Why We Sleep - by Matthew Walker


Why We Sleep - by Matthew Walker

Read: 2023-03-14

Recommend: 10/10

I know the importance of sleep, but I underestimated its importance. This book gives me a blueprint for how I can improve my sleep.


Here are some text that I highlighted in the book:

  1. Two-thirds of adults throughout all developed nations fail to obtain the recommended eight hours of nightly sleep.

  2. Routinely sleeping less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer.

  3. Fitting Charlotte Brontë’s prophetic wisdom that “a ruffled mind makes a restless pillow,” sleep disruption further contributes to all major psychiatric conditions, including depression, anxiety, and suicidality.

  4. Too little sleep swells concentrations of a hormone that makes you feel hungry while suppressing a companion hormone that otherwise signals food satisfaction. Despite being full, you still want to eat more.

  5. the deadly circumstance of getting behind the wheel of a motor vehicle without having had sufficient sleep.

  6. one person dies in a traffic accident every hour in the United States due to a fatigue-related error. It is disquieting to learn that vehicular accidents caused by drowsy driving exceed those caused by alcohol and drugs combined.

  7. Consider that we have known the functions of the three other basic drives in life—to eat, to drink, and to reproduce—for many tens if not hundreds of years now. Yet the fourth main biological drive, common across the entire animal kingdom—the drive to sleep—has continued to elude science for millennia.

  8. There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep (and detrimentally impaired when we don’t get enough).

  9. we are now forced to wonder whether there are any biological functions that do not benefit by a good night’s sleep. So far, the results of thousands of studies insist that no, there aren’t.

  10. Counter to common belief, there isn’t just one type of dementia. Alzheimer’s disease is the most common, but is only one of many types. For a number of treatment reasons, it is critical to know which type of dementia an individual is suffering from as soon as possible.

  11. Should you feel drowsy and fall asleep while reading the book, unlike most authors, I will not be disheartened.

  12. Everyone generates a circadian rhythm (circa, meaning “around,” and dian, derivative of diam, meaning “day”).

  13. It was a revolutionary discovery: de Mairan had shown that a living organism kept its own time, and was not, in fact, slave to the sun’s rhythmic commands.

  14. So long as they are reliably repeating, the brain can also use other external cues, such as food, exercise, temperature fluctuations, and even regularly timed social interaction. All of these events have the ability to reset the biological clock, allowing it to strike a precise twenty-four-hour note.

  15. Any signal that the brain uses for the purpose of clock resetting is termed a zeitgeber, from the German “time giver” or “synchronizer.”

  16. The twenty-four-hour biological clock sitting in the middle of your brain is called the suprachiasmatic (pronounced soo-pra-kai-as-MAT-ik) nucleus. As with much of anatomical language, the name, while far from easy to pronounce, is instructional: supra, meaning above, and chiasm, meaning a crossing point.

  17. That is, your circadian rhythm will march up and down every twenty-four hours irrespective of whether you have slept or not.

  18. For some people, their peak of wakefulness arrives early in the day, and their sleepiness trough arrives early at night. These are “morning types,” and make up about 40 percent of the populace. They 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, with a slight leaning toward eveningness, like myself.

  19. night owls are not owls by choice. They are bound to a delayed schedule by unavoidable DNA hardwiring. It is not their conscious fault, but rather their genetic fate.

  20. Society’s work scheduling, which is strongly biased toward early start times that punish owls and favor larks.

  21. melatonin is not a powerful sleeping aid in and of itself, at least not for healthy, non-jet-lagged individuals (we’ll explore jet lag—and how melatonin can be helpful—in a moment).

  22. Scientific evaluations of over-the-counter brands have found melatonin concentrations that range from 83 percent less than that claimed on the label, to 478 percent more than that stated.

  23. a typical profile of melatonin release. It starts a few hours after dusk. Then it rapidly rises, peaking around four a.m. Thereafter, it begins to drop as dawn approaches, falling to levels that are undetectable by early to midmorning.

  24. Those jets caused a biological time lag: jet lag.

  25. For every day you are in a different time zone, your suprachiasmatic nucleus can only readjust by about one hour.

  26. You may have noticed that it feels harder to acclimate to a new time zone when traveling eastward than when flying westward. There are two reasons for this. First, the eastward direction requires that you fall asleep earlier than you would normally, which is a tall biological order for the mind to simply will into action. In contrast, the westward direction requires you to stay up later, which is a consciously and pragmatically easier prospect. Second, you will remember that when shut off from any outside world influences, our natural circadian rhythm is innately longer than one day—about twenty-four hours and fifteen minutes. Modest as this may be, this makes it somewhat easier for you to artificially stretch a day than shrink it. When you travel westward—in the direction of your innately longer internal clock—that “day” is longer than twenty-four hours for you and why it feels a little easier to accommodate to. Eastward travel, however, which involves a “day” that is shorter in length for you than twenty-four hours, goes against the grain of your innately long internal rhythm to start with, which is why it is rather harder to do.

  27. One consequence of increasing adenosine in the brain is an increasing desire to sleep.

  28. Caffeine is not a food supplement. Rather, caffeine is the most widely used (and abused) psychoactive stimulant in the world. It is the second most traded commodity on the planet, after oil.

  29. Caffeine works by successfully battling with adenosine for the privilege of latching on to adenosine welcome sites—or receptors—in the brain. Once caffeine occupies these receptors, however, it does not stimulate them like adenosine, making you sleepy. Rather, caffeine blocks and effectively inactivates the receptors, acting as a masking agent. It’s the equivalent of sticking your fingers in your ears to shut out a sound. By hijacking and occupying these receptors, caffeine blocks the sleepiness signal normally communicated to the brain by adenosine. The upshot: caffeine tricks you into feeling alert and awake, despite the high levels of adenosine that would otherwise seduce you into sleep.

  30. In pharmacology, we use the term “half-life” when discussing a drug’s efficacy. This simply refers to the length of time it takes for the body to remove 50 percent of a drug’s concentration. Caffeine has an average half-life of five to seven hours. Let’s say that you have a cup of coffee after your evening dinner, around 7:30 p.m. This means that by 1:30 a.m., 50 percent of that caffeine may still be active and circulating throughout your brain tissue. In other words, by 1:30 a.m., you’re only halfway to completing the job of cleansing your brain of the caffeine you drank after dinner.

  31. Caffeine—which is not only prevalent in coffee, certain teas, and many energy drinks, but also foods such as dark chocolate and ice cream, as well as drugs such as weight-loss pills and pain relievers—is one of the most common culprits that keep people from falling asleep easily and sleeping soundly thereafter, typically masquerading as insomnia, an actual medical condition. Also be aware that 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, which is far from caffeine-free.

  32. Aging also alters the speed of caffeine clearance: the older we are, the longer it takes our brain and body to remove caffeine, and thus the more sensitive we become in later life to caffeine’s sleep-disrupting influence.

  33. This powerful combination of abundant adenosine (high sleep pressure) and declining circadian rhythm (lowered activity levels) triggers a strong desire for sleep.

  34. how do you know whether you’re routinely getting enough sleep? While a clinical sleep assessment is needed to thoroughly address this issue, an easy rule of thumb is to answer two simple questions. First, after waking up in the morning, could you fall back asleep at ten or eleven a.m.? If the answer is “yes,” you are likely not getting sufficient sleep quantity and/or quality. Second, can you function optimally without caffeine before noon? If the answer is “no,” then you are most likely self-medicating your state of chronic sleep deprivation.

  35. In the event it helps, I have provided a link to a questionnaire that has been developed by sleep researchers that will allow you to determine your degree of sleep fulfillment. Called SATED, it is easy to complete, and contains only five simple questions.

