Deep Sleep: What Is It? What Are the Benefits?

Situated between the “light” sleep phase and the “  REM  ” sleep phase, this is the most important time of the night. Indeed, it is at this moment that sleep has the greatest impact on our development (particularly in terms of the brain, memory, and the growth of immune defenses).

Deep sleep is the third stage of the slow-wave phase. It occurs after the transition from wakefulness to sleep, after passing through a phase of light sleep. Upon entering deep sleep, the muscles completely relax and the body goes into a state of standby. 

Brain activity slows down 

During this phase, brain activity slows down. Brain waves, regular and broad, oscillate slowly. This is sometimes referred to as “delta sleep”: the brain becomes less and less receptive to external stimuli. 

Noise and light are much less likely to wake the sleeper. If the sleeper is woken up in the middle of this phase, it will be very difficult for them to “emerge.” 

The most restorative phase 

Deep sleep is the most restorative. Its role is crucial for the recovery of the body and organism, but also for staying healthy. Indeed, at this precise moment:

• The brain does a sort of “emptying”: the cerebrospinal fluid evacuates waste coming from the brain
• Memory consolidates information absorbed during the day: the hippocampus and cortex sort and store memories
• The secretion of growth hormones is promoted, particularly in children.

• Energy production occurs by metabolizing ingested glucose
• The body’s immune defenses are strengthened.

Deep sleep time varies depending on the individual, particularly their age. 

Deep sleep: How long does it last? 

In adults and adolescents, there is approximately 1 hour and 40 minutes of deep sleep per night. This duration tends to decrease with age. 

In children, this phase plays a more important role. In newborns, it simply does not exist. 

The deep sleep phase occurs precisely at the beginning of the night. Sleeping longer does not specifically increase the duration of this sleep phase. 

Deep sleep: what proportion? 

The deep sleep phase represents 20 to 25% of a night. We can therefore see that despite its importance, it does not last that long. For example, its proportion is much lower than that of light sleep. It is therefore essential to have a complete sleep cycle to access this phase of deep, slow-wave sleep. 

The benefits of deep sleep? 

Although all phases of the night play a crucial role in the body’s recovery and regeneration, deep sleep occupies a special place given its many health benefits. 

Deep sleep: restorative sleep 

First, deep sleep allows you to recover from the physical and psychological fatigue accumulated during the day. At this precise moment, the brain stores the energy needed to be in good condition the next day. It is therefore important to have a sufficient amount of deep sleep to be in good shape. 

Moreover, this phase is essential for the growth of children: it promotes the production of growth hormones. 

Deep sleep and memory 

Another essential benefit of deep sleep is its ability to maintain memory. During this phase, everything that happened during the day becomes a memory. This way, the memory is consolidated. 

During this phase, the cerebrospinal fluid removes waste and toxins accumulated during the day. In particular, it eliminates beta-amyloid protein, which is partly responsible for Alzheimer’s disease. 

Deep sleep against illness 

Getting enough sleep is essential for maintaining immunity and optimizing your immune system. The immune system is highly active during this phase of deep sleep. Enjoying good, deep sleep increases your chances of avoiding certain chronic diseases such as type 2 diabetes. 

Given the benefits of deep, slow-wave sleep, it may be worth optimizing it to achieve highly restorative nights. But then, how do you start increasing its duration? 

Practice regular physical activity 

To get the most out of your sleep, and especially the benefits of the deep sleep phase, it’s recommended to exercise. Indeed, exercising two hours before going to sleep can boost this phase and help you get a better night’s sleep overall. Ideally, you should exercise regularly, several times a week. 

Sleeping in doesn’t promote deep sleep 

There’s no point in deliberately sleeping in to improve this deep sleep phase. This occurs at the beginning of sleep (not at the end of the night). It’s better to take a nap in the middle of the day. 

If you need professional advice to boost your sleep, you can make an appointment via teleconsultation. 

Lack of deep sleep: consequences 

Certain poor lifestyle habits can impact the quality of deep sleep. In addition to the fatigue and moodiness that a lack of deep sleep and sleep disturbances can cause, there can be more serious consequences. 

Deep sleep and alcohol 

When we don’t get enough sleep, we risk neglecting the quality of our deep sleep. But poor lifestyle habits can also impact this crucial phase. 

Consuming too much alcohol before bed or drinking alcohol regularly reduces the time spent in deep sleep, even if you fall asleep more quickly.

Alcohol can cause nights to be more fragmented and cause you to wake up more, which is not good for the proper functioning of your sleep cycle. Recovery is not complete. Therefore, avoid alcohol if you want to optimize your sleep. 

The consequences of a lack of deep sleep 

Lack of deep sleep can be responsible for a large number of diseases, such as diabetes, obesity, but also strokes. 

Today, there are therapies and medical methods to improve the quantity and quality of deep sleep. Be careful, however, sleeping pills are not a solution to promote restorative sleep.