Author: Matthew Walker
Why We Sleep: Unlocking the Power of Sleep and Dreams Matthew Walker 2017
What is sleep (Why We Sleep)
Why We Sleep: The main purpose of sleep is to rewire our body and brain so that we can sustain another waking cycle. Sleep helps the brain perform many functions that contribute to our survival: learning, remembering, and getting rid of memories, making logical conclusions, and informed choices. Sleep debugs the mechanism of emotional response, which allows us to cope with the social and psychological challenges of the new day.
Sleep organizes the space of virtual reality, in which our mind mixes past and present knowledge and builds complex associative links, thus awakening creativity.
Sleep strengthens the immune system, allowing the body to resist all kinds of infections and diseases. Sleep regulates appetite, supports the intestinal microflora, and takes care of the health of the cardiovascular system.
There are three main factors that affect a person’s overall well-being: sleep, exercise, and nutrition. The author is sure that sleep in this triad is an absolute favorite. Compared to the damage that one sleepless night does to our physical and mental health, the equivalent lack of food or physical activity only slightly affects the state of the body.
Thus, the importance of sleep in our lives cannot be overestimated.
How does sleep occur
There are two different, independent systems by which the brain determines whether you want to sleep or stay awake:
• internal daily clock that sets the circadian rhythm;
• adenosine – a chemical that accumulates in the brain and causes an irresistible desire to sleep.
The ratio of these two factors determines how alert and attentive you are during the day, how tired you feel in the evening, and even partly how well you will sleep.
circadian rhythm. Any living creature that has lived on Earth for more than a few days develops its own circadian, or daily, rhythm. This mechanism determines when your body will tend to wake up and when it wants to sleep. It also controls other rhythmic patterns, such as food intake, basal body temperature, metabolic rate, and the production of many hormones.
The 24-hour body clock that sets the circadian rhythm based on daylight is called the suprachiasmatic nucleus. Focusing on sunlight, this clock sets the biological rhythm of a person in approximately one day.
With the onset of the morning, the circadian rhythm starts many biological processes in the body, giving us the strength to actively live the day. Then these processes gradually subside and after a while completely disappear – we fall asleep.
It is important to note that it is the suprachiasmatic nucleus that controls the mechanisms of wakefulness and sleep, and not vice versa. The circadian rhythm will repeat itself every 24 hours, whether you are sleeping or not.
Even though we all follow a 24-hour cycle, its peak points can be very different. For some people, the peak of wakefulness occurs in the early morning, and already in the early evening, they feel very sleepy. Such people are called larks. They make up approximately 40% of the population. Others prefer to go to bed late and sleep until noon. Such people are called owls, and they make up about 30% of the population. The remaining 30% are located between the morning and evening types, with a slight bias in one direction or the other.
The belonging of an adult to the type of owls or larks, or his chronotype, is largely determined by genetics. We cannot transform ourselves into a different type of person by sheer force of will. That is why the established rules of the game in society are unfair.
The morning work schedule puts owls in a losing position: their brains just don’t have time to wake up, which is why they can’t demonstrate their true potential, because the peak of their form occurs at a time when the rest of the workday comes to an end. Owls are more likely than others to suffer from sleep deprivation, which is why they deteriorate their health and increase the risk of depression, anxiety disorders, diabetes, cancer, heart disease, and strokes.
The suprachiasmatic nucleus also regulates the sleep-wake cycle through the hormone melatonin. Circulating in the blood, melatonin carries the body signal about the onset of twilight. It helps the brain regulate the timing of sleep by signaling the onset of darkness, but, as many mistakenly think, does not have much effect on the occurrence of sleep itself.
As the night progresses, the concentration of melatonin in the blood slowly decreases, and with the dawn, its action ceases. The absence of melatonin in the blood informs the brain that the sleep period has come to an end and it is possible to give a wake-up signal.
Adenosine If melatonin begins to be produced in the late afternoon, then adenosine accumulates in the brain from the very beginning of the waking period. Every minute its concentration in the body increases. The longer you stay awake, the more adenosine accumulates by the start of your next sleep period.