  36. more often than not dream time is stretched out and prolonged relative to real time.

  37. replaying every ninety minutes.

  38. While it is true that we flip-flop back and forth between NREM and REM sleep throughout the night every ninety minutes, the ratio of NREM sleep to REM sleep within each ninety-minute cycle changes dramatically across the night. In the first half of the night, the vast majority of our ninety-minute cycles are consumed by deep NREM sleep, and very little REM sleep, as can be seen in cycle 1 of the figure above. But as we transition through into the second half of the night, this seesaw balance shifts, with most of the time dominated by REM sleep, with little, if any, deep NREM sleep.

  39. As we will discover in chapter 6, a key function of deep NREM sleep, which predominates early in the night, is to do the work of weeding out and removing unnecessary neural connections. In contrast, the dreaming stage of REM sleep, which prevails later in the night, plays a role in strengthening those connections.

  40. In this way, sleep may elegantly manage and solve our memory storage crisis, with the general excavatory force of NREM sleep dominating early, after which the etching hand of REM sleep blends, interconnects, and adds details.

  41. How do these different electrical brain changes explain why you are conscious in one state (wake), non-conscious in another (NREM sleep), and delusionally conscious, or dreaming, in the third (REM sleep)?

  42. FM waves run out of steam quickly, like a muscle-bound sprinter who can only cover short distances. AM broadcasts employ a much slower (longer) radio wave, akin to a lean long-distance runner. While AM radio waves cannot match the muscular, dynamic quality of FM radio, the pedestrian pace of AM radio waves gives them the ability to cover vast distances with less fade.

  43. We therefore consider waking brainwave activity as that principally concerned with the reception of the outside sensory world, while the state of deep NREM slow-wave sleep donates a state of inward reflection—one that fosters information transfer and the distillation of memories.

  44. 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)

  45. It wouldn’t take long before you quickly left the gene pool.

  46. “Nothing in biology makes sense except in light of evolution.”

  47. Without exception, every animal species studied to date sleeps, or engages in something remarkably like it.

  48. It suggests that dream (REM) sleep is the new kid on the evolutionary block. REM sleep seems to have emerged to support functions that NREM sleep alone could not accomplish, or that REM sleep was more efficient at accomplishing.

  49. absence of evidence is not evidence of absence.

  50. Both sleep stages are therefore essential. We try to recover one (NREM) a little sooner than the other (REM), but make no mistake, the brain will attempt to recoup both, trying to salvage some of the losses incurred. It is important to note, however, that regardless of the amount of recovery opportunity, the brain never comes close to getting back all the sleep it has lost.

  51. If you compare the electrical depth of the deep NREM slow brainwaves on one half of someone’s head relative to the other when they are sleeping at home, they are about the same. But if you bring that person into a sleep laboratory, or take them to a hotel—both of which are unfamiliar sleep environments—one half of the brain sleeps a little lighter than the other, as if it’s standing guard with just a tad more vigilance due to the potentially less safe context that the conscious brain has registered while awake. The more nights an individual sleeps in the new location, the more similar the sleep is in each half of the brain. It is perhaps the reason why so many of us sleep so poorly the first night in a hotel room.

  52. I should note that REM sleep is strangely immune to being split across sides of the brain, no matter who you are. All birds, irrespective of the environmental situation, always sleep with both halves of the brain during REM sleep. The same is true for every species that experiences dream sleep, humans included. Whatever the functions of REM-sleep dreaming—and there appear to be many—they require participation of both sides of the brain at the same time, and to an equal degree.

  53. Individuals who are deliberately fasting will sleep less as the brain is tricked into thinking that food has suddenly become scarce.

  54. Visit cultures that are untouched by electricity and you often see something rather different. Hunter-gatherer tribes, such as the Gabra in northern Kenya or the San people in the Kalahari Desert, whose way of life has changed little over the past thousands of years, sleep in a biphasic pattern. Both these groups take a similarly longer 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. There is also evidence for a mix of the two sleep patterns, determined by time of year. Pre-industrial tribes, such as the Hadza in northern Tanzania or the San of Namibia, sleep in a biphasic pattern in the hotter summer months, incorporating a thirty- to forty-minute nap at high noon. They then switch to a largely monophasic sleep pattern during the cooler winter months.

  55. Both you and the meeting attendees are falling prey to an evolutionarily imprinted lull in wakefulness that favors an afternoon nap, called the post-prandial alertness dip (from the Latin prandium, “meal”).

  56. What becomes clearly apparent when you step back from these details is that modern society has divorced us from what should be a preordained arrangement of biphasic sleep—one that our genetic code nevertheless tries to rekindle every afternoon. The separation from biphasic sleep occurred at, or even before, our shift from an agrarian existence to an industrial one.

  57. Apparent from this remarkable study is this fact: when we are cleaved from the innate practice of biphasic sleep, our lives are shortened. It is perhaps unsurprising that 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 as American males. These napping communities have sometimes been described as “the places where people forget to die.” From a prescription written long ago in our ancestral genetic code, the practice of natural biphasic sleep, and a healthy diet, appear to be the keys to a long-sustained life.

  58. The total amount of time we spend asleep is markedly shorter than all other primates (eight hours, relative to the ten to fifteen hours of sleep observed in all other primates), yet we have a disproportionate amount of REM sleep, the stage in which we dream. Between 20 and 25 percent of our sleep time is dedicated to REM sleep dreaming, compared to an average of only 9 percent across all other primates!

  59. To the first of these points, we have discovered that REM sleep exquisitely recalibrates and fine-tunes the emotional circuits of the human brain (discussed in detail in part 3 of the book). In this capacity, REM sleep may very well have accelerated the richness and rational control of our initially primitive emotions, a shift that I propose critically contributed to the rapid rise of Homo sapiens to dominance over all other species in key ways.

  60. More specifically, 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. (If your mind immediately jumped to particular colleagues, friends, and public figures who lack these traits, you may well wonder about how much sleep, especially late-morning REM-rich sleep, they are getting.)

  61. NREM sleep helps transfer and make safe newly learned information into long-term storage sites of the brain. But it is REM sleep that takes these freshly minted memories and begins colliding them with the entire back catalog of your life’s autobiography.

  62. An infant brain without sleep will be a brain ever underconstructed.

  63. The core symptom of autism is a lack of social interaction. Individuals with autism do not communicate or engage with other people easily, or typically.

  64. Infants and young children who show signs of autism, or who are diagnosed with autism, do not have normal sleep patterns or amounts. The circadian rhythms of autistic children are also weaker than their non-autistic counterparts, showing a flatter profile of melatonin across the twenty-four-hour period rather than a powerful rise in concentration at night and rapid fall throughout the day. Biologically, it is as if the day and night are far less light and dark, respectively, for autistic individuals.

  65. Autistic individuals show a 30 to 50 percent deficit in the amount of REM sleep they obtain, relative to children without autism

  66. Alcohol is one of the most powerful suppressors of REM sleep that we know of.

  67. The newborns of heavy-drinking mothers spent far less time in the active state of REM sleep compared with infants of similar age but who were born of mothers who did not drink during pregnancy.

  68. Newborns of heavy-drinking mothers did not have the same electrical quality of REM sleep.

  69. Alcohol significantly reduced the amount of time that the unborn babies spent in REM sleep, relative to the non-alcohol condition. That alcohol also dampened the intensity of REM sleep experienced by the fetus, defined by the standard measure of how many darting rapid eye movements adorn the REM-sleep cycle. Furthermore, these unborn infants suffered a marked depression in breathing during REM sleep, with breath rates dropping from a normal rate of 381 per hour during natural sleep to just 4 per hour when the fetus was awash with alcohol

  70. 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. Often, the babies will even try to get back some of that missing REM sleep once they have cleared it from their bloodstream, though it is not easy for their fledgling systems to do so.

