1What Does Healthy Sleep Look Like?
You know that feeling of quiet bliss as you drift into sleep? That moment of tranquility where you are poised over the realm of sweet oblivion? How about that delicious feeling of waking up refreshed, like you’ve just slipped into the pool on a hot summer day?
Perhaps those are cruel questions. Since you’re reading this book, experiences of tranquil sleep might be a distant memory, so obliterated by nights of struggling with insomnia that you hardly believe they ever existed. Or maybe you’ve always been a “bad sleeper,” and this fabled experience of enjoying sleep is the unicorn you’ve chased for years. Perhaps your sleep isn’t so bad, but you can’t help but wonder if it couldn’t be—or shouldn’t be—better. Maybe if you slept eight to ten hours every night like Usain Bolt does, you’d be the fastest man on Earth … or at least have started training for that 5K. Or maybe you wonder if there are sleep hacks that, if deployed perfectly, could make you smarter, sexier, funnier, and all around more “optimized” as a human.
Whether you’re desperate for a sleep cure or simply sleep curious, I bet you’ve googled things like, “How much sleep do I need?” “What temperature is optimal for sleep?” “Tricks for falling asleep in 5 minutes.” “Hacks for getting better sleep.” But the answer to better sleep does not lie in the tips and tricks that you crave. Instead, it lies in the radical, but simple, idea that healthy sleep comes from having a good relationship with sleep. This means having an accurate understanding of how sleep works, both scientifically and experientially; knowing what you need to do to help your sleep thrive, and just as important, what you need to refrain from doing so as not to cramp its style. This means having appreciation and trust for your body’s natural ability to sleep well, and being able to adapt with your sleep through the inevitable trials and tribulations of life.
This book will teach you how to do these things. It is meant for people who struggle with their sleep—those who can’t turn off their brain when they go to bed at night, who stare at the ceiling (or their snoring spouse) with spite, who carry bricks of fatigue throughout their day, who worry that their sleeplessness will break down their body and mind, who crave rest that actually feels restful. I see you. I feel your struggle—that exhausting back-and-forth between hopelessness and desperation for satisfying sleep. And I have good news for you.
Insomnia is treatable. As a clinician with a short attention span and an almost pathologically strong sense of empathy, the only type of treatment I can do day in and day out is treatment that works (and works quickly). That’s why, after my clinical psychology PhD training at Boston University, I chose to specialize in behavioral sleep medicine during my medical psychology residency and postdoctoral fellowship at the Duke University School of Medicine. Now, as a sleep researcher and clinician certified by the American Board of Behavioral Sleep Medicine, I spend most of my time helping people overcome insomnia. I am deeply gratified by helping patients go from “I’ve lost my ability to sleep” to “I can’t believe it, but I’m a good sleeper” within a matter of weeks. I enjoy instilling hope for those who have been fighting a lonely battle for years. For delivering results using nothing more magical than scientifically based methods for resetting their sleep physiology and way of talking to themselves about sleep.
I wrote this book because people were asking me on Twitter about insomnia all the time, and my passionate responses never could fit within 280 characters. I wanted to write an up-to-date, laser-focused book on insomnia that was not simply a “layman’s version” of sleep textbooks, but rather a fireside chat that treated my readers as intelligent, curious people capable of self-determination. I wanted to provide them with explanations that made sense and actually addressed their questions about insomnia—a collection of the scientifically sound but down-to-earth things I would say to my patients. So, I set out to write this book with the hope that people with insomnia will find within it the answers to their burning questions, and a practical plan to help them rekindle their love affair with sleep.
Let’s get started.
To rebuild a good relationship with sleep, we have to get to know it. Like an old friend that you’ve drifted away from, what you think you know about sleep might not be true, or at least not true anymore. So, let’s start with a blank slate. You’ve got a wide-open mind, and you’re ready to get to know this wonderful thing called “sleep” from scratch.
What Is Sleep?
You would think that sleep is easily defined. But like jazz, it’s actually hard to pin down a definition beyond, “You’ll know it when you experience it.” Scientists are still working on understanding exactly what it is, how it works, and why it happens. But so far, here’s what we know with confidence:
Sleep happens naturally, usually at more-or-less regular intervals.When we’re asleep, we’re less responsive to our surroundings than when we’re awake, but more responsive than if we were in a coma.Brain activity is different during sleep compared to during wakefulness.When we don’t sleep well for a long time, we feel bad, or our health or functioning may be negatively affected.What Isn’t Sleep?
Sleep isn’t your brain or body “shutting off.” As you’ll see, it’s an active and dynamic state.Sleep isn’t a skill you can (or need to) learn through hard work. It’s an involuntary state that sometimes happens to you, and you can welcome it or allow it, but you can’t summon it or control it.Sleep isn’t the solution to all your problems. Expecting so will disappoint you and strain your sleep.What Happens During Sleep?
