Why We Sleep

Matthew Walker

📚 GENRE: Health & Wellness

📃 PAGES: 368

✅ COMPLETED: August 24, 2023

🧐 RATING: ⭐⭐⭐⭐⭐

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Short Summary

Added up, the combined benefits of sleep are miraculous. In Why We Sleep, sleep scientist Matthew Walker discusses why sleep is vital to all aspects of our health, how it works, and ways we can improve it. 

Key Takeaways

1️⃣ The Miracle of Sleep — There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep. In short, there’s virtually nothing but good that comes with good sleep. It helps every single area of your life. It aids memory and recall, enhances mind and body performance, sparks creativity and innovation, supports your immune and metabolic systems, protects the heart, keeps you emotionally stable, and leads to a longer and healthier life. It’s a miracle drug available to you every night. Aim for at least 8 hours. 

2️⃣ Use It or Lose It — The brain can never recover all the sleep it has been deprived of. In other words, you can’t “catch up” on sleep. The myriad of benefits sleep offers are available every night, but there’s no compensating for, or catching up on, massive sleep debt. Sleep is a biological necessity and should be prioritized every night. 

3️⃣ Sleeping Pills: Not a Good Option — Like alcohol, sleeping pills act more like a sedative and do not induce natural, healthy sleep. They work by sedating the prefrontal cortex and other regions of the brain, leading to “sleep” that is light and not very restorative. Even worse, they are barely effective at knocking you out and have been shown to increase your risk of cancer and death. CBT-I training is a much more healthy and reliable way of dealing with chronic insomnia. 

Favorite Quote

“Widening the lens of focus, there are more than twenty large-scale epidemiological studies that have tracked millions of people over many decades, all of which report the same clear relationship: the shorter your sleep, the shorter your life. The leading causes of disease and death in developed nations — diseases that are crippling healthcare systems such as heart disease, obesity, dementia, diabetes, and cancer — all have recognized causal links to a lack of sleep.”

Book Notes 📑

Ch. 1: To Sleep...

  • Matthew Walker, PhD — The author of this book, Walker is a professor of neuroscience and psychology at UC Berkeley, the director of the Center for Human Sleep Science, and a former professor of psychiatry at Harvard University. He has devoted his life to understanding sleep and the myriad of benefits that come with it. 
  • Got Sleep? — Routinely sleeping less than 6-7 hours is one of the worst things you can do to yourself. To put it simply, the shorter you sleep, the shorter your life span will be. A balanced diet and exercise are vitally important to health, but sleep is considered by many to be the top dog in this trinity. The physical and mental consequences caused by a bad night of sleep are far worse than the absence of food or exercise for one day.  Some of the consequences of poor sleep over a long period of time include:
    • Immune System — Your risk of cancer doubles when you don’t sleep well. Your immune system simply doesn’t perform as well when you don’t sleep. 
    • Alzheimer’s Disease — Lack of quality sleep is one of the main drivers of Alzheimer’s disease.
    • Blood Glucose Levels — A bad night of sleep will send your blood glucose levels all over the place, often to levels that would classify you as a pre-diabetic. 
    • Artery Blockage — Bad sleep contributes to blocked arteries and sets you on the path toward cardiovascular disease, stroke. And heart failure. 
    • Appetite — When you don’t sleep well and are tired, you tend to eat more. That’s because a lack of sleep encourages a hormone that makes you feel hungry while silencing a companion hormone that signals that you’re full. 
    • Drowsiness at the Wheel — Interestingly, there are more deaths due to drowsiness at the wheel than there are deaths due to drunk driving and driving under the influence of drugs combined. 
  • Sleep Benefits — There are a huge number of brain and body benefits that come with sleep. There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep. In short, there’s virtually nothing but good that comes with good sleep. It helps every single area of your life.
    • Quote (P. 7): “Within the brain, sleep enriches a diversity of functions, including our ability to learn, memorize, and make logical decisions and choices. Benevolently servicing our psychological health, sleep recalibrates our emotional brain circuits, allowing us to navigate next-day social and psychological challenges with cool-headed composure. We are even beginning to understand the most impervious and controversial of all conscious experiences: the dream.”
    • Quote (P. 7): “Downstairs in the body, sleep restocks the armory of our immune system, helping fight malignancy, preventing infection, and warding off all manner of sickness. Sleep reforms the body’s metabolic state by fine-tuning the balance of insulin and circulating glucose. Sleep further regulates our appetite, helping control body weight through healthy food selection rather than rash impulsivity. Plentiful sleep maintains a flourishing microbiome within your gut from which we know so much of our nutritional health begins. Adequate sleep is intimately, tied to the fitness of our cardiovascular system, lowering blood pressure while keeping our hearts in fine condition.”
    • Quote (P. 8): “Emerging from this research renaissance is an unequivocal message: sleep is the single most effective thing we can do to reset our brain and body health each day — Mother Nature’s best effort yet at contra-death.”
    • Quote (P. 8): “Personally, I should note that I am in love with sleep (not just my own, though I do give myself a non-negotiable eight-hour sleep opportunity each night). I am in love with everything sleep is and does.”
  • Chapter Takeaway — The number of benefits that come with sleep are almost innumerable. Every part of your brain and body benefit from consistent, high-quality sleep. It leads to better performance in every area of your life. It should be a priority in your life. 

Ch. 2: Caffeine, Jet Lag, and Melatonin

  • Sleep & Wake Factors — There are two factors that are constantly in play and determine when you want to sleep and when you want to be awake. It is the balance between these two factors that dictates how alert and attentive you are during the day, when you will feel tired and ready for bed at night, and how well you will sleep. These two factors are:
    • Circadian Rhythm — A 24-hour clock built into your brain that creates a cycling, day-night rhythm that makes you feel tired or alert at regular times of night and day. 
    • Adenosine: Sleep Pressure — We all have a chemical substance called adenosine that builds up in our brain and creates “sleep pressure.” The longer you’ve been awake, the more adenosine builds up in your brain and the sleepier you feel. 
  • Circadian Rhythm — Your circadian rhythm is an internal 24-hour clock within your brain that communicates to other regions of the body and essentially tells them what time it is and how to function based on the time of day. Circadian rhythm helps to determine when you want to wake and when you want to be asleep. 
  • Circadian Rhythm & Sunlight — Sunlight essentially resets your circadian rhythm every day. That’s why it’s important to try to get some sun in the morning, because it resets your internal clock. The interesting thing, however, is that sunlight isn’t necessary — our bodies seem to have their own biological rhythms. In 1938, researchers from the University of Chicago tested this by secluding themselves in total darkness for 32 days to see what happened. One of their big discoveries was that humans generate their own circadian rhythm without external light from the sun. The reason sunlight is key is that it helps the body reliably know the time of day and when it’s time to rise in the morning and unwind at night; the brain uses sunlight to reset our circadian rhythm. 
  • Suprachiasmatic Nucleus — This is the actual 24-hour clock in our brain. This is basically where circadian rhythm takes place. It is composed of 20,000 neurons, not much considering the brain is composed of 100 billion neurons. This component of the brown controls many behaviors, including when we want to be awake and asleep.
  • Circadian Rhythm & The Body — Your circadian rhythm activates many mechanisms in the brain and body during the daylight hours that are designed to keep you awake and alert. These mechanisms are then ratcheted down at night to prepare you for sleep. Body temperature is one example. Whether you are awake or asleep, your body temperature will rise and peak in the morning/early afternoon and fall at night. Core body temperature is just one of the many functions of the body that are impacted by circadian rhythm. Your circadian rhythm is basically communicating with your body all the time. 
  • Different Rhythms — Although everyone has a circadian rhythm, we are all on slightly different rhythms, or chronotypes. Some people naturally awake earlier and fall asleep earlier. Others naturally wake up later in the day and go to sleep later. Much of circadian rhythm is strongly dictated by genetics. The responsibilities of everyday life can be harder for natural night owls because they are forced to get up early to start the day. When this happens, their prefrontal cortex — considered the “head office” of the brain and the region that controls high-level thought and emotions — isn’t quite “awake” yet, so they don’t perform quite as well to begin the day. 
  • Melatonin — Your suprachiasmatic nucleus communicates its repeating signal of night and day to your brain and body using a circulating messenger called melatonin. The rise in melatonin begins soon after dusk, being released into the bloodstream from the pineal gland, an area situated deep in the back of your brain. Melatonin acts like a powerful bullhorn, shouting out a clear message to the brain and body: “It’s dark, it’s dark.”
  • Melatonin: Not A Good Sleep Aid — Melatonin’s role is to regulate the timing of when sleep occurs by signaling darkness throughout the brain and body. Contrary to popular belief, it does not have influence when it comes to generating sleep. Essentially, melatonin provides the instruction to start sleep, but does not participate in sleep itself. Melatonin is therefore not a very effective sleep aid. It’s also not regulated by a governing body, like the FDA. Because of its effects on sleep timing, the one time melatonin is useful is when you have traveled a long distance and are experiencing jet lag. 
  • Melatonin: How It Flows — Melatonin typically accumulates and peaks in the brain around dusk/nighttime. Once sleep is underway, it decreases during the night and into the morning hours. In the morning, as sunlight enters the brain through the eyes (even closed eyelids), a brake pedal is applied to the pineal gland, which shuts off the release of melatonin. The absence of melatonin signals to the brain and body that the finish line of sleep has been reached. 
  • Adenosine: Sleep Pressure — A chemical called adenosine is building in your brain every minute of the day. Adenosine is referred to as “sleep pressure” because the longer you are awake, the more it builds and the more you naturally want to sleep. Adenosine resets when you sleep. If you don’t sleep, it will keep building up. This is why, eventually, you WILL sleep, even if you’ve had a couple of bad nights of sleep. Adenosine will eventually win out. Along with the circadian return, adenosine is the second factor that causes you to sleep. 
  • Caffeine: An Adenosine Blocker — Contrary to popular belief, caffeine does not give you energy. Instead, it “blocks” adenosine molecules from attaching to their receptors in the brain. This in turn leads to you feeling more awake. Adenosine never stops building, even with caffeine present. When the caffeine eventually leaves your receptors, all of that built-up adenosine hits you at once. This is the “caffeine crash.” Caffeine is the second most traded commodity behind oil. 
    • Quote (P. 27): “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.”
    • Quote (P. 28): “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.”
  • Caffeine: Long Half-Life — Caffeine has an average half-life of 5-7 hours. If you have a cup of coffee after your evening dinner, around 7:30 p.m., this means that by 1:30 a.m. 50% of that caffeine may still be active and circulating in your brain. In other words, by 1:30 a.m., you’re only halfway to completing the job of cleansing you brain of the caffeine you drank after dinner. By having even as much as 25-50% of that caffeine still circulating in your brain and body, you are hurting your chances of sleeping well. 
  • Sleep Deprivation — Sleep resets adenosine levels. Sleep deprivation occurs when you simply don’t get enough sleep and adenosine continues to build up in your brain. When you don’t sleep (or don’t sleep well) adenosine levels stay high and carry over to the next day, which makes you feel tired and groggy. You feel sleep deprived. Interestingly, you do get a boost in the afternoon because your circadian rhythm peaks and makes you feel awake. So even if you’re sleep deprived, you do get a second wind in the mid-morning/early afternoon thanks to your circadian rhythm. Eventually, after several bad nights of sleep, adenosine will win out at night because adenosine levels are really high and your circadian rhythm bottoms out. See Figure 7 for a visual. 
  • Quote (P. 35): “If you look at Figure 7 once again, the graveyard shift misery you experience around 6 a.m. can be explained by the combination of high adenosine sleep pressure and your circadian rhythm reaching its lowest paint. The vertical distance separating these two lines at 3 a.m. is large, indicated by the first vertical arrow in the figure. But if you can make it past this alertness low point, you’re in for a rally. The morning rise of the circadian rhythm comes to your rescue, marshaling an alerting boost throughout the morning that temporarily offsets the rising levels of adenosine sleep pressure.”
  • Chapter Takeaway — There are two factors that drive sleep: circadian rhythm and adenosine. Circadian rhythm regulates when your internal 24-hour clock. Sunlight resets your circadian rhythm in the morning. As adenosine builds in your brain, you feel more and more sleepy. If you sleep bad for several nights in a row, you will eventually accumulate so much adenosine that it overpowers you and almost “forces” you into a sleep. Melatonin is not a good sleep aid. 