  71. During the fourteen hours of total shut-eye per day that a six-month-old infant obtains, there is a 50/50 timeshare between NREM and REM sleep. A five-year-old, however, will have a 70/30 split between NREM and REM sleep across the eleven hours of total daily slumber. In other words, the proportion of REM sleep decreases in early childhood while the proportion of NREM sleep actually increases, even though total sleep time decreases. The downgrading of the REM-sleep portion, and the upswing in NREM-sleep dominance, continues, throughout early and midchildhood. That balance will finally stabilize to an 80/20 NREM/REM sleep split by the late teen years, and remain so throughout early and midadulthood.

  72. Our analogy of the Internet service provider is a helpful one to return to.

  73. deep sleep may be a driving force of brain maturation, not the other way around.

  74. “Why do most 16-year-olds drive like they’re missing part of their brain? Because they are.” It takes deep sleep, and developmental time, to accomplish the neural maturation that plugs this brain “gap” within the frontal lobe. When your children finally reach their mid-twenties and your car insurance premium drops, you can thank sleep for the savings.

  75. 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.

  76. 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. No matter how loud you enunciate the order, no matter how much that teenager truly wishes to obey your instruction, and no matter what amount of willed effort is applied by either of the two parties, the circadian rhythm of a teenager will not be miraculously coaxed into a change. Furthermore, 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.

  77. “No child needs caffeine.”

  78. That older adults simply need less sleep is a myth. Older adults appear to need just as much sleep as they do in midlife, but are simply less able to generate that (still necessary) sleep. Affirming this, large surveys demonstrate that despite getting less sleep, older adults reported needing, and indeed trying, to obtain just as much sleep as younger adults.

  79. Instead, I recommend you first explore the effective and scientifically proven non-pharmacological interventions that a doctor who is board certified in sleep medicine can provide.

  80. As a reference anchor, most sleep doctors consider good-quality sleep to involve a sleep efficiency of 90 percent or above. By the time we reach our eighties, sleep efficiency has often dropped below 70 or 80 percent; 70 to 80 percent may sound reasonable until you realize that, within an eight-hour period in bed, it means you will spend as much as one to one and a half hours awake.

  81. Their regressed circadian rhythm, instructed by an earlier release of melatonin, left them no choice.

  82. Instead, I advise two modifications for seniors. First, wear sunglasses during morning exercise outdoors. This will reduce the influence of morning light being sent to your suprachiasmatic clock that would otherwise keep you on an early-to-rise schedule. Second, go back outside in the late afternoon for sunlight exposure, but this time do not wear sunglasses. Make sure to wear sun protection of some sort, such as a hat, but leave the sunglasses at home. Plentiful later-afternoon daylight will help delay the evening release of melatonin, helping push the timing of sleep to a later hour.

  83. the parts of our brain that ignite healthy deep sleep at night are the very same areas that degenerate, or atrophy, earliest and most severely as we age.

  84. The older adults forgot far more of the facts by the following morning than the young adults—a difference of almost 50 percent. Furthermore, those older adults with the greatest loss of deep sleep showed the most catastrophic overnight forgetting.

  85. look cautiously promising

  86. Said unkindly, older adults don’t have much further to fall in terms of getting worse, sometimes called a “floor effect,” making it difficult to estimate the real performance impact of sleep deprivation.

  87. older adults, may, in fact, need more sleep than they themselves can naturally generate, since they benefit from an improvement in sleep quality, albeit through artificial means.

  88. As for the prescription cost, well, there isn’t one. It’s free. Yet all too often, we shun the nightly invitation to receive our full dose of this all-natural remedy—with terrible consequences.

  89. We will come to learn that sleep is the universal health care provider: whatever the physical or mental ailment, sleep has a prescription it can dispense.

  90. 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.

  91. Those who were awake throughout the day became progressively worse at learning, even though their ability to concentrate remained stable (determined by separate attention and response time tests). In contrast, those who napped did markedly better, and actually improved in their capacity to memorize facts. The difference between the two groups at six p.m. was not small: a 20 percent learning advantage for those who slept.

  92. It was early-night sleep, rich in deep NREM, that won out in terms of providing superior memory retention savings relative to late-night, REM-rich sleep.

  93. the more deep NREM sleep, the more information an individual remembered the next day

  94. It all sounds like the stuff of science fiction, but it is now science fact: the method is called targeted memory reactivation.

  95. forgetting is the price we pay for remembering.

  96. sleep is able to offer a far more discerning hand in memory improvement: one that preferentially picks and chooses what information is, and is not, ultimately strengthened.

  97. Muscle memory is, in fact, brain memory.

  98. practice, with sleep, that makes perfect

  99. fitting with the pianist’s original description, those who were tested after the very same time delay of twelve hours, but that spanned a night of sleep, showed a striking 20 percent jump in performance speed and a near 35 percent improvement in accuracy

  100. In other words, your brain will continue to improve skill memories in the absence of any further practice.

  101. Sleep had systematically identified where the difficult transitions were in the motor memory and smoothed them out. This finding rekindled the words of the pianist I’d met: “but when I wake up the next morning and sit back down at the piano, I can just play, perfectly.”

  102. Which is to say that sleep helped the brain automate the movement routines, making them second nature—effortless—precisely the goal of many an Olympic coach when perfecting the skills of their elite athletes.

  103. it was the number of those wonderful sleep spindles in the last two hours of the late morning—the time of night with the richest spindle bursts of brainwave activity—that were linked with the offline memory boost.

  104. The 100-meter sprint superstar Usain Bolt has, on many occasions, taken naps in the hours before breaking the world record, and before Olympic finals in which he won gold. Our own studies support his wisdom: daytime naps that contain sufficient numbers of sleep spindles also offer significant motor skill memory improvement, together with a restoring benefit on perceived energy and reduced muscle fatigue.

  105. Struck by the weight of damning scientific evidence, the Guinness Book of World Records has stopped recognizing attempts to break the sleep deprivation world record.

  106. 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.

  107. 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. Sixty years of scientific research prevent me from accepting anyone who tells me that he or she can “get by on just four or five hours of sleep a night just fine.”

  108. if you are drowsy while driving, please, please stop. It is lethal.

  109. The number of people who can survive on five hours of sleep or less without any impairment, expressed as a percent of the population, and rounded to a whole number, is zero.” There is but a fraction of 1 percent of the population who are truly resilient to the effects of chronic sleep restriction at all levels of brain function. It is far, far more likely that you will be struck by lightning (the lifetime odds being 1 in 12,000) than being truly capable of surviving on insufficient sleep thanks to a rare gene.

  110. It was as though, without sleep, our brain reverts to a primitive pattern of uncontrolled reactivity. We produce unmetered, inappropriate emotional reactions, and are unable to place events into a broader or considered context.

  111. cognitive behavioral therapy for insomnia (CBT-I)

  112. E. Joseph Cossman: “The best bridge between despair and hope is a good night’s sleep.”

  113. there was a 40 percent deficit in the ability of the sleep-deprived group to cram new facts into the brain (i.e., to make new memories), relative to the group that obtained a full night of sleep.

  114. In terms of memory, then, sleep is not like the bank. You cannot accumulate a debt and hope to pay it off at a later point in time. Sleep for memory consolidation is an all-or-nothing event.

  115. The two most feared diseases throughout developed nations are dementia and cancer. Both are related to inadequate sleep.

  116. One in ten adults over the age of sixty-five now suffers from Alzheimer’s disease.

  117. Sleep represents a new candidate for hope on all three of these fronts: diagnosis, prevention, and therapeutics.

  118. More telling, perhaps, is the fact that sleep disturbance precedes the onset of Alzheimer’s disease by several years, suggesting that it may be an early-warning sign of the condition, or even a contributor to it.

