Why We Sleep by Matthew Walker: a review

I picked up a copy of Why We Sleep by Matthew Walker randomly at a bookstore a few years ago where it sat on my shelf for some time. I’m not sure what compelled me to purchase it that day but I guess it had something to do with my reasonable notion that sleep was important, especially from a productivity standpoint so maybe there was something I was missing and could learn. For now, I’d like to note the structure of this post which will be: a few takeaways or interesting points from the first one hundred pages (one-third of book and in the hopes it will inspire you to read it for yourself), my personal experiences and notes with sleep, followed by essential criticisms which I want to get in the habit of checking after reading non-fiction books. So, without further ado, let’s begin with five from the first one hundred.

1. 1. 1. A note on circadian rhythms: every animal which lives longer than several days adheres to an internal, biological circadian rhythm of some sort. In humans (us), this rhythm helps regulate the release of hormones, our metabolic rate, preference time for eating and drinking, and even our emotions. All are inexplicably tied to this clock within our brains. The time of day even has an impact on athletes at the highest level of performance, the Olympics, with late afternoon being the optimal time to hold races for best performance. You can find out more about this in the article here. Also, here is a link to read into Jean-Jacques d’Ortous de Mairan who first discovered the notion of circadian rhythms, not in animals, but in plants. The leap to find this rhythm in humans required an even bigger leap of resolution. The challenge ultimately fell on the shoulders of Nathaniel Kleitman and graduate student Bruce H. Richardson from the University of Chicago who spent a month in Kentucky’s own Mammoth Cave. They found that their our own biological clocks were slightly longer than one day, not precisely one day. They also found that Richardson, who was younger than Kleitman by over a decade, had a longer circadian rhythm. The idiosyncrasies of our own biological clocks, however, are naturally kept in check by the sun which makes sense as it is the most reliable signal we experience. Still, it is not the only stimulus which helps balance our natural rhythms. The regulator of our circadian rhythm is the suprachiasmatic nucleus which is a tiny part of our brain that sits right above where the nerves from our eyes meet and switch. The suprachiasmatic nucleus is able to get a read of the light from those nerves which it uses to help it regulate our circadian rhythm.
      2. When the suprachiasmatic nucleus begins to notice reduced light, which is usually after dusk, it begins to instruct the pineal gland to release melatonin. Melatonin is only really a notice for your body to prepare for sleep as it does not have a direct role in sleep itself. It peaks in the early morning hours and then quickly begins to fade which also acts as a notice for your body that it is soon time to wake up. There is another force which is independent of this part of your circadian rhythm called sleep pressure. Sleep pressure is due to the build up of adenosine in your brain. All through your waking hours this chemical, adenosine, is accumulating in your brain and as it increases throughout the time awake so too does your desire to fall asleep. This pressure typically peaks around 12 to 16 hours of wakefulness. What’s interesting however is when caffeine is brought into the mix (or more than likely, ingested). Caffeine simply has a masking effect on adenosine in the brain by attaching to their designated receptors. However, it doesn’t prevent the build up of adenosine in your brain. That is why when your liver finally breaks down the caffeine in your system, adenosine which had been building up in your brain rushes to fill the receptors left by caffeine which induces a sudden build up of sleep pressure causing what some people feel as a “crash”. Another problem with caffeine is its long half-life. It can take between five and seven hours to break down half of the caffeine which has been ingested. So, if you have an afternoon coffee at 3pm to help you push through the last few hours of work, that means there could still be a decent amount of caffeine circulating in your brain at 10pm when you may be getting ready for bed. Now, I am not trying to push you away from coffee, not in the slightest. I personally am an avid coffee drinker but my use has had its own experimentation as well to find what best works for me. Usually, this entails a 20oz mug made an hour or so after I wake up which I drink throughout the morning with the last sips consumed after I have finished eating lunch. By delaying my coffee intake until after I have woken up and adding a little on top of my lunch, I was able to basically eliminate my urge for another mid-afternoon cup.