Ch. 3: Defining and Generating Sleep

  • Measuring Sleep & Rapid Eye Movement (REM) — The gold standard of measuring sleep is the polysomnography, which measures sleep by recording signals from the three different regions listed below. Interestingly, when you’re in a deep sleep, your brain is as active as it is during the day when you’re wide awake. 
    • Brainwave Activity
    • Eye Movement Activity
    • Muscular Activity 
  • Two Types of Sleep: NREM & REM — There are two basic types of sleep: Non-rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep. When somebody is really knocked out and asleep, they engage in REM sleep. In this phase of the sleep cycle, the eyes are darting around quickly and your brain is super active; basically as active as it is during the day when you’re wide awake. REM sleep is where we do our dreaming. Below is a look at brainwave activity during NREM and REM sleep compared to when you’re awake. Notice the slow, rhythmic brainwave activity that occurs during REM sleep. Also notice how similar your brainwave activity is when you’re awake and when you’re in REM sleep. 
  • Sleep Cycle — There are five stages of the sleep cycle, and we typically go through the cycle 4-5 times a night (or about every 90 minutes). NREM sleep comprises the first four stages of sleep and REM sleep is the fifth stage. In each stage, we fall deeper and deeper into sleep. The REM stage is where we do our dreaming. In this stage, our eyes dart around like crazy and our brain is super active. 
  • NREM Sleep & Memory — As you drift deeper and deeper into sleep, your brain is initiating a file-transfer process. The long-range brainwaves of deep sleep will move memory packets (recent experiences) from a short-term storage site to a more permanent long-term storage location. Essentially, your brain is solidifying memories during sleep. 
  • Wake State vs. REM Sleep — Your brain is basically as active during REM sleep as it is when you’re awake. But there’s a difference between what is going on in the brain in these two states. When you’re awake, the brain is interacting with the sensations of the outside world. When you’re in REM sleep, emotion, motivations, and memories are being engaged with.
    • Quote (P. 53): “It is not sensations from the outside that are allowed to journey to the cortex during REM sleep. Rather, signals of emotions, motivations, and memories (past and present) are all played out on the big screens of our visual, auditory, and kinesthetic sensory cortices in the brain. Each and every night, REM sleep ushers you into a preposterous theater wherein you are treated to a bizarre, highly associative carnival of autobiographical themes. 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).”
  • Paralyzed! — We do our dreaming in the REM stage of sleep. To protect ourselves from harm, our brain sends us into a state of temporary paralysis during REM sleep so we can’t act out our dreams and get hurt. Our involuntary muscles — the ones that control automatic operations like breathing — continue to work, but all other muscles go completely limp.
    • Quote (P. 53): “Gearing up for the leap into REM sleep, however, an impressive change occurs. Mere seconds before the dreaming phase begins, and for as long as that REM sleep period lasts, you are completely paralyzed. There is no tone in the voluntary muscles of your body. None whatsoever. If I were to quietly come into the room and gently lift up you body without waking you, it would be completely limp, like a rag doll.”
  • Chapter Takeaway — There are two main types of sleep, both essential to us: NREM and REM sleep. Both of these types of sleep make up the five-phase sleep cycle, with NREM dominating the first four phases and REM dominating the fifth. REM sleep is where we do our dreaming. During this phase, our brain is as active as it is when we’re awake and we are completely paralyzed to prevent ourselves from acting out our dreams and experiencing harm. 

Ch. 4: Ape Beds, Dinosaurs, and Napping with Half a Brain

  • Everything Sleeps — Literally every animal species known to man sleeps in some form or fashion. The types and ways different species go about getting sleep may be different, but everything sleeps. Even sharks sleep. They can’t close their eyes because they don’t have eyelids, but even they sleep. The fact that all animal species participate in sleep shows how valuable it is. 
  • Not Everything Gets REM Sleep — Not every animal species gets REM sleep and drifts off into dreams. All species get NREM sleep, however. In many ways, we’re lucky that we get REM sleep because we didn’t always drift into it. REM sleep is something we acquired over time as we evolved from sleeping in trees (where going into REM sleep and framing could lead to bad injuries) to sleeping on the ground. 
  • What’s Gone Is Gone — You can’t “make up” sleep. If you miss out on sleep for whatever reason, there’s no catching up, regardless of how much time you put yourself in bed. The brain will try, but it can’t get there. It tries by first trying to recover NREM sleep before moving into REM sleep. The consequences of missing sleep are bad.
    • Quote (P. 64): “That humans (and all other species) can never ‘sleep back’ that which we have previously lost is one of the most important take homes of this book, the saddening consequences of which I will describe in chapters 7 and 8.”
  • Interesting Fact — Dolphins and some species of birds can sleep with half a brain at a time. One half of a dolphin’s brain has to stay awake at all times to maintain required movement in the water. But the other half disengages and falls into NREM sleep. 
  • Biphasic Sleep — Modern society has changed our sleep pattern. Our sleep pattern used to include overnight sleep and an afternoon nap (biphasic sleep pattern). This is the type of sleep pattern we were designed to have. There are still places around the world where biphasic sleep is the norm, but we have for the most part abandoned it entirely. Because we were designed to have a biphasic sleep pattern, each day we experience an afternoon lull called the post-pea dial alertness dip. Having a biphasic sleep pattern has been shown to improve overall health.
    • Quote (P. 69): “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. This brief descent from high-degree wakefulness to low-level alertness reflects an innate drive to be asleep and napping in the afternoon, and not working. It appears to be a normal part of the daily rhythm of life. Should you ever have to give a presentation at work, for your own sake — and that of the conscious state of your listeners — if you can, avoid the midafternoon slot.”
  • REM Sleep & Creativity — REM sleep has a direct role in sparking creativity. NREM sleep helps transfer newly learned information into long-term storage sites of the brain. But it is REM sleep that takes these fresh memories and begins colliding them with the entire back catalog of your life and all of your total memories. These collisions during REM sleep spark new creative insights as links are created between unrelated pieces of information. This linking of new and old ideas and memories is what creativity is. It leads to new and original ideas. 
  • Chapter Takeaway — Everything sleeps! Sleep is so valuable to every animal species that they all participate in it. Biphasic sleep, where we sleep at night and take an afternoon nap, is the sleep pattern we were genetically and biologically designed to have. 

