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

There is no need to say much about the benefits of a good night's rest, which is an important component of the life of any individual. A person tired during the day dreams of getting home as quickly as possible and, having said hello to his soft pillow, finds himself in the kingdom of Morpheus.

Sleep is our adaptation to the real world. Thanks to sleep, our internal resources and the strength spent during the day are restored, and mental, physical and emotional performance is maintained at the proper level. A person who has no problems with sleep at night feels rested in the morning and is completely ready to conquer new heights.

Sleep consists of several phases and stages of electrical activity in our brain, which clearly and consistently replace each other. Surprisingly, only developed warm-blooded animals (mammals, birds) are able to sleep the way people do.

Deep sleep, which is one of the stages of slow-wave sleep, is responsible for the recovery processes occurring in the body during a night's rest. What is deep sleep? What changes occur in the human body during deep sleep? How long should deep sleep last and can it be increased? Today we will discuss these and other important issues regarding deep sleep and its effect on our body.

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 .

Sacrificing sleep for the sake of anything is a stupid idea.

Phrase from the book “Just Space”

A comfortable bed, a clear conscience and the absence of the Internet contribute to sound, healthy sleep. By overcoming the temptation to complete important tasks, finish watching a movie, or finish reading an article, you will give yourself priceless moments of relaxation. There will be a new day for business! It will begin with a surge of energy and positivity, provided that you have had enough rest to recuperate.

Why sleep is so important

Our wise ancestors said: it is better to undereat than not sleep. This postulate has been confirmed by scientific research in different countries of the world. The main conclusion that scientists came to is this: a person’s life expectancy depends on the duration of sleep.

Chronic lack of sleep has a negative effect on the body and contributes to the development of serious diseases:

weakening of the functions of the cardiovascular system;
deterioration of brain function - the emergence of a tendency towards dementia, poor mood and performance;
risk of developing type 2 diabetes mellitus;
the appearance of excess weight;
decreased immunity, the body's resistance to colds and viral diseases. If a prophylactic vaccination was given, its effectiveness decreases.

Each of these phenomena can reduce the quality of life and lead to serious health problems.

Deep sleep concept

Human sleep is a cyclical process; during a night's rest, two phases alternate. They are conventionally called slow and fast. The duration of the slow-wave sleep phase of an adult lasts 1.5-2 hours. This is followed by a period of REM sleep, which lasts 5-10 minutes. During the night, 4-5 cycles change. The closer a person is to awakening, the shorter the slow-wave sleep phase becomes and the longer the fast sleep phase.

It turns out that with 8 hours of sleep, the duration of slow-wave sleep is 6.5 hours. In the structure of sleep, it is the slow phase that ensures deep sleep. It consists of 4 stages:

Light sleep, falling asleep, dozing - a borderline state between reality and sleep. A person’s muscles relax, his consciousness becomes confused, you can talk to him, but do not count on complete adequacy.
Falling asleep, falling asleep - sensitive, capable of being interrupted by the slightest external influence. But gradually the heart slows down, the body temperature decreases, and consciousness turns off.
Deepening sleep. Doctors call this stage delta sleep.
Immersion in the stage of slow delta sleep, in the mode of minimal energy consumption. The muscles of the body are completely relaxed, the pulse and breathing rhythm are slowed down, the brain is disconnected from the outside world. Dreams come to a deeply sleeping person. It is difficult to wake him up, and if he succeeds, the one who wakes up will be disoriented and “broken.”

The deep sleep phase is extremely important, since during this period processes take place for a person to fully rest:

the human body relaxes due to a decrease in the activity of the sympathetic nervous system;
restoration processes are actively underway;
slow down metabolic processes;
pulse becomes rare;
anabolic hormones are produced - growth hormone and testosterone;
The production of stress hormones – adrenaline, cortisol, etc. – decreases.

If slow-wave sleep is necessary for a person to fully function the body, then the REM sleep phase restores mental functions. Therefore, sound productive sleep is considered a universal cure for any disease.

How much sleep does a person need to get enough sleep?

The number of hours of sleep at night depends on the person's age. Moreover, lack of sleep, which is fraught with weakness, fatigue, and drowsiness, is no less dangerous than oversleeping. People who sleep long hours are more likely to suffer from cardiovascular diseases. The inexorable statistics are as follows: 12% of people who sleep less than 6 hours a day may die prematurely; among those who sleep for more than 9 hours, the risk of leaving before their due date reaches 30%!

The optimal option for an adult aged 25 to 65 years is considered to be a sleep duration of 7-9 hours. The individual characteristics of the body will suggest the most correct number, but within these two hours.