The body and brain do some truly amazing things during sleep. Some of these include:
Clearing out toxins from the cerebrospinal fluid (your brain “juices”)Releasing human growth hormone and sex hormonesRepairing damaged tissue and maintaining healthy tissueReviewing and organizing new informationRegulating emotionsPracticing new skillsNotice that I didn’t say, “Sleep does amazing things for us.” This is an important hair to split, because we shouldn’t be treating sleep as a performance enhancer or tool. When we do, we unfairly put a lot of pressure on sleep to perform. Instead, consider sleep to simply be the enjoyable byproduct of these biological activities. In other words, sleep is neither our master nor servant, neither the answer to our problems nor the blame for them. It’s hard to switch to this mindset, especially if you’ve been struggling with insomnia for a while, so be patient with yourself! Just start to notice whether you ever expect sleep to serve you (e.g., “I need to sleep so I can do well at my interview tomorrow”), and put a pin in this data point to examine later when you read part III, Getting Deeper into the Relationship.
The body and brain processes mentioned above take place during a few different types of sleep (sometimes referred to as “stages”) that tend to tag-team in a pattern throughout the night. I’m not a fan of referring to types of sleep as “stages,” because it’s not like we’re working through levels of a video game, where the goal is to go as far as possible, and you have to start over if you don’t reach your objective. Not at all! It’s more like sampling at a buffet, with second, third, and more helpings: alpha waves to start, then some spindles with K-complexes on the side, maybe some slow waves now (or REM, depending on what the brain’s in the mood for), and then some more spindles to cleanse the palate. Yum! That’s why I don’t like to call different types of sleep “light” or “deep”; they imply “worse” or “better,” whereas a good night of sleep needs all the different types of sleep (and wake), the same way a good meal needs a balance of vegetables, protein, and grains. Unfortunately, official sleep science terminology includes “stages,” so that’s what I’ll use here to minimize confusion.
Stage 1 (Restful Wake)
Stage 1 is considered the lightest type of sleep because we are easily woken from it, and during it, we may not feel like we’re sleeping at all. That’s why it’s sometimes called “restful wake.” It takes up only about 5 percent of a typical night, serving mostly as a transition between waking and other types of sleep.
Stage 2 (Light Sleep)
Even though Stage 2 is considered “light sleep,” it is actually an active and important time for the brain. This stage produces electrical activity bursts called spindles, which help our brains to cement new learning. There are also K-complexes, a twitch in the electroencephalogram (EEG) waveform we don’t fully understand, which might reflect a moment where the brain scans the environment for new inputs. When you learn new things during the day, whether it’s French verb conjugations or how to serve a tennis ball, your brain fires up sleep spindles during Stage 2, and you wake up with more mastery of the skill than you had when you went to bed. This type of sleep takes up approximately 45 percent to 55 percent of the night. Yes, you read that correctly … fully half the night is supposed to be spent in this “light” stage of sleep, and it’s time well-spent!
Stage 3 (Slow Wave Sleep, Deep Sleep)
This type of sleep is called “slow wave sleep” because the brain activity you see on an EEG looks like big, rolling waves, unlike the usually tight, frenetic smaller waves we have when awake or in other types of sleep. During Stage 3, the brain’s lymphatic system does important janitorial work to clear toxins from the brain. It also releases growth and sex hormones, helps us to cement new learning, and engages in general rest and restoration … all nice things. People usually refer to Stage 3 as “deep sleep,” but please don’t think this means it’s the only good type of sleep, or that it’s better than the others—this is a common myth! In fact, Stage 3 sleep is only supposed to take up about 15 percent to 20 percent of a typical night for a healthy adult sleeper, and even less if they’re past middle age. This type of sleep mostly happens during the first half of your night.
Rapid Eye Movement Sleep
Rapid eye movement, or REM, sleep is very different from the other three (those are collectively known as “non-REM” stages). During REM, your major muscles are deactivated, your eyes move behind closed lids, and your brain’s EEG pattern looks almost like when awake. The brain is very active—it sorts through memories, makes sense of emotions, makes decisions about what to keep and what to lose. Think of a detective sorting through their wall of interlinked mug shots and news clippings and question marks with an intense soundtrack playing in the background. With all this action, it’s no surprise that REM is also when most of our dreaming happens.