Ch. 5: Changes in Sleep Across the Life Span

  • Sleep Before Birth — While in the mother’s womb, babies get a ton of sleep. The majority of their time is spent sleeping, and much of it is spent in REM sleep. They have not yet developed the paralysis that prevents movement during REM sleep, so, once in awhile, the mother will feel a “kick.” This is the result of the fetus moving around during REM sleep. 
  • Autism & Sleep — Some researchers believe there could be a causal link between autism and sleep. Autism, a developmental disorder that impairs the ability to communicate and socially interact with others, is usually diagnosed in a child sometime in their first 2-3 years of life. It’s been discovered that people with autism get far less sleep, especially REM sleep, than others, which leads to a lack of synapses (neuron connections) in the brain. 
  • Alcohol, Sleep, and Babies — A pregnant woman should never have any amount of alcohol during pregnancy or in the immediate aftermath of breast feeding. Alcohol consumed by the mother is essentially passed on directly to the child in the womb. During the breast feeding stage, any amount of alcohol consumed by the mother is present in the breastmilk that the baby is ingesting. Alcohol has been shown to significantly hurt the baby’s sleep, specifically REM sleep. REM sleep is absolutely crucial to an unborn and newborn child. During REM sleep, the child’s brain is developing rapidly; significant lapses in sleep could lead to autism or some other social condition. 
  • Childhood Sleep — During the early years of life, babies and small children are in a polyphasic sleep pattern where they sleep and wake up several times per day. This is what drives parents nuts. Gradually over time they work up to a biphasic sleep pattern where they require overnight sleep and a daily nap. Even later down the line they graduate to the monophasic sleep pattern that most adults around the world have. 
  • Childhood Sleep & Circadian Rhythm — The big reason why babies and small children have such an irregular sleeping pattern early in life is due to their circadian rhythm. The suprachiasmatic nucleus that represents our 24-hour clock and regulates our circadian rhythm is not fully developed right away. It takes a lot of time to develop in the brain. At 3-4 months old, a baby will start to show some signs of developing a circadian rhythm. By age 4, a child will usually have the suprachiasmatic nucleus fully developed and their sleep patterns are much more predictable. 
  • Brain Develops Back to Front — The brain usually develops back to front. This is why many children and teenagers make questionable decisions — the frontal lobe, where rational thinking and critical decision-making functions reside, is still being developed. Sleep plays a big role in brain development, which is why it’s especially important for kids and teenagers to get their sleep. Therefore, because of its harmful effects on sleep, children and teenagers should avoid caffeine. 
  • Sleep Patterns Over Time & Circadian Rhythm — As small children, our circadian rhythm is naturally turned forward compared to adults. This is why children fall asleep earlier in the night and wake up earlier in the morning — it’s how their circadian rhythm is wired early in life. As we get to the teenage years, our circadian rhythm is sped up. We now naturally fall asleep later in the night and wake up later in the morning. Eventually as adults, our circadian falls into the happy medium area. This fact is important for parents to understand.
    • Quote (P. 93): “If this remains perplexing to parents, a different way to frame and perhaps appreciate the mismatch is this: asking your teenage son or daughter to go to bed and fall asleep at 10 p.m. is the circadian equivalent of asking you, their parent, to go to sleep at 7 or 8 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 7 the next morning and function with intellect, grace, and good mood is the equivalent of asking you, their parent, to do the same at 4 or 5 a.m.”
    • Quote (P. 94): “Sadly, neither society nor our parental attitudes are well designed to appreciate or accept that teenagers need more sleep than adults, and that they are biologically wired to obtain that sleep at a different time from their parents. It’s very understandable for parents to feel frustrated in this way, since they believe that their teenager’s sleep patterns reflect a conscious choice and not a biological edict. But non-volitional, non-negotiable, and strongly biological they are. We parents would be wise to accept this fact, and to embrace it, encourage it, and praise it, lest we wish our own children to suffer developmental brain abnormalities of force a raised risk of mental illness upon them.”
  • Sleep Declines — As we age into our midlife and elderly years, our levels of deep NREM sleep decline. REM sleep stays relatively stable, but the quantity and quality of deep NREM sleep begins to fall drastically in your 40s. By the time you’re 70, you will have most 80-90% of your deep youthful sleep. These stats mainly refer to our electrical sleep quality, or the brainwave activity going on when we sleep. But he fact is: declines in good, high-quality sleep in our midlife and elderly years are connected to many mental and physical health issues. Sleep has to be prioritized.
  • “I Gotta Pee!” — One issue that contributes to declines in sleep as we get older is sleep fragmentation, mainly caused by a shrinking bladder that sends us to the bathroom more often during the night. Frequent trips to the bathroom directly contribute to declines in sleep efficiency, which is basically how much time you’re actually asleep while in bed. If you’re in bed for 8 hours and are asleep for all 8 hours, that’s 100% sleep efficiency. Sleep scientists consider a 90% sleep efficiency to be good. Mortality and physical health risks are significantly higher for elderly people with poor sleep efficiency rates. 
  • Older Folks & Circadian Rhythm — Elderly people have a circadian rhythm that is significantly sped up, meaning they naturally go to bed and wake up earlier because melatonin is released in their brain earlier in the day compared to younger adults. Problems occur when an older person dozes off around 4 or 5 p.m. but then tries to stay up later to hang with the family (for example) before then attempting to go to sleep again later in the night. Adenosine has already been burned during the 5 p.m. snooze, which makes it hard to fall asleep again a few hours later. This type of cycle is pretty common and happens regularly. The result is insomnia and poor sleep quality. One trick that can help is to try to delay the circadian rhythm by avoiding light in the morning and going outside for some sunlight in the early afternoon. 
  • Brain Degeneration & Sleep — Walker and his team have discovered that the parts of our brain that ignite healthy deep sleep at night are the same areas that degenerate earliest and most severely as we age. What this means is that we naturally have a harder time getting good, high-quality sleep as we get older. Therefore, poor sleep is a big contributor to physical and mental diseases, and overall risk of death, as we age.
    • Quote (P. 102): “More generally, these and similar studies have confirmed that poor sleep is one of the most underappreciated factors contributing to cognitive and medical ill health in the elderly, including issues of diabetes, depression, chronic pain, stroke, cardiovascular disease, and Alzheimer’s disease.”
      • Takeaway — It gets harder to sleep as we get older because the parts of the brain that regulate sleep begin to degenerate. It’s critical that we prioritize sleep throughout our life, including in our late years. 
  • Chapter Takeaway — We need sleep. Badly. All of us. But especially infants, children, and teenagers, because those are the critical years where the brain is developing quickly. Sleep, especially deep NREM and REM sleep, is essential to the development of synapses and neural highways and networks in the brain. Our circadian rhythm shifts quite a bit as we grow up — from an early cycle as children to a late cycle as teenagers. Eventually our circadian rhythm settles somewhere in the middle as we transition to adulthood. It gets harder to get high-quality sleep as we get old, but it’s just as important as it is at any other point in our life. 

Ch. 6: Your Mother and Shakespeare Knew

  • Miracle Drug — If the benefits that sleep provides every single night (some of which are outlined in the fictitious ad above 👆) were presented as a medication, it might be considered a miracle drug. The bottom line is that sleep is unbelievably healthy and helps us in so many ways. It heals emotional wounds, helps you learn and remember, helps you figure out problems, and prevents sickness and infection by aiding the immune system. It is the universal health care provider: whatever the physical or mental ailment, sleep can help it. 
  • Learning & Memory — 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.
    • Before Learning — Every night, sleep refreshes our ability to make new memories. It does so by transferring memories from the hippocampus to the neocortex. The hippocampus is a long, finger-shaped structure in your brain that serves as a short-term reservoir, or temporary information warehouse, for accumulating new memories and learning. The hippocampus has a limited storage capacity, almost like a camera roll or a USB memory stick. The hippocampus can’t hold any more information that exceeds its storage capacity. Sleep transfers memories from the temporary, short-term storage site (hippocampus) to the neocortex, which is a permanent memory storage location and has way, way more space. This transfer then frees up the hippocampus for more memories and learning. Specifically, deep NREM sleep is responsible for this transfer.
      • Quote (P. 111): “In that moment, we had just become privy to an electrical transaction occurring in the quiet secrecy of sleep: one that was shifting fact-based memories from the temporary storage depot (the hippocampus) to a long-term secure vault (the cortex). In doing so, sleep had delightfully cleared out the hippocampus, replenishing this short-term information repository with plentiful free space.”
      • Quote (P. 115): “By transferring memories of yesterday from the short-term repository of the hippocampus to the long-term home within the cortex, you awake with both yesterday’s experiences safely filed away and having regained your short-term storage capacity for new learning throughout that following day. The cycle repeats each day and night, clearing out the cache of short-term memory for the new imprinting of facts, while accumulating an ever-updated catalog of past memories.”
    • After Learning — The second benefit of sleep for memory comes after learning. Sleep essentially acts as a “save” button on those newly created memories and learning files. In this way, sleep protects newly acquired information by cementing it in the neocortex, which helps us retain memories and information and prevents them from fading away in our memory. This is why you’re better off sleeping before a big test than studying all night — sleeping “locks in” the information you’re learning and memories you’re creating. Specifically, NREM sleep is what locks in the information, and sleep has been proven to aid memory retention by between 20-40% in clinical trials compared to people who stay awake. 
    • Sleep to Forget? — Another way sleep impacts memory is by helping you retain information you need while letting stuff you don’t need slide by the wayside. To use an analogy, sleep does this for you by creating filters in your brain — allowing you to select only what you need to save while discarding that which you do not. 
  • Practice + Sleep Makes Perfect — Sleep’s impact on memory means that practice doesn’t make perfect; practice with sleep makes perfect. Walker and colleagues have conducted trials and experiments proving that sleep helps cement, and even improve, physical and mental skills that you’re in the process of learning. Walker showed that sleep has a way of identifying where the difficult transitions are in your motor memory and smoothing them out. Put simply — without sleep, your skill development is hindered. 
  • Sleep & Sports: Get 8 Hours! — Because sleep plays a significant role in skill/motor skill development, and also brings a myriad of other physical and mental benefits, athletes and sports teams have started to prioritize it. Sleep also aids tremendously in recovery — it accelerates physical recovery from inflammation, stimulates muscle repair, and restocks cell energy in the form of glucose and glycogen. You need at least 8 hours of sleep every night to achieve peak performance. In 2015, the International Olympic Committee even published a statement highlighting the importance of sleep in athletic development across all sports for men and women.
    • Quote (P. 128): “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. In the years since our discovery, numerous studies have shown that sleep improves the motor skills of junior, amateur, and elite athletes across sports as diverse as tennis, basketball, football, soccer, and rowing.”
    • Quote (P. 129): “Obtain anything less than 8 hours of sleep a night, and especially less than 6 hours a night, and the following happens: time to physical exhaustion drops by 10-30%, and aerobic output is significantly reduced. Similar impairments are observed in limb extension force and vertical jump height, together with decreases in peak and sustained muscle strength. Add to this marked impairments in cardiovascular, metabolic, and respiratory capabilities that hamper an underslept body, including faster rates of lactic acid buildup, reductions in blood oxygen saturation, and converse increases in blood carbon dioxide, due in part to a reduction in the amount of air that the lungs can expire. Even the ability of the body to cool itself during physical exertion through sweating — a critical part of peak performance — is impaired by sleep loss. And then there is injury risk.”
      • Takeaway — You need at least 8 hours of sleep to give yourself a chance to achieve peak physical and mental performance every day. Athletes and sports teams are beginning to see this and are prioritizing sleep. 
  • Sleep & Creativity — Creativity is ultimately being able to link multiple different past ideas together to create something new. Sleep is the perfect place for these connections to take place — it provides a nighttime theater for your brain to test out and build connections between vast stores of previous information and memories. REM sleep (the dream state) is mostly responsible for creativity. 
  • Chapter Takeaway — You need to get at least 8 hours of sleep to achieve peak mental and physical performance. Performance drops off considerably with less than 8 hours. Every night, sleep transfers short-term memories from the hippocampus to the neocortex, which frees up the hippocampus for new memories and learning.

