Why Exactly is Sleep Important?

Sleep is a fundamental process that takes up a significant portion of our lives, to help ensure we operate optimally on both a physiological and psychological level. Compared to during the day, numerous changes to our body and brain occur during the night, however, there are even more changes that occur as the night progresses. The importance of sleep is vital in terms of our physiological and psychological functioning and well-being. Whilst various factors impact sleep, such as eating behaviours, alcohol consumption and screen time usage, establishing a good routine and prioritising sleep are necessary to live a fun and active life each and every day.

About Sleep

Sleep is a period of rest constituted by an altered state of consciousness where voluntary bodily processes are suspended, and awareness of external stimuli is reduced.

Internal body clocks control the sleep-wake cycle on a 24-hour repeating rhythm, called a circadian rhythm. Broadly, there are numerous circadian clocks throughout the body that consequently affect every cell, tissue and organ within the body and how they operate. More specifically, within the brain, the central circadian clock is responsible for and coordinates sleep. Despite being an internal biological clock, the circadian sleep-wake cycle can be altered and affected by external factors and the environment.

Through scientific measurements of brain activity and findings from sleep studies, we know that the sleep cycle is divided into two phases: rapid eye movement (REM) and non-rapid eye movement (nREM). These phases are then further divided into four distinct stages.

Importance of sleep 

​​​​Sleep is fundamental to us all. Our bodies have a biological need for sleep that only increases the longer we have been awake. This links back to the concept of homeostasis, the process by which one’s body maintains the stability and regularity of its systems.

Throughout the day our bodies work tirelessly to keep us functioning as normal in both voluntary and involuntary ways. Thus, our bodies are primed, vigilant and expending energy. This can be taxing to the body and so sleep is required to return the body to its natural resting state, as well as to repair and restore our body, mind, and brain ready for the next day.

Fundamentally, sleep is pivotal for physiological and psychological well-being and functioning. Therefore, when sleep is altered or tampered with there are an array of subsequent repercussions. In turn, sleep initiation (i.e., the ability to fall asleep), sleep quality, and sleep duration vary from person to person so ensuring you maintain a healthy sleep-wake cycle is a must!  

How does sleep affect our health? 

Sleep is a fundamental process that takes up a significant portion of our lives to help ensure we operate optimally on both a physiological and psychological level. Both the body and brain undergo numerous changes during sleep that are necessary to sustain our active and fast-paced lifestyles. During sleep, there are numerous notable changes in the core body processes that restore, reinforce, and maximise one’s physiological and psychological functions. People who awaken often or sleep insufficient amounts are at a higher risk of coronary heart disease, high blood pressure, obesity, and stroke, according to the CDC.

What happens to our brain and body during sleep?

Here are some of the main ways in which our body and brain change during sleep.

Circulatory and respiratory systems

Blood pressure, heart rate and breathing rates all fall as the parasympathetic system (a branch of the autonomic nervous system that consists of a network of nerves that relaxes the body, conserves energy and regulates bodily functions) takes control of the body.1

Muscle movement

During the nREM stages, one’s muscles increasingly relax and total energy expenditure drops. Contrastingly, during the REM stage, individuals experience a condition termed atonia, where most of the muscles are paralysed, to prevent individuals from acting out or responding to the contents of their dreams. However, the eye muscles remain active as they dart back and forth hence the “rapid eye movement” name of the stage. In line with this, the respiratory muscles operate as normal.2

Cellular restoration

The restorative theory attests that the body needs to restore itself, therefore sleep allows cells the time to repair and grow. As part of this, numerous processes take place such as muscle repair, protein synthesis, tissue growth, and hormone release.17

Metabolism and gastrointestinal function

According to the various circadian clocks that operate in different body organs, there is variation in the way the body handles fat. As a result, the body handles fat differently when eating at unusual times. When individuals fail to get enough quality sleep this may lead to

