1-Page Summary

Walker states that sleep is universal in animals (even in insects and worms). These deep biological roots suggest that sleep is a vital function and that it isn’t simply a vestigial byproduct of evolution.

(Shortform note: At least one study disputes the claim that sleep is a vital function, showing that a certain type of fly is “virtually sleepless.” The findings of the study thus present a different perspective when it comes to the biological role of sleep.)

Part 1: How Sleep Works

Walker begins by discussing the mechanisms regulating sleep as well as the human sleep cycle.

Sleep Rhythm

He explains that there are two mechanisms that regulate sleep: the circadian rhythm and adenosine.

1. Circadian rhythm—regulated by melatonin (produced by the suprachiasmatic nucleus in the brain), it’s the natural “wake drive,” which responds to light and darkness and thus makes you stay awake during the day and wanes at night.

(Shortform note: In the first edition, Walker had written that “every living creature on the planet with a life span of more than several days” has a circadian rhythm. In his blog, researcher Alexey Guzey says that this is false—brewer’s yeast, which lives for more than 20 days, does not go through this cycle. Walker addresses this point in the second edition by changing the phrasing to “most living creatures on the planet” (emphasis ours). He also clarifies in his blog that there are exceptions to the seemingly universal phenomenon, mentioning mammals that don’t seem to have a circadian rhythm.)

2. Adenosine—a chemical that causes “sleep pressure,” or the increased desire to sleep. It rises consistently throughout the day without sleep. Sleep naturally happens when your adenosine is at its highest and your circadian “wake drive” is at its lowest. In the morning, your wake drive starts up again and your adenosine has been depleted by sleep—you feel awake because you’ve reduced the adenosine-circadian gap.

Walker says that this explains an odd phenomenon: Pulling an all-nighter and getting a second wind in the morning. Your adenosine keeps rising, so when your wake cycle dips at 3AM the gap is larger and you feel tired. But at 8AM, your wake cycle restarts and closes the gap and you feel more awake.

(Shortform note: It’s best to avoid pulling an all-nighter, but if you must, you can minimize the disruption to your sleep routine by keeping yourself awake until your next bedtime. Stay hydrated, and resist the urge to take a long nap—stay active, chew gum, or smell rosemary, peppermint, or coffee to help keep you up.)

What Happens When You Disrupt Your Rhythm

Too much sleep disruption can lead to a sleep deficit, or the difference between the amount of sleep you need and the amount of sleep you get. This comes with unpleasant symptoms such as drowsiness even after sleeping and a lack of concentration.

(Shortform note: Keeping a sleep diary can give you a clearer picture of your sleep habits, making it easier to determine any problems. Fill in your bedtime, wake-up time, length of time it takes to fall asleep, number of times you wake up and for how long, and caffeine and alcohol consumption for at least one week, then review the data to determine underlying causes of sleep disruption.)

The Human Sleep Cycle

Your brain switches between two types of sleep: rapid eye movement (REM) and non-REM (NREM) sleep. Walker explains that each type has different functions:

(Shortform note: Walker indicates five stages of sleep—one stage of REM and four stages of NREM—but other sources such as the American Academy of Sleep Medicine, the Sleep Foundation, and the National Institute of Neurological Disorders and Stroke say there are four stages: NREM 1, the point of crossing over from wakefulness to sleep; NREM 2, when your heart rate slows and eye movements stop; NREM 3, deep sleep; and REM, the dream state.)

How Sleep Changes From Childhood to Adulthood

Part 2: The Importance of Sleep

In this section, Walker covers the benefits of sleep and how sleep deprivation harms you.

The Benefits of Sleep

He says that getting good sleep improves your brain in three ways:

  1. Sleep improves long-term factual recall by securing memories for the long term and clearing out short-term memory to make room for new information. (Shortform note: Sleeping for too long may have an interesting effect on memory, as in the case of a man from North London who was in a coma for three weeks. He woke up with memories of things that didn’t really happen. One possible theory is that his brain was trying to fill that three-week gap with made-up memories based on real memories that he had stored.)
  2. Sleep prunes memories worth forgetting. (Shortform note: A 2019 study on mice found that melanin concentrating hormone (MCH) neurons helped the brain forget unimportant information during REM sleep. This could help researchers better understand—and possibly come up with treatments for—memory-related diseases and disorders.)
  3. Sleep increases “muscle memory” or motor task proficiency. (Shortform note: While Walker writes that it’s connected to NREM sleep, the Division of Sleep Medicine at Harvard School suggests that motor learning is linked to REM sleep.)

How Sleep Deprivation Harms You

Walker goes on to explain three ways that sleep deprivation is harmful to the brain:

1. Sleep deprivation worsens attention and concentration. Performance progressively worsens with greater sleep deficit, which is especially harmful for those who are performing high-risk activities like driving. (Shortform note: In the original text, Walker wrote that there are more vehicular accidents caused by drowsy driving than by alcohol and drugs combined. He has since removed this vague claim from the book and revised it to include statistics, saying it’s hard to objectively quantify the number of accidents due to drowsy driving versus driving under the influence.)

2. Sleep deprivation worsens emotional control. Walker says that when you’re sleep deprived, your amygdala (the part of your brain that controls emotion) can run amok, leading to 60% more emotional reactivity. Sleep disruption is a common symptom of all mood disorders. However, sleep deprivation actually makes one-third of depression patients feel better. (Shortform note: Guzey notes that Walker downplays the benefits of sleep deprivation—studies suggest that it’s beneficial to about 45-50% of patients with depression. Walker clarifies that these findings emerged after the book was written.)

3. Sleep deprivation may contribute to Alzheimer’s. Sleep loss may disrupt memory formation as well as the glymphatic cleanup system, which clears out Alzheimer’s-associated plaques. (Shortform note: A study suggests that sleeping on your side can help decrease the chances of developing Alzheimer’s and other neurological diseases.)

Diseases Linked to Sleep Deprivation

In addition to the damage it causes the brain, sleep deprivation disrupts the normal function of many physiological processes, likely contributing to the following:

A Note on the Studies in Why We Sleep

Many of the population studies cited in Why We Sleep are correlational—for example, their results show that people who sleep less are more likely to have heart disease, after controlling for many other factors. But the causation of these results is unclear—some other factors that predispose people to heart disease (like a high baseline level of stress) could also reduce sleep.

To address this, the experimental studies Walker cites attempt to link lack of sleep to a middle physiological state, which itself is causative for the disease. For instance, a lack of sleep increases blood pressure, which the medical consensus believes is causative for heart disease.

Ideally, the “smoking gun” experiment would be to randomize people into normal-sleep and low-sleep groups for years, then observe the rate of disease. However, this is impractical (it’s hard to run very long studies like this and impossible to double-blind) and likely unethical (if low sleep is already believed to cause severe disease).

Part 3: The Science of Dreams

Most vivid dreaming happens during REM sleep. Walker says that your visual, motor, memory, and emotional areas of the brain are active. Your prefrontal cortex (governing rationality) is muted. Some people are even capable of lucid dreaming, meaning they’re able to voluntarily control their actions within their dream. (Shortform note: One study found that you can increase your chances of having lucid dreams by combining three techniques: reality testing, breaking up your sleep, and mnemonic induction of lucid dreams.)

Benefits of Dreaming and REM Sleep

Walker says there are three ways dreaming and REM sleep are good for you:

  1. REM dreaming blunts emotional pain from memories—the brain seems to reprocess upsetting memories and emotional themes in a way that retains the useful lessons while lessening the visceral emotional pain. (Shortform note: Walker attributes this only to REM sleep, but neuroscientist Rebecca Spencer posits that NREM sleep also plays a role.)
  2. REM sleep increases your understanding of other people’s emotions—sleep-deprived people more often interpret faces as hostile and aggressive. (Shortform note: This works both ways: While sleep-deprived individuals view other people more negatively, other people also view sleep-deprived people as more unpleasant.)
  3. REM sleep creates novel connections and a higher-level comprehension of ideas, and increases your ability to solve creative problems. (Shortform note: In fact, it may be possible to manipulate your brain to solve problems during sleep.)

Part 4: The Current State of Sleep

Walker finishes by covering sleep disorders, sleep disruptors, and ways to get better sleep.

Sleep Disorders

He explains that there are three sleep disorders that people commonly experience:

1. Somnambulism (sleepwalking)—the act of walking and performing other behaviors while asleep. It happens during NREM sleep. (Shortform note: A 2021 study suggests that men who sleepwalk may have a higher risk of developing Parkinson’s disease. The two share a common neural pathway and both involve involuntary movements, confusion, and amnesia.)

2. Insomnia—defined as making enough time for sleeping, but having insufficient sleep quantity or quality, for more than three months. The most common triggers are emotional concerns or distress. (Shortform note: Researchers suggest that physical and emotional stress—from discrimination in the workplace and financial pressure due to unemployment, for example—may be the reason behind the sleep disparity between people of color and white people.)

3. Narcolepsy—a not-awake, not-asleep state marked by three symptoms: sudden bouts of extreme sleepiness, sleep paralysis (waking up in REM sleep during muscle atonia), and cataplexy (sudden loss of muscle control while awake). (Shortform note: It can be hard to diagnose narcolepsy because its symptoms overlap with the symptoms of depression, hypothyroidism, sleep apnea, and epilepsy, among other conditions.)

What Stops You From Getting Good Sleep

Walker names jet lag as an increasingly common sleep disruptor. It affects travelers by disturbing the circadian rhythm. He says it can take you up to 10 days to readjust to a 10-hour time difference. (Shortform note: There are several ways to minimize the effects of jet lag, such as hydrating adequately and exposing yourself to natural light at your destination.)

He says that even those who aren’t traveling face five major influences that have drastically changed how we sleep:

1. Caffeine—blocks adenosine receptors, thus reducing how much you feel the desire to sleep. (Shortform note: If you can’t shake the habit of drinking a hot beverage late in the afternoon or evening, try herbal teas that may help promote sleep and relaxation.)

