Book Summary • Why We Sleep: Unlocking the Power of Sleep and Dreams - by Matthew Walker20 Jul 2020
Mr Walker should have called his book “Go the F*CK to sleep” because he continuously talks about how we don’t get enough sleep even though there are many, many benefits to sleep. Sadly, that book-title was already taken.
“Why we sleep” is a great read, here are my takeaways. There are a lot, because it’s a great book.
You need 8 hours of sleep, but you don’t get it
Humans need more than seven hours of sleep each night to maintain cognitive performance. More than a third of individuals in industrialized societies sleep less than five to six hours a night during the week.
After ten days of just seven hours of sleep, the brain is as dysfunctional as it would be after going without sleep for twenty-four hours. Three full nights of recovery sleep (i.e., more nights than a weekend) are insufficient to restore performance back to normal levels after a week of short sleeping. Finally, the human mind cannot accurately sense how sleep-deprived it is when sleep-deprived.
There is a lot of “sleep procrastination” caused by late-evening television and digital entertainment. Even a hint of dim light—8 to 10 lux—has been shown to delay the release of nighttime melatonin in humans.
Sleep == good
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- the coolheaded ability to regulate our emotions each day—a key to what we call emotional IQ—depends on getting sufficient REM sleep night after night.
- Sleep has proven itself time and again as a memory aid: both before learning, to prepare your brain for initially making new memories, and after learning, to cement those memories and prevent forgetting.
- following a night of sleep you regain access to memories that you could not retrieve before sleep.
- Practice does not make perfect. It is practice, followed by a night of sleep, that leads to perfection.
- Sleeping encourages creativity. This task is accomplished using a bizarre algorithm that is biased toward seeking out the most distant, nonobvious associations, rather like a backward Google search. In ways your waking brain would never attempt, the sleeping brain fuses together disparate sets of knowledge that foster impressive problem-solving abilities.
- “sleep on it.” Interestingly, this phrase, or something close to it, exists in most languages (from the French dormir sur un problem, to the Swahili kulala juu ya tatizo)
- By improving sleep quantity, quality, and regularity, Harvey and her team have systematically demonstrated the healing abilities of sleep for the minds of numerous psychiatric populations.
- Associated with the pulsing rhythm of deep NREM sleep comes a ten- to twentyfold increase in effluent expulsion from the brain. In what can be described as a nighttime power cleanse, the purifying work of the glymphatic system is accomplished by cerebrospinal fluid that bathes the brain.
- Those participants who obtained seven to nine hours’ sleep in the week before getting the flu shot generated a powerful antibody reaction, reflecting a robust, healthy immune system. In contrast, those in the sleep-restricted group mustered a paltry response, producing less than 50 percent of the immune reaction their well-slept counterparts were able to mobilize.
- a brief dose of short sleep can affect your cancer-fighting immune cells.
- Controlled sleep laboratory studies in smaller samples show that children with longer total sleep times develop superior IQ, with brighter children having consistently slept forty to fifty minutes more than those who went on to develop a lower IQ.
Not sleeping is bad, m’kay
- Scientists have studied airplane cabin crews who frequently fly on long-haul routes and have little chance to recover. Two alarming results have emerged. First, parts of their brains—specifically those related to learning and memory—had physically shrunk, suggesting the destruction of brain cells caused by the biological stress of time-zone travel. Second, their short-term memory was significantly impaired.
- An infant brain without sleep will be a brain ever underconstructed
- Many of the major psychiatric disorders, such as schizophrenia, bipolar disorder, major depression, and ADHD are now considered disorders of abnormal development, since they commonly emerge during childhood and adolescence. Could be due to bad sleep in childhood! Faulty pruning of brain connections in schizophrenia caused by sleep abnormalities is now one of the most active and exciting areas of investigation in psychiatric illness.
- Imbalances in synaptic connections are common in autistic individuals: excess amounts of connectivity in some parts of the brain, deficiencies in others. The circadian rhythms of autistic children are also weaker than their non-autistic counterparts. Existing evidence in humans is simply correlational, however. Just because autism and REM-sleep abnormalities go hand in hand does not mean that one causes the other.
- Sleep six hours or less and you are shortchanging the brain of a learning restoration The difference between the two groups was not small: a 20 percent learning advantage for those who slept.
- After four hours of sleep for six nights, participants’ performance was just as bad as those who had not slept for twenty-four hours straight
- Ten days of six hours of sleep a night was all it took to become as impaired in performance as going without sleep for twenty-four hours straight.
- When participants were asked about their subjective sense of how impaired they were, they consistently underestimated their degree of performance disability.
- With chronic sleep restriction over months or years, an individual will actually acclimate to their impaired performance, lower alertness, and reduced energy levels.
