Why do we need SLEEP?

We spend around a third of our lives snoozing but despite years of research, scientists still aren't entirely sure why

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The urge to sleep is all-consuming, and is equally as important as food to keep us alive. Sleep is common to mammals, birds and reptiles, and has been conserved through evolution, even though it prevents us from performing tasks such as eating, reproducing and raising young.

There have been many theories about why we sleep, from a way to rest after the day's activities or a method for saving energy, to simply a way to fill time until we can be doing something useful, but all these ideas are flawed. The body repairs itself just as well when we sit quietly, we only save around 100 calories a night by sleeping, and we wouldn't need to catch up on sleep during the day if it were just to fill empty time at night.

Theory 1

ENERGY CONSERVATION

We save around 100 calories per night by sleeping; metabolic rate drops, the digestive system is less active, heart and breathing rates slow, and our body temperature drops. However, the calorie saving equates to just a single glass of milk, which, from an evolutionary perspective, does not seem worth the accompanying vulnerability.

Theory 2

EVOLUTIONARY PROTECTION

An early idea about the purpose of sleep is that it is essentially a protective adaptation to fill time. For example, prey animals with night vision might choose to sleep during the day to avoid being spotted by predators. However, this theory cannot explain why sleep-deprived people fall asleep in the middle of the day.

Theory 3

RESTORATION

One of the major problems caused by sleep deprivation is a decrease in cognitive function, accompanied by a drop in mood, and there is mounting evidence that sleep is involved in restoring the brain. However, there is little evidence to suggest that the body undergoes more repair during sleep compared to waking rest or relaxation.