2. Light—nowadays, artificial light constantly fills our homes and disrupts our circadian rhythm. Blue light is most problematic, suppressing melatonin at twice the levels of warm light. (Shortform note: Blue light may have an even bigger impact on children, as they’re more sensitive to light and have bigger pupils.)

3. Constant temperature—in modern times, thermostats homogenize temperatures, suppressing the biological systems that use temperature changes throughout the day as sleep cues. (Shortform note: If it’s too hot and you have no access to air-conditioning, cool your body temperature by avoiding exercising at night, avoiding anything spicy, and stashing your pillowcases in the fridge.)

4. Alcohol—a sedative that causes what appears to be sleep but is really more like anesthesia. It causes you to wake up throughout the night and prevents you from getting REM sleep. Walker encourages total abstinence from alcohol. (Shortform note: A less puritanical approach comes from The Sleep Foundation, who recommend that you stop drinking alcohol at least four hours before bedtime.)

5. Alarms—cause acute stress responses when you wake up, spiking your cortisol levels, heart rate, and blood pressure. (Shortform note: One study suggests that changing your alarm from a jarring sound to an upbeat song can help combat sleep inertia, that disoriented state you’re in upon waking up.)

How to Get Better Sleep

Walker provides a number of tips on how you can start getting better, less interrupted sleep.

More Tips to Help You Sleep

In The Sleep Revolution: Transforming Your Life, One Night at a Time, Arianna Huffington devotes a chapter to sleep tips, tools, and techniques. While there are many overlaps with While We Sleep (such as limiting blue light, avoiding alcohol, and getting the temperature right), she offers some additional tips that Walker doesn’t mention:

Improving Sleep in Society

Walker argues that sleep deprivation goes far beyond individual sleep practices. He says that our society has structurally locked in sleep deprivation in two ways: First, work schedules disrupt sleep. Companies associate hours worked with productivity and tend to see sleep as an indulgence of the weak. Second, school schedules disrupt sleep: Early start times disrupt children’s circadian rhythms. Walker offers ways to improve sleep quality in society:

(Shortform note: The sleep landscape continues to change with technological advancements that we can use to improve our sleep. In 2021, the FDA approved SleepCogni for medical use. Clinical trials have shown that SleepCogni, a data-supported device, can reduce insomnia in just seven days. In the hospitality industry, where sleep is an essential part of a hotel guest’s stay, a scientist predicts some ways in which the experience of sleep will change, including bed covers and sheets made of high-tech thermal regulation fabrics and pillows that can detect sleep activity.)

Shortform Introduction

You're probably getting less sleep than you should be. Many people are more chronically sleep-deprived than they realize, and the punishments for this are severe—reduced productivity and happiness, and increased risk of a panel of diseases. Why We Sleep: Unlocking the Power of Sleep and Dreams discusses the mechanisms of sleep, its importance and major benefits, and the best ways to get better sleep.

About the Author

Matthew Walker, Ph.D.—self-branded “Sleep Diplomat”—is the director of the Center for Human Sleep Science, which investigates the role of sleep in human health. He’s also a professor of neuroscience and psychology at the University of California, Berkeley and was previously a professor of psychiatry at Harvard Medical School.

He has published over 100 scientific studies, mostly on sleep science, and has appeared on numerous television programs, including 60 Minutes, BBC News, and CBS This Morning.

Beyond TV programs and podcasts, Walker spreads the gospel of sleep through events, forums, and workshops—his 2019 TED Talk was one of the fastest to reach a million views, according to his website. His other pursuits within the field of sleep include serving as scientific counsel to companies like Fitbit, Google, and sleep therapy company Shuni.

In 2020, he won the Carl Sagan Prize for Science Popularization, which is given to researchers who’ve made science more accessible to the general public.

Walker’s official website states that he earned his Ph.D. in neurophysiology from the Medical Research Council (MRC) in London. However, in a blog post critiquing Walker’s book, researcher Alexey Guzey points out that the MRC does not grant Ph.D. degrees. Walker’s Wikipedia page states that he received his Ph.D. from Newcastle University, and that his research was funded by the MRC. It is unclear why there is a discrepancy in information.

Connect with Dr. Matthew Walker:

The Book’s Publication

Why We Sleep: Unlocking the Power of Sleep and Dreams, published in 2017 by Simon & Schuster, is Walker’s first book. It became a New York Times Best Seller and landed at the top of the Sunday Times Bestseller list in the U.K.

The Book’s Context

Historical Context

Walker sees insufficient sleep as a global problem, originally writing that the World Health Organization (WHO) even considers it a health epidemic. He has since corrected this information, saying that it should have been attributed to the Centers for Disease Control (CDC). (It’s worth noting that the CDC currently doesn’t seem to consider insufficient sleep an epidemic. Blogger Guzey speculates that the source of the error might be CDC’s modified stance on sleep loss, from “public health epidemic” to “public health problem,” though this happened two years prior to the book’s publication.) Walker writes that society doesn’t seem to give sleep much importance in part because science hasn’t sufficiently explained why we need it.

Historically, there wasn’t much scientific experimentation in the field of sleep prior to the 20th century, and the “study” of the field was largely centered around dream interpretation. Sleep science began to progress in 1952, when researchers first observed the rapid-eye movement phase of sleep. Walker writes that in the last two decades, there has been an “explosion of discoveries,” a “research renaissance” that reveals how sleep works and just how important it is.

Intellectual Context

While the book is classified under the genre of popular science—an interpretation of science geared toward a general audience—Walker and other researchers have cited it in academic papers. (You can find a list of citations on Google Scholar.)

The Book’s Strengths and Weaknesses

Critical Reception

Positive reviews say that Why We Sleep is a fascinating, engaging read and that Walker is adept at explaining complex scientific concepts to a general audience. However, even those who give the book positive reviews (including Microsoft founder Bill Gates) note that Walker doesn’t always back up his claims with solid evidence.

The most comprehensive criticism comes from researcher Alexey Guzey, whose blog post claims that Why We Sleep is full of errors and contradictions, exaggerates the problem of lack of sleep, and misrepresents research. His blog post goes through Chapter 1, questioning or disputing the information from Walker’s book point by point. Guzey explains that he spent 130 hours fact-checking this one chapter to give readers an idea of the density of errors in the book. He cautions readers against taking everything in the book as fact. Since the publication of his blog post, readers have sent Guzey other errors that they found. (Note: We include these, along with Guzey’s findings, in this guide.)

In a podcast interview where he discusses sleep, Walker responds to critics and says that a critical part of good scholarly conduct is correcting errors, and he addresses some of the errors that he found and that other people have pointed out. In a 2019 blog post, Walker addresses some of the questions that have been raised about his book and mentions that he released a second edition to correct errors in the 2017 edition. While there is no record of a second edition online, the version this guide is based on does contain Walker’s corrections.

Some readers have noted how reading Why We Sleep has made them even more anxious about lack of sleep. Walker addresses this in his blog and has included a caveat in the revised version of the introduction that notes that the book isn’t meant to treat sleep disorders and advises reader discretion.

Commentary on the Book’s Approach

Why We Sleep includes a huge amount of scientific information, but Walker makes it more engaging by presenting it in layman’s terms and using easy-to-grasp analogies. The result is an educational read that is friendlier and more appealing than an academic paper. However, Walker himself notes that should you nod off while reading the book, he wouldn’t take offense and would in fact be delighted.

Our Approach in This Guide

In this guide, we’ve combined some chapters and grouped together connected concepts that may have appeared in separate sections or chapters. We’ve also omitted chapter 1, which serves as an introduction and an overview of the contents of the book. The chapters of this guide discuss the following subjects:

Where applicable, we’ve included the errors and comments listed in Guzey’s blog post and other sources. We’ve also added commentary to expand on ideas in the book, such as counter-arguments or sleep studies that came out after the book was published.

Part 1: How Sleep Works | Chapter 2: Your Daily Sleep Rhythm

(We’ve omitted chapter 1, which is an introduction that serves as an overview of topics explored in later chapters.)

Walker states that sleep is universal in animals, even in insects and worms, despite its apparent drawbacks (vulnerability to predators, loss of time for productivity). When a biological feature is preserved deep in evolutionary history, it is usually a critical function. He argues that this must mean sleep is a critical function, and it’s crucial to understand why it’s important.

(Shortform note: At least one study disputes the claim that sleep is a vital function, showing that a certain type of fly is “virtually sleepless.” The findings of the study thus present a different perspective when it comes to the biological role of sleep.)

How Sleep Rhythm Works

Walker says that sleep is regulated by two mechanisms: the circadian rhythm and adenosine.

Circadian Rhythm

The first mechanism, the circadian rhythm, is regulated by melatonin (produced by the suprachiasmatic nucleus in the brain). He describes this as a natural “wake drive,” making you stay awake during the day and waning during the night.

(Shortform note: In the first edition, Walker had written that “every living creature on the planet with a life span of more than several days” has a circadian rhythm. In his blog, researcher Alexey Guzey says that this is false—brewer’s yeast, which lives for more than 20 days, does not go through this cycle. He writes that some people may dismiss this point as minor, thinking that brewer’s yeast doesn’t count as an animal. However, he still thinks it’s crucial to mention this information because it counters Walker’s assertion that all living creatures have a circadian rhythm. Walker addresses this point in the second edition by changing the phrasing to “most living creatures on the planet” (emphasis ours). He also clarifies in his blog that there are exceptions to the seemingly universal phenomenon, mentioning mammals that don’t seem to have a circadian rhythm.)

Circadian rhythms vary from person to person, dictating when they naturally wake up and have maximum energy. Walker says that this proves that the idea of “morning people” and “night owls” is real.

Can a Night Owl Become a Morning Person?

It’s very hard to change your chronotype (your biological propensity to sleep at particular hours), but given the way work and school schedules are currently structured, you might be looking to override your biology. Here are some tips to help night owls become morning larks:

At Night

In the Morning

Adenosine

The second sleep-regulating mechanism, adenosine is a chemical that causes “sleep pressure,” or the increased desire to sleep. Walker explains that this rises consistently through the day without sleep, making you feel more tired. Sleeping depletes adenosine, which means you wake up with a decreased desire for sleep.