  • Altered secretion of the hunger hormones, leptin (which Increases the feeling of being full after eating) and ghrelin (which increases appetite)
  • Diminished responsiveness to insulin (the hormone that helps convert sugars to energy)
  • Increased consumption of food, particularly high-calorie foods
  • Decreased physical activity3

Hormones and endocrine system

The body produces different hormones at different times of the day. Sleep and the internal body clock are vital in regulating the secretion and production of several hormones including:

  • Melatonin, which helps promote sleep
  • Growth hormones that support metabolism, bone, and muscle development
  • Cortisol, the body’s stress hormone
  • Leptin and ghrelin, which control one’s appetite

Whilst night-time hormone levels fluctuate due to the different sleep stages, daytime hormone levels are also affected by sleep quality.3


During sleep, cytokines are produced, these are proteins with immune-boosting effects and serve as fuel for the white blood cells. Lack of sleep impacts the production of cytokines, thereby making one more susceptible to bacteria and viruses.4

Emotional well-being

During sleep, there is increased activity in regions of the brain which are associated with emotional regulation. Consequently, this helps support healthy brain function and emotional stability, so lack of sleep impedes this.18

Brain function

The brain plasticity theory attests that sleep is necessary for brain function as it allows one’s neurons to reorganise within the brain. Moreover, during sleep, the brain’s glymphatic (waste clearance) system clears out waste from the central nervous system. This removal of toxic by-products that accumulate throughout the day allows the brain to work more efficiently the following day.

Moreover, sleep contributes to memory consolidation (transferring memories from short-term to long-term memory stores), erasing/forgetting redundant information that typically clutters the nervous system. Sleep also affects cognitive function in terms of learning, memory, problem-solving, creativity, decision-making, focus and concentration.

How much sleep do humans need?

Broadly, sleep experts recommend around 7 to 9 hours of sleep per night. Whilst this figure remains valid for adults aged over 18 years, the recommended sleep duration for younger individuals varies as it is significantly dependent on their age.

Below are the recommended hours of sleep, including naps, for each age group:

  • Babies 4 months to 1 year – sleep 12 to 16 hours per day
  • Children 1 to 2 years – sleep 11 to 14 hours per day
  • Children 3 to 5 years – sleep 10 to 13 hours per day
  • Children 6 to 12 years – sleep 9 to 12 hours per day
  • Teenagers 13 to 18 years – sleep 8 to 10 hours per day

Additionally, individuals who nap should aim to nap between 20-30 minutes as this allows for light sleep to boost alertness without entering deep sleep. This nap duration allows the body to cycle through the sleep stages, prevent grogginess, and avoid disrupting one’s evening sleep. The nap should ideally be taken 8 or more hours before bedtime, often before 3 pm as this is when our circadian rhythm is at its lowest.5

Importance of sleep for our mental health

Having a good night’s sleep is fundamental for maintaining our baseline mental health. Both acute and chronic sleep deprivation or sleep problems dramatically affect one’s mood and are associated with various psychiatric conditions. There is thought to be a complex relationship between mental health and sleep. That means mental health conditions affect sleep, which then impacts our ability to cope with such conditions.  

Fluctuating brain activity during the different phases and stages of sleep can have profound effects on emotional and mental health.  When we’re asleep, the brain works to evaluate and filter thoughts and memories. Therefore sufficient sleep, especially REM sleep, is necessary for the processing of emotional information.6 

In terms of mental health problems, research suggests that impaired sleep contributes to the formulation of new and maintenance of pre-existing mental health conditions.7

How does eating affect our sleep?

