Why Do We Sleep?

Whilst we can appreciate that sleeping does, in fact, make us feel better, we’re yet to answer the question “why do we sleep?” with a unifying theory. After a good night of sleep, we feel more alert, more energetic, happier, and we can function better throughout the day. Scientists aren’t 100% sure why we need sleep, however, there are a number of theories.

One way to think about the function of sleep is to compare it to hunger. Hunger is a protective mechanism that evolved to make sure we consume the nutrients which our bodies require. Eating and sleeping are both regulated by internal mechanisms. If we go without food, we trigger an uncomfortable sensation of hunger. Likewise, going without sleep makes us feel quite sleepy. Just as eating relieves those hunger sensations and restores the body with nutrients, sleeping relieves that sleepiness and ensures we can operate to our full potential.

But the question remains, why exactly do we sleep? Scientists have looked at several different theories. Despite agreeing that we need sleep, scientists can’t fully agree on as to why we need sleep. There are a few leading theories:

Resting Theory

We are constantly on the go in a highly active anabolic state.

As a result of this intense activity which requires energy, being awake may only be a temporary state. We use this state of awakening as a time to refuel and reproduce. The reason we sleep is to gain relief from this hyperactive state so that we can fully function – physically and mentally.

The theory of rest is supported by the fact that certain genes only switch on during sleep. Some of these genes are directly linked with mental health conditions such as schizophrenia and depression.

Recuperation Theory

Sleep is a period of time where our bodies heal physically.

Animals in hibernation have to catch up on sleep once they emerge. Resting in a dark, quiet place does not fulfil their need for sleep if the conscious brain does not shut down.

Whilst we are in that period of sleep, something occurs within the mind which may hold the psychological reasons as to why we sleep.

Sleeping is Learning Theory

Sleeping may be the period of time where the brain organises and files important memories, whilst discarding unwanted information.

A sleep experiment carried out by Turner et al, oversaw 40 people sleep for 26 minutes per night. The people were given cognitive tests which showed their working memory deteriorated by 38% over four days. Without REM sleep, people found it much harder to complete memory tasks and solve problems.

Sleep to Dream Theory

“That, if then I had waked after a long sleep, will make me sleep again; and then, in dreaming, the clouds me thought would open and show riches ready to drop upon me; that, when I waked I cried to dream again”

– William Shakespeare

Perhaps Shakespeare was right all along. Matt Walker, the lead scientist at the Berkeley Sleep and Neuroimaging Laboratory, has developed a theory where REM dreaming allows people to process difficult or stressful memories in a relatively stress-free environment. When a stressful event occurs, there is a surge of chemicals in the brain. These are usually chemicals such as serotonin, dopamine, and norepinephrine, usually connected to arousal, emotion, and cognition. The REM stage of sleep is a low monoaminergic environment, ideal for processing trauma.


Despite appreciating that sleep makes us feel better, scientists are yet to discover a unifying theory as to why we sleep. If you wish to further understand sleep, we suggest you watch the following clip from Russell Foster –


Written by: Downland Bedding Posted on: 15th June 2016