Sleep naturally happens when your adenosine is at its highest and your circadian “wake drive” is at its lowest. In the morning, your wake drive starts up again and your adenosine has been depleted by sleep—you feel awake because you’ve reduced the adenosine-circadian gap.

Walker says that this explains an odd phenomenon: Pulling an all-nighter and getting a second wind in the morning. Your adenosine keeps rising, so when your wake cycle dips at 3AM the gap is larger and you feel tired. But at 8AM, your wake cycle restarts and closes the gap and you feel more awake.

(Shortform note: It’s best to avoid pulling an all-nighter, but if you must, you can minimize the disruption to your sleep routine by keeping yourself awake until your next bedtime. Stay hydrated, and resist the urge to take a long nap—stay active, chew gum, or smell rosemary, peppermint, or coffee to help keep you up.)

Stay On Rhythm to Avoid Sleep Deficit

Too much sleep disruption can lead to a sleep deficit, or the difference between the amount of sleep you need and the amount of sleep you get. How do you know if you have a sleep deficit? Walker suggests a few signs:

(Shortform note: Walker doesn’t mention another common sign of a sleep deficit: mood changes and/or irritability. Irritability may be due, in part, to increases in stress hormones like cortisol and norepinephrine.)

Later in this guide we’ll discuss how to improve your sleeping habits and reduce your sleep deficit.

(Shortform note: Keeping a sleep diary can give you a clearer picture of your sleep habits, making it easier to determine any problems. Include bedtime, wake-up time, length of time it takes to fall asleep, number of times you wake up and for how long, and caffeine and alcohol consumption. Fill it out for at least a week, then review it to see if you have a consistent sleep schedule and are giving yourself enough time to sleep. Review the data, then think about what could be the underlying cause of sleep disruptions, if any.)

Chapters 3-5: The Human Sleep Cycle

Now you understand how your sleep rhythm gives a regular schedule of sleep from night to night. Next, we’ll look into how, within a single night, your brain cycles between different phases of sleep. This is important to understanding the function of sleep for your brain.

In summary, your brain switches between two types of sleep—REM (rapid eye movement) and non-REM (NREM) sleep. The two types of sleep have different functions:

When you sleep, your brain goes through sleep cycles that each last about 90 minutes. Each sleep cycle generally begins with NREM sleep, then ends with REM sleep. As one cycle ends, the next begins. In total for a single night, there’s about an 80/20 split between NREM/REM sleep. You can see this in a sleep graph here:

why_we_sleep_cycles.png

(Shortform note: While Walker indicates five stages of sleep—one stage of REM and four stages of NREM—other sources such as the American Academy of Sleep Medicine, the Sleep Foundation, and the National Institute of Neurological Disorders and Stroke say there are four stages: NREM 1, the point of crossing over from wakefulness to sleep; NREM 2, when your heart rate slows and eye movements stop; NREM 3, deep sleep; and REM, the dream state.)

How Sleep Cycles Change Through the Night

On the graph, notice that not all sleep cycles look the same. As the sleep progresses through the night, a greater fraction of each cycle is spent in REM sleep.

Why would the sleep cycles be unbalanced in this way? Why not just have all sleep cycles look the same, with 80% in NREM and 20% in REM?

Walker hypothesizes that it’s similar to tidying up a house: First, NREM declutters, then REM gets into the finer points of cleaning and organizing.

(Shortform note: One way to think about this is that an animal might be interrupted in the middle of the night. If an animal could only sleep three hours in one night, it’d make sense for the more critical functions to be performed first, with the later functions being a luxury if the animal could sleep a full night. This may suggest that NREM performs a more vital function for survival.)

Also beware of what this means for cutting your sleep short. If you normally sleep eight hours, and one night you have to cut your sleep to six hours, then you’re not just losing 25% of sleep—you might be losing 60-90% of your REM sleep.

Likewise, Walker warns that going to sleep later than usual might cut short your NREM sleep.

(Shortform note: It’s unclear why Walker says that going to sleep at a later time would cut the sleep cycle from the front end—the NREM stage—rather than the tail end, or the REM stage. A report by the Committee on Sleep Medicine and Research states that the average individual’s sleep cycle begins in NREM 1, regardless of when you go to sleep. The exceptions are newborns and those with neurological disorders such as narcolepsy.)

What REM and NREM Look Like

REM and NREM are distinguishable by measuring electrical activity in the brain. REM is characterized by fast (30-40 Hz), frenetic activity that looks the same as being awake. Walker explains that wakeful thought looks frenetic because many different neural signals are occurring at once throughout the brain. It’s similar to a roomful of people singing different songs at once. The summation of all the voices just looks like noise.

REM sleep is where dreams happen. A few odd things happen during REM sleep:

If REM sleep looks like wakefulness, how can an observer distinguish someone who’s dreaming from being awake? Muscle atonia—during REM sleep, your voluntary muscles are completely limp. Your brain does this to prevent you from acting out your dreams, since fighting an enemy might cause you to accidentally punch your surroundings.

REM Sleep and Sleep Paralysis

Researchers believe that sleep paralysis is a mix of both wakefulness and REM sleep—some parts of your brain wake up before others, so you’re in a conscious state but the muscle atonia persists. While the exact cause is unknown, studies suggest that those with sleep-related conditions and problems may be more likely to experience sleep paralysis.

A researcher from Cambridge University suggests doing the following in the event of a sleep paralysis episode:

In contrast, NREM is characterized by slow (3-4 Hz) waves that propagate far from the frontal cortex to the back of the brain. Instead of people singing different songs, the roomful of people sing one song in unison. That billions of neurons can do this together is awe-inspiring.

What’s the function of these slow NREM waves? By being lower frequency, slow NREM waves can propagate further without attenuation, like AM radio waves. Walker suggests this is useful in transferring memories far across the brain, from temporary memory stores toward more permanent storage. It also allows communication across the brain for different sections to collaborate on their shared experience.

(Shortform note: One study suggests that progressing through the NREM stages, going deeper into slow-wave sleep, is connected to the recuperative qualities of sleep. The study found that study subjects who were awoken frequently reported feeling less energetic and generally more irritable than those who got fewer, but continuous, hours of sleep. This effect of interrupted sleep can explain the kind of exhaustion that new parents and doctors on call may feel.)

Walker gives one last detail: Sleep spindles (bursts of activity) occur at the end of slow waves, possibly serving a function to block external sensory input from disrupting sleep. People with more sleep spindles are heavier sleepers.

How Sleep Changes From Childhood to Adulthood

Babies

Fetuses spend almost all of their time in a sleep-like state. They don’t yet have the part of the brain that causes muscle-atonia during sleep, thus explaining why babies in the womb kick and punch.

Walker explains that during the last two weeks of pregnancy, REM sleep in fetuses ramps up to 12 hours a day. This causes rapid synaptogenesis, or the building of neural pathways throughout the brain. In experiments with rat fetuses, disturbing REM sleep stalls construction of the cerebral cortex.

Alcohol impedes REM sleep in fetuses and babies, causing abnormal synaptogenesis. Walker suggests that this abnormal wiring of neurons is connected to autism—once the construction of neural connections is disrupted, a fetal brain may never fully regain normal function.

(Shortform note: Walker originally wrote that “infants of heavy-drinking mothers showed a 200% reduction” in the measure of vibrant electrical activity that indicates REM sleep versus those born of moms who didn’t consume alcohol. In his blog, Guzey points out the numerical error—it’s not possible to show a reduction of more than 100%. In his own blog, Walker acknowledges the error and says that the second edition would reflect the correction.)

Walker writes that because REM sleep is involved in emotional recognition and social interaction, disrupting REM sleep in utero might contribute to the development of autism spectrum disorder.

(Shortform note: A 2020 study found that sleep difficulties in infants who were later diagnosed with autism may be linked to a change in the size of the hippocampus, a key part of the brain related to learning and memory. So far, studies have only found a correlational, not causal, relationship between sleep difficulties and autism.)

Childhood

While they’re born with very irregular sleep patterns, babies eventually show more regular sleep patterns starting at four months, as their suprachiasmatic nucleus—the part of the brain that controls circadian rhythms—develops.

With age, total time sleeping decreases, and the fraction of time spent in REM sleep decreases. Walker explains that now that the synaptogenesis of REM tapers off, NREM plays a larger role in brain refinement, pruning the associations that are most valuable and unique to that child’s life.

He says to consider NREM to actually cause cognitive development in children—changes in deep NREM sleep always come before cognitive milestones, up until the final cognitive milestone in late adolescence, which is the development of rationality in the frontal lobe.

How to Deal With Bedwetting

NREM sleep is vital to a child’s cognitive development, so it’s important to manage sleep disruptions like bedwetting, or nocturnal enuresis. This childhood problem has various causes, including sleep apnea, and can make it difficult for both child and parent to go back to sleep after cleaning up. It’s estimated that 25% of five-year-olds wet the bed at least once a month.

If both you and your child are losing sleep over this, The Sleep Foundation lists some ways to help you address the problem:

Teens

In puberty, teens develop a later biological clock than adults, preferring to stay up later and wake later. This isn’t just teens being rebellious—it’s in their biological nature. Asking teens to sleep at 10PM is like asking adults to sleep at 7PM.

Walker theorizes that this is evolutionarily helpful for teens to gain independence from their parents (having time to be awake while their parents are sleeping). Moreover, teens do so collectively, and so they get private time to socialize.

(Shortform note: Research from the University of Michigan seems to support this, suggesting that teens are hormonally driven to stay up late to socialize with peers away from adults.)

Unfortunately, in modern day, schools start at a very early hour (largely to match the circadian rhythms of adult parents). It’s far out of sync with the natural circadian rhythm of teens, so they tend to sleep late and wake up far earlier than they naturally would.

Considering all this, Walker says that if you’re a parent, there’s no need to get frustrated at your teenage kid for seemingly being lazy and sleeping too much, when their environment is heavily geared against their biological tendencies.