Maintaining proper nutrition and a healthy body weight is important when it comes to sleep. How well we sleep can often be attributed in part to our eating behaviour. This is important given the widely understood association between insufficient sleep and elevated risks of obesity.8

Food consumption

Insufficient sleep often results in increased food consumption, increased snacking and irregular meals. Increased consumption without an equivalent increase in energy expenditurecan lead to excess glucose, which is stored as fat. Furthermore, following sleep deprivation individuals possess a greater tendency to select high-calorie food that provides less nutritional value and an elevated risk of weight gain whilst also reducing the quality of sleep.9,10


Leptin and ghrelin, which regulate appetite and hunger, are disrupted thanks to inadequate sleep. In turn, it could be argued that these chemical imbalances contribute to the poor nutritional choices one makes when they are sleep deprived since their body is not functioning as it normally does.11

Does Alcohol Impact Sleep?

Alcohol is a central nervous system depressant that slows down brain activity. Whilst its sedative effects can induce feelings of sleepiness and relaxation, excessive alcohol consumption has been linked to poor sleep quality and duration. Alcohol consumption results in less time spent in the all-important REM stage of sleep which often leaves the individual feeling less refreshed the following day.  How detrimental alcohol will be to sleep will be very specific to you as a person.  You should certainly avoid drinking too close to bedtime to give your body the necessary time to process the alcohol before going to sleep. Doing so has been found to improve the quality of sleep.12 

Does screen time really affect our sleep?

Evidence suggests that screen time and the usage of electronic devices before bed does affect our sleep, for the following reasons:

Short-wavelength blue light

Blue light emitted from electronic devices can interfere with the body’s natural sleep-wake cycle through its substantial impact on the secretion of melatonin, a hormone produced in response to darkness that signals to the body that it is time to fall asleep. Children and adolescents are thought to be more detrimentally affected by blue light since they may be hypersensitive to its effects because their eyes let in more light.13  

Content of media consumed

The type of content one consumes feeds into your ability to sleep. Emotionally provocative content (such as exciting, scary, or violent media) can boost alertness, impede sleepiness, and hinder sleep initiation.14

Differences in devices

The type of device one uses before bed will also affect their sleep. Whilst there is still much research taking place as researchers are yet to confidently determine whether or not certain devices are worse than others, experts attest that devices that require interactive usage affect sleep more adversely.14,15 Similarly, the closeness of devices also plays an impact given that smartphones may impact melatonin levels more than televisions since they are used in closer proximity.16

Tips on how to get more sleep

Relatively simple lifestyle changes, an efficient night-time routine, and the adoption of healthy habits that help promote sleep are all necessary to ensure we get our recommended hours of sleep each night. Here are some tips you can adopt to help get more sleep:

  • Establish and adhere to a realistic bedtime even during the weekends and holidays
  • Attempt to wake up at the same time each day to establish a good sleep-wake cycle
  • Maintain a comfortable sleep environment in terms of temperature, light levels, and bedding
  • Avoid screen usage at least one whole hour before bed, instead enjoy some light reading
  • Nap responsibly, ideally in the morning or early afternoon and for no longer than 20 minutes 5
  • Abstain from caffeine, alcohol, and large meals before bed
  • Exercise regularly, but not close to bedtime
  • Keep a sleep diary/log to track your sleep habits

If you suffer from any ongoing sleeping problems at night or suffer from continuous daytime fatigue, then consider contacting a healthcare professional for guidance.


Sleep is a fundamental process that takes up a significant portion of our lives in order to help ensure we operate optimally on both a physiological and psychological level. Both the body and brain undergo numerous changes during sleep that are necessary to sustain the active and fast-paced lifestyles we all conduct during the day. Whilst the amount of sleep we require differs between ages, the impact of externalities such as eating behaviours, alcohol consumption and screen time usage affects us all regardless of age. Fundamentally, we must get enough sleep to prevent any problems or disorders from manifesting as well as for living each day as best we can.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Jaskirat Kanwal

Masters of Science – MSc, Applied Neuropsychology. University of Bristol, UK

Jaskirat currently works in pharmaceutical care and in the mental health sector. Given their extensive background in psychology, they’re currently seeking to undertake their DClinPsych. They hope to study further, and continue in academia and research, with hopes to ultimately become an HCPC registered clinical neuropsychologist.

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