Why We Sleep

The world is full of theories, and corresponding books, about things that will make you healthier or prevent disease. Nearly all of them are scams, either intentional or created through the placebo effect and the human tendency to see patterns that don't exist. The rare ones that aren't have a certain pattern: they're grounded in our best understanding of biology, align with what our body wants to do anyway, have been thoroughly studied using proper testing methodology, and don't make money for powerful corporations.

I'm fairly sure this is one of those rare ones that isn't a scam. And, if so, it's rather important and worth your attention.

Matthew Walker is a professor of neuroscience and biology at the University of California at Berkeley, where he's the founder of the Center for Human Sleep Science. He's not a doctor; he started medical training, but (as he says in the book) found himself more attracted to questions than answers. He's a professional academic researcher who has been studying sleep for decades. This book is a combination of summary of the current state of knowledge of academic sleep research and a plea: get more sleep, because we're literally killing ourselves with the lack of it.

Walker opens the book with a discussion of the mechanisms of sleep: how we biologically fall asleep and why, how this has changed over time, and how it changes with age. Along with that, he defines sleep: the REM and NREM sleep cycle that you may have already heard of, how it manifests itself in most people, and where dreams fit in. The second part then discusses what happens when you sleep, with a focus on what goes wrong when you don't. (Spoiler: A lot. Study after study, all cited and footnoted, has found connections between sleep and just about every aspect of mental and physical health.) The third part does the same for dreams, fitting them into the picture along with a scientific discussion of just what's going on during dreams. The fourth and final part tackles the problem: why don't we get enough sleep, and what can we do about it?

I will warn in advance that this book will make you paranoid about your sleeping patterns. Walker has the missionary zeal of an academic who has sunk his teeth into something really important that society needs to take into account and will try to drown you in data, analysis, analogies, and sheer earnestness until you will believe him. He wants you to get at least seven, and preferably eight, hours of sleep a night. Every night, with as little variation as you can manage. Everyone, even if you think you're someone who doesn't need as much sleep (you're probably not). There's a ton of science here, a great popularization of a whole field of research, but this is also a book that's trying to get you to do something.

Normally, that sort of book raises my shields. I'm not much of a believer in any book of the general genre of "most people are doing this basic part of life wrong, and should do it my way instead." But the hallmarks of good science are here: very widespread medical consensus, no corporate interest or obvious path to profit, and lots of studies (footnoted here, with some discussions of methodology — although not the statistical details, which will require looking up the underlying studies — and careful caveats where studies indicate correlation but may not find causes). And Walker makes the very telling point early in the book that nearly every form of life on the planet sleeps in one way or another (defined as a daily recurring period of time during which it doesn't respond to outside stimulus), which is a strong indicator of universal necessity. Given the vulnerability and loss of useful hours that come with sleep, one would expect some species to find an evolutionary path away from it if it were dispensable. But except for extremely short-lived species, we've never found a living creature that didn't sleep.

Walker's argument for duration is also backed up by repeated studies on human capability before and after various quantities of sleep, and on studies of the sleep phases in various parts of the night. Study after study used six hours as the cutoff point and showed substantial deterioration in physical and mental capabilities even after only one night of short sleeping. (Reducing sleep to four hours is nearly catastrophic.) And, more worrisomely, that degradation is still measurable after "catching up" on sleep on subsequent nights. Sleeping in on weekends doesn't appear to fully compensate for the damage done by short-sleeping during the week.

When Walker gets into the biological reasons for sleep, one starts to understand why it's so important. I think the part I found the most fascinating was the detailed analysis of what the brain is doing while you sleep. It's not inactive at all, even outside of REM sleep. Walker and other sleep researchers have done intriguing experiments showing how different parts of the sleep cycle transfer memories from short to long term storage, transfer physical skills into subconscious parts of the brain, discard short term memories that the conscious brain has tagged as being unwanted, and free up space for new knowledge acquisition. REM sleep appears to attempt to connect otherwise unrelated memories and bits of knowledge, inverting how association normally works in the brain, thus providing some concrete explanation for sleep's role in creativity. And (this research is fairly new), deep NREM sleep causes temporary physical changes in the brain that appear to be involved in flushing metabolic waste products away, including the plaque involved in Alzheimer's.