  119. Alzheimer’s disease is associated with the buildup of a toxic form of protein called beta-amyloid, which aggregates in sticky clumps, or plaques, within the brain.

  120. The more amyloid deposits there were in the middle regions of the frontal lobe, the more impaired the deep-sleep quality was in that older individual.

  121. Those individuals with the highest levels of amyloid deposits in the frontal regions of the brain had the most severe loss of deep sleep and, as a knock-on consequence, failed to successfully consolidate those new memories. Overnight forgetting, rather than remembering, had taken place. The disruption of deep NREM sleep was therefore a hidden middleman brokering the bad deal between amyloid and memory impairment in Alzheimer’s disease.

  122. wakefulness is low-level brain damage, while sleep is neurological sanitation.

  123. Parenthetically, and unscientifically, I have always found it curious that Margaret Thatcher and Ronald Reagan—two heads of state that were very vocal, if not proud, about sleeping only four to five hours a night—both went on to develop the ruthless disease. The current US president, Donald Trump—also a vociferous proclaimer of sleeping just a few hours each night—may want to take note.

  124. the shorter your sleep, the shorter your life

  125. Progressively shorter sleep was associated with a 45 percent increased risk of developing and/or dying from coronary heart disease within seven to twenty-five years from the start of the study.

  126. This finding impresses how important it is to prioritize sleep in midlife—which is unfortunately the time when family and professional circumstances encourage us to do the exact opposite.

  127. a “global experiment” in which 1.5 billion people are forced to reduce their sleep by one hour or less for a single night each year. It is very likely that you have been part of this experiment, otherwise known as daylight savings time.

  128. this seemingly trivial sleep reduction comes with a frightening spike in heart attacks the following day.

  129. when the clocks move forward and we gain an hour of sleep opportunity time, rates of heart attacks plummet the day after.

  130. Inadequate sleep is the perfect recipe for obesity: greater calorie intake, lower calorie expenditure.

  131. Ample sleep can therefore restore a system of impulse control within your brain, putting the appropriate brakes on potentially excessive eating.

  132. short sleep (of the type that many adults in first-world countries commonly and routinely report) will increase hunger and appetite, compromise impulse control within the brain, increase food consumption (especially of high-calorie foods), decrease feelings of food satisfaction after eating, and prevent effective weight loss when dieting.

  133. key aspects of the human reproductive system are affected by sleep in both men and women. Reproductive hormones, reproductive organs, and the very nature of physical attractiveness that has a say in reproductive opportunities: all are degraded by short sleeping.

  134. 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. In those sleeping five hours on average, the infection rate was almost 50 percent. In those sleeping seven hours or more a night in the week prior, the infection rate was just 18 percent.

  135. 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.

  136. One such foreign entity that natural killer cells will target are malignant (cancerous) tumor cells. Natural killer cells will effectively punch a hole in the outer surface of these cancerous cells and inject a protein that can destroy the malignancy. What you want, therefore, is a virile set of these James Bond–like immune cells at all times. That is precisely what you don’t have when sleeping too little.

  137. We don’t have to imagine. A number of prominent epidemiological studies have reported that nighttime shift work, and the disruption to circadian rhythms and sleep that it causes, up your odds of developing numerous different forms of cancer considerably.

  138. Denmark recently became the first country to pay worker compensation to women who had developed breast cancer after years of night-shift work in government-sponsored jobs, such as nurses and air cabin crew. Other governments—Britain, for example—have so far resisted similar legal claims, refusing payout compensation despite the science.

  139. A large European study of almost 25,000 individuals demonstrated that sleeping six hours or less was associated with a 40 percent increased risk of developing cancer, relative to those sleeping seven hours a night or more.

  140. Poor sleep quality therefore increases the risk of cancer development and, if cancer is established, provides a virulent fertilizer for its rapid and more rampant growth. Not getting sufficient sleep when fighting a battle against cancer can be likened to pouring gasoline on an already aggressive fire. That may sound alarmist, but the scientific evidence linking sleep disruption and cancer is now so damning that the World Health Organization has officially classified nighttime shift work as a “probable carcinogen.”

  141. Thousands of genes within the brain depend upon consistent and sufficient sleep for their stable regulation. Deprive a mouse of sleep for just a day, as researchers have done, and the activity of these genes will drop by well over 200 percent. Like a stubborn file that refuses to be transcribed by a printer, when you do not lavish these DNA segments with enough sleep, they will not translate their instructional code into printed action and give the brain and body what they need.

  142. Neglect sleep, and you are deciding to perform a genetic engineering manipulation on yourself each night, tampering with the nucleic alphabet that spells out your daily health story.

  143. In fact, there are four main clusters of the brain that spike in activity when someone starts dreaming in REM sleep: (1) the visuospatial regions at the back of the brain, which enable complex visual perception; (2) the motor cortex, which instigates movement; (3) the hippocampus and surrounding regions that we have spoken about before, which support your autobiographical memory; and (4) the deep emotional centers of the brain—the amygdala and the cingulate cortex, a ribbon of tissue that sits above the amygdala and lines the inner surface of your brain—both of which help generate and process emotions. Indeed, these emotional regions of the brain are up to 30 percent more active in REM sleep compared to when we are awake!

  144. The Interpretation of Dreams (1899)

  145. Freud believed that he understood how the censor worked and that, as a result, he could decrypt the disguised dream (manifest content) and reverse-engineer it to reveal the true meaning (latent content, rather like email encryption wherein the message is cloaked with a code). Without the decryption key, the content of the email cannot be read. Freud felt that he had discovered the decryption key to everyone’s dreams, and for many of his affluent Viennese patients, he offered the paid service of removing this disguise and revealing to them the original message content of their dreams.

  146. A theory that cannot be discerned true or false in this way will always be abandoned by science, and that is precisely what happened to Freud and his psychoanalytic practices.

  147. The exercise, however, importantly reveals the dangers of generic interpretations that feel very personal and uniquely individual, yet scientifically hold no specificity whatsoever.

  148. Indeed, journaling your waking thoughts, feelings, and concerns has a proven mental health benefit, and the same appears true of your dreams. A meaningful, psychologically healthy life is an examined one, as Socrates so often declared. Nevertheless, the psychoanalytic method built on Freudian theory is nonscientific and holds no repeatable, reliable, or systematic power for decoding dreams. This, people must be made aware of.

  149. Of a total of 299 dream reports that Stickgold collected from these individuals across the fourteen days, a clear rerun of prior waking life events—day residue—was found in just 1 to 2 percent. Dreams are not, therefore, a wholesale replay of our waking lives. We do not simply rewind the video of the day’s recorded experience and relive it at night, projected on the big screen of our cortex. If there is such a thing as “day residue,” there are but a few drops of the stuff in our otherwise arid dreams. But Stickgold did find a strong and predictive daytime signal in the static of nighttime dream reports: emotions. Between 35 and 55 percent of emotional themes and concerns that participants were having while they were awake during the day powerfully and unambiguously resurfaced in the dreams they were having at night. The commonalities were just as clear to the participants themselves, who gave similarly confident judgments when asked to compare their own dream reports with their waking reports.

  150. Using this framework, we have found two core benefits of REM sleep. Both functional benefits require not just that you have REM sleep, but that you dream, and dream about specific things. REM sleep is necessary, but REM sleep alone is not sufficient. Dreams are not the heat of the lightbulb—they are no by-product. The first function involves nursing our emotional and mental health, and is the focus of this chapter. The second is problem solving and creativity, the power of which some individuals try to harness more fully by controlling their dreams, which we treat in the next chapter.