Adenosine is responsible for the need for sleep. The higher the concentration of adenosine in the brain, the more you want to sleep. This chemical enhances the signal in the brain regions responsible for sleep and dampens the signals in the lobes of the brain that stimulate wakefulness. As a result, when adenosine levels reach their peak, and for most people, this happens after 12-16 hours of being awake, you are overcome by an irresistible desire to sleep. At night, the brain excretes the daily dose of adenosine. In a healthy person, the breakdown of adenosine is completely completed approximately eight hours after the onset of sleep.
However, the signal to sleep given by adenosine can be artificially muted, which is what the vast majority of people do. We will return to this topic a little later when we talk about caffeine.
Not letting yourself get enough sleep, you become your own debtor: the amount of adenosine not eliminated overnight will remain in the body and continue to accumulate. The debt will roll over the next day, then the next, and eventually you will find yourself in a situation of chronic sleep deprivation. This condition is felt as chronic fatigue, which is manifested in many mental and physical illnesses.
During the night, our brain switches between two phases of sleep every 90 minutes: non-REM sleep (SEM) and REM sleep (REM). The ratio of the length of the phases within each one and a half-hour cycle changes. In the first half of the night, deep slow-wave sleep prevails, and in the second half, the dominance passes to REM sleep with small patches of FMS sleep.
According to the author’s theory, this interaction between non-REM and REM sleep helps the brain reconstruct and debug our neural connections while optimizing our limited memory storage. So sleep supports the mechanism of memory and solves the problem of storing memories. In the first stage, the brain filters out unnecessary information, and in the second stage, it connects the remaining information and adds details.
Now that we know how the phases of sleep relate to each other, let’s try to solve the problem. If you go to bed at midnight and wake up at 6 am, what percentage of your sleep are you losing? The first answer that comes to mind is 25%. However, in reality, you lose 60-90% of all REM sleep. We will return to the consequences of such a loss below. The same principle works the other way around: if you wake up at 8 am and go to bed at 2 am, you lose a lot of your FMS sleep.
Slow sleep. Slow sleep starts the process of memory consolidation. It helps to consolidate what has been deposited in the brain during the day and works to preserve information.
The brain waves of deep slow-wave sleep carry information from the temporary storage of the hippocampus to the more secure storage of the cerebral cortex, using the principle of long-wavelength radio signaling. As a result, you not only remember the necessary information for a long time but also get free space in the memory storage for the perception of new data.
Recovery of memory ability is associated with shorter periods of non-REM sleep during the second phase, namely with powerful bursts of electrical activity, or, as they are called, sleep spindles. The more sleep spindles a person has during sleep, the more information he is able to remember after waking up. As we age, the brain loses the ability to create sleep spindles, making it increasingly difficult for older people to remember new facts.
The concentration of sleep spindles is especially high during periods of slow sleep in the late hours of the morning. That is, if you sleep for six hours or less, you do not allow your brain to recover its ability to learn. This is especially critical for teenagers and students, whose circadian rhythm naturally shifts a couple of hours ahead for some time, and they simply cannot physically fall asleep early, and at the same time they must get up just as early.
According to the author’s research, a short daytime nap, which generates a significant amount of sleep spindles, not only helps to better remember the information received, but also significantly increases the memorization of motor skills, promotes energy recovery, and reduces muscle fatigue.
Quick sleep. First, REM sleep gives the brain the ability to recognize and classify filtered information, and link its elements to each other and to existing entities in the long-term memory store. All this helps us make smarter decisions and act appropriately to the situation.
Secondly, REM sleep takes care of our emotional and mental health. Dreams occur during REM sleep and serve as a form of night therapy. They help us separate the facts from the emotional component, which allows the brain to come to a decision in the morning on how to cope with the current situation. Remember the saying: the morning is wiser than the evening. No wonder it exists in almost all languages of the world.
In the process of REM sleep, we remember the details of an outstanding, valuable experience, create knowledge about them and integrate them into previously acquired memories, and at the same time forget or level out the negative emotions that may have accompanied the acquired experience. Memory is arranged in our favor: we can remember what happened in great detail, but we cannot re-experience the emotions accompanying the event.