The last part of the book is probably the most concretely useful: what can one practically do to get more sleep? There is quite a lot that's proven effective, but Walker starts with something else: sleeping pills.

Here, you can almost see the lines drawn by a lawyer around what Walker should say. He stresses that he's not a medical doctor while laying out study after study that all point in the same direction: sleeping pills are a highly dangerous medical fraud that will shorten your lifespan for negligible benefit in helping you fall asleep, while limiting your brain's ability to enter true sleep. They're sedation, sedation is not sleep, and the four billion dollar sleeping pill market is literally making everything worse.

The good news is there is an effective treatment for insomnia that works for many people; the better news is that it's completely free (although Walker does suggest some degree of medical supervision for serious insomnia so that some parts of it can be tailored to you). He walks through CBT-I (cognitive behavior therapy for insomnia), which is now the medically recommended primary treatment for insomnia, and takes apart the pieces to show how they line up with the results of sleep research studies. Alongside that are recommendations for improving sleep for people who don't have clinical insomnia but who aren't regularly getting the recommended amount of sleep. There are a lot of interesting bits here (and he of course talks about blue LED light and its relationship to melatonin cycles), but I think the most interesting for me was that you have to lower your core body temperature by a couple of degrees (Fahrenheit) to enter sleep. The temperature of your sleeping environment is therefore doubly important: temperature changes are one of the signals your body uses to regulate circadian rhythms (cold being a signal of night), and a colder sleeping area helps you lower your core body temperature so that you can fall asleep. (The average person does best with a sleeping room temperature of 65F, 18C.)

There's even more in here: I haven't touched on Walker's attack on the US tendency to push high school start times earlier and earlier in the day (particularly devastating for teenagers, whose circadian rhythms move two hours later in the day than adults before slowly returning to an adult cycle). Or the serious problems of waking to an alarm clock, and the important benefits of the sleep that comes at the end of a full night's cycle. Or the benefits of dreams in dealing with trauma and some theories for how PTSD may interfere with that process. Or the effect of sleep on the immune system.

Walker's writing style throughout Why We Sleep is engaging and clear, although sometimes too earnest. He really wants the reader to believe him and to get more sleep, and sometimes that leaks around the edges. One can also see the effort he's putting into not reading too much into research studies, but if there's a flaw in the science here, it's that I think Walker takes a few tentative conclusions a bit too far. (I'm sure these studies have the standard research problem of being frequently done on readily-available grad students rather than representative samples of the population, although the universality of sleep works in science's favor here.) Some of the recitations of research studies can get rather dry, and I once again discovered how boring I find most discussion of dreams, but for a first book written by an academic, this is quite readable.

This is one of those books that I want everyone to read mostly so that they can get the information in it, not as much for the enjoyment of reading the book itself. I've been paying closer attention to my own sleep patterns for the last few years, and my personal experience lines up neatly with the book in both techniques to get better sleep and the benefits of that sleep. I'd already reached the point where I was cringing when people talk about regularly going on four or five hours of sleep; this is an entire book full of researched reasons to not do that. (Walker points out that both Reagan and Thatcher, who bragged about not requiring much sleep, developed Alzheimer's, and calls out Trump for making the same brag.) The whole book may not be of interest to everyone, but I think everyone should at least understand why the World Heath Organization recommends eight hours a night and labels shift work a probable carcinogen. And, as Walker points out, we should be teaching some of this stuff in school health classes alongside nutrition and sex education.

Alas, Walker can't provide much advice on what I think is the largest robber of sleep: the constant time pressure of modern life, in which an uninterrupted nine hour sleep opportunity feels like an unaffordable luxury.

Rating: 9 out of 10

Reviewed: 2017-10-28