For other age categories the picture is as follows:

babies under 3 months should sleep up to 17 hours a day;
infants up to one year - 12 - 15 hours;
small children under 2 years of age require 12–14 hours of sleep;
preschool children 3–5 years old need 10–13 hours to sleep;
Primary school students under 13 years of age need 9–11 hours for proper rest;
teenagers 14–17 years old need 8–10 hours of sleep;
boys and girls aged 18–25 years, like adults, need 7–9 hours of sleep;
The group of elderly people over 65 years old should get 7 – 8 hours of rest every night.

In total, we spend about a third of our lives sleeping!

Rules for healthy sleep

In order to use your sleep hours productively and effectively, it is enough to follow simple rules, and even better, make them a norm of life - a good habit that preserves beauty, health and stimulation of life.

Go to bed on a different day than you plan to wake up. Ideally, for an adult, the time is determined from 22 to 23 hours. The developed reflex of going to bed at the same time helps you fall asleep quickly and easily.
On weekends, you can sleep longer, but no more than 1-2 hours; you won’t be able to sleep off “in reserve.” You will spend this time falling asleep for a long time at night.
Only in complete darkness at night is melatonin produced, a hormone that helps restore the body. Don't use night lights, but thick curtains to block out moonlight and street lamps will be very helpful.
Avoid late dinners, let 2-3 hours pass after the meal so that the process of digesting food is completed and nothing distracts you from sleep.
Fresh air acts like a sleeping pill, so ventilate the room before going to bed.
The air temperature in the bedroom should not be higher than 18-20°C; if it is too cool, cover up warmer or put on pajamas.
Create an individual bedtime ritual. His program should not contain exciting moments in the form of watching a “nightmare” on TV or reading a news feed on a tablet. Flip through your favorite book, talk on the phone with a loved one, chat with your children or pets.
Choose the optimal mattress, pillow, blanket for yourself.
Replace your old bed with a new modern model.
If you sleep on a sleeper sofa or chair, invest in a quality topper.

Psychologists do not recommend installing a TV in the bedroom. Consider this tip! A good habit before bed will be a cup of herbal soothing tea, a glass of warm milk with a teaspoon of honey, and a relaxing bath.

Causes of insomnia

Sleep disorders cause great damage to the body, so it is important to identify the cause of insomnia as early as possible and eliminate it. The most dangerous is considered to be prolonged insomnia, lasting more than 3 months. It can be provoked by a complex of reasons and this situation cannot be avoided without the help of specialists.

Doctors call the main provocateurs of sleep disturbances psychosocial tension, depressive states, active brain activity, non-compliance with sleep and wakefulness, thoughtless intake of stimulants (coffee, alcohol, drugs).

At risk of developing insomnia are the elderly, patients suffering from endocrine, infectious and neurological diseases. It is not always in a person’s power to eliminate the somatic causes of disturbances in the most important physiological process, but by observing sleep hygiene, insomnia can be alleviated.

Is it good to sleep during the day?

For a small person, daytime naps are a must. For a big person, taking a nap during the day is not forbidden. People who have the opportunity to rest in the middle of the day have improved memory and increased concentration. A nap will restore strength, reduce the likelihood of depression, cardiovascular problems and will not cause insomnia.

But you shouldn’t get carried away; long naps are not beneficial. It disrupts the rhythm of life, the functioning of the endocrine system and leads to insomnia at night. Rest during the day should be:

no longer than 20-30 minutes in the interval from 13 to 15 hours of the day;
on a comfortable sleeping place (sofa, sofa, armchair);
without loud sounds, bright lights and other irritating factors.

Experienced daytime nappers recommend drinking a cup of coffee or tea before resting; the drink will take effect within 20 minutes and will make it easier to wake up. After a day's rest, a short warm-up for the muscles is useful.

How to learn to wake up early

For early risers, this issue is irrelevant; they wake up easily and do not experience the torment of prolonged waking up. There are “pigeon” people for whom getting up early is not a difficult task either. Night owls really suffer from waking up early. Some useful tips for them:

go to bed not too late and not after a hearty dinner with a tablet;
wake up at the first sound of the alarm clock, do not put off getting up for another 5 minutes;
turn on invigorating music and as much light as possible;
drink a glass of water;
do pleasant, easy gymnastics to rhythmic music;
wash your face with cool water, if you can, use a contrast shower;
Charge your body with energy with a hearty breakfast!

Everyone who decides to change the rhythm of life is convinced of the benefits of getting up early. Early risers have a better chance of receiving a pleasant surprise from fate.