Ch. 7: Too Extreme for the Guiness Book of World Records

  • Attention & Concentration — One brain function that buckles with even a small dose of sleep deprivation is concentration. Sleep scientists have tested and proven this numerous times. In one study, test subjects who were kept up all night for a single night experienced an over 400% increase in lapse of concentration compared to a group that were allowed to sleep for 8 hours. What’s wild is that the group that received 7 hours of sleep per night for 10 straight nights exhibited lapses in concentration equal to someone who stayed up 24 hours straight. For many busy people, 6 or 7 hours of sleep is the norm every night, so this finding is alarming. 
  • Sleep Deprivation: A Whole New World — Several sleep studies have proved that people who are experiencing sleep deprivation don’t even really realize it. Individuals with chronic sleep restriction over months or years actually get used to their impaired performance, lower alertness, and reduced energy levels. This low-level exhaustion becomes their accepted norm. Caffeine plays a role in this — many people caffeinate themselves around the clock and therefore don’t feel the full effects of sleep deprivation.
    • Quote (P. 137): “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.”
      • Takeaway — Many people are in a constant state of sleep deprivation and don’t know it. They come to accept poor performance and low energy levels and fail to understand the critical role sleep plays in their constant state of exhaustion. 
  • Use It or Lose It — The brain is incapable of recovering lost sleep, even when you try to “sleep it off” on the weekend following a big trip, for example. This is one of the big reasons it’s important to give yourself an 8-hour sleep opportunity every night. 
  • Drowsiness at the Wheel — Drowsiness at the wheel is responsible for many, many deaths every year. In one study, sleep scientists proved that people who are awake for 19 straight hours are as cognitively impaired as those who are legally drunk. At 15 hours of being awake, your cognitive nosedive begins. This means you will begin to experience cognitive decline at 10 p.m. after getting up to start your day at 7 a.m. By 2 a.m., you will be as cognitively impaired as a person who is considered legally drunk. This means that driving after being awake for 15-16 straight hours significantly increases your chances of getting in a car crash. Over 1.2 million accidents are caused by sleepiness every year in the U.S.
    • Quote (P. 138): “Operating on less than 5 hours of sleep, your risk of a car crash increases threefold. Get behind the wheel of a car when having slept just 4 hours or less the night before and you are 11.5 times more likely to be involved in a car accident.”
    • Quote (P. 140): “You may find it surprising to learn that vehicle accidents caused by drowsy driving exceed those caused by alcohol and drugs combined. Drowsy driving alone is worse than driving drunk.”
  • Drowsiness & Alcohol — Drowsiness and alcohol have a multiplicative relationship, meaning they magnify each other, like two drugs whose effects are harmful by themselves but produce dire consequences when experienced together. Driving while drowsy and drunk is extremely, extremely dangerous to yourself and others. 
  • Power Naps — It’s great to take naps. But naps alone aren’t enough. You need 8 hours of sleep per night to give yourself the best chance of performing well and staying healthy, mentally and physically. If you want to throw a nap in on top of that 8 hours, that’s even better. But naps and caffeine alone are no substitute for the learning, memory, emotional, complex reasoning, and decision-making benefits that come with deep, extended overnight sleep. 
  • Emotional Sleep — In addition to the many other benefits already discussed, sleep is critical to your emotional health. When you are sleep deprived, you have a harder time managing your emotions and stress. What happens is this: When you sleep well, the amygdala — the part of your brain that triggers emotions like fear and anger and is responsible for your fight or flight response — is linked nicely with your prefrontal cortex, which manages logical thought and decision-making. When you don’t sleep well, that connection is lost, resulting in an emotional experience that is wide-ranging. You experience a variety of emotional swings when you’re sleep deprived.
    • Quote (P. 146): “Analysis of the brain scans revealed the largest effects I have measured in my research to date.  A structure located in the left and right sides of the brain, called the amygdala — a key hot spot for triggering strong emotions such as anger and rage, and linked to the fight-or-flight response — showed well over a 60% amplification in emotional reactivity in the participants who were sleep-deprived. In contrast. the brain scans of those individuals who were given a full night’s sleep evinced a controlled, modest degree of reactivity in the amygdala, despite viewing the very same images. 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.”
    • Quote (P. 148): “Insufficient sleep does not, therefore, 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.”
  • Sleep & Mental Health — There is no major psychiatric condition in which the person is sleeping normally. This is true of depression, anxiety, post-traumatic stress disorder (PTSD), schizophrenia, and bipolar disorder. This does not necessarily mean that sleep causes these mental health disorders, but there is a link. When you are sleep deprived, you just simply don’t operate as well or feel as good in any capacity. Poor sleep is a contributor to mental health issues.
    • Quote (P. 150): “I am not suggesting that all psychiatric conditions are caused by absent sleep. However, I am suggesting that sleep disruption remains a neglected factor contributing to the instigation and/or maintenance of numerous psychiatric illnesses, and has powerful diagnostic and therapeutic potential that we are yet to fully understand or make use of.”
    • Quote (P. 151): “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.”
  • Sleep & Alzheimer’s Disease: Part 1 — Although we still don’t know much about Alzheimer’s disease and poor sleep is not the only thing responsible for cognitive decline and other related neurodegenerative diseases, poor sleep over a lifetime could contribute to Alzheimer’s. Over 60% of patients with Alzheimer’s disease have at least one sleep disorder, and we naturally lose deep NREM sleep as we age. Deep NREM sleep plays a big role in memory. Some studies have shown that Alzheimer’s patients suffer significant sleep disruption well before they are diagnosed with the disease, signaling a possible link between the two. 
  • Sleep & Alzheimer’s Disease: Part 2 — 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. Amyloid plaques are poisonous to neurons, killing the surrounding brain cells. What is strange, however, is that amyloid plaques only affect some parts of the brain and not others. There is some evidence that amyloid buildup that occurs in the middle regions of the frontal lobe — a location critical for producing NREM sleep — is particularly lethal to our ability to sleep well. And when we don’t sleep well, more beta-amyloid builds in the brain. It’s a nasty cycle.
    • Quote (P. 161): “Inadequate sleep and the pathology of Alzheimer’s disease interact in a vicious cycle. Without sufficient sleep, amyloid plaques build up in the brain, especially in deep-sleep-generating regions, attacking and degrading them. The loss of deep NREM sleep caused by this assault therefore lessens the ability to remove amyloid from the brain at night, resulting in greater amyloid deposition. More amyloid, less deep sleep, less deep sleep, more amyloid, and so on and so forth. From this cascade comes a prediction: getting too little sleep across the adult life span will significantly raise your risk of developing Azheimer’s disease.”
  • Sleep: A Power Cleanse for the Brain — Sleep acts as a power cleanse for the brain. As we sleep, the glymphatic system in the brain releases cerebrospinal fluid that literally bathes the brain and cleanses it. This deep power cleanse clears debris and bad chemicals from the brain and allows us to wake up the next morning feeling refreshed, clear, and efficient. One of the bad actors that this power cleanse clears from the brain is beta-amyloid, the poisonous protein associated with Alzheimer’s. 
  • Chapter Takeaway — After 10 straight days of 7 hours of sleep, rather than 8, you will be as cognitively dysfunctional as someone who has been up for 24 hours straight. Get 8 hours of sleep! It is critical to performance and concentration. Drowsiness at the wheel is extremely dangerous. A lifetime of poor sleep may contribute to buildup of amyloid protein in your brain, and, as a result, Alzheimer’s. 

