Why We sleep summary
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Why We Sleep Summary and Review | Matthew Walker

The New Science of Sleep and Dreams


Why We Sleep argues that sleep is one of the most important but least understood aspects of our life. Matthew Walker aims to bridge this knowledge. As a neuroscience professor, Matthew describes how modern science has allowed us to better understand behavior we all engage with. Sleep is key to good physical and mental health, while dreaming inspires creativity. Dream deprivation is associated with poor cognitive performance today and in the future, with diseases like dementia. Importantly, there are ways you can improve your sleep, and Matthew Walker provides them in this book.

Matthew Walker’s Perspective

Matthew Walker is an English scientist and professor of neuroscience and psychology at the University of California, Berkeley. He is one of the most high-profile public intellectuals focused on the subject of sleep. As an academic, Walker has focused on the impact of sleep on human health. He has contributed to over 100 scientific research studies.

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Disclaimer: This is an unofficial summary and analysis.

Routinely Psychotic: REM-Sleep Dreaming

Matthew Walker describes dreaming as an experience where we become flagrantly psychotic. Although this might sound worrying, the author provides five reasons why dreaming is a naturally psychotic experience. 

  1. Last night when you were dreaming, you started to see things that were not there. Hence, you were hallucinating.
  2. In your dream, you would have believed things that could not have possibly been true. Hence, you were delusional.
  3. You would have become confused about time, place, and person. Hence, you were disoriented.
  4. Your dream would have been characterized by wildly fluctuating emotions. Hence, you were affectively labile.
  5. Finally, you woke up this morning and completely forgot about your dream experiences. Hence, you are suffering from amnesia.

If you were to experience any one of those five symptoms while you were awake, you would be seeking psychological or psychiatric treatment. However, during sleep and dreaming, it seems to be both a normal biological and psychological process.

Dream Creativity and Dream Control

“Sleep is the single most effective thing we can do to reset our brain and body health each day — Mother Nature’s best effort yet at contra-death.” – Matthew Walker

The vast majority of your dream experiences will have occurred during a sleep stage called rapid eye movement (REM). REM sleep, potentially due to these dream experiences, has been associated with two main benefits. The first of these benefits is the advancement of dream creativity and control.

During REM sleep, and dreaming specifically, the brain starts to combine information. Your dreams are a compound of what you’ve recently learned and a back catalog of autobiographical information that you’ve got stored in your brain. Based on the act of combining these areas of information, your brain starts to build novel connections. Matthew Walker describes REM as being like group therapy for memories. Through this pattern of informational alchemy at night, we create a revised mind wide web of associations. In your waking life, these associations can kickstart novel insights that can help solve problems. This is why you may have experienced waking up to new solutions. No wonder the saying isn’t “Stay awake on a problem.” Instead, people tell you to sleep on a problem. This saying is now supported by substantial evidence.

Dreaming as Overnight Therapy

The second benefit of REM sleep is essentially how it works as a form of overnight therapy. It’s during dream sleep we can take the sting out of difficult, even traumatic, emotional experiences. Sleep almost removes that emotional, bitter rind from the memorable experiences we’ve had during the day. Hence, we can wake up the next morning feeling better about those experiences. Based on this, Walker suggests you think of dream sleep as emotional first aid. Dream sleep offers a nocturnal balm that soothes the painful stinging edges of challenging experiences. So, it’s not just time that heals all wounds. Instead, it’s time spent in dream sleep that provides you with emotional healing.

Too Extreme for the Guinness Book of World Records: Sleep Deprivation and the Brain

Research and personal experience consistently show that a lack of sleep will prevent your brain from effectively creating new memories. Matthew Walker offers an analogy to explain this point. It is almost as though without sleep, the brain’s memory inbox shuts down, and you can’t commit new experiences to memory. So, those new incoming informational emails are simply bounced, and you end up feeling as though you’re amnesiac.

On top of struggling to form new memories, a lack of sleep is also associated with longer-lasting memory issues. Research shows that a lack of sleep will lead to an increased development of a toxic protein in the brain called beta-amyloid. Beta-amyloid is associated with Alzheimer’s disease. This protein can build up when sleep-deprived, as nighttime sleep encourages the breakdown of this toxic protein. Hence, if you’re not getting enough sleep every night, more of that Alzheimer’s-related protein will build up. The more protein that builds up, the greater your risk of developing dementia in later life.

Cancer, Heart Attacks, and a Shorter Life: Sleep Deprivation and the Body

“The shorter your sleep, the shorter your life. The leading causes of disease and death in developed nations—diseases that are crippling health-care systems, like heart disease, obesity, dementia, diabetes, and cancer—all have recognized causal links to a lack of sleep.” – Matthew Walker

As well as impacting your brain, sleep deprivation can also impact your body. Firstly, we know that sleep deprivation affects the reproductive system. We know that men who are sleeping only five to six hours a night have a testosterone level comparable to someone ten years their senior. Therefore, a lack of sleep will age you by almost a decade in terms of that aspect.

