The ratio and duration of the phases of slow and fast sleep in a healthy person

What happens during sleep?

Sleep takes up almost a third of our lives. Just imagine, out of the 70 years a person has lived, he spends about 23 years sleeping. The issue of sleep worried people even before the new era - Aristotle studied sleep and wrote a treatise on it. Significant progress in the study of sleep was made only in 1924: German psychiatrist Hans Berger invented the electroencephalograph, a device that records the electrical activity of the brain. And in 2021, scientists Michael Young, Jeffrey Hall and Michael Rosbash received the Nobel Prize for the discovery of a “molecular clock” that synchronizes the body with solar activity.

This mechanism appeared in the process of evolution in all living organisms. It regulates all life processes, and frequent failures in its operation can lead to serious health problems.

During sleep, the human body does a lot of work to prepare for a new period of activity:

• restores resources spent during the day
• the brain processes and filters information, removing unnecessary
• muscles relax and recover
• growth hormone is produced
• the immune system is restored

Photo: healthline.com

Two stages of sleep: fast and slow sleep

Sleep has a cyclical structure and consists of two phases: fast and slow.

Immediately after falling asleep, the slow phase begins and is replaced by the REM phase - this phase change is called the sleep cycle. On average, the length of the cycle is 90 minutes, 4-5 such cycles take place per night. Interestingly, closer to the morning, the duration of slow-wave sleep decreases, and fast sleep increases. During this time, the muscles have time to fully recover. Theoretically, to feel rested, you need to wake up at the end of a 90-minute cycle.

Both phases are very important for a person. REM sleep is responsible for mental abilities - it processes emotions and impressions, analyzes all the information received during the day. The heart rate increases, the body temperature rises, the brain seems to be reliving the events of the past day. Memories overlap each other, which is why strange dreams arise in this phase.

REM sleep is responsible for restoring muscles, organs and the immune system. The body relaxes, blood pressure drops, brain activity decreases significantly - it can only remove unnecessary information and send the necessary information to long-term memory. The pineal gland actively produces growth hormone, which is needed for the restoration of tissues and muscles.

Human sleep phases by time and their characteristics

Human sleep consists of cycles. Each cycle in turn includes 5 stages, 4 of which occur in the phase of slow or deep sleep. The last fifth stage of the cycle is REM sleep.

The duration of one cycle is approximately 1.5-2 hours. Accordingly, in 8 hours of sleep a person goes through 4 or 5 cycles.

Half of your sleep is occupied by the light stage of non-REM sleep. About 25% of sleep is taken up by the fast phase ( REM sleep or the REM phase - rapid eye movement).

Sleeping extra is structurally different from the standard 8 hours of rest. For example, after 9-10 hours of sleep, the fast phase predominates in the cycles. Deep sleep, which is needed to restore the body, becomes less. This explains why you can't get enough sleep. After all, it is the slow, deep one that gives that very feeling of vivacity.

The duration of sleep phases is influenced by a person’s emotional state. Recent stress and depression can reduce the quality of your sleep.

What are circadian rhythms and how are they related to sleep?

Circadian rhythms are our internal schedule according to which all internal processes of the body operate. Almost all living things have it: animals, plants, fungi and even bacteria. The main reference point for rhythms for humans is light, for some inhabitants of the sea it is the ebb and flow of the tides, and for different living beings there are different factors. Human circadian rhythms adjust physiological processes to daylight hours, so weakness is felt when changing time zones, night shifts, and decreased daylight hours in winter.

How does the circadian mechanism work?

The change of day is recognized by photoreceptors in the eyes. Excited by light, they send a signal about the change of day and night along the optic nerve to the brain. The signal is received by the main regulator of circadian rhythms - the hypothalamus, from where the signal goes to the pineal gland. During the day, this gland actively produces cortisol (a stress hormone that helps us stay awake), and at night it produces melatonin. It was described in detail in the article: Melatonin: what is it and what is it for .

