Deep sleep phase: how long does it last and how to increase it to normal

A person spends a third of his life sleeping, which means it is extremely important for health. What is its significance?

For decades, psychologists and neurologists have been studying sleep and its impact on well-being and performance.

Nowadays, due to the fast pace of life, stress and hard work, the problem of lack of sleep is especially acute. After reading this article, you will learn the secrets of perfect sleep and awakening.

How long should the deep sleep phase last?

The deep phase on average occupies 75-80% of sleep duration . The rest of the time is usually REM sleep. The phases replace each other several times during the night. During 8 hours of sleep this happens at least 4-5 times.

After falling asleep, the deep phase of sleep begins, which consists of 4 stages. After the end of deep or slow-wave sleep, REM sleep follows. By the way, the completion of one phase of deep sleep and one phase of REM sleep is called a cycle .

On average, one sleep cycle in a person lasts 90-120 minutes. If we take deep sleep to be 75% of the total sleep duration, it turns out that slow-wave sleep lasts about 65-90 minutes. Accordingly, the remaining 25-30 minutes fall into the REM sleep phase. In reality, REM sleep lasts less - about 10-15 minutes, and deep sleep - 75-85 minutes remaining from the cycle.

Considering that there are approximately 5 such cycles per night, we multiply the duration of the slow and fast phases by 5 and find that the total duration of deep sleep is approximately 400 minutes or almost 6.5 hours (with an 8-hour duration of total sleep).

In any case, exact numbers are difficult to know without special equipment that is used in sleep diagnostics. As morning approaches, the proportion of slow-wave or orthodox sleep in the cycle decreases, while the percentage of fast sleep phase increases. That is why it is very difficult to calculate the exact duration of the deep sleep phase without polysomnography .

Quality sleep: what is it like?

In 2021, the US National Sleep Foundation formulated recommendations for sleep quality. They concerned indicators that characterize the continuity of night rest, its structure, as well as the presence of episodes of daytime sleep. We present some standards in table form.

Index	Norm	Suitable for persons over 65 years of age	Not the norm for people under 65
Sleep continuity
Sleep latency (speed of falling asleep)	≤15 minutes	31-60 minutes	45-60 minutes
Awakenings lasting more than 5 minutes	Up to 2 times per night	Up to 3 times	≥4 times
Time awake after sleep onset	≤20 minutes	31-60 minutes or more	≥41 minutes (≥51 minutes for teenagers)
Daytime nap
Number of episodes per day	0 (up to 1 for teenagers)	0-3	≥4
Duration	≤20 minutes for adolescents; not defined for other groups	≤100 minutes	>100-120 minutes

But even this numerous list is not able to cover all the important parameters necessary for analyzing the quality of a night's rest.

Norm of deep sleep in children

During deep sleep, the child’s brain actively develops, so children need as much sleep as possible for intellectual development. However, in infants up to 3 months of age, the deep sleep phase is not observed. Instead, a normal restful sleep follows.

3 months after birth, nervous activity is activated, and with it deep sleep appears. In the first months of life, the duration of the slow phase is only 20-30 minutes . However, over time it increases to the physiological norm of an adult.

Consequences of lack of rest

It may seem that lack of sleep is not such a serious problem, and all the consequences of lack of sleep come down solely to daytime lethargy. In fact, as scientific experiments show, lack of night rest affects a person in much the same way as alcohol abuse.

Lack of sleep is:

fatigue, lethargy, lack of motivation;
bad mood, irritability, increased risk of depression;
impaired brain activity, problems with memory, learning and concentration;
decreased creativity and ability to quickly solve problems, difficulty making decisions;
inability to cope with stress and manage emotions;
impaired motor skills, increased risk of accidents;
weakened immune system, tendency to frequent colds and infectious diseases;
hallucinations and delusions are possible;
increased risk of stroke, diabetes, hypertension, Alzheimer's disease, and some types of cancer;
decreased sex drive;
premature skin aging.

In addition, scientists have found a direct link between lack of sleep and weight gain. The bodies of people suffering from lack of sleep produce increased amounts of cortisol, a hormone that increases appetite.

Deep phase in sleep structure

About 10-15 minutes after falling asleep, the deep sleep phase begins. At this time, restoration processes occur in the body: heart function improves, tissues are regenerated, and brain functions are normalized.

It is difficult to wake up a person who is in the slow phase of sleep. The reaction to external stimuli is minimal, so it can only be disturbed by loud sounds. Waking up in the slow or orthodox phase, a person will feel very drowsy. Especially if the duration of the current sleep was less than usual, that is, less than 7-8 hours.

Unlike the fast phase, during slow sleep the sleeper does not experience twitching of the arms or legs, there is no sleepwalking or talking in his sleep.

