2024-02-22 14:25:11
During the night, we have several sleep cycles, usually three to five. Each lasts on average 1h30 for adults, 50 minutes for newborns. These cycles are divided into several phases, with an alternation of slow-wave sleep and paradoxical sleep.
At the start of the night, we spend more time in slow-wave sleep, a recovery phase that lasts “around 1h15 on a 1h30 cycle”, explains Dr. Marc Rey, president of the National Institute of Sleep and Vigilance. Just before waking up, the opposite happens. REM sleep (a period during which we dream) takes precedence over slow-wave sleep.
In a baby, the pattern is still different. An infant begins the night with a period of restless sleep which will become paradoxical sleep, before diving into a calmer phase which will become slow-wave sleep. “We don’t have an explanation yet. These differences are probably linked to the fact that a baby’s brain is not yet mature. believes Dr Rey.
Light slow wave or deep slow wave sleep, what are the differences?
When we fall into sleep, the brain gradually slows down its activity. At beginning of falling asleep, in what we call “the light slow sleep », the body maintains a certain muscular tone. The slightest noise can wake us up.
The cycle continues with a phase of “ deep slow-wave sleep » during which the heart rate and breathing slow down sharply, the muscles relax and the body temperature drops. “If you are woken up during this phase, you will be quite confused,” observes Dr. Rey.
What is deep slow-wave sleep used for?
This period of sleep is essential for rest and recovery, as Dr. Rey explains: “It is during deep slow-wave sleep that the body secretes growth hormone. » This hormone, necessary for the proper development of children, also has a function of repair of bones, tissues and cells, at all ages.
It is also during deep slow-wave sleep that the brain memorizes and consolidates learning, for example training or a course taken during the day.
A nap is not really a substitute for slow-wave sleep
Some people feel the need to compensate for a short night’s sleep with a nap. This is sometimes the case in older people whose total sleep duration naturally tends to shorten, with less time spent in deep slow-wave sleep.
Sleep experts are not opposed to napping in the early afternoon, but they recommend do not exceed 20 minutes so as not to disrupt the architecture of night sleep. “These twenty minutes of nap are enough to let go, but they are not enough to enter into deep slow-wave sleep, unless you are really in sleep debt like night workers can be,” observes Dr. Rey.
How to preserve slow-wave sleep?
Dr Rey recommends firstly go to bed at the same time every day : “This regularity will help you enter deep slow-wave sleep more easily. »
Another tip: stay active and move as much as possible during the day. “Physical activity affects slow-wave sleep because it increases the need for muscle repair. Furthermore, by reducing stress, it improves deep slow-wave sleep. he explains.
If this physical activity is practiced at the end of the day, it is better to wait two or three hours before going to bed. This delay will allow the body to lower its temperature, an essential condition for falling asleep properly.
Sleeping poorly: what are the risks?
Bad nights (shifted work, anxiety, etc.) do not allow the body to recover sufficiently during slow-wave sleep phases. Fatigue sets in. And over time, other health consequences may appear:
Weight gain
“A person who is sleep deprived tends to eat more because leptin production,satiety hormone and ghrelin,hormone that stimulates appetite, are disturbed,” explains the specialist. Ultimately, poor sleep can lead to weight gain.
No more anxiety and depression
Sleep is essential for mental balance. When we sleep poorly, we risk becoming anxious and depressed over time.
Less immune defenses
A body that does not have its account of deep slow-wave sleep defends itself less well against infections. It is in fact during this phase that the immune system memorizes the antigens with which it is confronted. “It has been shown that a person who sleeps all night after a vaccine develops fewer antibodies,” notes Dr. Rey. “Sleep is not a waste of time! » he wants to point out.
To know : Physical activity and its impact on sleep will be in the spotlight on Friday March 15, 2024, during the 24th Sleep Day. The program is available on the website of the National Institute of Sleep and Vigilance.
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