Minimalistic depiction of the book Why We Sleep with moon symbol

Why We Sleep - Summary, Review & Thoughts

We spend 1/3rd of our life sleeping. But why do we sleep? We don’t live in a sleep loss epidemic?

Why Everyone Needs To Sleep

Everyone sleeps. But why?

Sleep has been shown to be a basic need for nearly all species on Earth. Almost all animals sleep.

It is one of the most basic needs of every human being. Sleep is essential for maintaining a healthy mind and body. And we do not sleep for one reason, but for a magnitude of them.

Sleep is essential for our brain. Our ability to learn, memorize, maintain emotional balance or make logical decisions depends on sleep. It is also the basis of creativity. And sleep isn’t just essential for your brain, your whole body needs it. It reforms your body’s metabolic state, regulates your appetite and even keeps your cardiovascular system going.

Lack of sleep has many negative consequences. It undermines your immune system and increases your chances of cancer, Alzheimer’s disease, cardiovascular disease, or many other unwanted outcomes. Sleep disturbances also contribute to all major mental illnesses, such as depression and anxiety. Of course, missing one night’s sleep doesn’t immediately lead to various diseases, but it will still impact you throughout that day.

Sadly in the work environment where sleep deprivation is all too common it can even act as a chain-reaction where the lack of sleep of one superordinate is transmitted on like a virus, infecting even well-rested employees. Insufficient sleep does not just increase the urge to eat, it also reduces productivity, motivation, creativity and happiness. Lack of sleep is also linked to worse self-control, a more abusive nature of behaviour, higher chance of lying and more ethical deviance.

It is also scientifically proven that missing sleep makes you less attractive and impacts reproductive systems in various ways. Men experiencing sleep loss will have significantly lower testosterone virility which also leads to feeling tired more often and having trouble concentrating. Women experience a drop in follicular-releasing hormones, have a higher chance of abnormal menstrual cycles and issues of sub-fertility reducing the ability to get pregnant.

Common Misconceptions About Sleep

  • When you’re sleep deprived, you don’t know how sleep deprived you are.
  • You can’t sleep back any missed sleep.
  • Missing sleep makes you take longer for any task, even just dressing yourself.
  • Teenagers become tired later in the day due to changes in their circadian rhythm.
  • There are “night owls” and “morning larks”. The peaks and lows in the rhythm of every person are different. These are heavily influenced by their chronotype.
  • Older adults still need just as much sleep as younger adults. Lack of sleep in older adults is associated with an increased risk of poor health.
  • Taking sleeping pills does not guarantee natural sleep. Sleeping pills have numerous downsides (insomnia, poor quality sleep, health risks) and the benefits are minimal at best. CBT-I therapy for insomnia is a great behavioural alternative.

How Sleeping Works

Mainly two factors regulate wakefulness and sleep, the circadian rhythm and sleep pressure (also called sleep drive). Circadian Rhythm & Sleep Pressure(Sleep drive).

Text saying: "Circadian Rhythm & Sleep Pressure"

Circadian Rhythm

Circadian rhythm is your inner 24-hour rhythm. It not only controls when you are awake or asleep, but it also includes your preferred time for drinking, mood, emotions, metabolic rate and release of different hormones.

Even the likelihood of breaking an Olympic record has been tied to a specific time of the day, being maximal at the natural peak of the human circadian rhythm in the early afternoon.

Our innate biological rhythms are not exactly 24-hour. The average duration of the endogenous biological clock in human adults is about 24 hours and 15 minutes, slightly longer than a day. Which is why our brain uses additional signals to regulate itself.

Solar light systematically resets an inaccurate internal timer. Daylight is the most reliable repetitive signal and the most important signal our brain uses, but there are many more. All signals that the brain uses for this purpose are called “Zeitgeber”.

Circadian rhythms even determine body temperature. Body temperature throughout the day.

Although every human has a 24-hour pattern, the highs and lows are different for each. An important role in this is their chronotype.