      3. When you go to sleep your perception is essentially cut off from the external world. This doesn’t mean that your sensory organs are not still working, only that their convergence zone in the center of the brain is blocked off by the thalamus during sleep. This part of your brain decides which information gets sent up the change of command to your cerebral cortex where you become aware of it. When scientists are studying sleep, they use electrode signals from brainwave activity, eye movement activity, and muscle activity. It was the eye movement in particular which helped researchers get a notion that sleep had different stages and from there they were able to discern REM (rapid eye movement) sleep and NREM (non-rapid eye movement) sleep with the latter having four stages. The four stages are related to the depth of NREM sleep being experienced with the higher stages noting deeper NREM sleep and increased difficulty waking someone up. While you sleep you are constantly cycling through these stages approximately every ninety minutes. However, the rotation through each stage of sleep is not quite even as the first half of the night is dominated by NREM sleep and REM has a higher presence in early morning hours. Science can still not quite explain why we sleep in cycles and how they work. I found Walker’s discussion on brainwave patterns using Figure 9 as quite interesting. He shows the brainwaves of wakefulness, NREM, and REM sleep. I didn’t know that your brainwaves while awake are really that random and unpredictable while NREM is the opposite. What’s even more profound is that REM sleep actually looks very similar to wakefulness and several parts of the brain are even more active during this stage of sleep than they are in your waking life. You can not distinguish wakefulness from REM sleep simply by reading brainwaves. What’s interesting though is that while REM is alive and sporadic, your brainwaves during deep NREM sleep are much slower and rhythmic. There is also a rolling R or a purrr in the brainwaves every now and then. This is a sleep spindle which usually occurs at the end of each brainwave. Matt Walker states that “the more powerful and frequent an inividual’s sleep spindles, the more resilient they are to external noises that would otherwise awaken the sleeper” (pg. 49). I had heard of the stages of sleep before but never of sleep spindles! REM also had a feature which I found interesting and that was “atonia” which refers to your body becoming completely limp and essentially paralyzed. Why? It may be because there are powerful movement brainwaves occurring, since, as I just wrote, your brainwaves in REM sleep are nearly identical to waking life. Thus, by paralyzing your body and essentially trapping your self in your mind, your brain is protecting you from acting out the motions in your dreams. Perhaps some people have also experienced this while awake in sleep paralysis cases.
      4. All animals sleep or perform a function which resembles it. What resembles it you might ask? That would be behavioral features like immobility, reduced response to external world and easily reversible. These features need to be observed especially in small insects where it is currently impossible to measure brainwaves. Scientists have even observed active and passive phases in unicellular organisms which correspond to the light-dark cycles of the planet. When you look at the sleep requirements, it seems somewhat erratic where humans need eight hours of sleep, lions and tigers around fifteen hours, an elephant about four hours while a tiny brown bat takes home the crown of sleep champion by averaging nineteen hours per day. Can you imagine only being awake for five hours everyday? We still haven’t quite been able to figure out the correlation between the animal and the amount of time they spend asleep. It is a mystery. In fact, a lot about sleep in the animal kingdom is a mystery. Matthew Walker brings up fur seals which are partially aquatic animals. On land they have NREM and REM sleep but when they are in water they have almost no REM sleep. Scientists have documented seals for up to two weeks in water without any REM sleep while surviving off of small doses of NREM sleep alone. When looking at the animal kingdom, scientists are coming under the impression that REM sleep could even be a relatively new evolutionary phenomenon since birds and mammals have full blown REM sleep but scientists have yet to show clear signs of REM sleep in insects, amphibians, fish and most reptiles. The last interesting point I want to mention is about the white-crowned sparrow, which breeds in Alaska and the Canadian Arctic and migrates over the continental United States and Mexico over winter. This bird shows an unprecedented ability to forego sleep during the migratory season. Researchers found that if you sleep deprive this bird in a laboratory during the migratory season it shows no ill-effects but if the experiment is repeated outside of the migratory season then this sparrow suffers greatly as all animals do when sleep deprived. How the white-crowned sparrow does this is unknown.