(Shortform note: If pushing for a later start time in your school district isn’t a viable option, you may be able to help your teen get better sleep by enforcing a set bedtime. One study found that adolescents with parent-set bedtime schedules got more sleep and were more alert and less tired during the day.)

Adulthood and Old Age

Sleep quality starts deteriorating in your late 20s, with deep NREM sleep becoming impaired in length and power. In your late 40s, you’ll get 70% less deep sleep than you had as a teenager; by age 70, you’ll have lost 90% of deep sleep. Unfortunately, less NREM sleep worsens your ability to cement new memories as you grow older.

You often hear of the elderly sleeping little at night, so the natural conclusion is that the elderly just need less sleep. But Walker says this could be a myth. The elderly might be sleeping less because they’re unable to sleep for as long. This means they could still benefit from more sleep.

(Shortform note: The National Institute on Aging says that older adults needing less sleep is a common misconception. Older people still need seven to nine hours of sleep a night.)

Why Do Seniors Sleep Less?

Walker notes that seniors have three things that keep them from enjoying more restorative sleep: 1) They sleep less than younger people, 2) they have less efficient sleep, and 3) they want to sleep earlier. This is caused by:

There are several other factors that exacerbate the poor sleep quality of seniors:

(Shortform note: Another factor that Walker doesn’t mention is menopause, which can cause sleep problems in middle-aged women. Forty percent of women in their late 40s to early 50s experience issues like insomnia, sleep apnea, and sleep disruption caused by hot flashes or restless leg syndrome. These problems begin at perimenopause and last until postmenopause—a period of about seven years. If you’re at this stage, increase your chances of having a good night’s sleep by avoiding big meals and spicy food before bedtime (as these can lead to hot flashes), reducing stress and managing anxiety that may keep you up at night, wearing lightweight clothes to bed, and having a change of clothes on hand so that you won’t have to get up in case of night sweat. Hormone replacement therapy may help with sleep difficulties but poses risks for some women.)

Walker says that all this causes lower sleep efficiency—people in their 70s have 80% sleep efficiency, meaning they stay awake in bed for 1.5 hours when trying to sleep eight.

There are a few ways for seniors to get better sleep:

(Shortform note: Seniors who don’t get enough sleep are more prone to accidents and falls, so the Sleep Foundation suggests some sleep safety tips: Keep a phone or a list of important phone numbers on your nightstand, but avoid keeping a cellular phone nearby—the notifications, bright screen, and temptation to scroll can keep you up. Have easily accessible light switches and clear pathways of hazards like cords and furniture to reduce your risk of tripping or falling if you need to get up in the middle of the night.)

Shortform Commentary: How Much Sleep Do We Need at Each Stage?

The National Sleep Foundation consulted a panel of 18 experts who reviewed hundreds of sleep studies to determine the appropriate sleep durations for each age group:

Other organizations, such as the American Academy of Sleep Medicine and the Sleep Research Society, have made similar recommendations.

Babies, young children, and teens need more sleep as they’re still growing and developing. To determine how much sleep you need, the Sleep Foundation recommends considering your overall health, daily activities, and sleep patterns.

The Ideal Human Sleep Pattern

Walker explains that native pre-industrial tribes show a biphasic sleep pattern, with seven to eight hours at night and a 30- to 60-minute nap in the afternoon. At night, they sleep two to three hours after sunset, awaking around dawn. He says there are two reasons this sleep pattern is advantageous:

What about supposed historical styles of sleeping, like segmented sleep (two periods of sleep at night, separated by a few hours of wakefulness)? Walker argues this is mostly a remnant of old cultural practices, and not a natural way to sleep. He says that no evidence suggests a biological desire to wake up for a few hours in the middle of the night.

(Shortform note: Award-winning author and professor A. Roger Ekirch, Ph.D. writes that many cultures in pre-industrial societies practiced segmented sleep and thought it to be completely natural. According to Ekirch, sleeping more than once a day was common not just in siesta countries like Spain and Italy but across preindustrial Europe, the Middle East, Africa, Asia, the Americas, and Australia. While he doesn’t say that segmented sleep was the predominant pattern, he does argue that monophasic sleep is a relatively new way to sleep in Western societies, brought on by artificial lights and changing cultural norms. He adds that some people’s difficulty obtaining monophasic sleep may be the residual effects of a previously dominant pattern.)

Human evolution has changed not only sleep patterns, but also sleep periods. Walker explains that, relative to great apes, humans sleep less (eight hours in humans versus 10-15 hours in apes) and have more intense REM sleep (20% in humans versus 9% in apes). He hypothesizes this evolved as follows:

(Shortform note: Research also suggests that the human need for shelter and a warm bed originated in great ape species, who have been shown to build complex sleeping platforms. This nesting behavior may have contributed to the evolution of great apes and may give us a greater understanding of how human sleep patterns evolved. One theory is that nest-building led to improved sleep quality, which in turn led to better brain function and development.)

Part 2: The Importance of Sleep | Chapter 6: How Sleep Benefits the Brain

Walker says that getting good sleep improves your brain in three ways:

1) Sleep Improves Long-term Factual Recall

Your brain stores different memories in different places. The hippocampus stores short-term memory with a limited capacity; the cortex stores long-term memory in a large storage bank.

The slow-wave, pulsating NREM sleep moves facts from the hippocampus to the cortex. This has two positive effects: 1) It secures memories for the long term, and 2) it clears out short-term memory to make room for new information, improving future learning.

Have you ever woken up recalling facts that you couldn’t recall before sleeping? Walker says this happens because sleep may make corrupted memories accessible again.

(Shortform note: Sleeping for too long may have an interesting effect on memory, as in the case of a man from North London who was in a coma for three weeks. He woke up with memories of things that didn’t really happen—going on an interview with MI6, owning a private plane, and expecting twins with his girlfriend. One possible theory is that his brain was trying to fill that three-week gap with made-up memories based on real memories that he had stored, such as a plane he saw in a movie and friends having twins.)

2) Sleep Prunes Memories Worth Forgetting

Sleep doesn’t preserve all memories equally strongly—Walker says that somehow, the brain knows which memories are useful and worth preserving, and which ones are useless and discardable.

This has been shown in experiments where subjects are given a list of words and instructed which words to remember and which to forget. Students who get to take a nap show stronger memories for the appropriate words, compared to students who don’t nap.

(Shortform note: A 2019 study on mice found that melanin concentrating hormone (MCH) neurons helped the brain forget unimportant information during REM sleep. This could help researchers better understand—and possibly come up with treatments for—memory-related diseases and disorders.)

3) Sleep Increases “Muscle Memory” or Motor Task Proficiency

You might struggle with a motor task (like playing a tough sequence on a piano), but after sleeping, be able to play it flawlessly. Sleep seems to transfer motor memories to subconscious habits.

(Shortform note: While Walker writes that motor memory is connected to NREM sleep, the Division of Sleep Medicine at Harvard School suggests that motor learning is linked to REM sleep. They acknowledge that researchers have varying views when it comes to the sleep stages linked to memory, but that the overall evidence suggests that sleep in general is important for memory and learning.)

Potential Forms of Sleep Therapy

Now that we understand the impact of sleep on the brain, Walker urges us to imagine how we can apply this knowledge to the creation of useful therapies:

The Sleep Research Revolution

While conducting tests in a lab enables researchers to more closely observe patients and reattach wires that fall off during sleep, new at-home methods of sleep tracking are helping researchers more extensively study sleep orders and come up with more useful therapies. Some of the new approaches to testing are:

Chapter 7: How Sleep Deprivation Harms the Brain

While getting great sleep is good for the brain, sleep deprivation is unambiguously harmful for the brain. Walker discusses three ways sleep deprivation is damaging: it worsens attention, worsens emotion control, and contributes to Alzheimer’s Disease.

Sleep Deprivation Worsens Attention and Concentration

Walker notes that sleep deficits—the difference between the amount of sleep you need and the amount you actually get—are very bad for attention and concentration. They add up over time, and performance progressively worsens with greater sleep deficit. Having 10 six-hour nights of sleep is equal in damage to one all-nighter, as is six four-hour nights of sleep.

(Shortform note: Research suggests that it takes four days to make up for one hour of sleep debt, and sleeping in on the weekend doesn’t make up for it, especially if it’s a chronic problem. Try adding an hour or two a night until you get back on track, then stick to a consistent sleep schedule.)

Think you can get by on six hours of sleep? Chances are, you can’t. Walker explains that less than 1% of the population is able to get six hours of sleep and show no impairment (this is largely genetic and relates to the BHLHE41 gene). Everyone else is just fooling themselves and propping up their energy with caffeine. He says that power naps aren’t a magic bullet either—they’re most effective at the onset of fatigue, not when you’re already sleep deprived.

Sleep deprivation is an insidious problem because when you’re sleep deprived, you don’t know how poorly you’re performing. (This is like being drunk and thinking you’re far more capable of doing things than you actually are.) And if you’re chronically sleep-deprived, your low performance becomes a new baseline, so it’s hard for you to see just how badly you’re performing.

The High Risk of Sleep Deprivation

Walker warns that the combination of reduced concentration and an inflated sense of your capabilities in a sleep-deprived state is especially harmful during high-risk activities, like driving. To put the risk into perspective:

(Shortform note: In the original text, Walker wrote that there are more vehicular accidents caused by drowsy driving than by alcohol and drugs combined. He has since removed this vague claim from the book and revised it to include statistics, saying it’s hard to objectively quantify the number of accidents due to drowsy driving versus driving under the influence.)

Why do sleep deficits cause more accidents? Part of it is delayed reaction time. Another part is a “microsleep,” where your eyelids shut for just a few seconds and you go unconscious and lose motor control. If you’re in a car going 60 mph, falling asleep for just a few seconds could result in a terrible accident.

How to Tell If You’re Too Drowsy to Drive—and What to Do About It

According to Walker, the number of accidents related to drowsy driving is somewhere between 70,000 to 1.2 million (see above Shortform note). Keep yourself from turning into a statistic by knowing the telltale signs that you’re too sleepy to get behind the wheel:

Here are some things you can do to stay safe on the road:

Sleep Deprivation in the Medical Field

Impaired attention and concentration have dire consequences in the medical field—Walker reports that sleep-deprived residents show greater risk of medical errors, surgical errors, misdiagnoses, and careless deaths. (Recall that after 22 hours without sleep, performance is impaired to the same level as being legally drunk.)

