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When Does the Body Repair Itself During Sleep?

There is more than a sliver of truth in the saying ‘we need our beauty sleep’! Our bodies are in fact programmed to perform life-essential repairs and maintenance while we sleep. But exactly when does the body repair itself during sleep?

A Typical Night’s Sleep

If you thought you dropped off to sleep and that was it until you woke up the next morning, you’re oversimplifying the process… Sleep in fact happens in cycles, and we typically go through 4 to 6 of these cycles during a good ‘night’s’ sleep. 

Note, however, that sleep patterns and quality vary between individuals as it’s often influenced by factors like age, health, medications, and environment.

For most of us though, a sleep cycle itself consists of 3 NREM stages and a REM stage and lasts about 90 minutes. 

Non-Rapid Eye Movement (NREM) Sleep

Each stage of NREM sleep progressively leads to deeper sleep. 

  1. Stage 1 NREM (light) sleep lasts only a few minutes (about 1-7 minutes per cycle) and is a bridge between wakefulness and sleep. It gets shorter with each sleep cycle i.e. it may last 7 minutes on the first cycle but by the last one, will be around a minute in duration.
  2. Stage 2 NREM (light) sleep is also relatively brief (10 – 25 minutes) although it gets longer with each cycle i.e. 10 minutes during the first sleep cycle and 25 minutes by the last one.
  3. Stage 3 NREM (deep or slow wave sleep) lasts 20 – 40 minutes per cycle and gets shorter with each cycle*. Deep sleep is important for body repairs as most of the intensive action happens then.

* The longer intervals of deep sleep (around 40 minutes per cycle) mostly occur during the first 3 hours. They then shorten (to around 20 minutes) as you transition to progressively longer periods of lighter Stage 2 NREM sleep alternating with REM sleep as the night continues.

Rapid Eye Movement (REM) Sleep

After deep sleep, your body cyclically switches to REM (Rapid Eye Movement) sleep throughout the night. 

REM sleep is just as important as deep sleep because your brain does its housekeeping then. Typically, the first REM phase lasts around 10 minutes but by your last sleep cycle, should be around 40 – 60 minutes. Overall, you spend almost a quarter of your sleeping time (20-25%) in REM sleep, or you should!

Note: during NREM stages your brain is less active, which allows the rest of your body to carry out its repair work. Or rather, it switches into a type of ‘guardian’ mode where it becomes less responsive to external stimuli so your body can focus on essential repair work. This is why it’s harder to wake someone up during deep sleep phases.

Repairs Throughout the Night

Now that you know HOW you sleep, here’s what happens WHEN you sleep!

While deep sleep is most important in terms of when the body does major repairs to itself, various other repair processes and supportive activities do happen throughout the night as well. 

For simplicity, let’s break down your night’s sleep into early, middle, and late phases, and look at what typically happens during these stages. 

Early Sleep (Hours 1 – 3)

This is the all-important first few hours during which your body goes through the longest and most intense deep sleep cycles. 

At this time, your body releases hormones like cortisol, progesterone, and growth hormone. These encourage relaxation, prepare your body for deep sleep, and set the stage for intense tissue repair and muscle growth.

You do cycle through REM Sleep phases as well during early sleep but they are relatively short because your body must prioritise physical repairs. Even so, your brain is still busy consolidating memories, and probably reviewing skills learned during the day.

The Importance of Deep Sleep For Body Repairs During The Early Sleep Phase

During these longer, deep sleep phases, your body:

  • Repairs and rebuilds muscle tissues.
  • Renews damaged tissues throughout the body.
  • Strengthens bones and joints.

Middle Sleep (Roughly Hours 4 – 6)

As physical repairs ramp down, your deep sleep cycles gradually get shorter throughout the middle sleep period. 

You begin to spend more time in the lighter transitional NREM Stage 2 sleep, which allows a balance of mental processing and body repairs. 

Your digestive system continues to process the food you’ve consumed during the day, particularly your last meal. This releases essential nutrients so your system can absorb them for use in ongoing muscle recovery, immune system function, and tissue growth activities.

During the latter stages of middle sleep, your liver steps up its detox processes to filter the day’s toxins from your blood. This is another important process because accumulated toxins in the bloodstream can lead to chronic health conditions, and impact cellular health.

At the same time, your REM sleep stages get longer as your brain becomes more active. It begins to tackle complex cognitive processes like problem solving, creativity, and emotional processing.

Late Sleep (Final Hours)

Towards the final hours of your sleep, deep sleep cycles are at their shortest as your body spends more time in NREM Stage 2 and REM sleep. 

Most of the essential physical body repairs are done by now. Your lungs do a detox to get rid of mucous and debris from your respiratory system – you may start coughing or feel some congestion during this process. 

And finally, at the very end, your large intestine absorbs the remaining water and vitamins from your digestive tract to keep you hydrated and ‘vitamised’ as your core temperature rises in preparation for waking up.

Meanwhile… your brain has been intensely busy using the longer REM sleep phases to further consolidate memories, integrate new information with existing knowledge, and prepare you for the day ahead.

To summarise: 

  • The early sleep phase predominantly focuses on physical repair, 
  • The middle phase involves a balance of physical and mental activities, 
  • The late phase emphasises brain function and detoxification.

Additional Ways the Body Repairs Itself During Sleep

Tissue, muscle, and bone repairs aren’t the only maintenance your body does during sleep! Other systems also take advantage of the lull in physical activity to do their own R and M.

Immune System Support 

As you sleep, your immune system increases the production of infection fighting, inflammation busting proteins called cytokines. So, sleep is important for maintaining a strong immune system.

Hormone Regulation

During sleep, the production of important hormones such as melatonin and growth hormone peaks. We touched on this earlier but growth hormone in particular is important for tissue repair and muscle growth. Melatonin helps regulate sleep cycles and supports antioxidant activity.

Free Radical Neutralisation 

Throughout your waking hours, your body is bombarded by processes that cause oxidative stress. Even mandatory activities, like eating, cause it. Oxidative stress in turn creates free radicals, which are unstable molecules that can cause cellular damage, ageing, and disease.

When you sleep, your body can fight back and neutralise these harmful little molecules to protect your cells and improve overall health.

Conclusion: When Does the Body Repair Itself During Sleep?

When you head for bed tonight, consider this – sleep is not just a way to while away the hours until sunrise! It is also not ‘just’ a time of rest… Rather, each of the various sleep stages is part of a complex natural biological process designed to allow your body to repair itself. 

From tissue and muscle repair during deep sleep in those all-important first few hours, to brain recuperation in REM sleep… Getting a good night’s sleep is not just a convenient saying; it’s a biological necessity!

Elizabeth Garvey
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