Ch. 8: Cancer, Heart Attacks, and a Shorter Life

  • Shorter Sleep = Shorter Life — Every major system, tissue, and organ in your body suffers when you are sleep deprived. There are no benefits that come with poor sleep. Every part of your body and mind feels better and performs better when you sleep well. Terrible health consequences come with consistently poor sleep. Sleep is critical to enjoying a long and healthy life.
    • Quote (P. 164): “Widening the lens of focus, there are more than twenty large-scale epidemiological studies that have tracked millions of people over many decades, all of which report the same clear relationship: the shorter your sleep, the shorter your life. The leading causes of disease and death in developed nations — diseases that are crippling healthcare systems such as heart disease, obesity, dementia, diabetes, and cancer — all have recognized causal links to a lack of sleep.”
  • Unhealthy Sleep, Unhealthy Heart — Many studies have revealed the dangers of poor sleep on the heart. One showed that shorter sleep was associated with a 45% increased risk of developing and/or dying from coronary heart disease within seven to twenty-five years from the start of the study. As we get older and our body naturally begins to break down anyway, the impact of poor sleep on the cardiovascular system escalates.
    • Quote (P. 165): “Adults 45 years or older who sleep fewer than 6 hours a night are 200% more likely to have a heart attack or stroke during their lifetime, as compared with those sleeping 7-8 hours a night. 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.”
  • Sleep & Blood Pressure — Blood pressure is one of the big ways sleep impacts the heart. Just a small amount of sleep deprivation can pump up pressure in the veins of your whole body, stretching and distressing the vessel walls. A small amount of sleep deprivation also speeds up your heart rate and significantly elevates systolic blood pressure. Basically, poor sleep leads to high blood pressure and elevated heart rate, which together contribute to the narrowing of your coronary arteries and vessel walls where blood travels to the heart. As these arteries and vessels narrow, blood has a harder time reaching the heart, and you could end up having a cardiac event of some sort.
    • Quote (P. 166): “One cause of a coronary artery blockage is atherosclerosis, or the furring up of those heart corridors with hardened plaques that contain calcium deposits. Researchers at the University of Chicago studied almost 500 healthy midlife adults, none of whom had any existing heart disease or signs of atherosclerosis. They tracked the health of the coronary arteries of these participants for a number of years, all the while assessing their sleep. If you were one of the individuals who were obtaining just 5-6 hours each night or less, you were 200-300% more likely to suffer calcification of your coronary arteries over the next 5 years, relative to those individuals sleeping 7-8 hours. The deficient sleep of those individuals was associated with a closing off of the critical passageways that should otherwise be wide open and feeding the heart with blood, starving it and significantly increasing the risk of a coronary heart attack.”
  • Sleep & the Sympathetic Nervous System — Sleep does a lot of damage to the heart via the sympathetic nervous system, which is responsible for cortisol release and our fight-or-flight mode. It also regulates heart rate and blood pressure. When you don’t sleep well, the sympathetic nervous system runs rampant and is overactive. The body essentially gets “stuck” in a fight-or-flight state. This can last years of you aren’t sleeping well consistently. When your sympathetic nervous system is overactive, blood pressure and heart rate remain elevated, and excess cortisol — a stress hormone — is released in the blood. Cortisol constricts your arteries and blood vessels even further, contributing to even more problems.
    • Quote (P. 167): “With few exceptions over the past half century, every experiment that has investigated the impact of deficient sleep on the human body has observed an overactive sympathetic nervous system.”
  • Interesting Fact — Hospital records around the world show a spike in the number of heart attacks following a Daylight Savings event where we turn our clocks forward by one hour and lose sleep for that one night. The reverse happens when Daylight Savings has us turn our clocks back so we gain an hour of sleep — there are comparably fewer heart attacks on that day. 
  • Sleep, Insulin Resistance, and Type 2 Diabetes — Poor sleep leads to insulin resistance, which prevents your body from efficiently clearing excess glucose (sugar) in your bloodstream. Normally, when you eat and glucose enters the bloodstream, your body will attempt to clear anything that exceeds its standard balance levels by releasing insulin into the blood from the pancreas. Instructed by insulin, the cells of your body will open special channels on their surface that operate like roadside drains during a downpour. They have no problem clearing the excess glucose in your blood. If the cells of your body stop responding to insulin, however, they cannot efficiently absorb glucose from the blood. This is insulin resistance. Similar to roadside drains that become blocked or closed shut, the rising swell of blood sugar cannot be brought back down to safe levels. At this point, the body has transitioned into a hyperglycemic state. Should this condition persist, and the cells of your body remain intolerant to dealing with the high levels of glucose, you will transition into a pre-diabetic state and, ultimately, develop full-blown Type 2 diabetes.
    • Quote (P. 170): “Early warning signs of a link between sleep loss and abnormal blood sugar emerged in a series of large epidemiological studies spanning several continents. Independent of one another, the research groups found far higher rates of Type 2 diabetes among individuals that reported sleeping less than 6 hours a night routinely. The association remained significant even when adjusting for other contributing factors, such as body weight, alcohol, smoking, age, gender, race, and caffeine use.”
    • Quote (P. 170): “Does the state of diabetes impair your sleep, or does short sleep impair your body’s ability to regulate blood sugar, thereby causing diabetes? To answer this question, scientists had to conduct carefully controlled experiments with healthy adults who had no existing signs of diabetes or issues with blood sugar. In the first of these studies, participants were limited to sleeping 4 hours a night for just 6 nights. By the end of that week, these (formerly healthy) participants were 40% less effective at absorbing a standard dose of glucose compared to when they were fully rested.”
  • Sleep’s Impact On Weight: Leptin & Ghrelin — When you sleep poorly (around 4-5 hours), you are more likely to overeat and gain weight. This is because poor sleep decreases levels of the hormone leptin — which signals a sense of feeling full — and increases levels a hormone called ghrelin, which triggers a feeling of hunger. It’s a double whammy. Sleeping poorly also causes you to instinctively reach for higher-calorie foods. You just naturally crave them when you’re sleep deprived. This impulsive behavior is associated with a recent discovery that sleep loss increases levels of endocannabinoids, which are chemicals produced by the body that are very similar to cannabis. Like marijuana, these chemicals stimulate your appetite and lead you to snack.
    • Quote (P. 173): “By muting the chemical message that says ‘stop eating’ (leptin), yet increasing the hormonal voice that shouts ‘please, keep eating’ (ghrelin), your appetite remains unsatisfied when your sleep is anything less than plentiful, even after a kingly meal.”
    • Quote (P. 175): “Looking across the different studies, Van Cauter noticed that cravings for sweets (e.g., cookies, chocolate, and ice cream), heavy-hitting carbohydrate-rich foods (e.g. bread and pasta), and salty snacks (e.g. potato chips and pretzels) all Increased by 30 to 40% when sleep was reduced by several hours each night.”
  • Sleep & Body Composition — When you sleep poorly, your body tends to want to retain more fat. This has consequences for people who are sleeping poorly on a diet because the body will tend to burn more muscle than fat when in a calorie deficit. Poor sleep also makes you feel lethargic, which impacts how much you exercise. You’re more willing to exercise and burn calories when you’re feeling refreshed and energetic.
    • Quote (P. 178): “When you are not getting enough sleep, the body becomes especially stingy about giving up fat. Instead, muscle mass is depleted while fat is retained.”
    • Quote (P. 178): “The upshot of all this work can be summarized as follows: short sleep 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.”
  • Sleep & Low Testosterone — Poor sleep leads to low levels of the hormone testosterone. Low testosterone has a direct impact on a man’s sperm count, bone density, strength, ability to add muscle, and energy.
    • Quote (P. 179): “Sample the hormone levels circulating in the blood of these tired participants and you will find a marked drop in testosterone relative to their own baseline levels of testosterone when fully rested. The size of the hormonal blunting effect is so large that it effectively ‘ages’ a man by 10-15 years in terms of testosterone virility.”
    • Quote (P. 179): “With a genuine lack of malice, I proceed to inform them that men who report sleeping too little — or having poor-quality sleep — have a 29% lower sperm count than those obtaining a full and restful night of sleep, and the sperm themselves have more deformities.”
    • Quote (P. 179): “Add to this the fact that testosterone maintains bone density, and plays a causal role in building muscle mass and therefore strength, and you can begin to get a sense of why a full night of sleep — and the natural hormonal replacement therapy it provides — is so essential to this aspect of health and an active life for men of all ages.”
  • Sleep & The Immune System — Sleep fights against infection by aiding your immune system in the war effort against bad actors in your body. When you sleep well, your immune system is boosted. When you sleep poorly, you’re more vulnerable to infections and other bad things. Many clinical studies have proved this — you’re simply less likely to catch a flu, or something worse, when you are sleeping well. Sleep is critical to your immune response, which is why, when you do fall ill, you naturally want to sleep more. 
  • Sleep & Cancer — Because sleep is vital to your immune system’s ability to locate and kill bad cells and pathogens, poor sleep can make you vulnerable to cancer. One study found that sleeping 6 hours or less was associated with a 40% increased risk of developing cancer compared to those sleeping 7 hours or more. The World Health Organization has even classified nighttime shift work as a “possible carcinogen” because of its tendency to cause poor sleep. What follows are a few of the ways poor sleep impacts your immune system and leaves you vulnerable to cancer:
    • T Cells — When you sleep poorly, your body doesn’t produce as many killer T Cells, which are your immune system’s elite assassins that go out and terminate bad cells (e.g. cancer cells). Natural killer cells will effectively punch a hole in the outer surface of these cancerous cells and inject a protein that can destroy them. One study found that a single night of 4 hours of sleep swept away 70% of the natural killer T Cells in the immune system compared to people who slept 8 hours.
    • Inflammation & The Sympathetic Nervous System — As discussed in a previous chapter, sleeping poorly leads to an overactive sympathetic nervous system. An overactive sympathetic nervous system causes unnecessary and sustained inflammation in the body, something cancer cells love for many reasons. In short, inflammation helps cancer cells grow and spread around the body. 
    • Quote (P. 186): “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.”
  • Chapter Takeaway — Sleep deprivation has disastrous effects on your cardiovascular, metabolic, and immune system health. Poor sleep has been strongly linked to a myriad of health issues involving these systems, including heart attack, stroke, diabetes, cancer, and much more. There is not a single component of your mind or body that isn’t negatively impacted by poor sleep.

Ch. 9: Routinely Psychotic

  • REM Sleep: Brain Activity — Several areas of the brain “light up” on the MRI scanner when a person is engaged in REM sleep. These areas of the brain are especially active during REM sleep and contribute significantly to the content and structure of your dreams. These areas include:
    • Visuospatial Regions — The visuospatial regions are located at the back of the brain and enable complex visual perceptions. This is why dreams are so visual when you’re experiencing them. 
    • The Motor Cortex — The motor cortex manages movement. This is why many of your dreams involve movement (e,g. running, fighting, etc.)
    • The Hippocampus — The hippocampus is the area of the brain where short-term memories and learning are stored before being transferred to the neocortex during a night of sleep. 
    • The Amygdala — The amygdala is one of the deep emotional centers of the brain. This is why dreams typically contain a lot of emotion (e.g. fear, sadness, happiness, etc.). Some people even wake up from a dream in tears. In fact, the emotional regions of your brain are up to 30% more active during REM sleep than they are when you’re awake. Put simply, you’re typically more emotional when you dream than you are when you’re awake. 
  • REM Sleep: Logic Shuts Down — Contrary to the “hot spots” of the brain that light up during REM sleep outlined above, there are also areas that go icy cold. The most significant is the prefrontal cortex, also known as the CEO of the brain responsible for logical thinking and rational decision-making. REM sleep is therefore a state featuring strong activation in visual, motor, emotional, and autobiographical memory regions of the brain, yet a relative deactivation in regions that control rational thought.
  • REM Sleep: Predicting Dreams — Sleep scientists have arrived at a point where they can fairly accurately predict the nature and content of a person’s dream before they wake up just by analyzing a brain scan while they’re asleep. Through repeated testing, scientists have matched certain visuals (e.g. a car, a knife, a phone) with specific patterns of brain activity. As a result, they can tell if any of these pre-determined visuals are appearing in a person’s dream just by looking at their live brain scan and the brainwave activity being exhibited. 
  • Chapter Takeaway — Visual, motor, emotional, and autobiographical memory regions of the brain “light up” and are most active during REM sleep, which is where we do most of our dreaming. This is why most of our dreams tend to involve these features. The prefrontal cortex, interestingly, is suppressed during REM sleep — it turns icy blue on brain scans. 

Ch. 10: Dreaming as Overnight Therapy

  • REM Sleep: The Two Big Benefits — There are two big benefits that come when you drift into REM sleep and dream. The first involves your mental and emotional health. REM sleep has been shown to help you remove the emotion from a memory. The other involves creativity; REM sleep and dreaming helps your brain create new ideas. 
  • REM Sleep: Overnight Therapy — The first big benefit of REM sleep and dreaming is that it has a way of removing emotion from your memories. In other words, it helps you take the painful sting out of difficult, even traumatic, emotional episodes you have experienced during the day. This is why, when you think back on distant memories that were filled with emotion at the time, you don’t feel that same strong emotion that you felt in the moment. It’s also why you wake up without any feelings of fear or trepidation the morning after watching a scary movie or a Dateline episode and experiencing those emotions the night before. Again, this is why you wake up feeling a lot better after being completely triggered, frustrated, mad, fearful, etc. about something the day before. Sleep, particularly REM sleep, has a way of scrubbing your emotions from the day so you wake up the next morning with a reset.
    • Silencing Norepinephrine — The way REM sleep takes the emotions of your memories is by silencing a key stress chemical called norepinephrine, which is basically adrenaline in the brain. Norepinephrine is to the brain what adrenaline is to the body. Adrenaline’s real name is actually epinephrine. Norepinephrine is completely shut off in the brain when you enter the dream state, which in turn silences the anxiety that often comes with it.  
  • REM Sleep & PTSD — One of the reasons PTSD is a lingering issue is that the brain hasn’t disassociated emotion from the horrifying memories people like war veterans have. Every time a person with PTSD has a flashback, they experience the strong emotion they felt in the moment. The reason for this is that norepinephrine levels are very high in the brain, which blocks PTSD patients from entering the deep REM dream state. As a result, their brain can’t strip the emotion from the trauma memory. Progress has been made with a drug called prazosin, which has been shown to lower levels of norepinephrine in the brain. Many PTSD patients have reported good results with the drug, and it has been approved by the Veteran Affairs office and the US Food and Drug Administration. 
  • Chapter Takeaway — Sleep, particularly deep REM sleep, has a way of detoxing your memories, stripping away strong emotion that you felt during the day. This is why you often wake up feeling much better after experiencing strong fear, anger, frustration, etc. the day before. It’s also why distant memories no longer have the strong emotional impact they had in the moment. In this way, sleep acts as overnight therapy. 