First-year residents are now limited to 24-hour shifts and 80-hour weeks. Later-year residents have no such restriction, since the Accreditation Council for Graduate Medical Education claims the medical error studies were done only on first-year residents.

Walker explains that structurally, the medical system resists change for fear of limiting training volume. Also, older doctors may fear this encourages laziness, relative to what the attending doctors had to suffer through.

(Shortform note: In his original text, Walker stated that limiting residents to 16-hour shifts with an eight-hour rest period led to “400-600% fewer diagnostic errors.” He corrects this in the second edition, replacing the percentages with the phrase “significantly fewer.” Medical schools and teaching hospitals now recognize the importance of giving medical residents ample rest and have taken steps to address the problem. Some universities have sleep pods and hotel-style rooms where students can nap, while UCLA encourages residents to have “beeper buddies”— residents who can take colleagues’ beepers to give them time for uninterrupted rest.)

Sleep Deprivation Worsens Emotional Control

A baby that doesn’t get its nap time tends to get cranky. Adults are the same way.

The amygdala is the part of your brain responsible for emotions like fear and anxiety. Normally, it’s held in check by your prefrontal cortex (the rational part of your brain). However, Walker says that when you’re sleep deprived, this suppression is weakened, and your amygdala can run amok, leading to 60% more emotional reactivity. The highs can be higher, and the lows lower.

On the other side of fear and anxiety, he says that positive rewards and dopamine may be amplified by sleep deprivation too. Therefore, sleep deprivation can intensify sensation-seeking, risk-taking, and addiction.

More gravely, sleep may play an important role in mental illness. Walker provides suggestive evidence:

A Changing Stance on Sleep Deprivation as Treatment

Guzey writes that Walker downplays the benefits of sleep deprivation as the author notes that it works in 30-40% of patients with depression and ends up making 60-70% feel worse. Guzey states that, according to studies, it can be beneficial to about 45-50%. He writes that by misrepresenting the numbers, Walker may be discouraging people with depression from seeking this form of treatment.

In his blog, Walker clarifies that the findings that sleep deprivation can be beneficial to nearly half of patients with depression emerged after the book was written. He has revised the book to reflect his stance on sleep deprivation, changing the text from “sleep deprivation is not a realistic or comprehensive therapy option” to “sleep deprivation alone is not a realistic or comprehensive therapy option” [emphasis ours].

Guzey also takes issue with Walker’s seemingly contradictory statements on sleep deprivation. In an early chapter, Walker writes that thousands of studies prove that there are no biological functions that do not benefit from a good night’s sleep. But in a later chapter, he writes about the benefits of sleep deprivation. In his blog post, Walker responds to Guzey’s comment by saying that the positions aren’t contradictory, but instead demonstrate the breadth and complexity of the topic of sleep deprivation. It’s worth noting that Walker’s original statement that thousands of studies prove that no biological functions can benefit from sleep deprivation has been edited out of the second edition of the book.

Sleep Deprivation May Contribute to Alzheimer’s

While Walker says there is no definitive causal link between the two, he notes that sleep loss may contribute to Alzheimer’s through a few mechanisms:

It’s easy to see how a vicious cycle can occur—frontal lobe degeneration disrupts NREM sleep, which causes further frontal lobe degeneration.

Walker suggests that encouraging NREM sleep, through artificial brain stimulation if needed, might be therapeutic for Alzheimer’s. It could also be preventative, in the same way that cholesterol-reducing drugs protect against heart disease.

(Shortform note: A study suggests that sleeping on your side can help decrease the chances of developing Alzheimer’s and other neurological diseases. This is because the position may more effectively remove brain waste that causes the plaque buildup linked to Alzheimer’s. If you want to switch from sleeping on your back or your stomach to sleeping on your side, get a pillow that keeps your body aligned—plump enough to fit perfectly between your ear and shoulder, and firm enough to support your neck. Place a pillow between your knees to help align your back and hips, as well.)

Just How Bad Is Sleep Deprivation?

Given its damaging effects, sleep deprivation torture is recognized by many countries as unethical, but it’s still practiced by others (like the US in Abu Ghraib).

According to Walker, sleep deprivation doesn’t even work well. It reduces the quality of information (harms memory recall) and increases the risk of lying and false confessions in a desperate hope to get some sleep.

(Shortform note: Reports in 2021 confirm that some countries still use sleep deprivation as a form of torture. In Russia, a jailed Kremlin critic said that guards would wake him up every hour of the night. In Myanmar, a former detainee revealed how suspects had to sit through rotating interrogators throughout the night. An article about a tortured prisoner in China referenced a Human Rights Watch Report that detailed China’s torture methods, which included sleep deprivation, “tiger chairs” (to restrain suspects during interrogation), and “cell bosses” (detainees who abuse fellow prisoners).)

Chapter 8: How Sleep Deprivation Harms the Body

In addition to the damage it causes to the brain, sleep deprivation disrupts the normal function of many physiological processes, likely contributing to chronic diseases. In this chapter Walker covers nine health issues associated with sleep deprivation.

At a high level, sleep deprivation of even just one to two hours triggers the sympathetic nervous system (fight or flight response) and disrupts hormonal balances. He says that this also implies that sleep is necessary for the normal maintenance of physiology.

(Shortform note: Guzey includes a graph from this chapter that illustrates how average sleep time has decreased by more than two hours between the 1940s and 2000s. However, he has been unable to find the source of the data. He argues that evidence shows no reduction, or even suggests an increase, in sleeping time over this time period.)

A Note on the Studies in Why We Sleep

Many of the population studies cited in Why We Sleep are correlational—for example, their results show that people who sleep less are more likely to have heart disease, after controlling for many other factors. But the causation of these results is unclear—some other factors that predispose people to heart disease (like a high baseline level of stress) could also reduce sleep.

To address this, the experimental studies Walker cites attempt to link lack of sleep to a middle physiological state, which itself is causative for the disease. For instance, a lack of sleep increases blood pressure, which the medical consensus believes is causative for heart disease.

Ideally, the “smoking gun” experiment would be to randomize people into normal-sleep and low-sleep groups for years, then observe the rate of disease. However, this is impractical (it’s hard to run very long studies like this and impossible to double-blind) and likely unethical (if low sleep is already believed to cause severe disease).

1) Heart Disease

Walker claims that sleep deprivation has a number of effects related to cardiovascular disease:

A population study showed that shorter sleep was associated with a 45% increased risk of developing heart disease.

He notes an interesting finding: daylight savings time is a natural sleep experiment that typically increases or decreases sleep by one hour. When the clock moves forward and the population gets one less hour of sleep, there is a significant spike in heart attacks and the number of traffic accidents.

(Shortform note: Guzey writes that Walker seems to misrepresent studies on the relationship between sleep and cardiovascular health. Walker got some key figures wrong—saying that one study involved over half a million people when it involved 474,684, for example—and also included statistics about “cardiac arrests” that were not found in one paper. The author addresses this in an interview, correcting the erroneous numbers that he cited and saying that the paper referred to “cardiac events,” and not cardiac arrests as he had written. He also includes these corrections in his blog and in the second edition.)

2) Diabetes

Sleep deprivation reduces insulin responsiveness, which causes hyperglycemia.

Walker says that in a population study, those sleeping less than six hours a night showed higher rates of type 2 diabetes (after controlling for body weight, alcohol, smoking, and other factors).

(Shortform note: A study suggests that obese people who are night owls have a 37% risk of type 2 diabetes versus morning larks, who have just a 9% risk. You may not be able to change your chronotype, but you can change your lifestyle to help control your weight. Avoid having a big dinner, eat a healthy diet, and get enough exercise.)

3) Obesity and Weight Gain

As it relates to weight, sleep deprivation:

Walker describes an experiment in which subjects were randomized into a normal eight-hour sleep group, and a low four-hour sleep group. Both groups had the same amount of physical activity and free access to food, with the researchers closely monitoring their calorie consumption.

One might argue that decreased sleep naturally causes more calorie burn, but Walker points out that an all-nighter actually consumes only 147 more calories than sleeping. Sleep is metabolically more intense than you might guess.

Finally, if you’re losing weight and sleep deprived, the shift of where you lose the weight from differs. When sleep-deprived, 70% of weight loss comes from lean body mass like muscles, compared to under 50% with plentiful sleep.

(Shortform note: On the flip side, some weight-loss efforts may have a detrimental effect on sleep as studies suggest that going on a low-carbohydrate diet might end up keeping you up at night. This is because consuming fewer carbs leads to the decreased production of sleep-inducing melatonin, while more protein leads to the increased production of energizing epinephrine and norepinephrine, resulting in a one-two sleeplessness punch.)

4) Reproductive System

Sleep deprivation has an effect on both the inner and outer mechanisms of reproducing: your hormones and your ability to attract a mate.

Hormones

Walker says that in males, short sleep duration decreases testosterone, testical size, and sperm count.

(Shortform note: The study Walker uses to support his claim has a very small sample size of only 10 men, which may make its results less reliable.)

In females, he says sleep deprivation reduces follicular-releasing hormone (necessary for conception), increases abnormal menstrual cycles, and causes more issues with infertility.

Attractiveness

Your face is rated as less attractive and less healthy after one night of short sleep. So according to Walker, there might be something to the idea of “beauty sleep.”

(Shortform note: To make the connection between attractiveness and short sleep, Walker cites one study where two groups of participants were photographed: one group after eight hours’ sleep and another after just five hours’ sleep. The sleep-deprived group was rated as looking less attractive. However, Walker does not mention that the second group had been deprived of sleep for 31 hours prior to their night of reduced sleep. As one reviewer points out, there’s a big difference between someone who’s had five hours of sleep versus someone who’s had five hours of sleep after being awake for 31 hours.)

