Sleep Stages and Benefits of Deep Sleep

August 23, 2022 - Parul Saini, Webmedy Team

Updated Version - July 12, 2023

Sleep accounts for one-quarter to one-third of the human lifespan. A good night's sleep is just as important as regular exercise and a healthy diet. When you do not get quality sleep, your body suffers from serious physiological consequences.


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Sleep plays a role in functioning of the endocrine and immune systems. During sleep, most of the body's systems are in an anabolic state, helping to restore the immune, nervous, skeletal, and muscular systems.

In this article, we will describe the stages of sleep and benefits of a Deep Sleep.

Stages of Sleep

When you sleep, your brain cycles through four stages of sleep. Stages 1 to 3 are what's considered non-rapid eye movement (N.R.E.M) sleep, also known as quiet sleep. Stage 4 is rapid eye movement (R.E.M) sleep, also known as active sleep or paradoxical sleep.

Non-REM sleep occurs first and has three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep.

REM sleep, also known as paradoxical sleep, represents a smaller portion of total sleep time. It is the main occasion for dreams (or nightmares), and is associated with desynchronized and fast brain waves and eye movements.

The sleep cycle of alternate N.R.E.M and R.E.M sleep takes an average of 90 minutes, occurring 4 to 6 times in a good night's sleep. The sleep cycle normally proceeds in the order: first, N1, then N2, then N3, then N2, and finally R.E.M.

R.E.M sleep occurs as a person returns to stage 2 or 1 from a deep sleep. There is a greater amount of deep sleep (stage N3) earlier in the night, while the proportion of R.E.M sleep increases in the two cycles just before natural awakening.

Let’s go over the 4 stages of sleep:

  • Stage 1

    The first stage of the sleep cycle is a transition period between wakefulness and sleep. During stage 1 sleep:

    • Your brain slows down,
    • Your heartbeat, your eye movements, and your breathing slow with it,
    • Your body relaxes, and your muscles may twitch,

    This brief period of sleep lasts for around five to ten minutes. At this time, the brain is still fairly active and producing high amplitude theta waves, which are slow brainwaves occurring mostly in the brain's frontal lobe.

  • Stage 2

    People spend approximately 50% of their total sleep time during N.R.E.M stage 2, which lasts for about 20 minutes per cycle. During stage 2 sleep:

    • You become less aware of your surroundings,
    • Your body temperature drops,
    • Your eye movements stop, and
    • Your breathing and heart rate become more regular.

    The brain also begins to produce bursts of rapid, rhythmic brain wave activity, which are known as sleep spindles. In this phase, memory consolidation takes place. Brain gathers, processes, and filters new memories acquired from the previous day. Body then slows down in preparation for N.R.E.M stage 3 sleep and R.E.M sleep, which are deep sleep stages.

  • Stage 3

    Deep, slow brain waves known as delta waves begin to emerge during N.R.E.M stage 3 sleep. This stage of sleep is also called delta sleep. This is a period of deep sleep where any noises or activity in the environment may fail to wake the sleeping person. Getting enough N.R.E.M stage 3 sleep allows you to feel refreshed the next day. During N.R.E.M stage 3 sleep:

    • Your muscles are completely relaxed,
    • Your blood pressure drops, and breathing slows, and You progress into your deepest sleep.

    During this deep sleep stage, your body starts its physical repairs. Meanwhile, your brain consolidates declarative memories such as personal experiences and other things you have learned.

  • Stage 4

    R.E.M sleep begins approximately 90 minutes after falling asleep. At this time:

    • Your brain lights up with activity,
    • Your body is relaxed and immobilized,
    • Your breathing is faster and irregular,
    • Your eyes move rapidly, and
    • You start to dream.

    During R.E.M sleep, your brain's activity most closely resembles its activity during waking hours. However, your body is temporarily paralyzed. This is a good thing, as it prevents you from acting out your dreams.

    Like stage 3, memory consolidation also happens during R.E.M sleep. However, it is thought that R.E.M sleep is when emotions and emotional memories are processed and stored. Your brain also uses this time to cement information into memory, making it an important stage for learning.

Benefits of Deep Sleep

Glucose metabolism in the brain increases during deep sleep, supporting short-term and long-term memory and overall learning. Deep sleep is also when the pituitary gland secretes important hormones, like human growth hormone, leading to growth and development of the body. Other benefits of deep sleep include:

  • energy restoration,
  • cell regeneration,
  • increasing blood supply to muscles,
  • promoting growth and repair of tissues and bones, and,
  • strengthening the immune system.

Helpful Information

What are the different stages of sleep?