  151. REM-sleep dreaming offers a form of overnight therapy. That is, REM-sleep dreaming takes the painful sting out of difficult, even traumatic, emotional episodes you have experienced during the day, offering emotional resolution when you awake the next morning.

  152. it was the dreaming state of REM sleep—and specific patterns of electrical activity that reflected the drop in stress-related brain chemistry during the dream state—that determined the success of overnight therapy from one individual to the next. It was not, therefore, time per se that healed all wounds, but instead it was time spent in dream sleep that was providing emotional convalescence. To sleep, perchance to heal.

  153. It was only that content-specific form of dreaming that was able to accomplish clinical remission and offer emotional closure in these patients, allowing them to move forward into a new emotional future, and not be enslaved by a traumatic past.

  154. It turns out that the drug prazosin, which Raskind was prescribing simply to lower blood pressure, also has the fortuitous side effect of suppressing noradrenaline in the brain.

  155. There are regions of your brain whose job it is to read and decode the value and meaning of emotional signals, especially faces. And it is that very same essential set of brain regions, or network, that REM sleep recalibrates at night.

  156. Most significant is the issue of sunrise school bus schedules that selectively deprive our teenagers of that early-morning slumber, just at the moment in their sleep cycle when their developing brains are about to drink in most of their much-needed REM sleep. We are bankrupting their dreams, in so many different ways.

  157. sleep inertia—the carryover of the prior sleeping brain state into wakefulness in the minutes after waking up.

  158. Overall, problem-solving abilities rocketed up, with participants solving 15 to 35 percent more puzzles when emerging from REM sleep compared with awakenings from NREM sleep or during daytime waking performance!

  159. the REM-sleep brain was shortcutting the obvious links and favoring very distantly related concepts.

  160. It is sleep that builds connections between distantly related informational elements that are not obvious in the light of the waking day. Our participants went to bed with disparate pieces of the jigsaw and woke up with the puzzle complete. It is the difference between knowledge (retention of individual facts) and wisdom (knowing what they all mean when you fit them together). Or, said more simply, learning versus comprehension. REM sleep allows your brain to move beyond the former and truly grasp the latter.

  161. Little wonder, then, that you have never been told to “stay awake on a problem.” Instead, you are instructed to “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), indicating that the problem-solving benefit of dream sleep is universal, common across the globe.

  162. Lucid dreaming occurs at the moment when an individual becomes aware that he or she is dreaming.

  163. The term “somnambulism” refers to sleep (somnus) disorders that involve some form of movement (ambulation). It encompasses conditions such as sleepwalking, sleep talking, sleep eating, sleep texting, sleep sex, and, very rarely, sleep homicide.

  164. Understandably, most people believe these events happen during REM sleep as an individual is dreaming, and specifically acting out ongoing dreams. However, all these events arise from the deepest stage of non-dreaming (NREM) sleep, and not dream (REM) sleep. If you rouse an individual from a sleepwalking event and ask what was going through their mind, rarely will they report a thing—no dream scenario, no mental experience.

  165. Trapped between the two worlds of deep sleep and wakefulness, the individual is confined to a state of mixed consciousness—neither awake nor asleep. In this confused condition, the brain performs basic but well-rehearsed actions, such as walking over to a closet and opening it, placing a glass of water to the lips, or uttering a few words or sentences.

  166. For the most part, there is nothing pathological about sleepwalking or sleep talking. They are common in the adult population, and even more common in children. It is not clear why children experience somnambulism more than adults, nor is it clear why some children grow out of having these nighttime events, while others will continue to do so throughout their lives. One explanation of the former is simply the fact that we have greater amounts of deep NREM sleep when we are young, and therefore the statistical likelihood of sleepwalking and sleep talking episodes occurring is higher.

  167. They argued that he was unaware of his actions, and thus not culpable.

  168. Being sleep deprived is not insomnia. In the field of medicine, sleep deprivation is considered as (i) having the adequate ability to sleep; yet (ii) giving oneself an inadequate opportunity to sleep—that is, sleep-deprived individuals can sleep, if only they would take the appropriate time to do so. Insomnia is the opposite: (i) suffering from an inadequate ability to generate sleep, despite (ii) allowing oneself the adequate opportunity to get sleep. People suffering from insomnia therefore cannot produce sufficient sleep quantity/quality, even though they give themselves enough time to do so (seven to nine hours).

  169. Patients suffering from paradoxical insomnia therefore have an illusion, or misperception, of poor sleep that is not actually poor. As a result, such patients are treated as hypochondriacal.

  170. The first is sleep onset insomnia, which is difficulty falling asleep. The second is sleep maintenance insomnia, or difficulty staying asleep. As the actor and comedian Billy Crystal has said when describing his own battles with insomnia, “I sleep like a baby—I wake up every hour.”

  171. If any of the characteristics of insomnia feel familiar to you, and have been present for several months, I suggest you consider seeking out a sleep medicine doctor. I emphasize a sleep medicine doctor and not necessarily your GP, since GPs—superb as they often are—have surprisingly minimal sleep training during the entirety of medical school and residency.

  172. The emphasis on duration of the sleep problem (more than three nights a week, for more than three months) is important. All of us will experience difficulty sleeping every now and then, which may last just one night or several. That is normal.

  173. Approximately one out of every nine people you pass on the street will meet the strict clinical criteria for insomnia

  174. insomnia is almost twice as common in women than in men

  175. encompassing prescription sleeping medications and over-the-counter sleep remedies, is worth an astonishing $30 billion a year in the US is perhaps the only statistic one needs in order to realize how truly grave the problem is.

  176. Insomnia shows some degree of genetic heritability, with estimates of 28 to 45 percent transmission rates from parent to child.

  177. insomnia. However, their origins are not from within you, and therefore not a disorder of you. Rather, they are influences from outside and, once they are addressed, individuals will get better sleep, without changing anything about themselves.

  178. The two most common triggers of chronic insomnia are psychological: (1) emotional concerns, or worry, and (2) emotional distress, or anxiety.

  179. The sympathetic nervous system switches on in response to threat and acute stress that, in our evolutionary past, was required to mobilize a legitimate fight-or-flight response. The physiological consequences are increased heart rate, blood flow, metabolic rate, the release of stress-negotiating chemicals such as cortisol, and increased brain activation, all of which are beneficial in the acute moment of true threat or danger. However, the fight-or-flight response is not meant to be left in the “on” position for any prolonged period of time.

  180. Second are higher levels of the alertness-promoting hormone cortisol, and sister neurochemicals adrenaline and noradrenaline. All three of these chemicals raise heart rate.

  181. This was not the case for the insomnia patients. Their emotion-generating regions and memory-recollection centers all remained active. This was similarly true of the basic vigilance centers in the brain stem that stubbornly continued their wakeful watch. All the while the thalamus—the sensory gate of the brain that needs to close shut to allow sleep—remained active and open for business in insomnia patients.

  182. Simply put, the insomnia patients could not disengage from a pattern of altering, worrisome, ruminative brain activity.

  183. Emotions make us do things, as the name suggests (remove the first letter from the word).

  184. In short, emotions in appropriate amounts make life worth living. They offer a healthy and vital existence, psychologically and biologically speaking.

  185. The sleep-wake switch within the hypothalamus has a direct line of communication to the power station regions of the brain stem. Like an electrical light switch, it can flip the power on (wake) or off (sleep). To do this, the sleep-wake switch in the hypothalamus releases a neurotransmitter called orexin.

  186. Like a faulty light switch that endlessly flickers on and off, day and night, so goes the erratic sleep and wake experience suffered by a narcoleptic patient across each and every twenty-four-hour period.

  187. There are no simple answers, certainly none that science can (or perhaps should) offer—an additionally cruel tendril of an already heinous condition.