Chronotype is strongly determined by genetics. The society’s work schedule is strongly biased against owls and favors larks. About 40% of the population experiences a peak in the early morning and a low in the early night. Another 30% peak at dawn, with the rest of the population somewhere in between. These “evening types” and “morning types” are often referred to as “night owls” and “morning larks” respectively.

Often mentioned on the topic of sleep is melatonin but it is also frequently misunderstood.

Melatonin commences the event of sleep. It has little influence on generating sleep itself. Its main task is signaling the begin of night-time throughout the organism. Rise of melatonin in the body begins begins soon after dusk.

Once sleep is under way it slowly decreases in concentration across the night. As sunlight enters the eyes the next morning, even through closed lids, the release of melatonin is stopped.

Sleep Pressure

Sleep pressure is the second of two factors determining wake and sleep.

How is sleep pressure formed?

With every waking minute adenosine builds up in your brain, the longer you are awake the more adenosine will accumulate. One consequence of increasing adenosine is an increasing desire to sleep.

It is possible to artificially mute this signal, with caffeine. This psychoactive stimulant latches onto the receptors that would normally welcome adenosine. Caffeine blocks and effectively inactivates these receptors, the adenosine is still in your body to the same amount but the signaling has been blocked.

Caffeine has a half-life of about five to seven hours, the amount of time it takes for your body to remove 50% of its concentration in your body. With caffeine in your body sleep quality will be worse. Many products contain caffeine such as various teas, coffee(decaffeinated does not mean non-caffeinated), pills, dark chocolate and ice cream.

The “jolt” of caffeine does wear off as it removed from your system by an enzyme in your liver. How effective it is is different from person to person. Generally the older we are the longer it takes for caffeine to clear and the more sensitive we are to its sleep-disrupting influence.

While sleeping the brain starts removing the adenosine. After about 8 hours of sleep in an healthy adult the adenosine purge is complete. The urge to sleep.

As illustrated in the image, the bigger the difference between the circadian rhythm (Process-C) and the sleep pressure by adenosine (Process-S) the greater the urge to sleep. During the morning the difference is minimal, meaning there is a strong urge to be awake and alert. In the night (around 23:00 in the example above) the urge is the greatest.

In the example above we assume the person goes to sleep at 23:00 and has 8 hours of sleep.

Did we always sleep like this?

Humans used to sleep in a biphasic pattern. Now most people in developed nations sleep in a monophasic pattern.

There is also the case of pre-industrial tribes such as the Hazda tribe to mix the two patterns. They are biphasic during the hotter summer months and monophasic during cooler winter months.

The origin of biphasic sleep is not cultural, it is deeply biological. The true pattern of biphasic sleep consists of a longer bout of continuous sleep at night plus a shorter mid-afternoon nap.

Often we can feel the remains of this as we experience some drowsiness during mid-afternoon, just after the high-degree wakefulness that is the early-afternoon.

Biphasic sleep is still practised by cultures throughout the world. In small enclaves of Greece where siestas still remain intact such as the island of Ikaria man are much more likely to reach the age of ninety compared to American males. The book states it to be nearly four times as likely but there are no statistics to back these claims (more on that later).

Sleep Stages

There are two main types of sleep, REM sleep (rapid eye movement) and NREM (non–rapid eye movement) sleep. During a night of sleep we experience both stages of sleep multiple times in a somewhat repeating cycle.

During REM sleep, the brain is highly active, and vivid dreaming often occurs. It is characterized by rapid eye movements, hence the name.

A key function of NREM sleep which predominates early in the night is to remove unnecessary neural connections. REM sleep in contrast, the dreaming stage, prevails in strengthening connections.

NREM sleep can be further divided into 4 stages. The deeper into the stages the deeper the sleep is and the further brain activity slows down. Architecture of sleep.

REM sleep is vital for processing information. Which is why sacrificing sleep to study is a lost battle, as new insights are not actually kept in the brain due to missed sleep.