REM sleep with dreams tunes the parts of the brain responsible for reading and deciphering the emotional signals of others. If a person is deprived of dreams during REM sleep, emotional tuning loses its accuracy, and we lose the ability to read facial signals, determine the emotional state of others, and begin to mistake enemies for friends.
Thirdly, REM dreaming awakens in us the ability to be creative. REM sleep helps the brain create vast associations and weave new memories into our biography. As new mnemonic connections emerge, we are visited by creative insights. We begin to see what a set of disparate facts is in the aggregate, we create abstract complex knowledge and complexly organized concepts. Recall how children deduce complex grammatical structures in a language that has not yet been mastered. A one-and-a-half-year-old baby can compose a rather complex phrase if he gets enough sleep after he hears something similar for the first time.
Am I getting enough sleep?
Nearly 30 years of intensive research have shown that the human body’s recycling period is approximately 16 hours. After 16 hours of wakefulness, the body begins to lose strength. To maintain adequate functioning, a person needs at least eight to nine hours of sleep every day. Moreover, the lack of sleep on weekdays cannot be compensated for on weekends. Even a small decrease in sleep duration leads to serious consequences: for example, 10 days of seven hours of sleep will harm you in the same way as a whole day of wakefulness; and even three nights of so-called restorative sleep will not be able to return your performance to its previous level.
To understand if you are getting enough sleep, ask yourself a few simple questions:
1. After waking up early in the morning, can I go back to sleep at 10 or 11 am? If the answer is “yes”, you are most likely experiencing a lack of sleep or the quality of your sleep is poor.
2. Can I work at least half a day to the fullest without stimulating myself with caffeine? If the answer is no, you are most likely in a state of chronic sleep deprivation.
3. Can I wake up on time without an alarm? If the answer is no, then you need more sleep than you allow yourself.
4. Do I often re-read the same thing several times before I understand what it is about? Often this is a sign of chronic brain fatigue resulting from lack of sleep.
5. Do I remember the last few traffic lights while driving? Often the culprit of such absent-mindedness is a systematic lack of sleep.
How lack of sleep affects our body
One of the brain functions that even the slightest lack of sleep affects is concentration. The worst consequence for a person’s life is driving in a sleepy state. Lack of sleep causes a condition called microsleep. Such a dream lasts only a few seconds, but at this moment the human eyelids close and the brain loses the ability to perceive the world around us, and through all channels, and not just through the visuals. For a couple of seconds, you completely lose control over your own movements. You can move to another lane, or even drive into the oncoming one, knock down a pedestrian, crashing into another car.
Getting up at seven in the morning, having worked full time, and going out to meet friends, you are not much different from a drunk person. Like a drunk driver, you cannot fully concentrate on the road and your surroundings. And if you add alcohol to this, then the effect of such a cocktail will not be total, but multiplicative, that is, each factor will also enhance the effect of the other.
Worst of all, we are unable to adequately assess how much our well-being has worsened as a result of sleep deprivation. Equally, we underestimate the degree of decline in our performance. A person adjusts to a chronic lack of sleep and gets used to a lack of concentration, alertness, and energy. It turns out that millions of people spend the most productive years of their lives without reaching their psychological and physiological potential.
Inability to control emotions
As a result of the research, the author and his team found that in conditions of lack of sleep, we have much less control over strong emotions, such as anger, rage, and other reactions associated with the “fight or flight” principle.
After a full night of sleep, the prefrontal cortex (part of the frontal lobe of the brain, our main “brake”) remains closely connected with the amygdala – the emotional center of the brain. With sleep deprivation, the strong connection between these parts of the brain is broken, and we lose the ability to restrain atavistic impulses.
Moreover, lack of sleep provokes an uncontrolled surge of both negative and positive emotional reactions. The tendency to negative reactions can make a person feel worthless and doubt the value of life itself. And increased sensitivity to pleasure can lead to unnecessary risk and the development of bad habits.