  188. First, death ensued as quickly from total sleep deprivation as it did from total food deprivation. Second, rats lost their lives almost as quickly from selective REM-sleep deprivation as they did following total sleep deprivation. A total absence of NREM sleep still proved fatal, it just took longer to inflict the same mortal consequence—forty-five days, on average.

  189. it was simple bacteria from the rats’ very own gut that inflicted the mortal blow—one that an otherwise healthy immune system would have easily quelled when fortified by sleep.

  190. The problem is that some people confuse time slept with sleep opportunity time.

  191. https://sleepfoundation.org.

  192. Beyond longer commute times and “sleep procrastination” caused by late-evening television and digital entertainment—both of which are not unimportant in their top-and-tail snipping of our sleep time and that of our children—five key factors have powerfully changed how much and how well we sleep: (1) constant electric light as well as LED light, (2) regularized temperature, (3) caffeine (discussed in chapter 2), (4) alcohol, and (5) a legacy of punching time cards.

  193. More than a third of our brain is devoted to processing visual information, far exceeding that given over to sounds or smells, or those supporting language and movement.

  194. Edison did not create the first incandescent lightbulb—that honor went to the English chemist Humphry Davy in 1802.

  195. Before Edison, and before gas and oil lamps, the setting sun would take with it this full stream of daylight from our eyes, sensed by the twenty-four-hour clock within the brain (the suprachiasmatic nucleus

  196. The loss of daylight informs our suprachiasmatic nucleus that nighttime is now in session; time to release the brake pedal on our pineal gland, allowing it to unleash vast quantities of melatonin that signal to our brains and bodies that darkness has arrived and it is time for bed.

  197. The degree to which evening electric light winds back your internal twenty-four-hour clock is important: usually two to three hours each evening, on average. To contextualize that, let’s say you are reading this book at eleven p.m. in New York City, having been surrounded by electric light all evening. Your bedside clock may be registering eleven p.m., but the omnipresence of artificial light has paused the internal tick-tocking of time by hindering the release of melatonin. Biologically speaking, you’ve been dragged westward across the continent to the internal equivalent of Chicago time (ten p.m.), or even San Francisco time (eight p.m.).

  198. Artificial evening and nighttime light can therefore masquerade as sleep-onset insomnia—the inability to begin sleeping soon after getting into bed. By delaying the release of melatonin, artificial evening light makes it considerably less likely that you’ll be able to fall asleep at a reasonable time.

  199. Despite being just 1 to 2 percent of the strength of daylight, this ambient level of incandescent home lighting can have 50 percent of the melatonin-suppressing influence within the brain.

  200. Blue LED lights offer considerable advantages over incandescent lamps in terms of lower energy demands and, for the lights themselves, longer life spans. But they may be inadvertently shortening our own.

  201. few of us stare headlong into the glare of an LED lamp each evening. But we do stare at LED-powered laptop screens, smartphones, and tablets each night, sometimes for many hours, often with these devices just feet or even inches away from our retinas.

  202. Compared to reading a printed book, reading on an iPad suppressed melatonin release by over 50 percent at night. Indeed, iPad reading delayed the rise of melatonin by up to three hours, relative to the natural rise in these same individuals when reading a printed book.

  203. But did reading on the iPad actually change sleep quantity/quality above and beyond the timing of melatonin? It did, in three concerning ways. First, individuals lost significant amounts of REM sleep following iPad reading. Second, the research subjects felt less rested and sleepier throughout the day following iPad use at night. Third was a lingering aftereffect, with participants suffering a ninety-minute lag in their evening rising melatonin levels for several days after iPad use ceased—almost like a digital hangover effect.

  204. Due to its omnipresence, solutions for limiting exposure to artificial evening light are challenging. A good start is to create lowered, dim light in the rooms where you spend your evening hours. Avoid powerful overhead lights. Mood lighting is the order of the night. Some committed individuals will even wear yellow-tinted glasses indoors in the afternoon and evening to help filter out the most harmful blue light that suppresses melatonin. Maintaining complete darkness throughout the night is equally critical, the easiest fix for which comes from blackout curtains. Finally, you can install software on your computers, phones, and tablet devices that gradually de-saturate the harmful blue LED light as evening progresses.

  205. First, alcohol fragments sleep, littering the night with brief awakenings.

  206. Second, alcohol is one of the most powerful suppressors of REM sleep that we know of.

  207. one function of REM sleep is to aid in memory integration and association: the type of information processing required for developing grammatical rules in new language learning, or in synthesizing large sets of related facts into an interconnected whole.

  208. Memories remain perilously vulnerable to any disruption of sleep (including that from alcohol) even up to three nights after learning, despite two full nights of natural sleep prior.

  209. To successfully initiate sleep, as described in chapter 2, your core temperature needs to decrease by 2 to 3 degrees Fahrenheit, or about 1 degree Celsius.

  210. The hands, feet, and head are therefore remarkably efficient radiating devices that, just prior to sleep onset, jettison body heat in a massive thermal venting session so as to drop your core body temperature. Warm hands and feet help your body’s core cool, inducing inviting sleep quickly and efficiently.

  211. The need to dump heat from our extremities is also the reason that you may occasionally stick your hands and feet out from underneath the bedcovers at night due to your core becoming too hot, usually without your knowing.

  212. A bedroom temperature of around 65 degrees Fahrenheit (18.3°C) is ideal for the sleep of most people, assuming standard bedding and clothing.

  213. Lower than 55 degrees Fahrenheit (12.5°C) can be harmful rather than helpful to sleep, unless warm bedding or nightclothes are used.

  214. Scientists have, for example, gently warmed the feet or the body of rats to encourage blood to rise to the surface of the skin and emit heat, thereby decreasing core body temperature. The rats drifted off to sleep far faster than was otherwise normal.

  215. Before the body-cooling therapy, these groups had a 58 percent probability of waking up in the last half of the night and struggled to get back to sleep—a classic hallmark of sleep maintenance insomnia.

  216. the hot bath invites blood to the surface of your skin, giving you that flushed appearance. 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.

  217. Adding to the harm of evening light and constant temperature, the industrial era inflicted another damaging blow to our sleep: enforced awakening.

  218. If alarming your heart, quite literally, were not bad enough, using the snooze feature means that you will repeatedly inflict that cardiovascular assault again and again within a short span of time.

  219. Waking up at the same time of day, every day, no matter if it is the week or weekend is a good recommendation for maintaining a stable sleep schedule if you are having difficulty with sleep. Indeed, it is one of the most consistent and effective ways of helping people with insomnia get better sleep. This unavoidably means the use of an alarm clock for many individuals. 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.

  220. My favorite, however, is the shredder. You take a paper bill—let’s say $20—and slide it into the front of the clock at night. When the alarm goes off in the morning, you have a short amount of time to wake up and turn the alarm off before it begins shredding your money. The brilliant behavioral economist Dan Ariely has suggested an even more fiendish system wherein your alarm clock is connected, by Wi-Fi, to your bank account. For every second you remain asleep, the alarm clock will send $10 to a political organization . . . that you absolutely despise.

  221. Human beings, as we believe is true of all forms of terrestrial organisms, emerged from marine life. The ocean acts like a light filter, stripping away most of the longer, yellow and red wavelength light. What remains is the shorter, blue wavelength light. It is the reason the ocean, and our vision when submerged under its surface, appears blue. Much of marine life, therefore, evolved within the blue visible light spectrum, including the evolution of aquatic eyesight. Our biased sensitivity to cool blue light is a vestigial carryover from our marine forebears.