A sound sleep restores the energy spent during the day. As the best cosmetologist, he smooths out wrinkles, removes traces of daytime fatigue from the face, brings rest to the muscles and replenishes energy. They say that the stars of the night are holes in the floor of Heaven. Their rays bring streams of Universal wisdom to a sleeping person, so at night we become kinder and brighter. Hours of sleep are priceless!

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.

How does deep sleep affect how you feel after waking up?

The more the sleeper is in a state of deep sleep during the night's rest, the better and healthier he feels after waking up. A person who does not experience any problems with the duration of this phase of sleep, the level of physical endurance and mental activity increases noticeably. Such an individual feels full of strength and energy throughout the day, he quickly and efficiently solves the tasks assigned to him, and does not experience any difficulties with orientation in time and space.

A lack of deep sleep negatively affects immunity, nervous system function, concentration, coordination and appearance. An individual who did not fully rest at night looks tired and broken in the morning, has a rumpled appearance, gets tired quickly, and cannot concentrate his attention on the tasks assigned to him. For such a person, the risk of catching an infectious or cold disease increases several times!

Many people who have problems with deep sleep develop apnea syndrome (during sleep, breathing stops for several tens of seconds). If a person regularly experiences a lack of deep sleep, then he experiences serious disruptions in the functioning of the endocrine system. The body stops producing growth hormone. This can cause the development of obesity in people who have problems with excess weight.

Deep sleep is also characterized by manifestations of sleepwalking, nightmares and other mental disorders. In such cases, waking up a person during deep sleep is strictly prohibited, otherwise it will negatively affect his well-being and will only worsen his mental disorder.

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.

In our dreams we learn

We have at least two stages of sleep: deep sleep and paradoxical sleep (REM sleep). This can be seen in the electroencephalogram.
When we sleep, electrical activity sensors first detect the delta rhythm, which is characteristic of deep sleep. An hour later, features of the alpha rhythm characteristic of wakefulness appear. This lasts 15–20 minutes. This is that same paradoxical dream.
During paradoxical sleep, the brain sorts out the information that has accumulated during the day. Therefore, solutions to complex problems often come in dreams. The brain selectively transfers impressions of the current day into long-term memory, from the hippocampus to the large cortex. It’s like RAM and a hard drive: we will remember something new in a day for a long time, but we will forget something forever.
Memory rewriting depends on the emotional background. What evokes strong feelings in us is remembered longer. The more interesting the day was, the more intense the dreams.
The brain readily accepts into the hippocampus what is repeated more than once or is emotionally reinforced by something. Or what they threw into it right before bed.
Not everyone remembers dreams, but everyone has a phase of paradoxical sleep. If you wake up a person during a paradoxical sleep, he will say that he dreamed.

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.

Changes in the body

During delta sleep, normal physiological processes occur:

heart rate decreases;
breathing slows down;
relaxation of all muscles occurs;
it is difficult to get a person to wake up.

During the deep phase, the catabolism that occurred during the period of wakefulness is compensated, as evidenced by the facts of delta sleep prolongation in the following cases:

at the end of active physical activity;
during a period of sudden weight loss;
with thyrotoxicosis.

If you conduct an experiment in which you artificially deprive the subject of deep sleep, he will begin to complain about weakness and discomfort in the muscles. Delta sleep has a lot to do with memory processes. As a result of numerous experiments, it was determined that the deterioration of memory processes that occurs in the presence of prolonged insomnia has a direct connection with problems of the deep phase.

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

Age-related physiological changes in sleep and metabolism, as well as their disorders

Let's consider the changes in sleep physiology that manifest themselves in old age in any person without noticeable health problems. Of course, hormones and neurotransmitters, including those that are rarely heard, are involved in regulating the state of the body. Here is their list.