Alzheimer’s disease. Sleep deprivation as an adult is a key factor in determining whether you develop Alzheimer’s overtime. Amyloid protein is a toxic substance that is directly related to the development of Alzheimer’s disease. During sleep, the lymphatic system eliminates toxic debris, and if you deprive the body of sleep, then amyloid deposits will begin to grow in the brain, and in those departments where deep sleep is produced. Deep sleep disorder reduces the ability of the brain to clear amyloid plaques at night, leading to more amyloid deposition. Thus, lack of sleep and Alzheimer’s disease are locked in a vicious circle.
Heart diseases. By the middle of life, our body begins to wear out and lose the ability to restore the optimal physical and mental state. At this time, the impact of sleep on the health of the cardiovascular system dramatically increases. People aged 45 and older who sleep less than six hours a night have a 200% increased risk of heart attack or stroke compared to those who sleep seven to eight hours.
It is enough to reduce sleep for an hour so that the increased heart rate significantly increases blood pressure. In addition, lack of sleep destroys the tissue of blood vessels, especially the coronary arteries, and it is they that feed the heart. All this leads to heart failure, heart attacks, strokes, and other heart diseases.
Diabetes and weight gain. The less you sleep, the more you eat. Two hormones are to blame for this – leptin and ghrelin. Insufficient sleep lowers the level of leptin, which signals satiety, and increases the level of ghrelin, which awakens the feeling of hunger. With reduced sleep, a person begins to consume more calories, and not only the quantity, but also the quality of food changes. Shortened sleep increases cravings for sweets, heavy carbohydrate-rich foods, and salty snacks.
Over time, the body loses its ability to efficiently process calories and manage blood sugar levels. In a sleep-restricted state, cells resist insulin signals and refuse to take up glucose from the blood. Various research groups have independently been more likely to be diagnosed with type 2 diabetes in people who are accustomed to sleeping less than six hours a day.
Problems with the reproductive system. In men, sleep deprivation causes testosterone levels to drop. Short or poor-quality sleep reduces the number of sperm by 29%, while the sperm themselves have more pathologies.
In women who sleep less than six hours, the level of luteinizing hormone, which is necessary for the normal functioning of the reproductive system, decreases by 20%. Pregnant women who consistently sleep less than eight hours are much more likely to have a miscarriage in the first trimester than those who consistently sleep eight hours or more.
Immune system disorders and cancer. Sleep helps us fight infection and disease. It is not for nothing that when you get sick, the immune system immediately begins to influence the sleep system in order to get you to bed rest and be able to deploy a whole military operation against the disease.
Chronic lack of sleep weakens the immune system to the limit, and here the question of cancer already arises. Natural killer cells detect dangerous foreigners, such as cancer cells, and act on the lesion. They are your main defense against cancer.
A single night of four hours of sleep—for example, from 3 a.m. to 7 a.m.—destroys 70% of the natural killer cells circulating in the immune system relative to the amount seen in your body after eight hours of sleep. Imagine how weakened your immune arsenal is after a week of short or poor quality sleep, not to mention months or even years.
Particularly negative for the immune system is the effect of night shift work and the resulting disruption of the circadian rhythm. A link has now been established between sleep deprivation and cancer of the breast, prostate, uterine wall, and colon.
Five key factors affecting the amount and quality of sleep
Factor 1. Artificial light
The main negative effect of electric light is that it inhibits the production of melatonin, which should have begun to actively enter the brain with the advent of twilight. In the modern world, artificial light physiologically deceives us into believing that night is still day. So we wind back our internal daily clock two or three hours ago. As a result, sleep is postponed to an increasingly later time.
When we finally go to bed and turn off the night light, falling asleep is not so easy. It will take time for the body to start producing enough melatonin. Even a small light source with a power of 8-10 lux delays the release of melatonin, and the tiniest nightlight gives out at least twice as much.
Before we had time to cope with electric light, LEDs appeared. The receptors of the eye are most sensitive to short wavelengths of the blue spectrum, which is why blue light inhibits melatonin production many times more than yellow light from incandescent bulbs, even at the same radiation intensity. The use of LED devices, which include familiar electronic devices, has an extremely negative effect on the natural rhythm and quality of our sleep.