- Based on epidemiological studies of average sleep time, millions of individuals unwittingly spend years of their life in a sub-optimal state of psychological and physiological functioning, never maximizing their potential of mind or body due to their blind persistence in sleeping too little.
- However, even after three nights of ad lib recovery sleep, performance did not return to that observed at the original baseline assessment when those same individuals had been getting a full eight hours of sleep regularly.
- The recycle rate of a human being is around sixteen hours. After sixteen hours of being awake, the brain begins to fail.
- vehicle accidents caused by drowsy driving exceed those caused by alcohol and drugs combined
- Insufficient sleep does not push the brain into a negative mood state and hold it there. Rather, the under-slept brain swings excessively to both extremes of emotional valence, positive and negative.
- Relevant from a prevention standpoint, insufficient sleep during childhood significantly predicts early onset of drug and alcohol use in that same child during their later adolescent years, even when controlling for other high-risk traits, such as anxiety, attention deficits, and parental history of drug use.
- A research team in Italy examined bipolar patients during the time when they were in this stable, inter-episode phase. Next, under careful clinical supervision, they sleep-deprived these individuals for one night. Almost immediately, a large proportion of the individuals either spiraled into a manic episode or became seriously depressed
- if you don’t sleep the very first night after learning, you lose the chance to consolidate those memories, even if you get lots of “catch-up” sleep thereafter.
- a lack of sleep is fast becoming recognized as a key lifestyle factor determining whether or not you will develop Alzheimer’s disease. Getting too little sleep across the adult life span will significantly raise your risk of developing Alzheimer’s disease.
- Progressively shorter sleep was associated with a 45 percent increased risk of developing and/or dying from coronary heart disease
- Japanese study of over 4,000 male workers. Over a fourteen-year period, those sleeping six hours or less were 400 to 500 percent more likely to suffer one or more cardiac arrests than those sleeping more than six hours.
- Chronic sleep deprivation is now recognized as one of the major contributors to the escalation of type 2 diabetes
- Despite eating almost 2,000 calories during the buffet lunch, sleep-deprived participants dove into the snack bar. They consumed an additional 330 calories of snack foods after the full meal, compared to when they were getting plenty of sleep each night.
- Three-year-olds sleeping just ten and a half hours or less have a 45 percent increased risk of being obese by age seven than those who get twelve hours of sleep a night.
- Faces pictured after one night of short sleep were rated as looking more fatigued, less healthy, and significantly less attractive, compared with the appealing image of that same individual after they had slept a full eight hours.
- The less sleep an individual was getting in the week before facing the active common cold virus, the more likely it was that they would be infected and catch a cold.
- Considering that infectious illnesses, such as the common cold, influenza, and pneumonia, are among the leading causes of death in developed countries, doctors and governments would do well to stress the critical importance of sufficient sleep during the flu season.
- Examining healthy young men, Irwin demonstrated that a single night of four hours of sleep—such as going to bed at three a.m. and waking up at seven a.m.—swept away 70 percent of the natural killer cells circulating in the immune system, relative to a full eight-hour night of sleep.
- the World Health Organization has officially classified nighttime shift work as a “probable carcinogen.”
- based on epidemiological data, any adult sleeping an average of 6.75 hours a night would be predicted to live only into their early sixties
- Based on recent surveys and clinical evaluations, we estimate that more than 50 percent of all children with an ADHD diagnosis actually have a sleep disorder
- individuals who obtained less sleep in the preceding days are the same people who consistently select less challenging problems. They opt for the easy way out, generating fewer creative solutions in the process.
In short: if you don’t sleep enough, you’ll become a lazy, uncreative, unattractive, fat and forgetful person, who’ll die a lot sooner than those that do sleep.
Mid-day naps are good
- Study with 23,000 Greek adults: the end result was heartbreaking. None of the individuals had a history of coronary heart disease or stroke at the start of the study, indicating the absence of cardiovascular ill health. However, those that abandoned regular siestas went on to suffer a 37 percent increased risk of death from heart disease across the six-year period
- in the small enclaves of Greece where siestas still remain intact, such as the island of Ikaria, men are nearly four times as likely to reach the age of ninety
- Ideal sleep pattern seems to be: sleep period at night (seven to eight hours of time in bed, achieving about seven hours of sleep), followed by a thirty- to sixty-minute nap in the afternoon
- daytime naps that contain sufficient numbers of sleep spindles also offer significant motor skill memory improvement
- neither naps nor caffeine can salvage more complex functions of the brain,
- Alcohol is one of the most powerful suppressors of REM sleep that we know of
- Alcohol is readily absorbed in a mother’s milk.