With age, the production of orexins, neuropeptides secreted by a number of hypothalamic cells, weakens (the fact is that these cells die over time). Orexins maintain a state of wakefulness, and a significant lack of orexin leads to narcolepsy - sudden attacks of irresistible sleepiness during the day. Apparently, one of the reasons why the quality of sleep in older people is worse than in younger people is lower levels of orexin [7]. The quality of sleep decreases because orexin does not simply prevent a person from falling asleep. It softens the transition between sleep and wakefulness and, one might say, makes it smoother and more predictable [8]. Agree, understanding when you fall asleep is somehow more pleasant than “switching off” suddenly or rolling your head on the pillow, waiting for Morpheus to come.
Adenosine is one of the non-classical mediators that cause drowsiness. Adenosine is, in fact, part of the molecule of the “universal energy currency of the cell” - ATP, only without phosphate ions and without energy-rich chemical bonds. The longer a person did not sleep, the more energy he spent, and the higher the concentration of adenosine in his blood became. You can artificially reduce the sensitivity of cells to adenosine and temporarily banish fatigue by taking its receptor antagonist, caffeine. With age, in the cerebral cortex, the balance of activity of enzymes that help synthesize adenosine and enzymes that help convert it into the form of adenosine phosphates changes: the former begin to work significantly more than the latter. Because of this, adenosine levels in the brain increase. This is probably why older people more often feel sleepy, albeit “fake” [9]. If we consider age-related changes in sleep not at the level of cells and hormones, but more globally, this is what is discovered. With age, nighttime sleep becomes fragmented, a person wakes up frequently, so the overall quality of sleep decreases, even if you go to bed for a short time during the day [10]. In fact, this is a manifestation of nighttime insomnia. Insomnia is common in older people, but increasing age alone does not increase its likelihood. It is increased by the following risk factors: depression (especially often occurs after 65), death of a spouse, retirement, onset of dementia (about dementia, see the next section). Also, the manifestations of insomnia are enhanced by alcohol and medications often used by older people: antidepressants, carbidopa and levodopa (they are prescribed for the treatment of parkinsonism), adrenaline beta blockers (for heart disease; can cause nightmares) and corticosteroids [11].
With insomnia and fragmented sleep, glucose metabolism may be impaired. It occurs because the concentrations of ghrelin and leptin, the “saturation hormones,” change [12], and the sensitivity of cells to the most important “glucose hormone”—insulin—changes (by the way, it also depends on circadian rhythms). Regardless of total sleep time, in people of the same age, a greater proportion of slow-wave sleep is correlated with lower body weight and a lower risk of obesity [13].

Periodic limb movements during slow-wave sleep have been linked to an increased risk of heart disease and stroke. It is only important to understand that this connection is qualitative, not quantitative. For example, it is impossible to predict by the intensity of limb movements during sleep how quickly and with what probability a person will have a stroke, because the latter can be not only a consequence of sleep pathology, but also its cause [14].

Often, health problems manifest themselves as breathing disorders during sleep: snoring, sleep apnea, etc. They appear as a consequence of disruption of the neurons of the bridge. The pons is a region of the brain where one of the “wakefulness centers” is located - the reticular formation , a collection of neurons that maintain the body’s activity in good shape, at the level of wakefulness. Not far from them is the respiratory center. Therefore, if there are problems with one group of nerve cells, the second one often suffers. Fortunately, the vast majority of patients with such problems do not experience serious breathing problems while they are awake [15].

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.

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.

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.

The body is being repaired in a dream

The brain does some vital things only in sleep. For example, it cleanses itself of harmful substances and restores blood pressure. It induces homeostasis, so to speak.
There is a hypothesis that during wakefulness, internal organs do not communicate much with the brain - they say, it has more important things to do. And at night, the brain pays attention to the intestines, stomach, liver, etc. And looks at what needs to be done: repair, cleaning, tissue restoration, hormone correction, etc. You can imagine that this is a doctor who visits the patient a couple of times per day to adjust medications.
If you don't sleep for a long time, cognitive abilities also decrease, but you don't die from it.
They die not from lack of sleep itself, but from diseases that have accumulated due to missed “examinations” by the brain - and they just happen in a dream. Rats that were experimentally deprived of sleep for several days died from intestinal inflammation. Most likely, the brain did not have time to diagnose the intestines, and it became inflamed uncontrollably.

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.

Is the norm the same for everyone?

Most often, sleep standards are developed taking into account the age characteristics of patients. However, this is not the only basis for variability, both between individuals and within each individual from night to night.

Factors influencing variability in sleep standards
Between people	Individual
Age, gender, race, genetic factors including chronotype. Body weight, anxiety and depressive disorders and other diseases and conditions that can affect the quality of sleep. Concomitant diseases of internal organs, taking medications. Shift work	Environment: noise, light, temperature, the effect of the first night in a new place. Physical and intellectual activity before bed Lifestyle: caffeine consumption (strong tea and coffee), stressful work; Chronic pain, anxiety, depression; Different daily routines on weekends and weekdays.

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.

