Health & Fitness

Deep sleep: The secret to a good night’s sleep

A great deal happens during the night, though the luckiest of us simply seem to close our eyes and then open them again in the morning. Of the different phases of sleep that repeat in cycles, deep sleep is the most beneficial for the body and mind. Find out how the body repairs itself and helps you feel more restored each night, and take every opportunity to sleep more deeply.

Understanding the phases of sleep

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After the falling asleep phase, sleep takes place in alternating cycles of about 90 to 120 minutes each:

  • Light sleep and light slow-wave sleep (stages N1 and N2): for about twenty minutes, sleep is light. You can be awakened easily by a noise or a change in light. A transitional phase leads you gradually into deep sleep.
  • Slow-wave sleep, then very deep sleep (stages N3 and N4): you sleep more and more deeply; the body and mind are at rest, and the body regenerates.
  • Paradoxical sleep (stage N5): about 90 minutes after falling asleep, the paradoxical sleep phase ends the sleep cycle. Its name comes from the contradiction between intense brain activity and almost total immobility of the body. It is also called REM (Rapid Eye Movement) because of the jerky movements of the eyes under the closed eyelids. This is when dreams are most likely to occur and lasts 10 to 20 minutes per cycle. Your muscles are as if paralysed (if they are not, it is called sleepwalking).

This cycle occurs 4 to 6 times per night, depending on the individual. Deep slow-wave sleep is longer during the first few cycles. You tend to alternate between light and REM sleep at the end of the night. The body gradually prepares itself for waking up.

Now let’s take a closer look at deep sleep: why is it the most restorative and how can it be promoted?

What happens in the body during deep sleep?

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Deep sleep accounts for about 20% of the night’s duration in a healthy young adult. Brain activity is very slow, as is breathing and heart rate. The muscles are completely relaxed and blood pressure is also lowered. But despite this apparent calm, the body and brain are working hard:

  • The pituitary gland secretes hormones to stimulate cell reproduction and tissue repair. Around 1 am, skin cell division reaches its peak. Bones regenerate, and this hormonal activity also helps to form muscle fibres.
  • During sleep, you eliminate toxins, for example, through sweating and breathing.
  • Deep sleep supports the body’s immune function.
  • The connections between the neurons are optimal, supporting the learning and memory processes. During deep sleep, your memories are consolidated, and you process the emotions experienced during the day.

The importance of deep sleep is measured, especially during the day. Poor sleep quality leads to mood disorders, stress, and difficulty concentrating or memorising new information and so on.

How to improve the quality of your sleep

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It is very difficult to control the phases of sleep independently, but in general:

  • Increasing the length of your sleep will help you sleep soundly for longer.
  • As sleep is deeper and more restorative at the beginning of the night, going to bed early can help you sleep better.
  • Sleeping in a quiet place, away from screens and in the dark, will most likely make it easier for you to switch from light to deep sleep.
  • To overwork the body, eat early so that when you fall asleep, your digestion is complete.
  • Lowering your body temperature signals your body to fall asleep: you will sleep better in a temperate room than in an overheated one.
  • Avoid taking stimulants (alcohol, tobacco or caffeine) in the second half of the day.
  • Get active: exercise improves the quality of sleep in general. In addition, one study suggests that physical activity 1.5 hours before bedtime may increase the duration of deep sleep (by reducing the amount of REM sleep).

To get started now, browse the iFIT library and find a fitness routine that suits you. Meditation or yoga series could also help you sleep soundly.

Check out our Health & Fitness page for more advice.


Garbarino, S., Lanteri, P., Bragazzi, N.L. et al. Role of sleep deprivation in immune-related disease risk and outcomes. Commun Biol 4, 1304 (2021).

Dolezal BA, Neufeld EV, Boland DM, Martin JL, Cooper CB. Interrelationship between Sleep and Exercise: A Systematic Review [published correction appears in Adv Prev Med. 2017;2017:5979510]. Adv Prev Med. 2017;2017:1364387. doi:10.1155/2017/1364387