Structure

NREM and REM sleep alternate throughout the night cyclically. Falling asleep begins with the first, orthodox phase. It lasts about an hour and a half and takes place in four successive stages:

Decreased alpha rhythm on the EEG, appearance of low-amplitude theta rhythms. At this time, the person is in a state of half-asleep, which may be accompanied by the appearance of dream-like hallucinations. Thought processes continue, manifesting as daydreams and reflections on the events of the day. Often there is a solution to pressing problems.
The electroencephalogram records the predominance of theta waves, as well as the occurrence of characteristic increases in ri. At this, the longest, stage, consciousness turns off, the threshold of perception increases, but it is still possible to awaken the sleeping person.
The appearance of high-amplitude delta waves on the EEG. In the third phase of slow-wave sleep (from 5 to 8% of the total duration) they take up less than half the time. As the delta rhythm predominates, the deepest delta sleep occurs.
In the fourth phase, which accounts for up to 15% of the night's rest, consciousness is completely turned off, and it becomes difficult to wake up the sleeper. This period accounts for the majority of dreams; at the same time, the likelihood of manifestations of disorders (somnambulism, enuresis, nightmares) increases.

Stages of deep sleep

The deep sleep phase normally consists of 4 stages. Let's look at what happens to our body in each of them.

Nap . The muscles of the body gradually relax, while the brain continues to react to external factors. You can talk to a dozing person, but he is unlikely to be aware of what exactly he is saying. In other words, drowsiness is a borderline state between sleep and reality.
Falling asleep . During this period, consciousness turns off, but the person still reacts to external signals. At the same time, the heart slows down its rhythm and body temperature decreases. Sleep at the stage of falling asleep is very sensitive, so a person will easily wake up in the process of falling asleep if disturbed.
The beginning of deep sleep . The brain switches to the delta rhythm, during which sleep occurs.
Deep/slow-wave orthodox sleep . There is an increase in delta waves in the brain, due to which the body literally goes into a low-energy mode. During this period, the muscles are as relaxed as possible, and body temperature drops to the lowest possible level. The pulse and breathing rhythm slow down, and the brain does not respond to external factors at all. It is difficult to wake up a person who is in the delta stage of sleep. But if he wakes up, he will feel very weak and simply disoriented. In addition, most dreams occur in the delta sleep phase.

What is a dream

It’s hard to imagine, but today there is no absolute definition of sleep. To give a rough description of the term, sleep is a normal physiological state in which a person has a reduced reaction to the outside world and the goal of which is rest and recovery.

Previously, people had a very primitive idea of the physiology of sleep. They believed that during sleep the soul leaves the body and travels around the world (the global information field? the astral world?). What she sees during her “journey” is remembered by a person as dreams. Now we can say with confidence that we do not go to the astral plane in our dreams. However, the origin of the dream is still full of mysteries. Humanity is tens of thousands of years old, and during this time we have not figured out what sleep is! Somnology - the science of sleep - arose only about 50 years ago, and during this time, despite its fairly rapid development, it has not yet managed to answer questions about the physiology of sleep and its functions.

In fact, only three things are completely obvious.

The sleeper is in a state of relaxation and almost complete immobility.
During sleep, a person has a limited perception of reality. It is impossible to say that perception is “turned off” completely: it has been proven that sleeping people can react to odors, in addition, everyone can be woken up by the ringing of an alarm clock.
During sleep, amazing cyclical processes occur in the brain that distinguish sleep from wakefulness and other similar states: coma, fainting, hypnotic trance.

The subtleties are still unknown to scientists. However, they were able to study the structure of sleep and describe some of the processes occurring in the body while a person sleeps.

What else happens during deep sleep?

The stages of deep sleep and REM sleep differ from each other in the following ways:

During slow-wave sleep, the body's metabolism slows down.
During orthodox sleep, the activity of the sympathetic nervous system decreases. That is, the body is as relaxed as possible at this time.
Deep sleep is characterized by a decrease in heart rate. In the fast phase, on the contrary, the pulse often increases, especially when having emotional dreams.
In the slow phase, the production of adrenaline, cortisol and other stress hormones decreases. At the same time, anabolic hormones - testosterone and somatotropin (growth hormone) tend to a physiological maximum.
In deep sleep, recovery processes in the body are more intense.

Also, the difference between REM and NREM sleep lies in their effect on physiological systems. For example, REM sleep is more necessary for mental health, while slow sleep is more necessary for the normal functioning of the body.