Wake
Yes, if we’re going to walk through a healthy, typical night of sleep, we’re going to have to talk about wakefulness. A healthy adult of about thirty-five to sixty-five years old wakes about ten to sixteen times per night, though they don’t remember most of these brief awakenings. (Older adults wake even more frequently.) It’s normal to remember a few awakenings: going to the bathroom, adjusting your position, getting a sip of water, or being startled by a noise or dream. Don’t worry about these events interrupting your sleep. (I repeat: do not worry.) Your brain naturally interrupts your sleep multiple times per hour anyway. A dozen or so brief awakenings (including a few that you remember, each lasting a few minutes) is totally normal, so don’t get upset if your sleep tracker says you woke up ten or twenty times last night. Waking up briefly doesn’t mean you’re starting a sleep cycle over or missing out on a particular stage of sleep. An exception is if you have obstructive sleep apnea or other serious sleep disorders that wake you up every few minutes throughout the night (see chapter 16).
The Myth of Sleep “Cycles”
Our brains move through these types of sleep in a more or less predictable pattern, with some variations from night to night, person to person. This pattern is called sleep architecture. Just as I don’t like the terminology of sleep “stages,” I also don’t like to refer to sleep architecture patterns as “sleep cycles.” You may have heard that sleep cycles are ninety minutes long, and that you should try to time your wake-up alarm to be at the end of a cycle.
Nope. Forget that.
Sleep architecture doesn’t follow a lather-rinse-repeat pattern because so-called sleep cycles are not that neat. Even your own “cycles” are not the same shape or length during one night, and sleep architecture doesn’t look the same between you and me. Besides, the boundaries between the different “stages” of sleep are blurry. While one part of the brain is in Stage 2, another might have sidled on to REM.1 While most of the brain is awake, a Stage 2 sleep spindle or two can pop up here and there, and even Stage 3 slow waves might roll in briefly.2 During deep sleep, your brain isn’t all slow wave electrical activity. These undulating waves travel from brain region to brain region, like a tornado sweeping across the landscape of your cortex, the wrinkly outer layer of your brain. So, to say that someone “cycles” through sleep stages is like saying the Rolling Stones cycle through chords. It oversimplifies a complex, mysterious, and beautiful phenomenon. And because sleep architecture is so wonderfully messy, we can’t control it.
But don’t worry—you don’t need to control your sleep stages. Your brain will automatically adjust how much deep sleep versus REM sleep versus light sleep you get, in what sequence, and in which brain regions, all dependent on your current needs. This flexibility is a good thing! Some days you learn to serve a tennis ball and other days you watch emotional documentaries. Some days are long, and some are short. Your brain will know what to do with each type of sleep in each of these situations.
SOAPBOX MOMENT
Why is this “sleep cycle” idea so popular? I believe it’s partly driven by our collective desire to control sleep with technology. We’ll talk in detail about sleep gadgets in chapter 3, but for now, know this—you should trust your own brain before trusting a gadget that supposedly wakes you up at the “end of a cycle,” because (1) current gadgets are not actually good at discerning sleep stages and (2) this concept is arbitrary and irrelevant … it’s not like the sleep you get doesn’t count unless you somehow stick the landing with a perfectly timed bout of REM.
What Is Healthy Sleep (and the Eight-Hour Myth)?
Healthy sleep simply happens when your brain and body do all the functions they need to meet their needs. Ideally, healthy sleep is also sleep that you feel good about.
But, of course, what most people mean when they ask this question is, “How much sleep do I need?” I’m sure you’ve heard that you should get eight hours of sleep per night. This is like Dr. Google saying that you need eight glasses of water per day. Does this apply to Megan Rapinoe during the height of soccer training season, or me (a petite couch potato) during a Netflix marathon? Should a construction worker in the Arizona desert drink the same amount of water as a librarian in rainy Seattle?
The same logic applies to sleep. Not only do you and I differ in the amount (and timing) of sleep we need, we ourselves might change from day to day, week to week, season to season, and certainly over the course of our lives. When pregnant, sleep changes. When training for a marathon, sleep changes. When going through a breakup, moving from the city to the country, coping with jet lag, starting a job, losing a job, recovering from the flu, learning to play the trumpet, going through puberty, retiring3 … if you just saw your life flash before your eyes, close them and take a deep breath. Sleep changes a lot. This is normal. That’s because sleep is stretchy and resilient by design. Why?
Envision a band of early humans trying to survive on the savannah. Imagine if everyone in the tribe dropped into an uninterrupted sleep at the exact same time for the exact same duration, every night. If I were a saber-toothed tiger, I’d just camp out near this hominid buffet and leisurely sharpen my claws all day. I’d know that this completely predictable species will serve up a completely defenseless dinner every night.