- When babies consume alcohol-laced milk, their sleep is more fragmented, they spend more time awake, and they suffer a 20 to 30 percent suppression of REM sleep soon after
- The electrical brainwave state you enter via alcohol is not that of natural sleep; rather, it is akin to a light form of anesthesia. People consuming even moderate amounts of alcohol in the afternoon and/or evening are thus depriving themselves of dream sleep.
Caffeine is everywhere and stays in your body long time
- Caffeine has an average half-life of five to seven hours. So I’m not crazy for not handling coffee after 10 in the morning!
- Caffeine is prevalent in coffee, certain teas, and many energy drinks, and also foods such as dark chocolate and ice cream
- De-caffeinated does not mean non-caffeinated. One cup of decaf usually contains 15 to 30 percent of the dose of a regular cup of coffee
- Some people are very sensitive to caffeine’s effects. One cup of tea or coffee in the morning will last much of the day (that’s me!)
- Of concern is that administering caffeine to juvenile rats will also disrupt deep NREM sleep and, as a consequence, delay numerous measures of brain maturation and the development of social activity, independent grooming, and the exploration of the environment—measures of self-motivated learning.
How sleep works
There’s a lot of information in the book on how sleep works, which is all a great read. In short: when it comes to information processing, think of the wake state principally as reception (experiencing and constantly learning the world around you), NREM sleep as reflection (storing and strengthening those raw ingredients of new facts and skills), and REM sleep as integration (interconnecting these raw ingredients with each other, with all past experiences, and, in doing so, building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities).
The last two hours of sleep are precisely the window that many of us feel it is okay to cut short to get a jump start on the day. But these are very important hours!
Differences children and adults
As a parent myself, I found this information very important:
- the circadian rhythm of a young child runs on an earlier schedule.
- Children therefore become sleepy earlier and wake up earlier than their adult parents. Adolescent teenagers, however, have a different circadian rhythm from their young siblings.
- During puberty, the timing of the suprachiasmatic nucleus is shifted progressively forward: a change that is common across all adolescents, irrespective of culture or geography.
- the sixteen-year-old will usually have no interest in sleeping at nine p.m. Instead, peak wakefulness is usually still in play at that hour. By the time the parents are getting tired, as their circadian rhythms take a downturn and melatonin release instructs sleep—perhaps around ten or eleven p.m., their teenager can still be wide awake. A few more hours must pass before the circadian rhythm of a teenage brain begins to shut down alertness and allow for easy, sound sleep to begin. Parents want their teenager to be awake at a “reasonable” hour of the morning. Teenagers, on the other hand, having only been capable of initiating sleep some hours after their parents, can still be in their trough of the circadian downswing. asking your teenage son or daughter to go to bed and fall asleep at ten p.m. is the circadian equivalent of asking you, their parent, to go to sleep at seven or eight p.m. Asking that same teenager to wake up at seven the next morning and function with intellect, grace, and good mood is the equivalent of asking you, their parent, to do the same at four or five a.m.
- teenagers need more sleep than adults, and that they are biologically wired to obtain that sleep at a different time from their parents.
Society greatly disadvantages evening types
So teenagers are ‘evening types’ and they are greatly disadvantaged: they have to get up early to go to school and are sent to bed when they are not tired. However, they are not the only ones!
- About 40 percent of the populace are ‘morning types’ who prefer to wake at or around dawn, are happy to do so, and function optimally at this time of day. Others are “evening types,” and account for approximately 30 percent of the population. They naturally prefer going to bed late and subsequently wake up late the following morning, or even in the afternoon. The remaining 30 percent of people lie somewhere in between morning and evening types.
Evolution of sleep
- sleep was the first state of life on this planet, and it was from sleep that wakefulness emerged
- What if sleep is so useful—so physiologically beneficial to every aspect of our being—that the real question is: Why did life ever bother to wake up?
- birds and mammals evolved separately. REM sleep may therefore have been birthed twice in the course of evolution
How to sleep better
To successfully initiate sleep your core temperature needs to decrease by 2 to 3 degrees Fahrenheit, or about 1 degree Celsius. For this reason, you will always find it easier to fall asleep in a room that is too cold than too hot, since a room that is too cold is at least dragging your brain and body in the correct (downward) temperature direction for sleep.
When you get out of the bath, those dilated blood vessels on the surface quickly help radiate out inner heat, and your core body temperature plummets. Consequently, you fall asleep more quickly because your core is colder. Hot baths prior to bed can also induce 10 to 15 percent more deep NREM sleep in healthy adults.
Wake up only once. If you do use an alarm clock, do away with the snooze function, and get in the habit of waking up only once to spare your heart the repeated shock.
Read the book, there’s loads more interesting insights in there!