Features of circadian rhythms

1. Circadian rhythms are intrinsic in origin, although they are tuned by light. In 1729, French chronobiologist Jean-Jacques de Meran conducted an experiment with a plant: he closed it in a dark place and noticed that the plant opened and closed its leaves with a certain periodicity even in complete darkness. So Meran proved the existence of circadian rhythms in plants and suggested that they are similar to the circadian rhythms of human sleep and wakefulness.
2. Human circadian rhythms depend on light and are independent of temperature. With sudden changes in temperature, they hardly change, but they can change significantly with changes in daylight hours.
3. Circadian rhythms control the physiological processes of the body. Before waking up, the metabolic rate increases, the temperature rises, and blood circulation increases - this is how the body prepares for vigorous activity during the day. In the evening, all processes slow down, body temperature drops, muscles relax.

Features of the slow phase

There are 4 stages inside it. They all have different bioelectrical characteristics. As a person goes deeper into it, it becomes more and more difficult to wake him up.

To fall asleep, the brain begins to secrete a special substance. It causes lethargy and slows down your metabolism.

Periods

They include: nap, light, moderately deep and deep. The last two are collectively called delta sleep. At this time, specific delta waves are observed.

Signs

The sleeper begins to breathe slowly, his pulse slows down, and his eyes gradually stop moving.

Influence

The body is restored and healed, the body is filled with energy. The body is physically recovering.

What are the dangers of poor sleep?

Lack of sleep or too much sleep has a negative impact on your health. First of all, the brain and nervous system suffer from lack of sleep: memory and mental performance deteriorate, attention and concentration are dulled. In addition, poor sleep has a negative impact on your mental state. Lack of sleep disrupts the functioning of the amygdala, which is responsible for emotions. This leads to loss of self-control, anxiety and rash actions.

After poor sleep, the muscles do not have time to fully recover, so the physical condition is far from ideal. Regular sleep disturbances can lead to surges in blood pressure, heart disease, excess weight, diabetes, and an increased risk of stroke and cancer.

Scientists at the University of California found that those who sleep less than 6 hours are 4.2 times more likely to develop colds. At the same time, in subjects who slept more than 6 but less than 7 hours, there was no increase in the risk of developing a cold.

Photo: nccih.nih.gov

Causes of insomnia and sleep problems

On average, it takes 15 minutes for a person to fall asleep. If it takes you much longer, or you can’t fall asleep at all, think about whether you have insomnia. This is a sleep disorder where you can't fall asleep or keep waking up during the night. Insomnia can be acute (lasting less than 3 months) and chronic (lasting more than 3 months). Here are some common causes of poor sleep:

• Stress and psychological tension

The most common cause of insomnia. Appears when changing jobs, problems in your personal life, having a child, or moving. Before going to bed, try to leave all anxious thoughts and occupy your brain with other, calmer tasks: listen to your favorite music, read a book or do a puzzle. As soon as you feel sleepy, go to bed.

• Noise pollution

In most large cities, noise pollution levels exceed acceptable standards. The main sources of noise are cars, planes, and trains. High levels of noise pollution a person receives during the day increases adrenaline levels, causes headaches, increases heart rate and subsequently disrupts sleep.

The workplace, rest room and bedroom should be quiet. If your street is noisy in the evening, close the windows and hang thick curtains - they will act as additional sound insulation and darken the room. Take breaks throughout the day in complete silence.

Caffeine is a psychostimulant: it invigorates, increases mental and physical activity, relieves fatigue and drowsiness. A study from the University of Wisconsin in the USA has proven that large amounts of caffeine significantly increase anxiety. It is very difficult to fall asleep in an excited state, so reduce the dose of coffee to 1 cup per day and do not drink coffee, strong tea, or energy drinks in the afternoon.

It is a common belief that alcohol helps you fall asleep. This is true, but the quality of sleep suffers - alcohol prevents you from moving into the deep phase of sleep. In addition, even a small amount of alcohol before bed suppresses the production of growth hormone by 75%. Alcohol can be consumed in moderation, but no later than 3 hours before bedtime.

The culprits of poor quality sleep may be: deficiency of B vitamins, lack of calcium and magnesium. In addition, hunger and overeating interfere with sleep. Therefore, it is advisable to have dinner no later than 2 hours and no earlier than 4 hours before bedtime. After an early dinner, before going to bed, you can have a light snack of easily digestible foods.

Smartphones, tablets, laptops and TVs make it difficult to fall asleep. The light from their screens has a blue wavelength (bright, cool light). The brain mistakenly perceives this light as daylight and interferes with the production of melatonin, the sleep hormone.

