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Sleep is one of the most important but least understood aspects of our life, health and longevity. Until very recently, science had no answer to the question of why we sleep, or what good it served, or why we suffer such devastating health consequences when it is absent. Compared to the other basic drives in life – eating, drinking, and reproducing – the purpose of sleep remained elusive.
In Why We Sleep, neuroscientist and sleep expert Matthew Walker charts twenty years of cutting-edge research, looking at creatures from across the animal kingdom to find the answers that will transform our appreciation of sleep and reverse our neglect of it.
"A top sleep scientist argues that sleep is more important for our health than diet or exercise"
– The Times
"Vital [...] a life-raft"
"It had a powerful effect on me"
"I urge you all to read this book"
– Times Higher Education
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.
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 20 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 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. 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 shrink 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. 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 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 (expressed in the link between drowsy driving and car crashes), emotional stability, the cardiovascular system (think 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.
The worst part is, "catching up" on sleep is not a solution. 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 cause more damage. Caffeine keeps you awake by masking the effect of adenosine 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.
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 force to start school days early, 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, 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.
Matthew Walker's fascination with sleep has taken him from Nottingham to Harvard and on to the University of California, Berkeley, where he is currently Professor of Neuroscience and Psychology and Director of the Sleep and Neuroimaging Laboratory. He has published over 100 scientific research studies during the course of his twenty-year career. Why We Sleep is his first book.