5) Immune System

Walker goes on to explain that sleep deprivation reduces your ability to ward off infectious disease:

6) Cancer

Sleep deprivation increases cancer severity in three ways, according to Walker:

(Shortform note: In the first edition, Walker wrote that routinely sleeping six or seven hours a night doubles your risk of cancer. Researcher Guzey disputes this, saying that Walker doesn’t cite any studies to support this claim, and that a systematic review of 65 studies didn’t find a link between sleep duration and cancer risk. Walker modified the wording in the second edition to say that routinely sleeping six or seven hours a night “substantially increases your risk of certain forms of cancer.” Additionally, in his blog, he writes that short sleep isn’t linked to all types of cancer, but that it’s associated with increasing the risk of specific cancers, such as lung, ovarian, thyroid, and blood cancer.)

He also cites population studies that show a link between nighttime shift work and increased risk of cancer (common occupations include nurses and pilots). In response to these studies, Denmark now pays workers’ compensation to women who developed breast cancer after doing night-shift work in government-sponsored jobs.

(Shortform note: In the first edition, Walker had written that the WHO had classified nighttime shift work as a probable carcinogen, but reviewers questioned this information as they were unable to find any evidence that the WHO had said this. Walker corrects this in the second edition and in his blog, clarifying that the information was in fact from the International Agency for Research on Cancer, which is under WHO.)

7) Aging

Telomeres act as caps at the ends of DNA strands, protecting them from getting frayed—much like the plastic tips at the ends of shoelaces. They get shorter over time, a process which theoretically contributes to aging. Walker writes that sleep deprivation has been shown to hasten telomere shortening, thus implying an increase in aging.

(Shortform note: Guzey points out another percentage error in the section about sleep loss, gene activity, and DNA. Walker originally wrote that gene activity in mice drops by “well over 200%” when they’re sleep deprived, but he has since revised it to say that gene activity becomes “significantly impaired.”)

8) Decreased Athletic Performance

Sleep deprivation also worsens general athletic performance: getting less sleep decreases your aerobic capacity, time to exhaustion, and recovery, and it increases risk of injury and lactic acid generation.

In the first edition of the book, Walker included a graph showing that the likelihood of injury decreases the more sleep you get—those who get six hours of sleep a night are over 70% likely to get injured, while those who sleep nine hours a night have an under-20% chance of getting injured. Guzey notes that Walker cut out a portion of the source graph showing that those who get five hours a night are less likely to get injured than those who get six or seven hours. Statistician Andrew Gelman writes that this sort of data manipulation may count as research misconduct.

Walker has since replaced the graph with one that has just two values: one showing the pooled injury risk for those who less than eight hours, and one for those who got eight hours or more. In his blog, he writes that the updated graph better represents the study authors’ statistical analysis.

9) Death

Gravely, Walker states that sleep deprivation can directly cause death.

In rodent studies, REM sleep deprivation causes death over the same period as food deprivation—about 15 days.

In humans, sleep deprivation leading to death is uncommon (possibly since the natural urge to sleep is so strong). But lack of sleep could contribute to more acute causes of death like seizures, and thus be misreported.

(Shortform note: In the book’s first chapter, Walker writes that shorter sleep leads to a shorter life span. Guzey notes the lack of citation and shares a graph from one study that shows that the optimal number of hours of sleep is seven. It also shows that the mortality rate for five hours of sleep is very similar to that of eight hours of sleep. In his blog, Walker responds to this, saying that this was not the conclusion of the study—the study authors stated that “seven hours/day of sleep duration should be recommended to prevent premature death among adults.” He goes on to say that the study involved two assessments: 1) amount of sleep during the study, 2) whether the individuals were still alive years later. For some, the second assessment took place more than 20 years after the first, with no analysis of any changes in sleep patterns in between, which means that the study had limitations. Walker mentions other studies that support his assertions that shorter sleep is associated with a shorter life span.)

Walker’s strongest evidence that humans can die from sleep deprivation is a very rare inherited condition, fatal familial insomnia. In this disease, prion proteins destroy the thalamus, and the patient is totally unable to sleep, even with heavy sedatives. Severe disability sets in (dementia, speech disorders), and death occurs within 10 months. There are no treatments or preventions. This disease is autosomal dominant and found in only 40 families worldwide.

(Shortform note: In the book’s first chapter, Walker refers to a very rare genetic disorder (FFI) and how, after 12-18 months, a patient suffering from the disease will die. In the first edition, he wrote, “Though exceedingly rare, this disorder asserts that a lack of sleep can kill a human being.” This sentence has been removed from the second edition, possibly because it seems to run counter to Walker’s assertions in Chapter 12—that death from the lack of sleep due to FFI is scientifically inconclusive as there may be other factors at play. In his blog, Guzey refers to a passage from the Encyclopedia of Sleep that explains how FFI is a neurodegenerative disease, so sleep loss itself isn’t necessarily the cause of death.)

Evolutionary Reasoning for Sleep Deprivation’s Damage

Why would animals evolve so that sleep deprivation causes all these bad issues? Consider that in caveman days, times of low sleep may mean conditions that threaten survival (low food stores, tough weather, hostility with another tribe). The responses—hoarding calories, the “fight-or-flight” system, and decreased reproduction—might promote short-term survival but come at the expense of long-term well-being.

How Much Sleep Should We Get?

Let’s return to the question of normal sleep amounts.

On the lower end, you may have seen reports of hunter-gatherer tribes who sleep just 6.5 hours, leading to assertions that this is a universally “natural” state for all humans. They also are rarely obese.

But Walker says this is a misguided conclusion. In reality, the hunter-gatherer tribes are basically perpetually starving, since food is never abundant for long periods of time. Starvation naturally induces less sleep, so that animals stay awake longer to search for food. (This also decreases obesity.)

To wit, the average life span of hunter-gatherers is just 58 years, much shorter than humans in industrialized societies. In nutrition-rich situations, most humans need eight hours of sleep.

(Shortform note: While Walker claims that humans need eight hours of sleep now, as opposed to our hunter-gatherer ancestors’ 6.5 hours, Guzey cites studies suggesting that people who sleep just six hours a night might actually have the lowest mortality rate. There are also cases of people with a short sleep gene, which means they only need four to six hours of sleep a night with no adverse effects to their health. While not getting enough sleep can affect the average person’s performance and mood, natural short sleepers are typically driven and optimistic.)

Can You Sleep Too Much?

Some population studies show increased risk of death in those who regularly sleep more than nine hours, suggesting sleeping too much might be harmful. But the author argues this data is confounded by infection and cancers in long-sleeping people [though these confounds should already have been controlled for].

(Shortform note: Walker elaborates on this argument in his blog. He writes that one challenge of measuring sleep through surveys is that respondents don’t differentiate between being in bed and being asleep. Thus, the increased risk of death associated with long sleep may be due to poor-quality sleep and not too much sleep.)

Part 3: The Science of Dreams | Chapters 9-11: The Benefits of Dreaming

Dreaming is a bizarre experience. You’re unconscious, but you perceive intense vivid sensations and hallucinate things that aren’t there. You feel like you’re moving in the world, but your muscles are in a state of paralysis. You remember faces and memories that you haven’t thought about for years, maybe decades. You have no control over your emotions, swinging from intense rage and jealousy to exuberance. Finally, when you wake up, you promptly forget everything. If you experienced all of this while awake, you’d think you were having a psychosis episode.

It’s not surprising then that dreaming has had a complicated history. Walker explains that in the ancient past, Egyptians and Greeks wondered if dreams were divine gifts from gods.

Freud helped dispel this myth, firmly centering dreaming within the human brain. He considered dreams as expressions of repressed desires, and he built a psychological movement around interpreting dreams as such.

The Latest Dream Theories

Since Freud’s time, there have been several theories about the purpose of dreaming, such as memory consolidation (dreams are replays of waking life), activation synthesis (dreams enable us to make connections between memories), and emotion regulation (dreams are a manifestation of, and some sort of therapy for, our emotions). Answering the question of why we dream isn’t straightforward because dreams may serve many purposes. As one researcher puts it, “Asking what dreams are for is like asking what waking thought is for.”

Two of the newer theories that emerged in 2021 are:

The Science of Dreaming

Most vivid dreaming happens during REM sleep (though NREM sleep has some vague non-vivid dreaming, like “I was thinking about clouds”).

During REM dreaming, Walker says that your visual, motor, memory, and emotional areas of the brain are active. Your prefrontal cortex (governing rationality) is muted.

He says it may even be possible to predict what you’re dreaming about through fMRI.

We often think about the meanings of our dreams. Do dreams merely replay events of the day, or do they reflect our emotional concerns?

The Ethics of Dream Research

Advances in dream research have now made it possible to predict and, perhaps, eventually control dreams. While the pursuit of new knowledge is important, developments in the field of dream research do raise some questions and concerns:

It’s thus critical for scientists to establish policies to protect study participants, ensuring that they’re fully informed about experiments and the subsequent use of their data.

Benefits of Dreaming and REM Sleep

Dreaming and REM sleep have three major mental benefits: blunting emotional pain, increasing understanding of others’ emotions, and increasing creativity.

Benefit #1: REM Dreaming Blunts Emotional Pain From Memories

During REM dreaming, the brain seems to reprocess upsetting memories and emotional themes, retaining the useful lessons while blunting the visceral emotional pain. This might be why we can look back at painful memories without feeling the original full emotional intensity.

How might this happen? Walker explains that REM sleep is the only time that the stress hormone norepinephrine is absent from your brain, which possibly allows the brain to process upsetting memories in a “safe” environment.

He provides suggestive evidence:

Interestingly, dreaming about the upsetting content itself, or its emotional themes, is necessary to have this emotional blunting effect. REM sleep by itself does not.

(Shortform note: While Walker suggests that the dream state is responsible for processing emotional memories, neuroscientist Rebecca Spencer posits that NREM sleep also plays a role. She doesn’t explain the mechanism behind NREM sleep and its effect on emotions, but says that long naps—which mostly consist of dreamless NREM sleep—have been shown to decrease sensitivity to emotional stimuli in a subsequent waking state. However, she notes that the association between naps and emotional processing seems to be stronger in children than in adults. This may be because adults have a more mature hippocampus, which makes them hold onto memories longer, so a nap doesn’t give them adequate time to process emotional memories.)

