The Secret of Deep Sleep – What to Do to Sleep Better?

Meaning and functions of sleep

Sleep has two important functions — thanks to it, the body can recover and also save energy. Although these concepts are not mutually exclusive, in the scientific community there are supporters of two main theories - regenerative and evolutionary.

Regenerative theory assumes that the basic function of sleep is to allow the body, and especially the brain, to recover properly after a full day of exercise. During sleep, the brain undergoes a process of restoring protein reserves and replenishing glycogen and energy reserves.

According to the second theory - evolutionary - basic and at the same time The primary function of sleep is to conserve energy. Seen from this perspective, sleep can be compared to hibernation in animals. Hibernation, however, is not a rest after strenuous exercise in the warmer months, but a survival strategy — it is a method to reduce energy consumption during times of food shortage. In animals that hibernate, there is a decrease in body temperature with adaptation to the ambient temperature (enough not to expose themselves to excessive cooling). At the next stage, there is a maximum decrease in heart rate, the frequency of breathing decreases, brain activity decreases, and metabolism slows down. Thanks to this, the body uses less energy and increases its chances of survival in harsh conditions.

How long should a healthy sleep last?

According to data provided by the National Sleep Foundation, most people need 7-9 hours of sleep. However, some people need 10 hours of sleep, but these are special cases - professional athletes, exposed to exhausting physical exertion, people with depression or suffering from sleep apnea (which involves waking up 100-200 times during the night to catch air). There are also people who only need 6 hours of sleep and this does not affect their health and physical condition. The amount of sleep needed is therefore an individual matter.

A curious case (described in the books “Two cases of healthy insomnia” and “Biological Foundations of Psychology”) concerns two men who spent an average of only 3 hours a day sleeping and woke up rested. A lot of emotion is also aroused by the example of a 70-year-old woman, described in the 1970s, who devoted an average of about an hour a day to sleep, and often did not feel the need to sleep at all.

Effects of Sleep Deficit

Sleep is of great importance for the functioning of the body - it allows you to maintain mental and physical balance. Studies on the regenerative functions of sleep have shown that people who did not sleep for a week or even longer (experimenting or wanting to gain notoriety) noticed a number of unpleasant complaints in themselves and felt worse. Among the most common symptoms were dizziness, problems with concentration of attention, irritability, hand tremors and hallucinations. Short-term lack of sleep can stimulate some immune responses, however, prolonged insomnia causes disturbances in the functioning of the immune system.

Sleep is a time of intensive regeneration of nerve cells and the ordering and consolidation of all the information accumulated during the day. It is essential for maintaining productivity, creativity and the proper functioning of processes occurring in the body, such as:

• formation of neurotransmitters,
• production of new neurons (neurogenesis),
• the action of growth hormone,
• memory consolidation,
• regeneration of the nervous system,
• the action of the glymphatic system (cleansing the brain when the level of norepinephrine is too low),
• reaction time activity, memory, logical reasoning, decision making.

What is the importance of sleep phases?

In the electroencephalographic recording (EEG), which makes it possible to record the electrical activity of the brain using so-called surface electrodes, placed on the scalp, one can notice waves of small amplitude and high frequency. Based on EEG and other physiological measurements We can distinguish two types of sleep — NREM sleep and REM sleep.

NREM sleep is distinguished by high-amplitude, low-frequency EEG recording. During this phase of sleep, maintenance of muscle tone is noted, sometimes there are body movements to change position, for example, turning from side to side. The frequency of breaths is less, the heart rate decreases, intestinal motility slows down. It is in this phase that the strongest release of growth hormone occurs.

During falling asleep, transitions from the waking state through the four stages of sleep are visible in the EEG recording. The individual stages (1-4) are characterized by a gradual decrease in the frequency of EEG waves. The higher the stage of the NREM phase, the more difficult it is to wake a person who falls asleep. It turns out that if we wake a person in the course of NREM sleep, he is lost, does not know exactly what is happening around and is quickly able to fall into sleep again.

REM sleep, sometimes referred to as paradoxical sleep, is distinguished by another EEG recording, reminiscent of the wakefulness record. In this phase there is no muscle tension, however, contractions of the external eye muscles can occur, which result in rapid eye movements, as well as muscle contractions of the middle ear and limbs. This phase causes irregular breathing frequency, heart rate of contractions, average arterial pressure, and variable temperature. People who are awakened during the REM phase very often remember their dreams and are able to recount them. If they do not, they usually forget about them after 1-2 minutes.