How To Sleep Better

There are multiple things you can do to improve your sleep. The National Institute of Health offers 12 key tips for better sleep:

  1. Stick to a schedule
    Go to bed and wake up at the same time each day. Having an alarm clock for when you want to go to sleep might be very helpful.
  2. Exercise
    Try to exercise at least 30 minutes on most days but not later than 2 or 3 hours before sleep.
  3. Avoid caffeine and nicotine
    Coffee, colas, certain teas and chocolate all contain caffeine. Can take up to 8 hours before the effect wears off. A cup of coffee in the afternoon can already make it harder for you to fall asleep. Nicotine is another stimulant that causes light sleep. It also causes smoker to wake up too early in the morning due to nicotine withdrawal.
  4. Avoid alcoholic drinks before bed
    Alcohol robs you of REM sleep causing it to have a strong negative effect on memory formation. REM sleep is important for memory integration and association. It can also cause impairment of breathing at night. Overall is causes lighter sleep and worse sleep quality.
  5. Avoid large meals and beverages just before sleeping
    They can cause indigestion and you might have to interrupt your sleep to go to the bathroom.
  6. If possible, avoid medicine that delay or disrupt sleep
    Many medications disrupt sleep patterns. When you have trouble sleeping ask your health care provider if it is possible to take the sleep disrupting medicine during times of the day that is not right before bedtime.
  7. No naps after 15:00
    Late afternoon naps can make it harder to fall asleep at night.
  8. Relax before bed
    Have time for unwinding. Maybe have a bedtime ritual with an relaxing activity.
  9. Take a hot bath before bed
    The drop in body temperature can help you feel sleepy. The bath can also help you relax.
  10. Have a bedroom that is dark, cold and gadget free
    Get rid of anything that might distract from sleep such as noise, light or an uncomfortable bed. Gadgets such as a TV in the bedroom can also be a distraction and rob you from sleep. A comfortable mattress and pillow also contribute to better sleep. Turn clock’s faces out of view so you don’t worry about the time when trying to sleep.
    Keep the bedroom cold, around 18/19°C.
  11. Have the right sunlight exposure
    Daylight is key to regulating daily sleep patters. If possible wake up with the sun or use very bright lights in the morning. It is also recommended to get sunlight exposure in the morning and turn down lights before bedtime.
    Andrew Huberman from the Huberman Lab podcast is often quoted in his daily routine to get morning sunlight:” 2-10 minutes of sunlight exposure while walking for optic flow” is what he recommends.
  12. Don’t lie awake in bed
    If you stay in bed awake for more than 20 minutes or find yourself feeling anxious, get up and do something relaxing until you feel sleepy.

There are more ways to improve your sleep that have not been listed here obviously. Remember to give yourself enough sleep opportunity. To sleep 8 hours you need more than 8 hours of sleep opportunity. Even more than 8h30 maybe.

Avoiding blue light from devices such as TV screens or smartphones also significantly improves sleep quality. Replace LED lamps in the bedroom as well.

Don’t forget that some advice here might not work for you. Never make yourself feel anxious for not following everything.

How long should you sleep?

A keen eye might have noticed that the National Institute of Health does not advise to sleep a certain amount. It is highly debateable how much sleep a person needs. Especially the meaning of “needs” is another topic for itself.

Around 8 hours of sleep are a good benchmark for many. How much sleep each person wants and needs is highly individual. There are many people that need less or more. Give yourself enough sleep opportunity and don’t force yourself to sleep more than “needed”, if you feel refreshed and wake after 7 1/2 hours of sleep then continue doing so if that works for you. But if you need more than 8 hours of sleep also give yourself the opportunity to do so. If you feel chronically tired even after trying to improve sleep hygiene consult a doctor.


While reading the book I found valuable and entertaining passages I would like to share.

With our rich new scientific understanding of sleep, we no longer have to ask why sleep is good for us. Instead, we can’t help but wonder if there are biological functions that don’t conducive to good sleep. So far, thousands of studies have shown otherwise.

The overnight work of REM sleep, which normally assimilates complex memory knowledge, had been interfered with by the alcohol. More surprising, perhaps, was the realization that the brain is not done processing that knowledge after the first night of sleep. Memories remain perilously vulnerable to any disruption of sleep (including that from alcohol) even up to three nights after learning, despite two full nights of natural sleep prior.