  222. Sleeping pills do not provide natural sleep, can damage health, and increase the risk of life-threatening diseases.

  223. Sleeping pills, old and new, target the same system in the brain that alcohol does—the receptors that stop your brain cells from firing—and are thus part of the same general class of drugs: sedatives. Sleeping pills effectively knock out the higher regions of your brain’s cortex.

  224. there was no objective benefit of these sleeping pills beyond that which a placebo offered.

  225. Those taking sleeping pills were 4.6 times more likely to die over this short two-and-a-half-year period than those who were not using sleeping pills. Kripke further discovered that the risk of death scaled with the frequency of use. Those individuals classified as heavy users, defined as taking more than 132 pills per year, were 5.3 times more likely to die over the study period than matched control participants who were not using sleeping pills.

  226. Individuals taking sleeping pills were 30 to 40 percent more likely to develop cancer within the two-and-a-half-year period of the study than those who were not.

  227. Do these findings prove that sleeping pills cause cancer? No. At least not by themselves. There are also alternative explanations.

  228. Shouldn’t drug companies be more transparent about the current evidence and risks surrounding sleeping pill use? Unfortunately, Big Pharma can be notoriously unbending within the arena of revised medical indications. This is especially true once a drug has been approved following basic safety assessments, and even more so when profit margins become exorbitant. Consider that the original Star Wars movies—some of the highest-grossing films of all time—required more than forty years to amass $3 billion in revenue. It took Ambien just twenty-four months to amass $4 billion in sales profit, discounting the black market. That’s a large number, and one I can only imagine influences Big Pharma decision-making at all levels.

  229. Currently, the most effective of these is called cognitive behavioral therapy for insomnia, or CBT-I, and it is rapidly being embraced by the medical community as the first-line treatment.

  230. The obvious methods involve reducing caffeine and alcohol intake, removing screen technology from the bedroom, and having a cool bedroom. In addition, patients must (1) establish a regular bedtime and wake-up time, even on weekends, (2) go to bed only when sleepy and avoid sleeping on the couch early/mid-evenings, (3) never lie awake in bed for a significant time period; rather, get out of bed and do something quiet and relaxing until the urge to sleep returns, (4) avoid daytime napping if you are having difficulty sleeping at night, (5) reduce anxiety-provoking thoughts and worries by learning to mentally decelerate before bed, and (6) remove visible clockfaces from view in the bedroom, preventing clock-watching anxiety at night.

  231. One of the more paradoxical CBT-I methods used to help insomniacs sleep is to restrict their time spent in bed, perhaps even to just six hours of sleep or less to begin with. By keeping patients awake for longer, we build up a strong sleep pressure—a greater abundance of adenosine.

  232. going to bed and waking up at the same time of day no matter what. It is perhaps the single most effective way of helping improve your sleep, even though it involves the use of an alarm clock.

  233. In younger, healthy adults, exercise frequently increases total sleep time, especially deep NREM sleep. It also deepens the quality of sleep, resulting in more powerful electrical brainwave activity.

  234. older adult insomniacs were sleeping almost one hour more each night, on average, by the end of a four-month period of increased physical activity.

  235. One brief note of caution regarding physical activity: try not to exercise right before bed. Body temperature can remain high for an hour or two after physical exertion.

  236. reducing food intake to just 800 calories a day for one month, makes it harder to fall asleep normally, and decreases the amount of deep NREM sleep at night.

  237. you should avoid going to bed too full or too hungry, and shy away from diets that are excessively biased toward carbohydrates (greater than 70 percent of all energy intake), especially sugar.

  238. A hundred years ago, less than 2 percent of the population in the United States slept six hours or less a night. Now, almost 30 percent of American adults do.

  239. Each weekend, vast numbers of people are desperately trying to pay back a sleep debt they’ve accrued during the week. As we have learned time and again throughout the course of this book, sleep is not like a credit system or the bank. The brain can never recover all the sleep it has been deprived of. We cannot accumulate a debt without penalty, nor can we repay that sleep debt at a later time.

  240. There remains a contrived, yet fortified, arrogance in many business cultures focused on the uselessness of sleep.

  241. certain business leaders mistakenly believe that time on-task equates with task completion and productivity.

  242. Insufficient sleep robs most nations of more than 2 percent of their GDP—amounting to the entire cost of each country’s military. It’s almost as much as each country invests in education.

  243. The irony that employees miss is that when you are not getting enough sleep, you work less productively and thus need to work longer to accomplish a goal. This means you often must work longer and later into the evening, arrive home later, go to bed later, and need to wake up earlier, creating a negative feedback loop. Why try to boil a pot of water on medium heat when you could do so in half the time on high? People often tell me that they do not have enough time to sleep because they have so much work to do. Without wanting to be combative in any way whatsoever, I respond by informing them that perhaps the reason they still have so much to do at the end of the day is precisely because they do not get enough sleep at night.

  244. Reputation in business can be a make-or-break factor.

  245. [滥竽充数]social loafing. The term refers to someone who, when group performance is being assessed, decides to exert less effort when working in that group than when working alone. Individuals see an opportunity to slack off and hide behind the collective hard work of others.

  246. The lower the quality of sleep that the supervisor reported getting from one night to the next accurately predicted poor self-control and a more abusive nature toward employees the following day, as reported by the employees themselves.

  247. Allowing and encouraging employees, supervisors, and executives to arrive at work well rested turns them from simply looking busy yet ineffective, to being productive, honest, useful individuals who inspire, support, and help each other. Ounces of sleep offer pounds of business in return.

  248. western-dwelling workers in that time zone had less sleep opportunity time than the eastern-dwelling workers.

  249. an hour of extra sleep still returned significantly higher wages in those eastern locations, somewhere in the region of 4 to 5 percent. You may sniff at that return on the investment of sixty minutes of sleep, but it’s not trivial. The average pay raise in the US is around 2.6 percent. Most people are strongly motivated to get that raise, and are upset when they don’t. Imagine almost doubling that pay raise—not by working more hours, but by getting more sleep!

  250. (1) $80,000 a year, working normal work hours, and getting the chance for around eight hours of sleep, or (2) $140,000 a year, working consistent overtime shifts, and only getting six hours of sleep each night. Unfortunately, the majority of individuals went with the second option of a higher salary and shorter sleep. That’s ironic, considering that you can have both, as we have discovered above.

  251. Nike and Google are as shrewd as they are profitable. They embrace sleep due to its proven dollar value.

  252. In the mid-1990s, NASA refined the science of sleeping on the job for the benefit of their astronauts. They discovered that naps as short as twenty-six minutes in length still offered a 34 percent improvement in task performance and more than a 50 percent increase in overall alertness. These results hatched the so-called NASA nap culture throughout terrestrial workers in the organization.

  253. Proof comes from a recent scientific study demonstrating that one night of sleep deprivation will double or even quadruple the likelihood that an otherwise upstanding individual will falsely confess to something they have not done. You can, therefore, change someone’s very attitudes, their behavior, and even their strongly held beliefs simply by taking sleep away from them.

  254. Keep in mind that 5:15 a.m. to a teenager is not the same as 5:15 a.m. to an adult. Previously, we noted that the circadian rhythm of teenagers shifts forward dramatically by one to three hours. So really the question I should ask you, if you are an adult, is this: Could you concentrate and learn anything after having forcefully been woken up at 3:15 a.m., day after day after day? Would you be in a cheerful mood? Would you find it easy to get along with your coworkers and conduct yourself with grace, tolerance, respect, and a pleasant demeanor? Of course not. Why, then, do we ask this of the millions of teenagers and children in industrialized nations?

  255. US education systems have shifted to early school start times, while many European countries have done just the opposite.

  256. Add this all up, and you see that investing in delaying school start times—allowing students more sleep and better alignment with their unchangeable biological rhythms—returned a net SAT profit of 212 points. That improvement will change which tier of university those teenagers go to, potentially altering their subsequent life trajectories as a consequence.

