The Chernobyl disaster. The stranding of the Exxon Valdez. Car crashes. Suicide. Cancer. Heart attacks. Alzheimer’s disease. What does this list of calamities have in common?
Sleep, or rather a lack thereof, has either caused, or greatly increases the risk of this rather arbitrary and short list. Many more unpleasant things can be added to it. Neuroscientist Matthew Walker is a man on a mission: to impress upon you the importance of sufficient sleep. Why We Sleep is a book that is sure to make you lose some sleep, seeing that it is both fascinating and extremely well-written, but also deeply disturbing in showing the damage we inflict upon ourselves by cutting short our sleep. And, hopefully, it then proceeds to be a book that will make you get more sleep. This is the most important and influential book I have read this year.
Why We Sleep is divided into four parts, two parts dedicated to explaining what sleep is, how it is generated, why we do it and how and why we dream. The other two parts show the benefits of sleep, and the effects of sleep deprivation on brain, body, and society at large, and how we might change things for the better.
The last twenty years have brought many insights into the biology of sleep, and the first part of the book is absolutely fascinating. There are many things I could talk about here, so I will pick two findings Walker explains that were completely new to me.
Most of us will have heard of melatonin and how it rises and falls over 24 hours as a function of exposure to light and darkness (and how jetlag plays havoc with this). But melatonin is only part of the story. Say hello to adenosine, which normally works in lockstep with your circadian rhythm to regulate sleep and wakefulness. Adenosine accumulates in the brain while awake and builds up sleep pressure. It is only broken down during sleep, and the build-up of a normal 16-hour day takes about 8 hours to break down. The nasty thing about adenosine is it’s cumulative. Sleep too little, and you will not have broken all of it down. As you wake up, the build-up starts again, but now reaches higher levels than before. This is how you build up a sleep deficit during a regular workweek, even by sleeping an hour less than you should, and start feeling really tired by the end of the week.
Or what about the finding that the brain has a system equivalent to the body’s lymphatic system, called the glymphatic system, which drains metabolic waste products? At night, the glia cells that make up this system have been found to shrink by some 60%, allowing the brain’s cerebrospinal fluid to flush out metabolic debris. This includes beta-amyloid that forms the plaques in the brain responsible for Alzheimer’s disease, raising the distinct possibility that a lack of sleep could enhance the risk of developing Alzheimer’s.
“Our body may be asleep at night, but make no mistake, our brain is hard at work doing vital maintenance.”
Our body may be asleep at night, but make no mistake, our brain is hard at work doing vital maintenance. Walker shows himself to be a master communicator here, summarising results from many clinical and neurological studies. Not only does he explain things very well, his use of repetition and analogies make this topic easy to comprehend and accessible to a wide audience.
This, then, brings us to the effects of sleep deprivation. In short, large numbers of carefully controlled and conducted clinical studies show that there is no aspect of our health and well-being that is not affected by a lack of sleep: learning and memory formation, risk of injury during physical exercise, concentration (which so strongly shows in the link between drowsy driving and car crashes), emotional stability, the cardiovascular system (with sleep loss causing increased risk of heart attacks and permanently increased blood pressure), metabolism (sleep loss is implicated in diabetes and weight gain by upsetting the hormone balance that controls appetite), reproduction, the risk of developing Alzheimer’s and cancer later in life. Even DNA expression and telomere integrity are negatively affected (telomeres are like end caps on your chromosomes, keeping them from unravelling).
The worst part is, “catching up” on sleep is not going to negate the damage that a lack of sleep causes. You may feel better by reducing sleep pressure, and regain emotional stability, but your brain is not a bank where you can lend sleep and pay it off later. Sleep too little, and for quite a few things the damage is done. Systematically sleeping too little slowly deteriorates your health, often irreversibly. Sleeping pills and stimulants such as caffeine only add fuel to the fire, causing more damage. Caffeine keeps you awake by masking the effect of adenosine (which continues to build as you stay awake) and takes a very long time to be decomposed, resulting in more sleep deprivation and cycles of addiction. Sleeping pills, too, are harmful. No sleeping pill on the market actually induces natural sleep, instead bringing on a state of sedation much like alcohol does, which is not the same. In this state, the brain will not experience the benefits of deep sleep, with all the consequences described above.
“[…] your brain is not a bank where you can lend sleep and pay it off later”
Another fiendish aspect of sleep deprivation is that you can’t accurately judge just how sleep-deprived you are. Go without sleep for 22 hours and you are as impaired in your actions and judgments as someone who meets the legal definition of being drunk. Now remember that many doctors and nurses, people who make life-and-death decisions, regularly work extremely long shifts. Unnerving, no? The same goes for emergency workers and soldiers carrying firearms. Or what about children, who we often force to start school days early (this is especially true in the US, according to Walker), right when they are in a stage of their life where their circadian rhythm is naturally shifted forward in time and they need sufficient sleep for proper psychological development? We inflict years of sleep deprivation on them, all the while expecting them to actually learn things and absorb information.
Once Walker gets around to sketching how our industrialised Western society, with its 24/7, hurry-up mentality is literally depriving billions of people of the health benefits of normal sleep, I had a sinking feeling in my stomach. A public health crisis of enormous proportions has been slowly building for decades. Already many speak of epidemics of all sorts of afflictions in our society (obesity, depression, cancer etc.). But how many of us actually implicate a lack of sleep in this?
Walker is down to earth and honest. We don’t have all the answers yet, but there is overwhelming evidence to implicate insufficient sleep as a contributing factor to many health problems, more likely an important cause. The tide is changing, however slowly. The WHO has started recognising the effects of shift work on sleep as probably carcinogenic. Forward-thinking companies are allowing people to start working according to their chronotype (i.e. whether you’re a proverbial night owl or lark), and school times are being changed. But we need many changes, on all levels of society. Many institutions and companies are stuck in their old habits, and many still scoff at the spectre of sleep deprivation. We need to remove the stigma from wanting and requiring sufficient sleep. This has nothing to do with being lazy. The roadmap Walker offers in the last chapter is helpful in this regard.
As we all need sleep and most of us don’t get enough, this book is deserving of the widest possible audience. Luckily, Walker is more than up for the task and has written an engrossing book. Why We Sleep is one of the most important books I have read. If you read just one book this year, please make it this one, it’s almost guaranteed to improve your life.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
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