Sleep is an excellent healer, so to recover from illness or injury, doctors advise getting more sleep in order to recover from illness much faster

Normal duration

What is the norm for deep sleep? Its duration and quality are determined by the individual characteristics of the human body. For one, 4 hours of rest is enough, for another, to get enough sleep, you will need at least 10. The duration is also influenced by the age of the sleeper: in childhood it is up to 9-10 hours, in youth and maturity – about 8, and in old age it is reduced to a quarter of a day. The average ideal night's rest time is 7 or 8 hours, and the norm of deep sleep for an adult is determined by the percentage of phases.

If we take 8 hours of sleep as a basis, the duration of the deep period in a healthy person will average 20%. That is, in general it will take at least 90 minutes, and each of 4-5 cycles will take 20-25 minutes. When night rest is shortened or increased, the time of each phase decreases or increases accordingly. However, their ratio in percentage terms does not change, and the body recovers fully.

How to increase deep sleep phase

Ideally, it is better to sleep 8-9 hours a day. In this case, the duration of the deep sleep phase will be equal to 30-80% of the entire duration of rest. If slow-wave sleep is less than 30% of your total sleep, health problems may arise, such as heart function.

Health can also deteriorate when the deep sleep phase is extended. In this case, performance decreases and chronic fatigue syndrome often appears.

To increase the deep sleep phase, follow these recommendations:

Maintain a certain sleep schedule . Go to bed and wake up at the same time. And even on weekends.
Avoid drinking coffee, strong tea and other caffeine-containing drinks after 15:00 . Caffeine entering the body in the afternoon stimulates the nervous system. This in turn can shorten the duration of slow-wave sleep.
Don't smoke or drink alcohol before bed . Nicotine and strong drinks reduce the duration of deep sleep.
Finish dinner at least 3 hours before going to bed . Overeating at night interferes with good sleep. If you are hungry before bed, drink a glass of milk or fermented milk product. You can also eat 1-2 fruits at night, for example bananas, apples or pears.
Meditate before bed . Spiritual practices help you relax, which in turn has a positive effect on sleep. Read about how to meditate correctly in this article.
Play sports . In people who are “friendly” with sports, the deep sleep phase lasts longer compared to those who exclude physical activity.
Create favorable conditions for sleep . The temperature in the bedroom should be in the range of 17-21 C. At the same time, to avoid freezing, sleep under a warm blanket. During the warm season, go to sleep with the window open. Better yet, buy an air conditioner and turn it on for a few minutes before going to bed. Also, sleep with the curtains drawn tightly and in complete silence. All of the above helps increase the duration and depth of slow-wave sleep.

It is worth saying that the duration of slow-wave sleep, no matter how much you increase it, will not last longer than the physiological maximum. For example, the delta sleep phase in a healthy person should not exceed 30% of the total duration of night rest.

Prolongation of the deep sleep phase, identified by the results of polysomnography, may indicate hidden health problems. For example, these could be diseases of the brain or endocrine pathologies.

By the way, lack of deep sleep has an even more detrimental effect on health. It has been experimentally proven that reducing the duration of orthodox sleep to a minimum can lead to dire consequences.

Importance for the body

Healthy sleep is the key to vigor, good physical condition, health and energy. At this time, tissue regeneration and the production of hormones necessary for normal functioning are activated.

Lack of sleep negatively affects the functioning of the entire body, and especially the functioning of the brain. Chronic lack of sleep can lead to the following consequences:

Memory impairment and decreased attention. If you notice that it is becoming more difficult for you to concentrate on daily tasks, then this is a symptom of lack of sleep.
Irritability and depressed emotional state.
Decreased immunity. During a full night's sleep, cytokines are actively produced - protein compounds necessary to fight infectious and inflammatory processes.
Premature aging, deterioration of skin and hair.
Increased risk of obesity and cardiovascular diseases (arterial hypertension, coronary artery disease, atherosclerosis).

What time does the deep sleep phase begin?

To determine the depth and duration of slow-wave sleep, it is necessary to undergo polysomnography. During the procedure, sensors are connected to the patient’s body that monitor the rhythm of breathing, pulse, snoring, movements during sleep and much more. The study itself takes place in special sleep centers, where a bed is prepared for you, on which sleep diagnostics are carried out during the night. Specialists will monitor your sleep and your condition during sleep. And the information obtained using polysomnography will help doctors more accurately understand the causes of poor sleep, if you have them.

However, not every locality has an office for polysomnography. In this case, trackers for tracking the phases of REM and deep sleep will come to the rescue. They look like a regular bracelet with built-in motion, heart rate and body temperature sensors. During the night, a device located on the arm reads 3 of these indicators. Then, based on the data received, the bracelet's microchip builds a graph on which the entire sleep structure is visible. You can view the graph on your smartphone by connecting the tracker to your phone via Bluetooth.