To begin with, try to turn on only subdued lights in the rooms where you spend the evening hours. Keep the bedroom completely dark during the night. In big cities, window curtains alone are not enough. Hang blackout curtains on the windows, or better use a blackout effect fabric. Try not to use gadgets before going to bed and set them to a program or mode with a blue light filter.
Factor 2. Temperature
The temperature regime is perhaps the most underestimated factor influencing the ease of going to sleep and the quality of sleep itself. In order to fall asleep, the body must lower its temperature by about 1°C, which is much easier to do in a cool room than in a hot one.
Evolutionarily, the decrease in internal body temperature coincided with sunset. Light and temperature together affect evening melatonin levels.
Most of the heat transfer of the human body occurs through the hands, feet, and head. Before going to sleep, we release excess heat through them. However, in conditions of elevated indoor temperatures, a person’s skin hardly gives off heat, which makes it difficult to go to sleep. In addition, the temperature regime, like light, affects the level of melatonin production, and the lack of a signal about a natural decrease in the temperature in the environment delays the onset of sleep.
On average, the ideal temperature for sleeping indoors is 18.3°C. Of course, this value may vary depending on the physiology of a particular person, his gender, and age, but sleeping at our usual 23 ° C is not recommended.
Factor 3. Caffeine
Caffeine blocks and suppresses brain receptors responsible for receiving adenosine, a chemical that causes the need for sleep. By occupying the receptors, caffeine blocks the sleep signal and misleads us into feeling awake, despite the high levels of adenosine that would otherwise have tempted us to sleep.
Caffeine levels peak about half an hour after ingestion, but its half-life is five to seven hours. That is, having drunk coffee at 19.30, by half-past one in the morning you will have time to get rid of only 50% of caffeine. As long as your brain continues to fight the opposing power of caffeine, you can forget about light and quality sleep.
The metabolic ability of the body to eliminate caffeine is largely dependent on genetics. In some people, liver enzymes are better at breaking down caffeine than others. Someone can drink espresso at dinner and then fall asleep without any problems. However, it should be borne in mind that with age, the rate of caffeine elimination decreases in all people.
While caffeine circulates in the body, blocking adenosine, the latter continues to accumulate. Therefore, when your liver finally breaks the caffeine blockade, all the sleepiness that you felt before a cup of coffee, plus the adenosine accumulated during this time, will attack you. To counter such a blow, you will want to drink more coffee, and this already leads to addiction.
Remember that caffeine is found not only in coffee but also in certain types of tea and many energy drinks. It is found in some medicines, such as diet pills and painkillers, and is even found in chocolate and ice cream.
Factor 4. Alcohol
A glass of wine at night is said to help you fall asleep faster and sleep better throughout the night. Both of these are fundamentally wrong. Alcohol is one of the sedatives. It suppresses the firing of electrical impulses in neurons, which makes us think that it is calming. Although in fact, it suppresses the activity of the prefrontal cortex, which helps us control our actions and stay within the desired behavior. In the short term, a person relaxes and becomes more sociable and open. In the long run, he loses control of himself.
After some time after heavy drinking, the desire and ability to respond to external stimuli are sharply reduced, and we fall into an unconscious state that cannot be called sleep. Alcohol brings us out of the state of wakefulness but does not bring natural sleep. Drinking makes sleep fragmentary. We often wake up, and sleep loses its restorative capacity. We do not remember most of the night awakenings, so in the morning it seems to us that we were sleeping soundly, although this is not at all the case.
Alcohol is one of the most powerful REM sleep suppressors. It will take the liver and kidneys many hours to break down and remove from the body even a glass of wine drunk at dinner. At the same time, breaking down alcohol, our body produces by-product chemicals: aldehydes and ketones. Aldehydes block the brain’s ability to generate dream REM sleep. A prolonged lack of REM dreaming leads to what we call delirium tremens.