      5. The last bit of the first one-hundred pages which struck me was how sleep changes over our life span. A baby in the womb will spend almost all of it’s developmental life in a sleep-like state – much of which resembles REM sleep. That could be part of the explanation for kicks in the womb as the fetus still has not developed the atonia I noted before which prevents it from acting out sudden movement brainwave bursts which can occur during REM sleep. What’s even more fascinating is that in the last two weeks of pregnancy, the child’s REM sleep explodes to nine hours a day and then to twelve hours a day in the last week before it is born. This will never happen again in its lifetime. Right before being born is the most REM sleep you will ever experience. Then, to summarize the stages of development, a newborn will go on to perform an erratic sleep schedule because its circadian rhythm won’t begin to show signs of forming until three or four months. It is not until around the one year mark where the suprachiasmatic nucleus begins to reign in it’s circadian rhythm as the baby is now awake for more of the day. Around age four the child’s circadian rhythm gains the upper hand and now changes the child to a biphasic sleep schedule where the child can sleep long bouts at night and needs a nap during the day which they are soon able to shed to a completely monophasic sleep schedule, one it will keep for the rest of its life. REM sleep, which was at an all time high right before birth, continues to decrease well into the teenage years where it settles at about an 80/20 split of NREM to REM sleep. Teenagers undergo a dramatic shift in their circadian rhythm during puberty which pushes back their sleep pressure from the childhood years. It is part of the explanation why teenagers generally want to stay up later than children or even adults. This adjustment in their circadian rhythm eventually goes down in early adulthood. All through adulthood, unfortunately, our duration in the deep stages of NREM sleep decline for the rest of our lives and we are increasingly prone to fragmentation in our night’s sleep meaning that we will have increased bouts of waking up during the night. Sleep health is something to keep in mind and address throughout our lives.

These five points were some of the key takeaways and interesting insights I found in the first one-hundred pages of Why We Sleep by Matthew Walker. Of course, Walker goes into much greater detail than I have even tried to do here and there is certainly much more to it than what I have relayed. Through the other two-thirds of the book, Matthew Walker goes into great detail to describe what goes on in our bodies during sleep, the wins and losses on our health in which sleep has an impact, the implications to society of the individual’s sleep health, and what we might be able to do to improve our sleep quality. For me, it was a truly profound read and I definitely did not think that sleep could be so interesting. We must, however, get in to a practice of taking a skeptical view. During these write ups, I want to also look up any critiques that might be out there because, as we should know, life is incredibly complicated which allows for multiple views to be taken for the same concept. It is up to us then to decipher either side and decide where our interpretation might lie. Which argument is more compelling? I located only one article which was oriented to be vehemently opposed to Matthew Walker. This article is from a blog maintained Alexey Guzey. Alexey Guzey runs a personal blog but is also the president of New Science where he is listed as a writer and researcher who has had some work even featured on the BBC and Wired. New Science appears to be a fellowship program to sponsor aspiring researchers to progress scientific research and create metascience research to improve the field as a whole. It is no surprise then that Alexey is able to ask good questions even after reading a book as compelling as Why We Sleep. Matthew Walker obtained his graduate degree in neuroscience from the University of Nottingham in 1996 and got his Ph.D in neurophysiology from Newcastle University in 1999. He became an associate professor at Harvard Medical School in 2004 where he had been conducting sleep research. He left Harvard in 2007 and taught as a professor of neuroscience and psychology at University of California Berkeley where he founded and directed the Center for Human Sleep Science. After he published Why We Sleep in 2017, he became a sleep scientist at Google. Alexey Guzey does not take a complacent stance on Matthew Walker’s book. His whole article is extremely impressive and he only put chapter 1 under intense scrutiny. He spent 130 hours over two months to complete his rebuttal of Why We Sleep. It’s a dense article and I certainly don’t have the research chops to appreciate it or fully understand it. Alexey addresses some of Matthew Walker’s claims with additional studies to refute that short sleep has a detrimental effect on life span and increased cancer risk. Alexey is on the other side of the spectrum and hypothesizes that people who sleep only six hours a night might live longer. The graph Alexey provides is interesting but I