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Why We Sleep | Theories & Explanations


Written by Lauren

Last Updated: 22nd February, 2022

Most people naturally spend a large portion of their lives sleeping, yet many may not know the reasons and purposes behind why we sleep. Indeed, many experts still continue to debate and challenge the reasons and explanations behind the importance of sleep. 

This article will explore the various theories surrounding why we sleep, and the many ways sleep can benefit our mind and body. 

Purpose Of Sleep

Despite sleeping taking up a lot of our time, the exact reasons and purposes behind our need to sleep are still debated. Regardless, there are several probable theories as to why sleep is so important; these explanations are often centred around the brain, restoration and energy conservation. 

Did you know?
For an average person sleeping 8 hours per night, it is estimated that we spend about one-third of our lives sleeping✓ or attempting to sleep. This equates to roughly 229,900 hours, depending on the amount of time you spend sleeping and the duration of your lifetime.

In addition to the scientific theories, it is well-known that lack of sleep can also affect your mood, mental health and psychological wellbeing. Short term problems can include increased fatigue, reduced alertness, stress and impaired memory. If lack of sleep persists, you could face more serious health consequences, such as diabetes, depression, weight issues and high blood pressure. 

Therefore, sleep is not only essential to conserve cognitive and restorative functions but can also prevent numerous psychological and health problems. To maintain good health, it is recommended that adults get approximately 7-9 hours of sleep every night, with children getting 2 -3 hours more, depending on their age. 

Sleep Theories 

Over the years, experts have theorised the possible explanations for our need to sleep and continue to debate them today. These theories cover the brain and bodily functions, to evolutionary explanations. Below are some of the main scientific theories✓ behind why we sleep. 

sleep theories
  • Restoration Theory: A popular theory is that sleep is needed to restore and repair the body and maintain immune functions. Restorative functions include tissue growth, muscle repair and the release of important hormones. Restoration is also linked to memories, as it’s believed that short-term memories can be converted to long-term memories during REM sleep.  
  • Energy Conservation: As the name suggests, this explanation is about conserving energy. During sleep, the metabolism is lower, therefore energy demands can decrease. This may originate from early humans, who could rest as opposed to hunting at night, which was less efficient for the body. 
  • Brain Plasticity: This theory is associated directly with the brain and how sleep is required to make structural changes. While you sleep, it’s theorised that the brain undergoes organisation and growth regarding its structure and organisation. This development is essential for babies and infants, which is why they require more sleep. 
  • Inactivity Theory: Otherwise known as the evolutionary theory, it is believed that resting at night was developed centuries ago by humans and other species as a survival technique. Those who stayed inactive at night were more protected from injuries and other predators; this eventually evolved into what we consider sleeping time. 

Sleep Benefits 

For many, not getting enough sleep can leave us feeling tired, grumpy and lacking in energy. However, there are many more reasons why sleep is important for our mind and body. Here are some key points surrounding why we need sleep. 

sleep benefits
  • Memory: There is plenty of evidence to suggest that getting enough sleep can help with memory retention. It is believed that deep sleep can help you process fact-based information and research✓ has also stated that long-term memory can be formed while you’re sleeping. 
  • Blood Pressure: If you suffer from hypertension (high blood pressure), this could be due to regular lack of sleep. In a study✓ involving 36 hypertensive patients, it was found that insufficient sleep led to increased blood pressure and heart rate, which could present a risk for organ damage and cardiovascular diseases. 
  • Focus: Getting enough sleep each night can help maintain focus, concentration and other cognitive functions. Research✓ has also found that sleep deprivation can negatively impact attention, decision-making and vigilance. 
  • Weight: Lack of sleep can lead to problems with managing a healthy weight as it can disrupt the hormones which control appetite. A study✓ involving 276 adults found that those who slept too little or too much saw an increase in future body weight and fat gain. 
  • Mood: Most people have experienced firsthand how lack of sleep can make you feel more moody and irritable. However, there is also scientific research✓ that states that daily sleep quality and mood are connected. It’s also believed that lack of sleep can worsen symptoms of mental health conditions, such as anxiety and depression. 
  • Heart: Many experts claim that insufficient sleep can lead to an increased risk of heart disease and heart attacks. Studies✓ have also stated that maintaining a healthy sleep duration can be important for preventing cardiovascular diseases. 

Children & Sleep 

Sleep is important for everyone; however, sleep can also play an essential role in the development of infants and young children. While recommended sleep times can differ slightly; generally, newborns are expected to get between 14 -17 hours of sleep and infants between 12 -16 hours. This amount decreases with age, as toddlers are recommended between 11 -14 hours, and young children should have around 10 -13 hours of sleep each night. It is known that if children do not get sufficient sleep, their attention, memory, behaviour, learning and general health can suffer. 

children and sleep

In recent decades, there has been a lot of research✓ that explores why sleep is so important for children. This includes data that indicates that greater sleep efficiency in infants can lead to better problem-solving skills. It was also found that poor sleep in the first 2 years of life can negatively affect language learning in later childhood. Moreover, shorter sleep duration has also been connected to poorer emotional regulation, while young children with a healthy sleep routine were seen to have better emotional responses. 

Importance Of Dreams 

While sleep benefits are often associated with improved mood and cognitive functions, dreams can also play an essential part in why we sleep. Many believe that dreams can hold special meanings and truths; however, science has other theories and explanations surrounding the role of dreams. 

importance of dreams

A popular theory is the activation-synthesis model, first proposed in 1977. This theory states that dreaming happens when the brain tries to make sense of random signals coming from activated parts of the brain during REM sleep. The brain attempts to find meaning from this data; however, it can often be disjointed and nonsensical when it manifests into dreams. 

Another well-known explanation comes from the founder of psychoanalysis, Sigmund Freud. The theory is that dreams represent unconscious and repressed desires, such as wishes, thoughts and motivations. While this theory is often linked to modern-day dream interpretation, there is little scientific evidence to back this up, and many experts have debunked Freud’s dream explanations.

Frequently Asked Questions

Why do we sleep?

There are many theories and explanations surrounding why we sleep. These theories are often related to bodily and biological functions, such as restoration, repair and development. Other explanations discuss evolution and are linked to early humans.

Why do we need sleep?

Sleep is necessary for various reasons, and lack of sleep can lead to serious health consequences. Sleep is vital for maintaining cognitive functions, such as focus and memory. It also helps to keep your blood pressure, heart and weight healthy.

Why do we talk in sleep?

Otherwise known as somniloquy, sleep talking involves talking, mumbling or making incomprehensible sounds. 

There is no concrete reason as to what causes sleep talking, although some believe it’s connected to dreams. It is often harmless, but there is a chance it could be linked to other sleep disorders such as sleep apnea, sleepwalking or night terrors.

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