Benefit #2: REM Sleep Increases Understanding of Other People’s Emotions

Sleep deprivation reduces your ability to interpret subtle facial expressions. Sleep-deprived people more often interpret faces as hostile and aggressive.

(Shortform note: This works both ways: While sleep-deprived individuals view other people more negatively, other people also view sleep-deprived people as more unpleasant. Research from Walker’s team, published in 2018, found that sleep loss can be socially isolating, making people feel lonelier and avoid close contact with other people, which in turn sends a signal to other people to stay away. The lead author of the study suggests that the (supposed) decrease in sleep duration in the past few decades is linked to an increase in loneliness.)

Benefit #3: REM Sleep Increases Creativity

REM sleep creates novel associations between ideas, which Walker says increases creativity and problem-solving.

Informally, imagine the brain asking: “How can I connect what I’ve recently learned with what I already know, thus discovering insightful revelations? What have I done in the past that might be useful in solving this new problem?”

(Shortform note: Creativity is often associated with the arts, but there is plenty of room for creative imagination in science. For example, Walker cites Mendeleev, a chemist who developed the breakthrough periodic table of elements after happening upon the solution in a dream. A similar example is German chemist August Kekule—a popular anecdote credits his discovery of the structure of the benzene molecule to a dream about a snake biting its own tail.)

Walker describes three positive effects of REM sleep on creativity:

1) REM sleep increases the ability to solve creative problems. In an experiment, subjects who were asleep were woken up to solve anagrams (for example OEOSG = GOOSE). Those who were awakened from REM sleep solved 15-25% more puzzles and had faster response times than those who had woken up from NREM sleep or who solved problems while awake during the day.

Walker notes that it’s not just REM sleep itself but also the content that matters when it comes to problem-solving. In an experiment, subjects were given a maze to solve and given a chance to nap. People whose dreams were related to mazes were 10 times better at solving the maze upon waking versus people who didn’t dream about mazes.

(Shortform note: It may be possible to manipulate your brain to solve problems during sleep. In a study, participants were given puzzles to solve, each one associated with a different sound. While the participants slept overnight, the sounds associated with half of the unsolved puzzles were played. The next morning, participants showed a 55% improvement in solving the puzzles with sound cues, suggesting that the sounds had redirected their brains toward problem solving during sleep.)

2) REM sleep creates novel connections between distantly related concepts. Walker describes an experiment in which study participants were taught a long chain of ideas, such as A>B>C>D>E and so on. Those who slept and got REM-rich sleep—whether it was from one night’s sleep that included late-morning REM sleep or a 60- to 90-minute nap that included REM sleep—were more able to make distant connections, such as B>E.

In the same way, REM sleep lets your brain connect new experiences to old ones. If you have to solve a problem today, you might think back to a similar problem you solved five years ago.

(Shortform note: Research suggests that this memory-processing function of dreams enables you to use past experiences to prepare you for upcoming events. In a study, participants noted that half their dreams were related to past experiences, a quarter of their dreams were related to specific future events, and 40% of dreams contained elements of both past and future events. This suggests that you may be able to prepare yourself for a future event, like a presentation or a sports tournament, by thinking of related memories before you sleep.)

3) REM sleep finds the patterns among the noise. Even one night of sleep that includes REM sleep creates a higher-level comprehension of ideas, as demonstrated by toddlers who are better able to absorb new languages after getting some sleep. Walker also cites a study in which study participants were better able to find shortcuts for solving repetitive math problems after obtaining REM-rich sleep.

(Shortform note: Though Walker only lists the benefits of REM sleep for creativity, research published in 2018 shows that both NREM and REM sleep may play a role in creativity. The researchers suggest that the interplay between NREM sleep, which distills information from memories, and REM sleep, which works on forming new connections, facilitates creativity.)

Lucid Dreaming

Lucid dreamers are able to voluntarily control their actions within their dream.

Walker says that researchers can verify when someone is lucid dreaming by pre-arranging eye movements and hand signals while the subject is awake, then detecting the subject making those same eye movements and hand signals while sleeping (the hand signals are detected by fMRI—remember, you can’t move during REM sleep because of muscle atonia).

He notes that less than 20% of people are capable of lucid dreaming, suggesting it might not be a hugely advantageous capability.

How to Start Lucid Dreaming, According to Science

One study found that you can increase your chances of having lucid dreams in just one week by combining these three techniques:

Part 4: The Current State of Sleep | Chapter 12: Sleep Disorders

We’ve talked before about how sleep deprivation causes disease. Now we’ll discuss sleep disorders, or primary issues with abnormal sleep, and their consequences. In this chapter, Walker covers three major disorders: sleepwalking, insomnia, and narcolepsy.

Somnambulism (Sleepwalking)

Sleepwalking is the act of walking and performing other behaviors while asleep. Automatic, nonconscious routines are executed, like brushing teeth or opening the refrigerator.

Sleepwalking happens during NREM sleep, and not REM dreaming sleep (as some think). Neurologically, sleepwalking is accompanied by an unexpected spike in nervous system activity, causing the person to be stuck somewhere between sleep and wakefulness.

(Shortform note: A 2021 study suggests that men who sleepwalk may have a higher risk of developing Parkinson’s disease. The two share a common neural pathway and both involve involuntary movements, confusion, and amnesia.)

Sleepwalking is more common in children than adults, for unknown reasons—possibly because kids spend more time in NREM sleep than adults do.

How to Manage Sleepwalking

According to the Sleep Foundation, treatments for sleepwalking depend on factors like age, frequency, and severity. If sleepwalking episodes happen a little too often in your household, try the following:

Insomnia

Walker defines insomnia as making enough time for sleeping, but having insufficient sleep quantity or quality, for more than three months. Symptoms include difficulty falling asleep, waking up in the middle of night, and feeling unrefreshed in the morning.

He says that when they do sleep, insomniacs have more fragmented REM sleep and shallower brain waves in NREM.

One out of nine people suffer from insomnia. It’s twice as common in women than men, and more common in Black and Hispanic people than white, for unknown reasons.

The most common triggers of insomnia are emotional concerns or distress. The biological cause is linked to an overactive sympathetic nervous system, which raises body temperature and levels of cortisol and epinephrine. In turn, the thalamus, hippocampus, and amygdala all remain more active than in normal sleeping patients.

(Shortform note: Researchers suggest that physical and emotional stress may be the reason behind the sleep disparity between people of color and white people. Some of the possible sources of stress include discrimination in the workplace, fear and anger due to racial discrimination, and financial pressure due to unemployment and poverty—stressors that people of color experience to a greater degree than white people. People of color are also more likely to work irregular hours that affect their sleep schedules and may have more limited access to health care, so sleep problems are left untreated.)

Given the complex physiology of insomnia, it’s unlikely blunt instruments like sleeping pills will fix the root cause.

(Shortform note: More middle-aged women are reporting increasing levels of insomnia and are turning to sleeping pills for relief. But studies suggest that using prescription sleeping pills for one to two years doesn’t improve sleep quality or duration in this demographic.)

Narcolepsy

Narcolepsy is a disruption in a normal process. Typically, wakefulness is signaled by the neurotransmitter orexin in the hypothalamus; in sleep, this is shut off. But in narcoleptic patients, 90% of orexin-secreting cells are destroyed, and orexin receptors are downregulated. Walker explains that this insufficient signaling causes the body to exist in a not-awake, not-asleep purgatory throughout the day and night.

People with narcolepsy suffer from three symptoms:

(Shortform note: It can be hard to diagnose narcolepsy because its symptoms overlap with the symptoms of depression, hypothyroidism, sleep apnea, and epilepsy, among other conditions. It’s important to rule out other conditions before starting treatment for narcolepsy.)

At the time of the book’s publication, Walker noted that there were no effective treatments for narcolepsy, but there were several treatments that could help narcoleptics manage some of their symptoms:

New Treatments for Narcolepsy

A few products for treating narcolepsy emerged after the book was published. These include:

Chapter 13: What Stops You From Getting Good Sleep

Five influences have drastically changed how we sleep over the years: caffeine, light, temperature, alcohol, and alarms. We’ll also discuss an additional sleep disruptor that more and more people are starting to experience: jet lag.

1) Caffeine

Walker explains that caffeine blocks adenosine receptors, thus reducing how much you feel sleep pressure, or the desire to sleep. If you ever drink coffee and then feel a crash later, this comes from the caffeine wearing off and leaving you with the adenosine that’s been increasing all day. Walker provides some information to help you make smarter choices about your caffeine consumption:.

Tip to Manage Caffeine Intake

Walker says that if you must have caffeine, don’t drink it in the afternoon, and definitely not in the hours before sleep.

(Shortform note: If you can’t shake the habit of drinking a hot beverage late in the afternoon or in the evening, try replacing your coffee or black or green tea with an herbal alternative. Studies suggest that the following herbal teas may help promote sleep and relaxation: valerian root, chamomile, lavender, lemon balm, passionflower, and magnolia bark.)

2) Light

Light helps the suprachiasmatic nucleus regulate the circadian rhythm. In the natural world, sunset—or the onset of darkness—sends a signal to the pineal gland to secrete sleep-inducing melatonin. Walker points out that nowadays, artificial light bathes our homes and disrupts our circadian rhythm.

Any light is disruptive to the circadian rhythm. Electric light delays your 24-hour circadian rhythm by two to three hours each evening.

Walker emphasizes that blue light is most problematic, suppressing melatonin at twice the levels of warm light. Blue light is most emitted by digital screens like TVs, computer monitors, and smartphones.

Tips to Reduce Light Exposure

(Shortform note: Blue light may have an even bigger impact on children, as they’re more sensitive to light and have bigger pupils. While the same tips apply to children, you can go a step further by implementing gadget-free time an hour before bed and storing their devices outside their bedroom at night.)