disagree with him on the increased cancer risk. He states that Matthew Walker does not cite any studies that support his position anywhere in the book. However, I believe he does on page 185 and 186 where he talks about the work of Dr. David Gozal at the University of Chicago. In 2007 the World Health Organization even labeled night time shift work as a probable carcinogen due to the disturbance in the circadian rhythms of individuals. It appears, however, that studies have found contradictory results. Although, for me, I’d rather stay on the safe side. Alexey continues to conclude that Walker cannot make overarching statements about sleep as always being beneficial when there have been some studies on the benefits of slight sleep deprivation in the treatment of some forms of depression. To me, this felt like Alexey was nitpicking a little too much as in a later chapter Matthew Walker does make note of these studies himself. Alexey is making this analysis based on the first chapter of the book where general statements are made to introduce the material. Though, I do understand the need to be specific and correct. He makes further points about Fatal Familial Insomnia and how it is not the lack of sleep which kills the person. In my opinion it is a matter of classification akin to the question we recently had in the pandemic where we had to decide of what did people die from? He also points out that Matthew Walker seems to have invented that the World Health Organization declared a sleep loss epidemic. I also have been unable to locate where this was stated as it seems to have been conjured up. I’ll give this one to Alexey as I would prefer authors to properly cite a bold statement such as this. The last point has to do with Walker’s statement that two-thirds of adults in developed nations do not obtain the recommended amount of sleep. This percentage should have seemed quite high to me but Alexey also has a problem with the recommended amount of eight hours stating that within the literature it is quite unclear how we came up with this amount of time as it appears to just be an average which you can’t really apply to everyone. I believe Walker also addresses this later on in the book as he transitions his wording to recommend seven to nine hours of sleep opportunity meaning his recommendation is to get in to bed and not expect to wake up until seven to nine hours later. Based upon actual times you fall asleep it will of course be less than the sleep opportunity you allotted to yourself. Ultimately, I believe it comes down to the individual to find their optimal sleep opportunity time while keeping in mind the many examples of the effects of sleep deprivation which Walker discusses in later chapters. Alexey’s article is very good and meticulous. It appears to be great analytical work and I’d definitely recommend people to give it a read either before or after you read Why We Sleep by Matthew Walker. I think he teaches us a great lesson that nothing is clear cut even when it is told in such a compelling way. We should all be skeptics when presented with non-fiction work. Still, his critique is more so into specific details which Walker mentions and let’s face it. No one is perfect and errors are bound to happen in a 340 page book. Alexey is not trying to degrade the importance of high-quality sleep whatsoever. He concludes that the main negative outcomes have to do with the supposed harm recommending eight hours of sleep in such compelling terms, could have on people who get worried because their sleep routine doesn’t meet what is recommended and could in turn worsen their insomnia. I have a hard time getting behind this impact as naturally things need experimentation and self reflection. People need to be a bit more sure of themselves when they try to apply things they read. Especially when Walker is recommending a seven to nine hour sleep opportunity window and also states that if you get in to bed and are not tired then you should get up and do something until you are (while also providing a lot of information on how to reign in sleep pressure and the release of melatonin). He makes note of the negative outcomes worrying about not being able to fall asleep can have while you are laying in bed trying to fall asleep. He also provides numerous links for professional advice on sleep health and encourages working with a sleep professional if certain things apply to you Otherwise, Alexey is worried that you might waste an hour or so of your life everyday by sleeping more than you need to. In conclusion, I highly recommend Why We Sleep by Matthew Walker. I found his discussion on sleep to be much more intriguing than I ever would have thought. I had no idea so much was happening within our bodies while we sleep and the critical role it plays in our health. However, thanks to people like Alexey Guzey, we can also take these works with a grain of salt. Instead, we can work on experimenting with the lessons we find in the hopes that we can then apply them in a modified form to have a beneficial impact on our life. Anyway, do you think you could be getting more sleep? Are you satisfied with your sleep quality? Would you like to learn more about the inner workings of our sleep state?