Non-REM Sleep
Non-REM sleep makes up most of the time spent asleep and plays an essential role in physical recovery, immune function, and memory consolidation.
What Is Non-REM Sleep?
Non-REM (NREM) sleep refers to all sleep stages that occur before REM sleep. It accounts for approximately 75–80% of a typical night's sleep.
During Non-REM sleep, brain activity slows, muscles relax, and the body begins important repair and recovery processes.
The Three Stages of Non-REM Sleep
Stage N1
This is the lightest stage of sleep and acts as a transition between wakefulness and sleep.
- Lasts only a few minutes
- Easy to wake from
- Muscles begin to relax
Stage N2
N2 is a deeper stage of sleep and usually accounts for the largest proportion of total sleep time.
- Heart rate slows
- Body temperature decreases
- Brain activity becomes more organised
Stage N3 (Deep Sleep)
N3 is often called deep sleep or slow-wave sleep.
- Most difficult stage to wake from
- Important for physical recovery
- Supports immune function
- Helps consolidate memories
Why Is Non-REM Sleep Important?
Non-REM sleep allows the body and brain to recover from the demands of the day.
During deep sleep, growth hormone is released, tissues are repaired, and important immune system processes occur.
The brain also strengthens memories and removes metabolic waste products that accumulate during waking hours.
Deep Sleep and Ageing
As people get older, the amount of deep sleep they experience often decreases naturally.
Older adults may spend more time in lighter stages of sleep and wake more frequently during the night.
What Happens If Non-REM Sleep Is Reduced?
Inadequate Non-REM sleep may contribute to:
- Daytime tiredness
- Reduced concentration
- Impaired memory
- Slower physical recovery
- Lower resilience to illness
Key Takeaways
- Non-REM sleep makes up most of the night.
- It includes stages N1, N2, and N3.
- N3 is deep sleep and is important for recovery.
- Physical restoration mainly occurs during Non-REM sleep.
- Deep sleep naturally decreases with age.
- Good sleep habits help protect healthy sleep cycles.