Ch. 11: Dream Creativity and Dream Control

  • REM Sleep: Creativity & Problem Solving — The second big benefit of REM sleep is its ability to spark creativity and problem solving. REM sleep acts as a creative incubator, allowing you to fuse and blend recent and past memories together to create new ideas and solve problems. Clinical studies have demonstrated these benefits clearly.
    • Quote (P. 231): “Like an insightful interviewer, dreaming takes the approach of interrogating our recent autobiographical experience and skillfully positioning it within the context of past experiences and accomplishments, building a rich tapestry of meaning. ‘How can I understand and connect that which I have recently learned with that I already know, and in doing so, discover insightful new links and revelations?’ Moreover, ‘What have I done in the past that might be useful in potentially solving this newly experienced problem in the future?’ Different from solidifying memories, which we now realize to be the job of NREM sleep, REM sleep, and the act of dreaming, takes that which we have learned in one experience setting and seeks to apply it to others stored in memory.”
  • Sleep Inertia — That groggy, lethargic, “out of it” feeling you have after first awakening, especially from a deep sleep, is the result of your brain trying to switch from a NREM/REM sleep state to a wake state. The shift between these two states is pretty dramatic as the brain tries to alternate neurochemical chemicals. As a result, we linger in sleep mode for a few minutes while the brain toggles into wake mode.
    • Quote (P. 223): “The dramatic alterations in brain activity during NREM and REM sleep, and their tidal shifts in neurochemical concentrations, do not reverse instantaneously when you awaken. Instead, the neural and chemical properties of that particular sleep stage will linger, creating the inertia period that separates true wakefulness from sleep, and last some minutes. Upon enforced awakening, the brain’s neurophysiology starts out far more sleep-like than wake-like and, with each passing minute, the concentration of the prior sleep stage from which an individual has been woken will gradually fade from the brain as true wakefulness rises to the surface.”
  • Lucid Dreams — Hard to believe, but there is a small segment of the population who have the ability to become consciously aware of when they’re dreaming and then control the content of their dreams. This process is called lucid dreaming, and sleep scientists have demonstrated that it’s a real thing. Lucid dreamers can literally know when they’re dreaming and manipulate what goes on in their dreams. Just like everyone else, their body is paralyzed, but they are able to control what goes on in their dream. 
  • Chapter Takeaway — While deep NREM sleep is responsible for transferring and solidifying memories, REM sleep and dreaming allow your brain to fuse and blend together memories that are recent and those that are from your distant past to create new ideas and solve complex problems. Many people have had “ah ha!” moments right after waking up from a deep sleep. 

Ch. 12: Things That Go Bump in the Night

  • Somnambulism — Somnambulism refers to sleep disorders that involve some kind of movement. Sleepwalking, sleep talking, sleep eating, sleep texting, and sleep sex are examples. All of these events happen during NREM sleep rather than REM sleep. Sleep scientists believe this disorder is triggered by an unexpected spike in nervous system activity during sleep. Essentially the person gets “stuck” in a mode between wakefulness and sleep. In this mode, the brain can perform basic actions. Scientists have observed this disorder by watching brain activity of patients who are moving around during sleep in their labs. Although the brain activity they are seeing clearly shows that the person is in NREM sleep, the cameras in the room show the person moving around as if they are awake. 
  • Insomnia: What Is It? — Insomnia is the most common sleep disorder in the world, affecting 1 in 9 people you see every day, or 40 million Americans. It occurs when you give yourself plenty of time to sleep but are unable to generate sleep. It is NOT sleep deprivation, which occurs when you can generate sleep but simply don’t give yourself enough time in bed. There are two types of insomnia: (1) sleep onset insomnia, which is difficulty falling asleep; and (2) sleep maintenance insomnia, which is difficulty staying asleep. You can have one or both. Hispanics and African Americans have insomnia more than Caucasians, which may help explain why those two demographics also suffer more heart attacks and strokes, and have higher rates of diabetes, as sleep is linked to all of these issues. To be diagnosed with insomnia, you have to meet the following criteria:
    • Dissatisfaction With Sleep — Dissatisfaction with sleep quantity or quality (e.g. difficulty falling asleep, staying sleep, early-morning awakening)
    • Daytime Distress — Suffering significant distress or daytime impairment
    • Consistency — Has insomnia at least three nights each week for more than three months. This is important because everyone suffers a night or two of bad sleep when things get tough in life. To have true insomnia, you have to be suffering from poor sleep very regularly. 
    • No Medical Conflicts — Does not have any coexisting mental disorders or medical conditions that could otherwise cause what appears to be insomnia
    • Quote (P. 242): “What this really means in terms of boots-on-the-ground patient descriptions is the following chronic situation: difficulty falling asleep, waking up in the middle of the night, waking up too early in the morning, difficulty falling back to sleep after waking up, and feeling unrefreshed throughout the waking day. If any of the characteristics of insomnia fed familiar to you, and have been present for several months, I suggest you consider seeking out a sleep medicine doctor.”
    • Quote (P. 243): “Without belaboring the point, insomnia is one of the most pressing and prevalent medical issues facing modern society, yet few speak of it this way, recognize the burden, or feel there is a need to act.”
  • Insomnia: Causes — Sleep scientists estimate insomnia has a 25-45% transmission rate from parents to child, meaning it is partly genetic. Psychological, physical, medical, and environmental triggers are also responsible for insomnia. It’s important to note that external factors — like too much caffeine, bright light, and alcohol — are not considered part of what causes insomnia because they can be controlled. 
    • Quote (P. 243): “External factors that cause poor sleep, such as too much bright light at night, the wrong ambient room temperature, caffeine, tobacco, and alcohol consumption can masquerade as 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. Other factors, however, come from within a person, and are innate biological causes of insomnia.”
  • Insomnia: Psychological Triggers — The two most common triggers of chronic insomnia are psychological: (1) emotional concerns, or worry; and (2) emotional distress, or anxiety. The sympathetic system is the main culprit when it comes to these triggers. Having an overactive sympathetic nervous system keeps you in a fight-or-flight state and prevents your mind and body from relaxing in bed. As a result, your heart rate, blood pressure, and core body temperature are high, and the stress-hormone cortisol is released in your blood. All of it makes it very tough to sleep. To summarize, below are the ways an overactive sympathetic nervous system causes sleep difficulty and insomnia:
    • Core Body Temperature — First, the raised metabolic rate triggered by fight-or-flight nervous system activity, which is common in insomnia patients, results in a higher core body temperature. We need core body temperature to FALL/COOL to induce good sleep. This becomes more difficult in insomnia patients suffering a raised metabolic rate and higher operating internal temperature, including in the brain.
    • Cortisol, Adrenaline, and Norepinephrine — Second are higher levels of the alertness-promoting hormone cortisol, and sister neurochemicals adrenaline and norepinephrine. All three of these chemicals raise heart rate. Normally, our cardiovascular system calms down as we make the transition into light and then deep sleep. Elevated cardiac activity makes that transition more difficult. All three of these chemicals increase metabolic rate, additionally increasing core body temperature, which further compounds the first problem outlined above.
    • High Brain Activity — Researchers have placed healthy sleepers and insomnia patients in a brain scanner and measured the changing patterns of brain activity as both groups try to fall asleep. In the good sleepers, the parts of the brain related to inciting emotions (the amygdala) and those linked to memory retrospection (the hippocampus) quickly ramped down in their levels of activity as they transitioned toward sleep, as did basic alertness regions in the brain stem. This was not the case for the insomnia patients. Their emotion-generating regions and memory-recollection centers all remained active. Simply put, insomnia patients could not disengage from a pattern of alerting, worrisome brain activity.
    • Poor Quality of Sleep — Even if you are able to drift into a sleep with an overactive sympathetic nervous system, the quality of sleep an insomnia patient gets is often not great. The person wakes up periodically throughout the night without being aware of it, which means they don’t feel very refreshed in the morning and throughout the day. Their brainwave activity during sleep is shallower. 
    • Quote (P. 244): “Since psychological distress is a principal instigator of insomnia. researchers have focused on examining the biological causes that underlie emotional turmoil. One common culprit has become clear: an overactive sympathetic nervous system, which, as we have discussed in previous chapters, is the body’s aggravating fight-or-flight mechanism. 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. As we have already touched upon in earlier chapters, chronic activation of the fight-or-flight nervous system causes myriad health problems, one of which is now recognized to be insomnia.”
  • Insomnia: Don’t Do Sleeping Pills — As outlined above, the main issue with insomnia is psychological. Sleeping pills do not address the core issues of insomnia and should be avoided. There are non-pharmaceutical therapies out there that have demonstrated great promise that are a much better option. 
    • Quote (P. 246): “You can now understand how physiologically complex the underlying condition (of insomnia) is. No wonder the blunt instruments of sleeping pills, which simply and primitively sedate your higher brain, or cortex, are no longer recommended as the first-line treatment approach for insomnia by the American Medical Association. Fortunately, a non-pharmacological therapy, which we will discuss in detail in the next chapter, has been developed. It is more powerful in restoring naturalistic sleep in insomnia sufferers, and it elegantly targets each of the physiological components of insomnia described above.”
  • Narcolepsy — Narcolepsy is a sleeping disorder that most commonly occurs when you fall asleep randomly during the day. Daytime sleepiness is the most occurring form of narcolepsy, but there are other types, some of which are very scary and sad. The following symptoms make up the disorder:
    • Excessive Daytime Sleepiness — Involves daytime sleep attacks: overwhelming, utterly irresistible urges to sleep at times when you want to be awake, such as working at your desk, driving, or eating a meal with family or friends. Overall, narcolepsy and these daytime sleepiness episodes are very rare. The amount of sleepiness a narcolepsy patient feels when they fall asleep randomly during the day is equivalent to being up for 3-4 straight nights. 
    • Sleep Paralysis — The frightening loss of ability to talk or move when waking up from sleep. In essence, you become temporarily locked in your body. This occurs after waking up from REM sleep. As we know, REM sleep temporarily paralyzes the body to prevent you from moving around and harming yourself during sleep/dreaming. Sleep paralysis occurs when you wake up and the paralysis mode is still on for a few seconds. This is somewhat common and occurs for people who don’t have narcolepsy. I’ve actually had this happen a few times. 
    • Cataplexy — This one is very strange. It occurs when somebody’s body randomly falls into REM sleep mode while still being conscious. The person’s body will just collapse into REM sleep mode. Worst of all, positive and negative emotions are what trigger this event, meaning it occurs whenever a person experiences something high or low in life. Therefore, the person has to try to remain emotionally neutral at all times. Very sad. 
      • Quote (P. 250): “If you saw a patient collapse under the influence of cataplexy, you would be convinced that they had fallen completely unconscious or into a powerful sleep. This is untrue. Patients are awake and continue to perceive the outside world around them. Instead, what the strong emotion has triggered is the total (or sometimes partial) body paralysis of REM sleep without the sleep of the REM state itself. Cataplexy is therefore an abnormal functioning of the REM-sleep circuitry within the brain, wherein one of its features — muscle atonia — is inappropriately deployed while the individual is awake and behaving, rather than asleep and dreaming.”
  • Mechanics of Sleep — We understand what causes sleep (circadian rhythm and adenosine buildup), but we haven’t touched on the mechanics behind how sleep occurs. To understand how it all works, we have to understand the brain stem and the thalamus. These two control wakefulness: the sensory gate that perceives our world (thalamus) sits on top of the alerting, activating regions of the brain (brains stem) like a scoop of ice cream (thalamus) on a cone (brain stem). As the brain stem powers down at night, it removes its stimulating influence to the sensory gate of the thalamus. With the closing of the sensory gate, we stop perceiving the outside world, and thus we fall asleep. See below for a full explanation of the science behind the process and how a faulty sleep-wake switch is found in narcolepsy patients.
  • 8 Hours Is Right — The ideal amount of sleep every night for the average adult is 8 hours. Anything less is not great and can have bad health consequences if maintained for a long period of time. If you can get more than 8 hours, that’s even better. But 8 is a perfect target to shoot for. Infants and small children will and should sleep much longer as their brains are developing, but 8 hours is what adults should go for. 
  • Chapter Takeaway — There are over 100 known sleep disorders, insomnia being the most common. True insomnia occurs when you give yourself plenty of time to sleep, but simply can’t generate sleep on a consistent basis. Although insomnia is partly genetic, it is primarily caused by an overactive sympathetic nervous system, which causes elevated heart rate, blood pressure, cortisol, core body temperature, and brain activity. 