Unlike polysomnography, a sleep tracker provides imprecise data about your sleep. However, it is still able to show the overall picture of the dream. However, to find out the detailed structure of your sleep, you should undergo polysomnography, which will be prescribed by a sleep specialist.

Causes of poor sleep

Taking a long time to fall asleep, frequent awakenings at night and grogginess in the morning indicate the inadequacy of slow-wave sleep. Of course, the sleep situation can be improved, but first you need to determine the cause of poor sleep. Let's look at the main ones.

Stress . Conflicts in the family or at work, stressful professional activities, states of shock and other similar factors can worsen the quality of sleep.
Depression . Long-term depressed mood due to mental disorders is often the cause of insomnia.
Chronic diseases . First of all, the quality of sleep is affected by hormonal levels in the human body. For example, thyroid pathologies can disrupt sleep. Moreover, endocrine problems may not manifest themselves in any other way.
Uncomfortable posture during pregnancy . An enlarged abdomen in women during this period interferes with proper sleep. After the 12th week of pregnancy, sleeping comfortably on your side or back becomes more difficult. Therefore, expectant mothers have to adapt to physiological changes. Read about how to sleep during pregnancy here.

Of all the above reasons, stress has the greatest impact on sleep. If a person goes to bed with an unresolved and disturbing problem, sleep difficulties may arise. Anxious thoughts that appear in bed lead to painful and unsuccessful attempts to fall asleep. As a result, the duration of deep sleep is reduced, and in the morning a person feels sleep-deprived and tired.

Insomnia can be diagnosed if difficulty sleeping occurs for more than 5 nights in a row. But isolated and rare sleep disturbances are not classified as insomnia. However, if you cannot get enough sleep for more than 5 days in a row, consult your doctor.

In most cases, poor sleep is associated with frequent stress, moving and significant changes in life.

And a few more words about sleep health

When discussing healthy sleep, we cannot ignore sleep hygiene, physical activity and sleep-disordered breathing, which affect the stability and quality of night's rest.

"Timing"

There are currently no generally accepted standards for going to bed and waking up. The legend about the “correct” time to fall asleep and more useful hours of sleep remains an unconfirmed legend. However, most experts talk about the importance of maintaining a sleep-wake schedule. The following factors can lead to negative health consequences:

discrepancy between actual bedtime and internal biorhythms;
the habit of getting enough sleep on weekends, with regular lack of sleep on weekdays;
the so-called “social jet lag” - a nocturnal lifestyle on weekends, followed by a return to normal sleep and wakefulness during the work week;
generally unstable sleep and wake patterns (shift work).

Sleep disordered breathing

A common pathology is obstructive sleep apnea, i.e. frequent stoppages of breathing associated with mechanical closure of the pharynx by collapsing soft tissues. Such breathing pauses, among other things, destroy the structure of sleep. When breathing is interrupted and oxygen stops flowing into the blood, a signal is sent to the brain to wake up in order to tone the muscles of the pharynx, restore patency of the airways and begin to breathe normally. Because of this, the sleep cycle does not end, but starts anew after each such micro-awakening. As a result, the most important phases of deep sleep for the body may be almost completely absent in the structure of night sleep. This disrupts the production of hormones, leading to chronic fatigue and the inability to get enough sleep, even if a person spends a lot of time in bed.

Abnormal motor activity

A very common problem is the so-called restless legs syndrome and periodic limb movement syndrome during sleep. Restless legs syndrome is an obsessive urge to move your legs, usually worse in bed, that interferes with sleep and often causes insomnia. Periodic movements of the limbs (usually legs) occur after falling asleep, disrupt the normal course of sleep and often lead to excessive daytime sleepiness.

Other manifestations of pathological motor activity are sleepwalking (somnambulism) and teeth grinding (bruxism), which are quite different in their external manifestations.

Sleep quality can be assessed in different ways. But at the same time, scientists and doctors note the importance of developing an integrated approach that will increase the accuracy of predictions regarding the adverse consequences of poor night's rest, and will also allow us to determine individual sleep standards for each person, taking into account personal characteristics, lifestyle, social employment and other parameters. In the meantime, one of the main markers for both the patient and the doctor is quality of life. If sleep does not bring complete rest, and you want to sleep during the day, then you should consult a somnologist. And there is a high chance that it will help fix your problem.

How to get rid of insomnia and normalize the duration of deep sleep

After determining the cause of poor sleep, treatment should begin. Depending on it, the doctor prescribes sleeping pills, prescribes psychotherapy/hypnotherapy, or refers to specialists in other areas to treat the primary cause of insomnia.

At the same time, the somnologist should talk about proper sleep hygiene , as well as how to deal with stress.