REM sleep is about 8 hours per day for newborns, and on average only 2 hours in adults. The sleep of a small child is different from that of an adult, so the criteria for determining this phase differ from each other.

According to scientists, REM sleep plays a very important role in remembering. Affects the fixation of memory traces by removing unnecessary connections formed and accumulated by accident during the whole day. The process of eliminating these unnecessary connections therefore has an important purpose — it is necessary to clean the memory, so that only the most important, valuable information remains in our head.

What factors affect the quality of sleep?

Modern scientific research on sleep has identified a number of factors that affect sleep. Check out what to look out for to get a good night's sleep.

1. Avoid alcohol and overeating before bed

One of the often replicated myths is the belief that drinking high-percentage drinks in the evening has a positive effect on sleep.

Alcoholic beverages actually affect individual phases of sleep, but only in a negative way — they disrupt deep sleep and reduce its overall quality. Experts advise to avoid drinking alcohol before bed, as well as to limit any stimulants, such as coffee and drinks with a stimulating effect. The effect of caffeine lasts up to several hours (depending on metabolism), so it is worth paying attention to what time we reach for coffee. It is assumed that in the case of an average, healthy man, caffeine lasts about 4.5 hours, and in the case of a woman - for about 5 hours.

Healthy sleep is not only influenced by a balanced diet, eating healthy foods, meals rich in vegetables, fruits or limiting highly processed foods - other eating habits are also important. In the evening, it is worth avoiding overeating. According to research Eating late — especially when it's bedtime soon after eating — increases your risk of developing type 2 diabetes. This is due to high levels of endogenous melatonin, which is associated with reduced insulin production (decreased glucose tolerance).

Melatonin (the hormone that regulates the sleep-wake rhythm) usually occurs around 9 pm, and its highest concentration is recorded between 2:00 and 4:00 at night. So the optimal choice is to eat your last meal 2-3 hours before going to bed.

2. Plan your workout during the day

It might seem that intense training before bed is an excellent idea, however, this is another myth. After exhausting exercise, we may feel muscle fatigue, but the body is very stimulated. People who are unable to find time for exercise during the day are advised to take a warm bath, relaxation and breathing exercises or meditation after an evening workout.

Meditation and breathing exercises will also help people exposed to a lot of stress, which not only makes it difficult to fall asleep, but also affects the disruption of sleep phases, causing frequent awakenings. In many cases, it is he who is the cause of insomnia.

3. Avoid using screens

Another factor that interferes with sleep is exposure to blue light, the source of which can be the screens of phones, tablets or laptops. Blue light contributes to the inhibition of melatonin production, so it is better to avoid using the listed equipment 2-3 hours before bedtime.

4. Ventilate the bedroom

Too high a temperature in the room intended for sleeping and the lack of fresh air also adversely affect the quality of sleep. The optimum temperature for sleep is 18-21 degrees. Therefore, it is worth thoroughly ventilating the room before going to bed.

5. Take care of the right routine

Many studies have shown a relationship between the lack of regularity of a certain number of hours of sleep and metabolic parameters. It turns out that this irregularity negatively affects the feeling of appetite. There are theories that suggest that people who do not get a continuous, nutritious sleep at night and who do not take naps during the day are more likely to develop neurodegenerative diseases. It is suggested that this may be related to the cyclicity of the action of the “cleansing” system of the brain.

It is therefore a good practice the introduction of regular periods of falling asleep and waking up. It is recommended to aim for a repetitive amount of hours of sleep. Maintaining this cyclicity, also on weekends, is essential for the synchronization of the body and the quality of sleep.

If we want to take proper care of the physical health of the body and enjoy a functioning brain, we must always remember that the quality of sleep is of great importance for our life and sense of well-being.

^{Bibliography:}

1. ^{Podgórska A., “This is how the brain works. How to take care of its functioning wisely”, Foksal Publishing Group, Warsaw 2023.}
2. ^{Longstaff A., “Neurobiology — short lectures”, Wydawnictwo Naukowe PWN, Warsaw 2012.}
3. ^{Kalat J.W., “Biological foundations of psychology”, Wydawnictwo Naukowe PWN, Warsaw 2006.}
4. ^{Meddis R., Pearson A. J., Langford G., “An extreme case of healthy insomnia”, Elsevier Ireland Ltd., 1973.}
5. ^{Crick F., Mitchison G., “The function of dream sleep”, Nature, 30, 1983.}