Ch. 13: iPads, Factory Whistles, and Nightcaps

  • Sleep Difficulty — Many of us are behind tired. We struggle to sleep and, when we do, we struggle to stay asleep. There are a few primary factors that hurt our ability to sleep:
    • Constant Electric Light
    • Temperature
    • Caffeine
    • Alcohol 
  • Interesting Fact — Humans are predominantly visual creatures. 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.
  • The Light Spectrum — The visible light spectrum runs from shorter wavelengths (approximately 380 nanometers) that we perceive as cooler violets and blues, to the longer wavelengths (around 700 nanometers) that we sense as warmer yellows and reds. Sunlight contains a blend of all of these colors, and those in between. 
  • Blue Light Problems — When it comes to circadian rhythm and sleep, the light receptors in our eyes are most sensitive to blue light rays. We should avoid all light before bed so our circadian rhythm isn’t delayed and melatonin can release on time, but it’s particularly important to avoid blue light, which commonly comes from LED lights on our TVs, laptops, iPads, iPhones.
    • Quote (P. 268): “The light receptors in the eye that communicate ‘daytime’ to the suprachiasmatic nucleus are most sensitive to short-wavelength light within the blue spectrum — the exact sweet spot where blue LEDs are most powerful. As a consequence, evening blue LED light has twice the harmful impact on nighttime melatonin suppression than the warm, yellow light from old incandescent bulbs, even when their lux intensities are matched.”
    • Quote (P. 270): “Using LED devices at night impacts our natural sleep rhythms, the quality of our sleep, and how alert we feel during the day.”
  • Why Is Light Bad? — Light, especially blue light, delays our circadian rhythm (by about 2-3 hours) and therefore the release of melatonin in our brain that tells us it’s time to sleep. Light didn’t used to be an issue because we didn’t have easy access to it at night. It used to be pitch black at 5 or 6 p.m. and all we had was fire and lamps. But then Thomas Edison developed a marketable lightbulb in the 1870s that changed everything. Suddenly we had easy access to light at night. Later on, in 1997, LED lights that emit blue light rays were invented (the inventors won a Nobel Prize in 2014). Blue light is the worst kind of light for our circadian rhythm and is present in our TVs, iPads, laptops, iPhones, and more. Now light is a real problem.
    • Quote (P. 267): “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 24-hour clock within the brain (the suprachiasmatic nucleus). 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. Appropriately scheduled tiredness, followed by sleep, would normally occur several hours after dusk across our human collective. Electric light put an end to this natural order of things. It redefined the meaning of midnight for generations thereafter. Artificial evening light, even that of modest strength, or lux, will fool your suprachiasmatic nucleus into believing the sun has not yet set. The brake on melatonin, which should otherwise have been released with the timing of dusk, remains forcefully applied within your brain under duress of electric light.”
    • Quote (P. 268): “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.”
      • Takeaway — Light at night = delayed circadian rhythm = delayed melatonin release = poor sleep
  • How Much Light Is Bad? — Even a hint of dim light — 8 to 10 lux — has been shown to delay the release of nighttime melatonin in humans. A small bedside lamp pumps out twice as much: anywhere from 20 to 80 lux. A subtly lit living room will hum at around 200 lux. Despite being just 1-2% of the strength of daylight, this ambient level of home lighting can suppress melatonin release in the brain by up to 50%.
  • Overcoming Night Light — Bottom line, you want to reduce the amount of light you absorb at night. Putting lowered, dim lights in the rooms where you spend your evening hours is one way to reduce the amount of light you take in at night. Mood lighting is what you want. Another solution is to install blackout curtains or wear an eye mask. You can also set up your devices to gradually de-saturate the LED lights they give off as the day goes on. 
  • Alcohol = Sedative — Alcohol is technically a sedative, which surprises most people because it makes you social and outgoing. It binds to receptors in the brain and prevents neurons from firing their electrical impulses. The reason it makes you loose and willing to do crazy things is that it starts by sedating the prefrontal cortex, which is responsible for logic and decision-making. This part of the brain is huge for controlling impulses and behavior. When this region gets sedated, you are more likely to do wild things. Over time, alcohol begins to sedate other parts of the brain, which is why you eventually feel sluggish and disoriented. 
  • Alcohol Does Not Produce Sleep — By sedating parts of the brain, alcohol makes you feel sluggish and tired, eventually knocking you out pretty effectively. But what you are experiencing is not true sleep; you are simply being knocked unconscious by the sedative effects of alcohol. Sleep scientists know this because your brainwave activity when drunk and “asleep” is not the same as what occurs when you’re truly asleep. Even a little bit of alcohol in the afternoon/evening will significantly hurt your sleep. The best approach is to avoid it entirely. Other ways alcohol hurts sleep include:
    • Fragmented Sleep — Alcohol-infused sleep is fragmented, meaning it is not continuous and restorative because you wake up often throughout the night, even when you don’t realize it. 
    • REM Sleep Disruptor — Alcohol is one of the most powerful known suppressors of REM sleep. When the body metabolizes alcohol it produces by-product chemicals called aldehydes and ketones. The aldehydes in particular will block the brain’s ability to generate REM sleep. People consuming even moderate amounts of alcohol in the afternoon and/ or evening are depriving themselves of dream sleep.
  • Sleep Temperature: The Colder the Better! — Temperature is critical to your sleep. To initiate sleep, your core body temperate has to fall around 2-3 degrees. For this reason, a colder bedroom will always be better at inducing sleep than a warmer one. An ideal temperature is 65 degrees. There are thermal cells located in your brain within the hypothalamus and next to the suprachiasmatic nucleus (our internal 24-hour clock) that activate when your core temperature drops below a certain threshold. Together, your 24-hour clock and thermal cells signal the release of melatonin, which tells your brain and body that it’s time to sleep. Lowering the temperature in the bedroom is one of the first things insomnia patients are asked to do.
    • Quote (P. 275): “Your nocturnal melatonin levels are therefore controlled not only by the loss of daylight at dusk, but also the drop in temperature that coincides with the setting sun. Environmental light and temperature therefore synergistically, though independently, dictate nightly melatonin levels and sculpt the ideal timing of sleep.”
  • Lowering Core Body Temperature — Warm hands and feet help your body’s core cool, which induces sleep. Taking a warm shower also lowers your core body temperature. Splashing your face with water is also effective. This is because most of our body’s thermic release work is performed by three areas in particular: your hands, your feet, and your head. These areas are very efficient radiating devices that, just prior to sleep onset, release body heat in a massive thermal venting session that drops your core body temperature. This is one of the reasons we often instinctively stick our hands and feet out from under the covers — these areas are effective at releasing heat from the body, therefore lowering core body temperature.
    • Quote (P. 276): “It is no evolutionary coincidence that we humans have developed the pre-bed ritual of splashing water on one of the most vascular parts of our bodies — our face, using one of the other highly vascular surfaces — our hands… The act itself does have sleep-inviting powers, however, as that water, warm or cold, helps dissipate heat from the surface of the skin as it evaporates, thereby cooling the inner body core.”
  • Ditch the Bedding — The more bedding you have, the more your excessive body temperature is trapped inside your skin. We used to sleep with very minimal bedding and very few articles of clothing. Today, we have a lot of bedding and a lot of bed clothing. The less of this you have, the easier it will be to keep your core body temperature cool and sleep effectively. 
  • Why Warm Showers Work — Warm showers before bed are very effective at lowering core body temperature. The reason is that warm water on your skin encourages blood to rise to the surface of the skin (this is why you get a flushed-red appearance) and emit heat, which in turn decreases core body temperature. For this same reason, keeping your hands and feet warm is effective at lowering core body temperature.
    • Quote (P. 278): “Selectively warming the feet and hands by just a small amount (1°F or about 0.5°C) caused (in one study) a local swell of blood to these regions, thereby charming heat out of the body’s core, where it had been trapped. The result of all this ingenuity: sleep took hold of the participants in a significantly shorter time, allowing them to fall asleep 20% faster than was usual, even though these were already young, healthy, fast-sleeping individuals.”
    • Quote (P. 279): “A luxury for many is to draw a hot bath in the evening and soak the body before bedtime. We feel it helps us fall asleep more quickly, which it can, but for the opposite reason most people imagine. You do not fall asleep faster because you are toasty and warm to the core. Instead, 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 10-15% more deep NREM sleep in healthy adults.”
  • Alarm Clocks — Anybody who has been suddenly woken up from a deep sleep by an alarm clock knows how much it gets your blood pumping and heart racing. When an alarm clocks wakes you up like this, you experience a big spike in blood pressure and a shock acceleration in heart rate caused by an explosive burst of activity from your flight-or-flight system in the nervous system. If you hit snooze and do the same thing over and over, it can be damaging to your heart. 
  • Maintain a Sleep Schedule — 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. This is one of the most consistent and effective ways of helping people with insomnia get better sleep.
  • Chapter Takeaway — Light at night, temperature, caffeine, and alcohol all play a big role in sleep difficulty. Having a smart gameplan for each of these areas will enhance your chances of falling asleep quickly and sleeping well through the night. 