We also know that insufficient sleep impacts your immune system. After only one night of four to five hours of sleep, there is a 70% reduction in critical anticancer-fighting immune cells called natural killer cells. Hence, we know that short sleep durations can increase your risk of developing numerous forms of cancer. This list currently includes bowel, prostate, and breast cancer. In fact, the link between sleep deprivation and cancer is now so strong that the World Health Organization classifies any form of nighttime shift work as a probable carcinogen. So, in other words, these jobs may induce cancer due to a disruption of your sleep rate rhythms.

We also know that insufficient sleep impacts your cardiovascular system. During deep sleep at night, you receive what Matthew Walker calls a blood pressure medication. Your heart rate drops, and your blood pressure goes down. Therefore, if you’re not getting sufficient sleep, you’re not getting that reboot of the cardiovascular system. The result of missing this reboot is a rise in blood pressure. Subsequently, if you’re getting six hours of sleep or less, you have a 200% increased risk of having a fatal heart attack or stroke in your lifetime. The presence of this risk factor is supported by the phenomenon that is daylight savings time, which Matthew Walker describes as a global experiment performed on 1.6 billion people twice a year. When we lose one hour of sleep in the spring, we see a subsequent 24% increase in heart attacks the following day.

An important topic to consider is the recycling rate of humans. Or, more precisely, how long humans can last without sleep before seeing these declines. The answer appears to be about 16 hours of wakefulness. Once you get past 16 hours of being awake, that’s when we start to recognize mental deterioration and physiological deterioration in the body. We know that after you’ve been awake for 19 or 20 hours, your mental capacity while driving is as impaired as someone who is legally drunk. Therefore, as humans’ recycle rate is 16 hours, we then need about eight hours of sleep to repair the damage of wakefulness. Wakefulness essentially is low-level brain damage.

Caffeine, Jet Lag, and Melatonin: Losing and Gaining Control of Your Sleep Rhythm

If you’ve ever had a sleep problem, you’ve probably browsed the supplements section at your local pharmacy. The most common among those supplements is melatonin. However, many question whether melatonin actually works. The author only recommends taking melatonin if you’re going to be traveling and experiencing jet lag. To understand why Matthew Walker recommends this, you need to know how the body goes to sleep.

Your circadian rhythm is your level of energy or wakefulness throughout the day. Circadian rhythms are a cycle: most people will feel awake in the morning, experience a dip in the early afternoon, feel awake in the early evening and then get tired around bedtime. Recent research has increased our understanding of the circadian rhythm. Actually, the 2017 Nobel Prize in Physiology or Medicine was awarded to circadian rhythm researchers. At a simple level, our bodies produce melatonin to signal when it’s time for us to sleep.

In general, we’re better off trying to stimulate natural melatonin production than taking melatonin. Stimulating is better than medicating because there’s a second system our body uses for sleep. When we’re awake, our bodies gradually increase the concentration of adenosine in our brains. As more adenosine builds up, we experience more “sleep pressure,” or desire to sleep. The longer you stay awake, the more sleep pressure you experience. This is why you can still fall asleep in the middle of the day if you’re genuinely exhausted. When you sleep, your body dumps adenosine. In an ideal situation, you dump adenosine during a quiet period of your circadian rhythm so that you can have a truly deep sleep.

Morning Larks or Night Owls

“Asking your teenage son or daughter to go to bed and fall asleep at ten p.m. is the circadian equivalent of asking you, their parent, to go to sleep at seven or eight p.m. No matter how loud you enunciate the order, no matter how much that teenager truly wishes to obey your instruction, and no matter what amount of willed effort is applied by either of the two parties, the circadian rhythm of a teenager will not be miraculously coaxed into a change. Furthermore, asking that same teenager to wake up at seven the next morning and function with intellect, grace, and good mood is the equivalent of asking you, their parent, to do the same at four or five a.m.” – Matthew Walker

Everyone has a different circadian rhythm. For some people, their peak of wakefulness arrives early in the day, and their sleepiness trough arrives early at night. These are morning larks and make up about 40% of the population. These people tend to wake around dawn and function optimally at this time of day.

Other people are night owls and account for about 30% of the population. These people prefer going to bed late and waking up late the following morning.

The remaining 30% of the population is somewhere between a morning and evening type.

Your “type” is known as your chronotype, and it’s primarily determined by genetics. If you’re a night owl, it’s likely that one or both of your parents is a night owl. Sadly, society treats night owls as lazy since they don’t like to wake up until later in the morning. In addition, society’s work schedule favors morning types. Evening types are often forced into an unnatural sleep-wake rhythm to meet a certain work schedule. Thus, evening types are more often sleep-deprived.

The reason for different chronotypes within society is that humans likely evolved to co-sleep as families or even whole tribes. Hence, based on this, the benefits of genetically programmed variation in sleep/wake timing preferences can be understood. The night owls in the group would not be going to sleep until one or two a.m. and not waking until nine or ten a.m. Conversely, the morning larks would have retired for the night at nine p.m. and woken at five a.m. Consequently, the group as a whole is only collectively vulnerable (i.e., every person asleep) for just four rather than eight hours. Crucially, this process also allows everyone to still get eight hours of sleep. That’s potentially a 50 percent increase in survival fitness.

