Nevertheless, no one -so far- has managed to really clarify why we actually need to sleep. Many specialists have come up with plausible explanations, referred to as theories.

Primordial Function

When looking for the main reason of sleep, researchers try to find the primordial function, or, in simple terms, the first and most important reason why we sleep. To clarify the meaning of primordial function we can take the example of breathing. The primordial function of breathing is oxygenating our blood, but subsequently breathing helps us do much more. In the same manner, experts try to pinpoint the primordial function of sleep, yet sleep is still a partial mystery to us.

Sleep Theories

Possible answers to "Why do we sleep?" can be divided into two main groups: One explains the need for sleep as restorative function, which task is to balance biological processes which degrade as we are awake. The other group explains sleep on a energy-conserving basis.

• Energy conservation - When asleep our physical activity is kept at a minimum. Although our brain activity is very high, the energy consumed by our body remains low. This is also caused by about 1-2°C lowered body temperature which lowers our metabolic rate by about 20%. By lowering the metabolic rate, our body prepares itself for the coolest period in 24 hours.
• Restoration - The second group of theories sees sleep as a restorative function and is based on the idea that during sleep biological processes which degrade when we are awake are restored or compensated. Among the restorative functions is the task to restore our energy lost.

(1) Hobson, J. Allan. [Sleep. German] "Schlaf: Gehirnaktivität im Ruhestand". Aus dem Amerikan. übers. von Ingrid Horn. [Translated by Ingrid Horn]. Heidelberg, Spektrum der Wissenschaft Verlagsgesellschaft mbH, 1990