Our prehistoric ancestors needed restless night owls, bright-eyed morning larks, light sleepers, dead logs, middle-of-the-night risers, middle-of-the-day nappers, and sleepers of all sorts. This diversity saved lives and perpetuated our species. They needed wise elders who needed less sleep to watch over exhausted hunters, who probably needed more; they needed morning birds to get the bows strung bright and early, as well as night owls to keep an eye out for predators of the night.4 In summer, they needed to be stimulated by sunlight so they could hunt and gather, and in winter they needed to save energy because there wasn’t much hunting or gathering to do. When there was danger on the horizon, they needed to turn from sleepy to alert on a dime, but also to conserve energy when food was scarce.
This is why evolution made our sleep so diverse and dynamic. And this is why LeBron James sleeps twelve hours per night and Terry Gross probably doesn’t (unless she has a secret life as a professional weightlifter in addition to hosting the radio talk show Fresh Air).
Even if we had to boil the complex question of optimal sleep duration down to simple headlines, “eight hours” still wouldn’t be the best answer. For example, a recent large study of older Japanese adults found that those sleeping, on average, between five and seven hours per night had the lowest rate of death and dementia over time, compared to those who slept less or more.5 You might have guessed that less than five hours of sleep per night is not ideal, but perhaps you hadn’t considered that longer sleep durations can be associated with health problems too. In fact, in the most recent meta-analysis6 on the topic, data from more than forty-three thousand participants tracked over time showed that long sleep duration (eight hours per night or more) was linked to a 77 percent increased risk for dementia, whereas short sleep duration (less than six hours per night) was not associated with increased risk for dementia.7 I am not recommending that you prevent yourself from ever getting more than six hours of sleep per night. As we’ll see below, these types of studies don’t tell us the optimal amount of sleep for each of us.
So how come different studies seem to come up with different numbers? First, there’s no perfect agreement between researchers about what “short sleep” means,8 so we group hundreds or thousands of participants into this category, including ones who sleep less than five hours, but sometimes also including ones who sleep seven or eight hours, depending on where a particular research team decides to draw the line. When data are pooled together like this, it’s impossible to tell if it’s the five-hour sleepers or the seven-hour sleepers in the “short sleeper” group that are driving the results.
Second, researchers measure sleep differently. Some of these studies base their sleep duration analyses on a single questionnaire item asking, “Approximately how many hours do you sleep per night?” Other studies ask participants to painstakingly track their sleep for many nights using multiple tools, or measure their sleep using sophisticated equipment in the lab. It’s safe to assume that almost all headlines refer to ballparks and guesstimates.
Last, but not least, these different studies included different samples of people. Some followed young adults, others older adults; some followed people at risk for disease, while others followed only healthy people; some studies were done in the United States, others in Japan, the Netherlands, Turkey, or elsewhere. By now, you’ve gathered that headlines don’t tell the whole story, and that things can get quite messy when we dig into details.
One thing that pretty much all large-scale studies about sleep duration agree on: long sleep duration, usually defined as more than nine or ten hours per night, is associated with more health problems over time.
Does this mean you should never let yourself sleep more than nine hours? Or place any other specific limit or expectation on your nightly sleep duration? The answer is no. Here’s why:
Correlation is not causation. Just because people who sleep nine hours per night are statistically more likely to also have dementia doesn’t mean it’s the long sleep that causes dementia. Maybe it’s the other way around—having brain changes related to dementia causes someone to become sleepier. Or maybe both things are caused by a whole other factor. If your body tells you that you need nine hours of sleep, there’s no need to deprive yourself. But if it’s your thoughts that tell you you need a specific amount of sleep or else you’ll die young … we have some work to do in part III of this book.Someone who averages, say, seven hours per night sometimes sleeps more than that, and sometimes less … you’re allowed to have fluctuations.The problem with talking about averages is that you may not be average.9Even if you are average for your demographic, the type and amount of sleep you need may not match the average for the people in any particular study. For example, most of you are probably not Japanese sixty-seven-year-olds.It comes down to this: There is no single correct way to sleep. Many shapes and sizes of sleep are healthy if they answer your body’s needs at this time in your life.So Why Does the National Sleep Foundation (and My Doctor) Say I Should Get Seven to Nine Hours of Sleep per Night?
If you dig beneath the headlines, you’ll find that the National Sleep Foundation actually believes that anywhere between five and eleven hours “may be appropriate” for adults.10 That’s why it took this entire chapter to tell you about healthy sleep. It can’t be boiled down to just a couple of numbers.
Also, I think there is always some tension between public health messaging and individual health advice. There are likely more people who don’t give themselves enough opportunity to sleep (e.g., college students pulling all-nighters, professionals who are married to their email) than people who have chronic insomnia. So, a reasonable public health message, if it needs to fit in a headline, may err on the side of recommending more sleep than many people need (eight hours per night). But this is at the expense of many people with insomnia, especially older adults who are conscientious about sleep but simply don’t need eight hours.
Copyright © 2023 by Jade Wu