Lucid Dreaming

By definition, lucid dreaming is simply the act of knowing that you’re dreaming while you’re dreaming. Most people think of lucid dreaming as beginning to control what you’re dreaming. So, you gain volitional control, and you decide what’s going to happen during your dream. Scientists have designed experiments and demonstrated objectively that when people say that they’re doing something in a dream that they actually are. However, it seems unlikely they are controlling what they are dreaming.

It is possible to increase your chances of lucid dreaming. For example, before falling asleep, you can tell yourself that you will remember your dreams. Despite this, it is not particularly easy. Instead, it appears that only around 20 to 30% of the population are natural lucid dreamers. Based on this percentage, Matthew Walker highlights we are currently unsure if lucid dreaming is evolutionarily adaptive. Are the 20% in a more evolved state of dreaming? We do not currently know the answer to this question.

Why Naps Can Be Dangerous for Your Health

Naps can provide benefits for both your brain and your body. However, naps can also be a double-edged sword. While we’re awake during the day, we’re building up sleepiness or sleep pressure. This pressure allows you to fall asleep quickly and stay asleep. When we sleep, we release that sleepiness.

So, if you take a nap during the day, especially if you take it too late in the afternoon, you will actually release some of that sleepiness. Subsequently, this type of nap will make it that much more difficult to fall asleep and stay asleep. Hence, if you don’t struggle with your sleep, Matthew Walker believes you can nap regularly. However, if you find it difficult to fall asleep or stay asleep at night, you should avoid naps. Instead, try to build up your sleepiness.

The ideal nap depends on what you want from that nap. Different stages of sleep give you different types of brain and body benefits. However, if you want to avoid that grogginess you can often have after a long sleep, you should perhaps avoid naps that are longer than maybe 40 or 50 minutes in length. 

“They discovered that naps as short as twenty-six minutes in length still offered a 34 percent improvement in task performance and more than a 50 percent increase in overall alertness.” – Matthew Walker

Can Naps Help With Sleep Debt?

Sleep is not like a bank. You can’t accumulate a debt and then hope to pay it off at some later point in time. Instead, sleep is an all-or-nothing event. You can’t skip sleep during the week and then try to binge and oversleep at the weekend. This sleep binge will not make up for your previous lost sleep.

Human beings are the only species that deliberately deprive themselves of sleep. Hence, Mother Nature has never had to face the challenge of sleep deprivation during the course of evolution. Subsequently, humans have not evolved a safety net mechanism that overcomes sleep debt.

A New Vision for Sleep in the Twenty-First Century

“Humans are not sleeping the way nature intended. The number of sleep bouts, the duration of sleep, and when sleep occurs has all been comprehensively distorted by modernity.” – Matthew Walker

Matthew Walker offers five key tips to help your future be filled with an easier sleeping process:

  1. Try to maintain regularity. Go to bed at the same time every night and wake up at the same time every morning. Do this irrespective of whether it is the weekend or a weekday. Even if you’ve had a bad night of sleep, still wake up at the same time of day and reset.
  2. We need darkness in the evening to allow the release of a hormone called melatonin. Melatonin helps us maintain a healthy sleep time. Therefore, try to dim down half the lights in your home in the hour before bed. Stay away from screens, especially LED screens — they emit blue light that actually puts the brakes on melatonin.
  3. Keep your sleeping environment as cool as possible. Many of us have a bedroom that’s too warm in terms of temperature. An optimal temperature is about 68 degrees Fahrenheit or about 18 and a half degrees Celsius. Your brain and body need to drop their core temperature by about two or three degrees Fahrenheit to initiate good sleep. Hence, you’ll always find it easier to fall asleep in a room that’s too cold than too hot. 
  4. Avoid alcohol and caffeine. Alcohol is perhaps the most misunderstood drug when it comes to sleep. People believe it helps them fall asleep. That’s not true. Alcohol is a type of sedative, which means alcohol is basically just knocking your brain out. You’re not putting it into natural sleep. Research suggests that alcohol will fragment your sleep. So, you’ll wake up many more times throughout the night. Finally, alcohol also blocks dream sleep. Caffeine is also a problem. Many of us know that caffeine can keep us awake as it is a stimulant. However, few people know that even if you fall asleep fine and maybe you stay asleep after a coffee, the depth of your deep sleep will be lessened. 
  5. Do not stay in bed, awake. If you haven’t fallen asleep within 20 or so minutes, or you’ve woken up and you’re finding it difficult to fall back asleep, don’t stay in bed awake. Your brain quickly learns an association between your bed and being awake. Therefore, get up and go to another room. In the dim light, just read a book. No screens, no email checking, no food. Only when you feel sleepy should you return to bed. If you adopt this approach, you can re-learn the association between your bedroom and sleepiness.


We rate this book 4.6/5.

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