Deep sleep: definition, role, ideal duration

Definition: what is deep slow-wave sleep?

Deep sleep, or deep slow-wave sleep, is one of the four phases that make up a sleep cycle. On average, an adult has four to six sleep cycles per night, lasting 90 minutes each. Sleep breaks down as follows:

• Falling asleep;
• Slow wave sleep which includes light slow wave sleep and deep slow wave sleep;
• Paradoxical sleep (Rapid eye movement or REM);
• Awakening.

What is the difference with paradoxical sleep?

In slow-wave sleep, the electrical activity of the brain slows down more and more to reach deep slow-wave sleep. This is when the electrical activity of the brain is slowest, the body is completely relaxed, the muscles relax. “The depth of sleep is assessed by the difficulty in waking the subject. REM sleep is also deep but the electrical activity of the brain is very rapid, as in the waking state, which gives the impression that the subject is almost awake. In other words, behaviorally, he may be in a deep sleep. Eight times out of 10, the individual is able to tell a dream, whereas this only happens 2 to 5 times out of 10 in slow-wave sleep. This is even more rare in deep slow-wave sleep.explains Dr Marc Rey, neurologist specializing in sleep, president of the National Institute of Sleep and Vigilance (INSV).

Sleep well: what type of sleep is the most restorative?

Deep sleep is more physically restorative than paradoxical sleep since growth hormone (GH) is secreted during deep slow-wave sleep. “It is important in children but also in adults because growth hormone allows you to repair what you broke during the day in terms of muscle joints etc, but also consolidate the day’s learning“, develops the specialist. It also plays a leading role in the strengthening of the immune system and helps you stay healthy.

What are the consequences of a lack of deep sleep?

A lack of deep sleep promotes obesity and type 2 diabetes because the secretion of leptin, a hormone that suppresses appetite, and that of grhelin, a hormone that stimulates appetite, is disrupted. In other words, the less deep sleep we have, the more risk we have of gaining weight since we naturally tend to gravitate towards foods richer in sugars and fats.

Sleep deprivation also increases the risk of developing chronic disease. “Generally, it is difficult to separate the different stages of sleep into their role because it is impossible to eliminate deep slow-wave sleep while leaving light slow-wave sleep and paradoxical sleep since deep slow-wave sleep necessarily occurs after an episode of light slow-wave sleep.nuance Dr Marc Rey.

What is the ideal duration of deep sleep? How many hours per night?

What we know is that deep slow-wave sleep is more abundant in children and adolescents than in seniors. The duration of deep slow-wave sleep tends to decrease over the course of life and of course sleep is very important to consolidate what we learned during the day. “There are different types of memories, some are better consolidated in paradoxical sleep, this is the case of procedural memory, others like declarative memory would be better consolidated in slow-wave sleep. But the two phases of sleep are very important for consolidation of memorycontinues the neurologist specializing in sleep.

There are cycles where deep slow-wave sleep will last a long time and others where it will completely disappear. During the morning cycles, there is almost no more deep slow-wave sleep, this is why we have the impression of having lighter sleep in the second part of the night and that it is not useful There’s no point sleeping in to try to make up for the lack of deep sleep.

Little deep sleep phase: why?

Nighttime sleep is organized into cycles that include deep slow-wave sleep and paradoxical sleep. A cycle lasts 1h30 in adults. The amount of deep sleep in sleep cycles varies between the beginning of the night and the end of the night. “The beginning of the night is richer in deep slow-wave sleep, this is the reason why, if we are woken up 1 hour after we have fallen asleep, there is a chance that waking up will be particularly difficult in the sense that the sleep is very deep, which is what this is called sleep inertia (the brain having a lot of slow waves, waking up will take longer). At the end of the night the cycles are richer in paradoxical sleep, which is why when we wake up in the morning, we often have a dream in mind. explains our expert.

Cycles rich in deep slow-wave sleep depend on the subject’s habits. For example, a subject who is used to going to bed at 10:30 p.m. when he goes to bed at 2 a.m. begins his sleep with the 2 a.m. cycle, not the 10:30 p.m. cycle. He therefore has less deep slow-wave sleep when he goes to bed late. But if the subject goes to bed every evening at 12 a.m., he has his deep sleep between 12 a.m. and 2 a.m. because he always goes to bed after 12 a.m.

How to optimize deep sleep?

Several tips can help optimize deep sleep time:

• Practice daily physical activity for a minimum of 30 minutes at least 2 hours before bedtime;
• Take a lukewarm shower before sleeping to relax and ease the drop in our temperature that occurs during the night;
• Promote a calm environment before bed: noise and blue light should be avoided if possible two hours before going to bed;
• Fight against sleep disorders such as sleep apnea, restless legs syndrome and insomnia which can impair the quality of deep sleep;
• Adopt a healthy lifestyle: fight against stress, avoid having an unbalanced diet.