Neurodegenerative diseases and sleep

The most common neurodegenerative diseases are Alzheimer's disease [21], [22] and Parkinson's disease. Unfortunately, their fame is sad. In Alzheimer's disease, beta-amyloid plaques accumulate in neurons, and in Parkinson's disease, Lewy bodies (alpha-synuclein) are formed in neurons. The amount of amyloid in this case correlates with sleep quality in healthy people aged 60–65 years [23]. However, it is not a fact that sleep disturbances occur due to the increased content of this protein in neurons. The opposite has also not been proven: there is no reason to claim that lack of sleep provokes Alzheimer's disease. However, sleep disturbances can potentially help diagnose Alzheimer's disease at an early stage. This is also supported by the fact that as the symptoms of this dementia intensify, the severity of sleep disorders increases (the same applies to dementia with Lewy bodies - a disease that resembles Parkinson's disease in some symptoms, and Alzheimer's disease in some others.) In addition, despite frequent naps; in patients with Alzheimer's dementia, sleep duration is significantly reduced [24].

In Parkinson's disease, sleep becomes interrupted, the REM sleep phase is disrupted, the frequency of sleep spindles and the duration of slow-wave sleep decreases, and diurnal fluctuations in cortisol levels are smoothed out. It turns out that in Parkinson's patients, sleep and wakefulness are not clearly divided into periods, the boundaries between them are to some extent blurred.

In Huntington's chorea, sleep and wakefulness are fragmented [25]. A person is active at night and falls asleep late. He has a reduced proportion of REM sleep, an increased frequency of sleep spindles, and during stage 1 non-REM sleep, chorea can be observed - chaotic uncontrolled movements of the limbs, the main manifestation of this disease during wakefulness.

With ALS (amyotrophic lateral sclerosis), breathing disorders occur during sleep. REM sleep becomes intermittent, and the proportion of slow-wave sleep decreases. In addition, the course of daily fluctuations in cortisol is disrupted.

Interestingly, the manifestation of almost all of the above sleep disorders can be weakened with the help of phototherapy (periodic exposure to bright light) and organized (not uncontrolled!) melatonin intake.
Table 1. Summary table of associations of the most common sleep disorders with neurodegenerative diseases.

Age-related degeneration	Alzheimer's disease	Parkinson's disease	Huntington's chorea	Amyotrophic lateral sclerosis
Which neurons and structures are damaged?	Basal forebrain, locus coeruleus, cerebral cortex, dopaminergic neurons, orexin neurons, acetylcholine receptors	Basal forebrain, cerebral cortex, cholinergic neurons	Substantia nigra, dopaminergic neurons, orexinergic neurons	Basal ganglia, dopaminergic neurons	Motor neurons of the motor cortex, spinal cord and brain stem. Accompanied by a decrease in the activity of neurons that secrete serotonin
Sleep disorders	Fragmented sleep and wakefulness, out of phase with normal circadian rhythms, increased daytime sleepiness	Reduced total sleep time	Fragmented sleep, behavioral disturbances during REM sleep (moving limbs, making sounds)	Sleep and wakefulness are fragmented, the proportion of REM sleep is reduced	Breathing disorders during sleep, insomnia. The degree of deterioration in sleep quality corresponds to the severity of other manifestations of the disease
Signs of probable violations	Disturbance of the melatonin system of the brain	The order and timing of REM sleep	REM sleep behavior disorder	Many sleepy spindles	Various sleep disturbances (a likely sign of sleep apnea)
Circadian rhythm disorders	Peak and trough episodes are out of phase relative to normal circadian rhythms	Disturbances of the melatonin system and diurnal changes in core body temperature	Shift in periods of greatest and least activity, smoothed daily changes in cortisol concentration (peaks become lower and less pronounced)	Falling asleep is shifted to a later time, at night the patient shows increased activity compared to peers	Daily fluctuations in cortisol levels do not correspond to the normal rhythm
Non-REM sleep	Short slow-wave sleep	Short slow-wave sleep, few sleep spindles	Short slow-wave sleep, few sleep spindles	At the first, extended stage of sleep, chorea is observed. Many sleepy spindles	Short slow-wave sleep
REM sleep	Shortened REM sleep	Shortened REM sleep, increased activity of inducible NO synthase	REM sleep behavior disorder, symptoms of REM sleep appear during non-REM sleep	Shortened REM sleep, difficulty transitioning into it from non-REM sleep	Breathing disorders, short and fragmented REM sleep
Wakefulness	Fragmented wakefulness, frequent episodes of dozing, increased daytime sleepiness	Fragmented wakefulness, frequent episodes of dozing	Increased daytime sleepiness	Some studies indicate disturbances in awakening, but deviations from healthy peers in patients are insignificant	Increased daytime sleepiness
Treatment options for disorders	Phototherapy	Phototherapy, exercise, orexin/hypocretin receptor antagonists (used in mice)	Phototherapy	Setting the circadian rhythm by eating according to a clear schedule, alprazolam (restores circadian rhythms and slows down the decline in intelligence)	Melatonin preparations, mechanical ventilation (CPAP)

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.

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.