3) Constant Temperature

In natural environments, the temperature rises and falls with the day. This is used by the hypothalamus, along with light, to set the circadian rhythm. Our bodies react in kind—before sleep, the body cools, ejecting heat through densely perfused areas like your hands, feet, and face.

But in modern times, we use thermostats to homogenize our temperatures, suppressing the highs in the day and raising the lows with pajamas and blankets. Our brain doesn’t get the same signal about the day’s cycle that it used to.

Cooling your body temperature improves sleep. Walker mentions an experimental treatment during which people wear a bodysuit that circulates cool water. Among insomniacs and the elderly, this reduces time to sleep and increases the quality of NREM sleep.

Tips to Cool Down at Night

How to Sleep When It’s Just Too Hot

If you live in a tropical country or are in the middle of summer with no access to air-conditioning to cool your bedroom to an optimal temperature, you can increase your chances of getting a good night’s sleep with these tips:

4) Alcohol

Alcohol is a sedative, causing what appears to be sleep but is really more like anesthesia. It causes you to wake up throughout the night and prevents you from getting REM sleep.

In the process of metabolizing alcohol, your body produces aldehydes, chemicals that suppress REM sleep. Alcoholics are so sleep-deprived that their brain imposes REM-like behavior during wakefulness—resulting in hallucinations and scattered thinking. (Shortform note: An unfortunate vicious cycle can result here—alcohol disrupts sleep, which causes more fatigue and less behavior control when awake, which prompts more alcohol.)

Even for non-alcoholics, alcohol disrupts the normal processes of learning and complex knowledge when disrupting REM sleep.

Tip to Avoid the Effects of Alcohol

Walker encourages total abstinence from alcohol. A drink takes hours to fully degrade and excrete, and it’s even worse for people with alcohol flush reactions.

(Shortform note: A less puritanical approach comes from The Sleep Foundation, who recommend that you stop drinking alcohol at least four hours before bedtime. It’s worth noting that women seem to be affected earlier and with lower doses of alcohol than men. This is because they tend to weigh less and have less water in their bodies, leading to higher blood alcohol concentrations in their bodies.)

5) Alarms

Alarms cause acute stress responses when you wake up, spiking cortisol, heart rate, and blood pressure. This is not good for you. Even worse, snoozing the alarm causes multiple stress responses in quick succession.

Walker suggests several tips to lessen the stress of waking up:

(Shortform note: One study suggests that changing your alarm from a jarring sound to an upbeat song can help combat sleep inertia, that disoriented state you’re in upon waking up. But waking up naturally is still the better option—one survey found that natural wakers tended to feel more well-rested throughout the day, were more positive and productive, and made healthier choices.)

How Jet Lag Disrupts Sleep

While it doesn’t have the regular, universal influence on sleep as the first five factors, jet lag is another major sleep disruptor, affecting your sleep by disturbing your circadian rhythm.

How to Minimize Jet Lag

Walker writes that your body can only adjust to a new time zone at the rate of an hour per day, so it’ll take you 10 days to readjust to a 10-hour time difference. You can’t avoid jet lag entirely, but you may have a better chance of managing it with these tips:

Chapter 14: How to Get Better Sleep

Now that you know how sleep works and are more aware of the main sleep disruptors, you can implement practices to help you improve your sleep. Walker suggests the following actions:

(Shortform note: In Atomic Habits, James Clear writes that your environment shapes your behavior. You can thus form better habits by making sure that every object or space is only associated with one context; otherwise, your brain will have to decide between different actions associated with that environment. This means using your bed only for sleep—and not for other things like working on your laptop, watching TV, or scrolling through social media—will help create an association in your brain and you’ll naturally learn to become sleepy when you get in bed.)

Sleeping Pills Are Bad

Sleeping pills are typically sedatives that put the body into a state that doesn’t fully resemble sleep (similar to alcohol). Sleep looks different electrophysiologically—you don’t get the deepest brain waves, meaning you don’t get enough restorative deep sleep.

According to Walker, sleeping pills are no better than placebo when it’s time to fall asleep (even though self-reported satisfaction is higher). The lower quality of sleep causes daytime sleepiness.

Additionally, sleeping pills can kick off a heavily medicated vicious cycle:

Walker cites population studies that show that sleeping pills increase mortality in a dose-dependent way. Suggestive causes:

(Shortform note: We can’t rule out that upstream circumstances that disrupt sleeping and thus make people take sleeping pills are also causing all these other disease risks.)

Natural Alternatives to Sleeping Pills

Some people forgo sleeping pills in favor of a more natural remedy, like adaptogens—substances made of herbs and roots used in traditional Chinese and Ayurvedic treatments. They purportedly help regulate hormones and the body’s response to stress. Due to their stress-management properties, adaptogens may also help improve sleep. A review found that the following adaptogens may be the most effective sleep aids:

There’s little evidence that adaptogens can cause side effects like those that come from sleeping pills, but be cautious if you’re allergic to or intolerant of certain plants. Also talk to your doctor before trying adaptogenic supplements to rule out contraindications.

CBT for Insomnia

Cognitive behavioral therapy (CBT) is a common non-pharmacological method for changing behavior, shown to be more effective than sleeping pills. Walker explains that it’s commonly applied to depression, but there are variants for insomnia.

A big part of alleviating insomnia is redeveloping confidence around the ability to sleep. Thus, some practices force insomniacs to restrict their time in bed, maybe even to six hours or less. This builds up stronger sleep pressure, and so patients fall asleep faster and regain psychological confidence.

(Shortform note: According to Cognitive Behavior Therapy: Basics and Beyond, CBT begins with recognizing dysfunctional thoughts that negatively affect behavior. In the case of insomnia patients, these may be thoughts like, “I won’t be able to sleep,” which then keeps them from falling asleep. CBT for insomnia takes around six to eight sessions and may include cognitive and psychoeducational interventions to help patients reframe their thoughts about sleep, as well as a behavioral component like helping them improve sleep hygiene.)

Other Prescriptions for Sleep Issues

Walker mentions several other prescriptions that CBT therapists give their patients with sleep issues:

More Tips to Help You Sleep

In The Sleep Revolution: Transforming Your Life, One Night at a Time, Arianna Huffington devotes a chapter to sleep tips, tools, and techniques. While there are many overlaps with While We Sleep (such as limiting blue light, avoiding alcohol, and getting the temperature right), she offers some additional tips that Walker doesn’t mention:

Chapter 15: Society Causes Sleep Deprivation

Sleep deprivation goes far beyond our individual sleep practices. Walker argues that our society has structurally locked in sleep deprivation in two ways.

1) Work Schedules Disrupt Sleep

The ethos at many companies sees sleep as an indulgence for the weak. They lionize the road warrior who fearlessly crosses time zones on tiny amounts of sleep and answers emails at 1AM. In their minds, more hours worked equals more productivity.

This is short-sighted. The effects of sleep deprivation are costly to employers:

Another vicious cycle: People sleep less because of the amount of work they have to do, but their low sleep reduces their productivity and increases the work remaining.

(Shortform note: In Indistractable, Nir Eyal writes that employees feel the pressure to be “on” all the time—having to reply to late-night emails from their managers, for example. This constant pressure to be productive at all hours can cause employees to feel burned out, leading to reduced productivity and high employee turnover. By giving employees the time to rest and recharge, companies may be able to increase employee retention and satisfaction.)

Solutions for Employers

How the Covid-19 Pandemic Changed Sleep

During the Covid-19 pandemic, many people had more relaxed work schedules, as they were working from home and didn’t have to spend time commuting to and from the office. The combination of more time at home plus the pandemic environment changed sleep on three levels, according to Walker:

2) School Schedules Disrupt Sleep

To match parent’s schedules, primary and secondary school often begins at 8AM, and sometimes as early as 7AM. Kids whose parents can’t drive them to school may need to catch a long bus ride, meaning they must wake at 5:30AM or earlier. Remember that children have delayed circadian rhythms. Walker explains that this is akin to forcibly waking adults at 3:30AM every day. Society should push to change school schedules to better match the circadian rhythm of kids.

(Shortform note: The general public is becoming more aware of the importance of later school start times. In the U.S., a coalition called Start School Later is dedicated to educating the public about the issue, providing resources to communities and advocating for appropriate legislation. Their website lists schools in 46 states that have successfully implemented later school start times.)

Kids these days are sleeping two hours less per night, compared to children a century ago. Kids with lower sleep show lower motivation, academic performance, test scores, and IQ, as well as greater irritability, distraction, anxiety, substance abuse, and risk of traffic accidents.

In fact, many kids diagnosed with ADHD may actually have sleep disorders (Walker estimates >50% are misdiagnosed). Unfortunately, they’re treated with amphetamine (Adderall), causing even worse sleep problems.

(Shortform note: One expert notes that it’s unlikely for sleep disorders to be mistaken for ADHD, but that a lack of sleep can worsen ADHD symptoms.)

Chapter 16: Improving Sleep in Society

We’ve seen chronic sleep deprivation caused by a variety of factors, from the individual scaling up to the societal. Walker finishes with ways to improve sleep quality systemically:

Individual

Educational

(Shortform note: In Switch, the authors cite an example of how the general public learned about the concept of designated drivers: A Harvard professor got more than 160 TV programs to work the topic into their shows—as part of the script or as a poster in the background, for example. Within three years, 90% of Americans knew about designated driving, and there was also a decrease in alcohol-related crashes. A similar tactic might make the public more aware of drowsy driving.)

Organizational

(Shortform note: The sleep landscape continues to change with technological advancements that we can use to improve our sleep. In 2021, the FDA approved SleepCogni for medical use. Clinical trials have shown that SleepCogni, a data-supported device, can reduce insomnia in just seven days. In the hospitality industry, where sleep is an essential part of a hotel guest’s stay, a scientist predicts some ways in which the experience of sleep will change. These include bed covers and sheets made of high-tech fabrics that have thermal regulation and aromatherapy capabilities, and pillows that can detect sleep activity, massage the head and neck, and produce soothing sounds to encourage sleep.)

Exercise: Sleep Better Tonight

Think about how you can apply the book’s insights to get the best sleep possible.