Ch. 14: Hurting and Helping Your Sleep

  • No Sleeping Pills! — Sleeping pills are horrible for you. They do not provide natural sleep, can damage health, and increase the risk of life-threatening diseases. In fact, there has never been a sleeping medication that induces natural sleep. They may knock you out, but they do not send you into natural, healthy sleep. Worst of all, they are barely even effective.
  • Sleeping Pills & Alcohol — Like alcohol, sleeping pills are sedatives. They 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 sedative drugs. Sleeping pills basically sedate the higher regions of your brain’s prefrontal cortex, just like alcohol does. Adding to this are a number of unwanted side effects, including next-day grogginess, daytime forgetfulness, performing unconscious actions at night, and slowed reaction times during the day that can impact motor skills, such as driving. Taken together, all of these factors can lead to a viscous cycle of dependency.
    • Quote (P. 283): “True even of the newer, shorter-acting sleeping pills on the market, these symptoms instigate a vicious cycle. The waking grogginess can lead people to reach for more cups of coffee or tea to rev themselves up with caffeine throughout the day and evening. That caffeine, in turn, makes it harder for the individual to fall asleep at night, worsening the insomnia. In response, people often take an extra half or whole sleeping pill at night to combat the caffeine, but this only amplifies the next-day grogginess from the drug hangover. Even greater caffeine consumption than occurs, perpetuating the downward spiral.”
  • Rebound Insomnia — Another issue with sleeping pills is the “rebound insomnia” that it leads to. When people stop taking their sleeping pills, they often suffer far worse sleep, sometimes even worse than the poor sleep that led them to seek out sleeping pills to begin with. The reason this happens is because your brain gets accustomed to, and dependent on, the sleeping pills. Like many other prescription drugs, sleeping pills can be very addictive. 
  • Sleeping Pills: Not Effective — Many studies have demonstrated that sleeping pills are barely effective at producing “sleep.” A recent team of leading medical doctors and researchers examined all published studies to date on newer forms of sedative sleeping pills that most people take. Summarizing the findings, the committee stated that sleeping pills only produced “slight improvements in subjective and polysomnographic sleep latency” — that is, the time it takes to fall asleep. The committee concluded the report by stating that the effect of current sleeping medications was rather small and of questionable clinical importance.
  • Sleeping Pills: Higher Mortality Risk — There does appear to be a relationship between sleeping pill use and death. Several sleep scientists have demonstrated that people using sleep medications are more likely to die and develop cancer than those who do not. One of them found that those taking sleeping pills over the 2.5 years of the study were 4.6 times more likely to die than those who didn’t. Even occasional users — those defined as taking 18 pills or less per year — were 3.6 times more likely to die. The leading ways sleeping pill users tend to die include infection, car accidents, and cancer. The same study found that those taking sleeping pills were 30-40% more likely to develop cancer over the 2.5 years of the study than those who were not. 
  • Cognitive Behavioral Therapy for Insomnia (CBT-I) — The most effective way to treat insomnia is with CBT-I, not sleeping pills. CBT-I involves working with a therapist to address things like sleep environment and sleep habits. One of the more paradoxical CBT-I methods is to have insomniacs restrict time spent in bed, perhaps even to just 6 hours of sleep or less to begin with. By staying awake for longer, patients build up a strong sleep pressure (adenosine). Under this heavier weight of sleep pressure, patients fall asleep faster and achieve a more stable, solid form of sleep across the night. In this way, a patient can regain their psychological confidence in being able to self-generate and sustain healthy, rapid, and sound sleep, night after night. The patient then steadily increases time in bed back up to the recommended 8 or 9 hours. Other CBT-I tips include:
    • Reduce Alcohol & Caffeine — Limit how much you consume caffeine and alcohol, especially in the afternoon and evening
    • Regular Wakeup Time — Establish a regular bedtime and wake-up time, even on weekends
      • Quote (P. 293): “All 12 suggestions are superb advice, but if you can only adhere to one of these each and every day, make it: 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.”
    • Use Bed Only for Sleep — Go to bed only when sleepy and avoid sleeping on the couch early/mid-evenings
    • Hit the Restart Button — Never lie awake in bed for a significant time period. Instead, get out of bed and do something quiet and relaxing until the urge to sleep returns. Go sit on the couch for a bit and come back. 
    • No Napping — Avoid daytime napping if you are having difficulty sleeping at night
    • Relax 1 Hour Before Bed — Reduce anxiety-provoking thoughts and worries by learning to mentally decelerate before bed. This means you should get away from activities like reading or work that stimulate your mind. Watch TV. Chill out. 
    • Put the Clock Away — Remove visible clock-faces from view in the bedroom, preventing clock-watching anxiety at night
  • Sleep & Exercise — Exercise helps you sleep and sleep helps you exercise. Several studies have demonstrated that sleep helps you perform much better, mentally and physically. This is one of the reasons athletes are now prioritizing sleep. Across the board, your performance in workouts is much better on a day where you slept well. Avoid exercising three hours before bed; it warms up your core body temperature, which is the opposite of what we want to happen at night.
    • Quote (P. 294): “When sleep was poor the night prior, exercise intensity and duration were far worse the following day. When sleep was sound, levels of physical exertion were powerfully maximal the next day. In other words, sleep may have more of an influence on exercise than exercise has on sleep.”
    • Quote (P. 294): “It is clear that a sedentary life is one that does not help with sound sleep, and all of us should try to engage in some degree of regular exercise to help maintain not only the fitness of our bodies but also the quantity and quality of our sleep. Sleep, in return, will boost your fitness and energy, setting in motion a positive, self-sustaining cycle of improved physical activity (and mental health).”
    • Quote (P. 294): “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. Should this occur too close to bedtime, it can be difficult to drop your core temperature sufficiently to initiate sleep due to the exercise-driven increase in metabolic rate. Best to get your workout in at least 2-3 hours before turning the bedside light out (none LED-powered, I trust).”
  • Chapter Takeaway — Do not take sleeping pills! They don’t induce natural, restorative sleep and they have been shown to increase your risk of death, especially from cancer. On top of that, they’re barely even effective at sending you to “sleep.” The safe and proven methods of CBT-I are the best way to address insomnia and poor sleep. 

Ch. 15: Sleep and Society

  • Sleep: A Global Health Epidemic — Sleep neglect is such a problem that the World Health Organization now officially labels the lack of sleep around the world as a global health epidemic. One out of every two people across the developed world will not get the necessary sleep they need in a week. 
  • Sleep Deprivation: You Can’t Catch Up — 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. You either sleep, or you don’t. You either use it, or you lose it. 
  • Sleep & Work — Poor sleep has a direct impact on your performance at work. Sleep helps you be more creative, intelligent, motivated, innovative, efficient, productive, and effective at your job. It also puts you in a better mood, which helps you with the social side of work (e.g. teamwork and leading). All of this is lost when you sleep poorly. It’s almost like fighting an uphill battle — you enter the work day at a disadvantage.
    • Quote (P. 300): “Under-slept employees are not, therefore, going to drive your business forward with productive innovation.”
    • Quote (P. 300): “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.”
      • Takeaway — Poor sleep makes you slower and less productive at work. As a result, you end up working more hours to get your projects done compared to if you slept well and came to work with energy and focus.  
  • Interesting Fact — The Guinness World Record book in 1980 stopped recognizing attempts to break the world record for sleep deprivation because of how dangerous abstaining from sleep is. Guinness also removed all previous sleep deprivation record holders from the book to discourage anybody from trying to break it.
  • Sleep’s Impact On Mental Health — As discussed earlier in this book, sleep has a huge impact on how you feel mentally and emotionally. You are far more likely to be anxious, stressed, moody, and even experience hallucinations, when you are sleeping poorly. You just feel crappy. It’s also harder to focus and concentrate. 
  • Early School Start Times — Early school start times are having a big negative impact on young people in the U.S. Sleep is critical to brain development, especially in one’s early years of life. But over 80% of public high schools start before 8:15 a.m., robbing kids of the sleep they need to help their brain develop and avoid mental illnesses. As discussed earlier in the book, these same high schoolers have a circadian rhythm that is naturally delayed compared to adults. As a result, teenagers stay up late and have to force themselves to get up early to make it to school. All of this leads to a lack of sleep, especially REM sleep, which takes place later in the sleep cycle.
    • Quote (P. 310): “It is the lack of REM sleep — that critical stage occurring in the final hours of sleep that we strip from our children and teenagers by way of early school start times — that creates the difference between a stable and unstable mental state.”
  • More Sleep, Fewer Crashes — Early school start times have prevented kids from getting the critical sleep they need to help their brain develop and avoid mental health issues. It is also causing more car crashes among teenagers, which makes sense considering sleep deprivation and drowsiness are strongly linked to motor accidents.
    • Quote (P. 313): “When the Mahtomedi School District of Minnesota pushed their school start time from 7:30-8:00 a.m., there was a 60% reduction in traffic accidents in drivers 16-18 years of age. Teton County in Wyoming enacted an even more dramatic change in school start time, shifting from a 7:35 a.m. bell to a far more biologically reasonable one of 8:55 a.m. The result was astonishing — a 70% reduction in traffic accidents in 16-18-year-old drivers.”
  • Adderall — Most people know the name of the common ADHD medications: Adderall and Ritalin. But few know what these drugs actually are. Adderall is amphetamine with certain salts mixed in, and Ritalin is a similar stimulant, called methylphenidate. Amphetamine and methylphenidate are two of the most powerful drugs we know of to prevent sleep and keep the brain of an adult (or a child, in this case) wide awake. Unfortunately, many college students use Adderall to study for stressful tests in college.  
  • ADHD & Sleep — Based on recent surveys and clinical evaluations, it is estimated that more than 50% of all children with an ADHD diagnosis actually have a sleep disorder, yet a small fraction know of their sleep condition. Sleep disorders can cause people to exhibit similar mental and emotional habits that are found in ADHD. When somebody is diagnosed with ADHD, they are usually prescribed amphetamines to focus and stay alert. These make drugs hurt sleep, especially for someone who had a sleep disorder and was misdiagnosed.  
  • Cocaine: How It Works — Cocaine prevents electrical impulse waves from shooting down the length of the nerves in your body, including those that transmit pain. Addicts of the drug know this all too well, as their nose, and often their entire face, will become numb after snorting several lines of the substance, almost like having been injected with too much anesthetic by a dentist.
  • Sleep & The Medical Field — The negative effects of poor sleep are especially prevalent in the medical field, where doctors, nurses, and physicians are often very sleep deprived after working crazy shifts. Residents working a 30-hour straight shift will commit 36% 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 16 hours or less. Moreover, surgeons who have not been allowed at least a 6-hour sleep opportunity the night prior are 170% more likely to inflict a serious surgical error.
    • Quote (P. 320): “lf 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.”
      • Takeaway — Sleep deprived doctors and surgeons are much more likely to commit a serious error when operating on you. The shifts these people work are often crazy and leave little time to sleep. As we’ve learned in this book, sleep has a direct and significant affect on performance. 
  • Chapter Takeaway — Poor sleep is having a direct impact on society. Performance at school, work, and even in hospitals is being negatively affected by sleep deprivation. 

Appendix: 12 Tips for Healthy Sleep