  257. School bus schedules and bus unions are a major roadblock thwarting appropriately later school start times, as is the established routine of getting the kids out the door early in the morning so that parents can start work early. These are good reasons for why shifting to a national model of later school start times is difficult.

  258. But we know that there are children, many children, perhaps, who are sleep-deprived or suffering from an undiagnosed sleep disorder that masquerades as ADHD.

  259. more than 50 percent of all children with an ADHD diagnosis actually have a sleep disorder

  260. Few people, however, know why. Why did we ever force doctors to learn their profession in this exhausting, sleepless way? The answer originates with the esteemed physician William Stewart Halsted, MD, who was also a helpless drug addict.

  261. The injurious consequences are well documented. Residents working a thirty-hour-straight shift will commit 36 percent more serious medical errors, such as prescribing the wrong dose of a drug or leaving a surgical implement inside of a patient, compared with those working sixteen hours or less. Additionally, after a thirty-hour shift without sleep, residents make a whopping 460 percent more diagnostic mistakes in the intensive care unit than when well rested after enough sleep. Throughout the course of their residency, one in five medical residents will make a sleepless-related medical error that causes significant, liable harm to a patient. One in twenty residents will kill a patient due to a lack of sleep. Since there are over 100,000 residents currently in training in US medical programs, this means that many hundreds of people—sons, daughters, husbands, wives, grandparents, brothers, sisters—are needlessly losing their lives every year because residents are not allowed to get the sleep they need.

  262. Young doctors themselves can become part of the mortality statistics. After a thirty-hour continuous shift, exhausted residents are 73 percent more likely to stab themselves with a hypodermic needle or cut themselves with a scalpel, risking a blood-born infectious disease, compared to their careful actions when adequately rested.

  263. If you are about to undergo an elective surgery, you should ask how much sleep your doctor has had and, if it is not to your liking, you may not want to proceed.

  264. Mother Nature spent millions of years implementing this essential physiological need. To think that bravado, willpower, or a few decades of experience can absolve you (a surgeon) of an evolutionarily ancient necessity is the type of hubris that, as we know from the evidence, costs lives.

  265. This entrenched pomposity, prevalent in so many senior-driven, dogmatic institutional hierarchies, has no place in medical practice in my opinion as a scientist intimate with the research data. Those boards must disabuse themselves of the we-suffered-through-sleep-deprivation-and-you-should-too mentality when it comes to training, teaching, and practicing medicine.

  266. Why, then, can several western European countries train their young doctors within the same time frame when they are limited to working no more than forty-eight hours in one week, without continuous long periods of sleeplessness? Perhaps they are just not as well trained? This, too, is erroneous, since many of those western European medical programs, such as in the UK and Sweden, rank among the top ten countries for most medical practice health outcomes, while the majority of US institutes rank somewhere between eighteenth and thirty-second. As a matter of fact, several pilot studies in the US have shown that when you limit residents to no more than a sixteen-hour shift, with at least an eight-hour rest opportunity before the next shift, the number of serious medical errors made—defined as causing or having the potential to cause harm to a patient—drops by over 20 percent. Furthermore, residents made 400 to 600 percent fewer diagnostic errors to begin with. There’s simply no evidence-based argument for persisting with the current sleep-anemic model of medical training, one that cripples the learning, health, and safety of young doctors and patients alike. That it remains this way in the stoic grip of senior medical officials appears to be a clear case of “my mind is made up, don’t confuse me with the facts.”

  267. one that is epitomized in the words of a US senator who once said, “I’ve always loathed the necessity of sleep. Like death, it puts even the most powerful men on their backs.”

  268. Chernobyl nuclear power station on April 26, 1986. The radiation from the disaster was one hundred times more powerful than the atomic bombs dropped in World War II.

  269. One practice known to convert a healthy new habit into a permanent way of life is exposure to your own data.

  270. When it comes to the quantified self, it’s the old adage of “seeing is believing” that ensures longer-term adherence to healthy habits.

  271. Prevention is far more efficient than treatment, and costs far less in the long run.

  272. When I asked this same diverse set of individuals if they had received any education about sleep, the response was equally universal in the opposite direction: 0 percent received any educational materials or information about sleep.

  273. The goal would be twofold: change the lives of those children and, by way of raising sleep awareness and better sleep practice, have that child pass on their healthy sleep values to their own children. In this way, we would begin a familial transmission of sleep appreciation from one generation to the next, as we do with things like good manners and morality. Medically, our future generations would not only enjoy a longer life span, but, more importantly, a longer health span, absolved of the mid- and late-life diseases and disorders that we know are caused by (and not simply associated with) chronic short sleep.

  274. Thus, your “sleep credit score” would be calculated based on a combination of sleep amount and night-to-night sleep continuity.

  275. The less sleep you have had, or the more fragmented your sleep, the more sensitive you are to pain of all kinds.

  276. We can also ask patients about their regular sleep schedules on the standard hospital admission form, and then structure assessments and tests around their habitual sleep-wake rhythms as much as possible.

  277. Use dim, non-LED lighting at night and bright lighting during the day.

  278. Why are we not designing NICUs and their care systems to foster the very highest sleep amounts, thereby using sleep as the lifesaving tool that Mother Nature has perfected it to be?

  279. Within the space of a mere hundred years, human beings have abandoned their biologically mandated need for adequate sleep—one that evolution spent 3,400,000 years perfecting in service of life-support functions.

  280. I believe it is time for us to reclaim our right to a full night of sleep, without embarrassment or the damaging stigma of laziness.

  281. my inimitable publisher, Scribner, who believed in this book and its lofty mission to change society.

  282. My only hope is that this book represents a worthy match for all you have given to me, and it.

  283. Twelve Tips for Healthy Sleep

  284. 1. Stick to a sleep schedule. Go to bed and wake up at the same time each day. As creatures of habit, people have a hard time adjusting to changes in sleep patterns.

  285. Set an alarm for bedtime.

  286. 2. Exercise is great, but not too late in the day.

  287. 3. Avoid caffeine and nicotine.

  288. take as long as eight hours to wear off fully.

  289. 4. Avoid alcoholic drinks before bed.

  290. 5. Avoid large meals and beverages late at night.

  291. 6. If possible, avoid medicines that delay or disrupt your sleep.

  292. 7. Don’t take naps after 3 p.m.

  293. 8. Relax before bed. Don’t overschedule your day so that no time is left for unwinding. A relaxing activity, such as reading or listening to music, should be part of your bedtime ritual.

  294. 9. Take a hot bath before bed. The drop in body temperature after getting out of the bath may help you feel sleepy, and the bath can help you relax and slow down so you’re more ready to sleep.

  295. 10. Dark bedroom, cool bedroom, gadget-free bedroom.

  296. 11. Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside in natural sunlight for at least thirty minutes each day. If possible, wake up with the sun or use very bright lights in the morning. Sleep experts recommend that, if you have problems falling asleep, you should get an hour of exposure to morning sunlight and turn down the lights before bedtime.

  297. 12. Don’t lie in bed awake. If you find yourself still awake after staying in bed for more than twenty minutes or if you are starting to feel anxious or worried, get up and do some relaxing activity until you feel sleepy. The anxiety of not being able to sleep can make it harder to fall asleep.

  298. Tips for safe sleep in the elderly: (1) have a side lamp within reach that you can switch on easily, (2) use dim or motion-activated night-lights in the bathrooms and hallways to illuminate your path, (3) remove obstacles or rugs en route to the bathroom to prevent stumbles or trips, and (4) keep a telephone by your bed with emergency phone numbers programmed on speed dial.