Factor 5. Working schedule
The abrupt, rough interruption of sleep, by which we normally get ourselves to work, causes a rise in blood pressure and a spike in heart rate. But the alarm clock itself is not the worst thing that can happen to you. Where the greater danger lies in the snooze button. By disturbing your heart with the first alarm, you schedule another attack, and then another, and so on. Imagine the stress you put on your heart and nervous system throughout your life, most of which consists of working days.
To maintain a stable sleep pattern, always wake up at the same time, whether it’s a weekday or a weekend. Your body will get used to getting up and going to bed at the same time, and the alarm will no longer be needed. If you are still very afraid of oversleeping, make it a rule to get up with the first and only signal.
Healthy sleep rules
Stick to your sleep routine. Go to bed and get up every day at a certain time. A person has a hard time adjusting to changes in sleep patterns, and long naps on weekends won’t make up for the lack of sleep during the week—it will only make it harder for you to wake up on Monday mornings. According to the author, this rule is the main guarantee of compliance with sleep hygiene.
Do not engage in sports and active physical activity two to three hours before bedtime. Increased heart rate and elevated body temperature will keep you from falling asleep easily.
Do not abuse caffeine and nicotine. Both substances have a stimulating effect, as a result of which sleep comes harder and becomes superficial.
Don’t drink alcohol before bed. It takes away REM dreaming and generally makes sleep less deep.
Try not to eat too much or drink too much at night. A heavy dinner can disrupt digestion, which will interfere with normal sleep, and an abundance of liquid will make you wake up and go to the toilet often.
Be aware of what medications you are taking and always check with your doctor. Many medicines, including over-the-counter and herbal medicines, can cause insomnia.
Don’t take a nap after 3 pm. This will make it harder for you to fall asleep at night.
Try to relax before bed. Read, listen to music, or find your own ritual to help you calm down after a busy day.
Take a hot bath. Water will help lower your body temperature and make you feel sleepy.
Keep the bedroom dark and cool. Do not bring gadgets there and try not to use them before bed.
Get outside in natural daylight for at least half an hour each day. Daylight is a key factor in the regulation of sleep patterns.
If you can’t fall asleep for more than 20 minutes, get out of bed and do something relaxing until you feel sleepy. Fear of not falling asleep and anxious thoughts can make it difficult to fall asleep.
Top 10 Thoughts
1. Sleep is the most effective medicine in the human arsenal, which helps fight existing diseases and prevent the development of new ones.
2. Sleep helps the brain learn, remember new information and get rid of unnecessary things, make logical conclusions and informed choices, build healthy social relationships and engage in creativity.
3. Sleep is based on two mechanisms: the internal daily clock that sets the circadian rhythm, and adenosine, which accumulates in the brain and causes an irresistible desire to sleep. An artificial failure of the settings of both systems leads to sleep disturbance and health problems.
4. The human chronotype – a lark or an owl – is determined to a greater extent genetically, and forcing different people to live according to the same daily routine is fundamentally unfair.
5. There are two phases of sleep: slow-wave deep sleep in the early night and REM sleep in the early morning. Non-REM sleep is responsible for filtering incoming information and transferring data from short-term to long-term brain storage. REM sleep helps the brain connect information with each other and build complex associative chains.
6. Dreams occur during REM sleep and help:
a) relive the emotional experience of the past day and filter facts from sensory impressions; b) awaken creativity by weaving new events into the overall picture of the world, creating abstract concepts and abstract knowledge.
7. To maintain the healthy functioning of all systems, a person needs at least eight to nine hours of sleep – high-quality and uninterrupted.
8. Chronic lack of sleep is associated with many negative consequences. It leads to decreased concentration, inability to control your emotions, the development of Alzheimer’s disease and cardiovascular disease, increases the risk of cancer, leads to weight gain, diabetes, and problems with the reproductive system.
9. Key factors negatively affecting the quantity and quality of sleep: artificial light (electric and coming from the screens of electronic devices); increased temperature in the bedroom; an abundance of caffeine; any alcohol is taken at night and even during the day; inadequate work schedule.
10. The main rule of healthy sleep is to adhere to the regime: every day, including weekends, get up at the same time, preferably without an alarm clock, but if you can’t do without it, then in no case use the snooze function.