Sleep consists of two main types: Rapid Eye Movement (REM) and Non-Rapid Eye Movement (NREM), which are further divided into several stages. NREM sleep includes Stage 1 (light sleep), Stage 2 (onset of sleep), and Stage 3 (deep sleep or slow-wave sleep). REM sleep is the fourth stage, where dreaming and body revitalization often occur.

How much time do we typically spend in each sleep stage?

It varies between individuals, but on average, a typical sleep cycle lasts about 90 minutes and comprises all sleep stages. Adults spend roughly 5-10% of sleep time in Stage 1, 45-55% in Stage 2, 20-25% in Stage 3 (deep sleep), and 20-25% in REM sleep.

What is REM sleep and why is it important?

REM sleep is the stage characterized by Rapid Eye Movements, vivid dreams, and significant brain activity. It's important because it promotes learning, memory consolidation, mood regulation, and restoration of brain functions.

What is non-REM sleep and how does it differ from REM sleep?

Non-REM sleep includes Stages 1-3, ranging from light sleep to deep sleep. During non-REM, especially in deep sleep, your body repairs tissues, builds bone and muscle, and strengthens the immune system. Unlike REM sleep, dreaming is less common in non-REM sleep.

What happens during deep sleep?

Deep sleep is when your brain waves are at their lowest frequency, and your body is at its most relaxed. This stage is crucial for physical recovery, immune function enhancement, growth and development, and energy restoration.

Why is deep sleep so crucial for our health?

Deep sleep plays a vital role in restoring body function, promoting growth and repair of tissues and cells, strengthening the immune system, and contributing to memory consolidation. Lack of deep sleep can lead to fatigue, health issues, poor cognition, and mood disorders.

What are the benefits of deep sleep for the brain and body?

For the brain, deep sleep helps in memory consolidation and clearing waste products. For the body, it contributes to physical restoration, growth, cellular repair, and a strengthened immune system.

How does deep sleep impact memory and learning?

During deep sleep, the brain consolidates and processes the information learned during the day, turning short-term memories into long-term ones. This helps improve overall memory and cognitive function.

What can cause a lack of deep sleep?

Several factors can reduce deep sleep, such as aging, stress, poor sleep habits, medical conditions like sleep apnea, and certain substances like alcohol and caffeine.

What are the signs of poor quality sleep?

Signs of poor sleep quality can include difficulty falling or staying asleep, frequent wake-ups during the night, waking up still feeling tired, excessive daytime sleepiness, difficulty concentrating, and mood swings.

Can lack of deep sleep affect mood or mental health?

Yes, lack of deep sleep can negatively impact mood and mental health. It's associated with increased stress, anxiety, depression, mood swings, and difficulties in concentration and memory.

What is the role of sleep cycles in achieving deep sleep?

Sleep cycles are vital to achieving deep sleep. Each cycle lasts about 90 minutes and includes both non-REM and REM stages. Deep sleep primarily occurs in the first half of the night, in the earlier cycles.

Can certain medications or substances impact the stages of sleep?

Yes, substances like caffeine and alcohol, as well as certain medications like antidepressants or beta-blockers, can interfere with sleep stages, reducing the amount of time spent in deep and REM sleep.

How does age influence sleep stages and deep sleep duration?

As people age, they typically spend less time in deep sleep. This is a normal part of the aging process, but it can sometimes lead to feeling less refreshed upon waking.

How does sleep deprivation impact health and cognitive function?

Sleep deprivation can impair cognitive functions like attention, decision-making, and memory. It's also linked to health problems such as obesity, heart disease, diabetes, and a weakened immune system.

What is the connection between deep sleep and the immune system?

During deep sleep, the immune system releases proteins called cytokines, which help the body fight off infection or inflammation. Thus, adequate deep sleep is crucial for a robust immune response.

How can I track my sleep stages and deep sleep?

Various sleep tracking devices, including fitness trackers and smartwatches, can monitor your sleep stages. They typically use movement and heart rate to estimate your sleep patterns. Some even track brain waves through EEG.

Are there any disorders related to deep sleep, and how are they treated?

Yes, conditions like insomnia, sleep apnea, restless leg syndrome, and parasomnias can affect deep sleep. Treatment depends on the specific disorder and can include lifestyle changes, medication, and therapies like cognitive-behavioral therapy for insomnia (CBT-I) or continuous positive airway pressure (CPAP) for sleep apnea.

What's the difference between deep sleep and light sleep?

Light sleep serves as a transition phase between wakefulness and deep sleep. It's easier to wake up from light sleep than from deep sleep. Deep sleep is when the body goes through significant restoration and recovery processes.

Can the body compensate for a lack of deep sleep?

While the body can temporarily cope with a lack of deep sleep, chronic sleep deprivation can lead to numerous physical and mental health issues. Sleep cannot be fully compensated for by other activities.


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