But my favorite is the shredder. At night, you slide paper bills (e.g. $20) in front of the clock. When the alarm goes off in the morning, you have less time to wake up. Turn off the alarm before it starts shredding your money.

My Thoughts On "Why We Sleep" By Matthew Walker

Most of the content for this post here has been inspired from “Why We Sleep” by Matthew Walker.

Is Why We Sleep Worth Reading?

I personally enjoyed reading “Why We Sleep”. The book is filled with valuable and entertaining insight and gave me an perspective I haven’t had before on sleep.

There are plenty biological and neuroscientific facts on sleep. I personally do not care much about the names of certain brain regions and for me that came up a bit too much. The book is not a scientific paper and it shouldn’t be (more on that soon).

It is structured in a way that makes it possible to skip topics that are uninteresting to you. The author even encourages you to do so. Even by skipping areas of the book it reads very well.

One large chapter of the book is about dreams. I didn’t cover that topic at all on this post. Other topics of the book include evolution of sleep, sleep in the animal kingdom, relevant discoveries in sleep science, experiments done on sleep and more.

Onto the negatives.

When reading this you should stay aware of the fact that there is someone who is trying to sell it. The author wants the book to be popular, he tries to evoke strong emotions. He does so by overstating the relevance of certain parts. He did succeed at that, it became very popular with a somewhat strong following.

Some people experience worse sleep after reading the book.

Why? Was knowing the harsh reality of knowing that missing too much sleep will ruin your life too anxiety inducing? Well maybe, but another aspect that plays a big part here is that parts of the book contain wrong information. Some claims are just wrong and others are not supported by the given sources at all.

Early on in the book you will learn that the World Health Organization has declared a sleep loss epidemic throughout industrialized nations, that is wrong. They never did.

Negative percentages are used wrongly multiple times throughout the book. Reducing a positive number by a 100% brings it down to 0. But according to Walker, residents who are limited to no more than a 16h shift, with at least an 8h rest opportunity before the next shift, make a negative number of mistakes. Walker even made this mistake in academic paper of his.

These two mistakes are just examples of many more that can be found.

Many people seem to believe that they need 8 hours of sleep each night after reading the book, even if they lived well before by sleeping less. This leads to some people experiencing sleep anxiety as they can’t seem to get these 8 hours. By experiencing that anxiety they become unable to sleep at all and ultimately have to seek sleep therapy where they have to unlearn untruthful facts of the book to sleep normal again. Don’t take everything at face value, this is true with this book and any other. There are enough people that treat it as some sort of gospel, so be aware.

To conclude I definitely recommend Why We Sleep. It discuses a relevant area of our lives that isn’t talked about enough.

How Has Why We Sleep Helped Me?

Why We Sleep gave me a good overview of how sleep works and made me dive deeper into the concepts of sleep. It also made me more vary on fact checking books, even when written by a popular expert on a certain topic.

To conclude I would also like to share a technique that helps me fall asleep quickly other than just following the rules and practices mentioned previously.

I have forgotten the original source of where I had found it for the first time but another page I found explains it well, they call it the “body scan” technique.

Body scans are a type of meditation that feature a slow, focused attention to different parts of the body. Once you’re lying comfortably in bed, try these steps for a relaxing body scan:

  1. Start by taking a few deep breaths, to get your body into a state of relaxation.
  2. Bring your attention to your feet, noticing any sensations in your toes and if you’re holding any tension in this part of the body.
  3. If you notice discomfort here, acknowledge it and try to let go of any thoughts you have. Visualize the tension leaving the body through the breath.
  4. When you feel ready, shift your focus to your calf muscles, repeating the process of observing sensations, releasing thoughts, and visualizing tension leaving with each breath.
  5. Methodically move your attention to each part of your body, one-by one, moving from your feet to your forehead until you’ve scanned your entire body.


Written by Bryan Hogan


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