Photo: digitaltrends.com

• Health problems and medications

People with chronic pain or those who suffer from depression are at risk of developing insomnia. People with thyroid problems often suffer from insomnia: this is due to increased or decreased production of hormones.

If thyroid hormone levels are elevated, it is called hyperthyroidism. You feel increased activity, irritability, it seems as if you have a lot of energy - but this feeling is quickly replaced by fatigue. Problems arise with falling asleep: it is difficult for a person to relax, constantly being in an excited, nervous state.

If there is not enough thyroid hormone produced, a person feels apathetic and drowsy all day. Even if he sleeps for a sufficient number of hours, the feeling of fatigue and weakness will not go away.

• Circadian rhythm disruption

Due to stress, hard work days, night shifts, flights and other reasons, the body experiences a disruption in circadian rhythms. First of all, rhythms are affected by lighting, so it is difficult to fall asleep in daylight and stay awake at night. In addition, when it is light, the body does not produce the sleep hormone melatonin, which promotes quality sleep. To adjust your circadian rhythms, try to always fall asleep and wake up at the same time and follow the other recommendations described below. If necessary, use a melatonin supplement with food .

When is it better to wake up - in the stage of slow or fast sleep?

The moment during which a person wakes up depends on his state of health and well-being. The most comfortable and useful thing would be to wake up in any phase of sleep, but provided that the person woke up on his own and feels well.

Also, the best time to wake up is considered the first or second phase after the end of REM sleep. That is, waking up immediately after a dream is considered the most comfortable and useful (even if it happened due to an alarm clock, extraneous sounds or sensations). At this moment, a person reacts to sound or light signals, as well as to changes in ambient temperature. Therefore, it is better to get out of bed immediately after waking up, so that the body does not have time to move into the next phase.

If a person wakes up from external stimuli during the slow phase, he will feel tired, weak, lethargic and irritated. This is the worst time to wake up.

Having examined in detail the slow and fast phases of sleep, it is impossible to say with certainty which one is better. Since slow sleep is needed to restart and rest the body’s functions, and fast sleep is needed to restore protective functions. Both types of night rest are inherently related to each other and will benefit the person.

How to deal with insomnia: general recommendations

Basic recommendations for combating insomnia:

• Don't neglect sleep in favor of other activities. Perceive sleep as an important, pleasant and useful thing, and not wasted time.
• In the first half of the day, devote time to active activities and sports: this way you will spend more energy. Before going to bed, on the contrary, do calm things: read books, listen to relaxing music
• Do not be nervous. Think about all the important issues in advance, do not leave anxious thoughts while you fall asleep
• Do not take medications that cause nervous agitation before bed
• Avoid alcohol, caffeine and nicotine before bed
• Don't overeat before bed, but don't be too hungry either.
• Avoid using gadgets before bed or install blue light filters
• Create ideal conditions for sleep: no noise and minimal light. If getting rid of the noise is difficult, wear earplugs
• Maintain an optimal temperature in the bedroom: 18-21 degrees are considered suitable for sleep
• Ventilate the room: it’s easier to fall asleep in the fresh air
• Relax before bed: take a warm bath with scented candles, ask your loved ones to give you a massage
• Follow a routine and don’t disrupt your circadian rhythms: it’s much easier for your body to fall asleep and wake up at the same time
• Develop the habit of going to bed at sunset and getting up at dawn - natural light will help to establish the production of necessary hormones

If none of the measures listed above helps, be sure to consult a doctor. Your insomnia may be caused by a health problem.

What time should you go to bed?

Our internal sleep-wake schedule is cyclical. During the day, the body is at different levels of activity. The highest activity is observed from 8 to 18 hours - an ideal time for work and sports. After this, a decline in activity occurs, circadian rhythms prepare the body for sleep: the digestive system slows down, and the production of the sleep hormone melatonin begins. By 11 o'clock in the evening, activity becomes minimal, the speed of thinking slows down, and drowsiness sets in. Therefore, the best time for an adult to fall asleep is considered to be 10-11 pm.

If your lifestyle does not allow you to fall asleep at 10-11 pm, use the sleep calculator to determine the optimal time for going to bed depending on the time you get up.