It turns out that the physiological, cognitive, emotional, and social benefits of spending a third of our lives unconscious outweigh even the costs in time, opportunity to do other things, and inattention to threats. Our whole body, including our brain, is working hard as we sleep, to accomplish life-preserving tasks that can be best achieved when we’re not around to interfere. Quite simply, we are not complete without sleep.
Physical activity is not complete without sleep. While you sleep, your bones, blood vessels, digestive system, muscles (including your heart), and all your other body tissues heal from the damage you inflicted on them during the day. If you engaged in physical activity, your body will repair itself and grow stronger while you sleep. Physical activity without sleep, by contrast, leaves you more vulnerable to injury and illness than you would have been without the activity. If you’re not going to sleep, better not exercise.
Learning is not complete without sleep. Your memories consolidate and new information is integrated into existing knowledge. Studying for a test, memorizing a speech, or learning a language? Review right before bed, then sleep for seven to nine hours. Your brain will soak up the information like grass absorbing rain after a drought. Any motor skills you practiced—skiing or playing piano or walking up the stairs—get integrated, so that you’re better at them the next day. The benefits of practice come not during the practice itself but during sleep; without it, your skill will actually decline, no matter how much you practice. If you’re not going to sleep, you’re studying and practicing for nothing.
Emotions are not complete without sleep. You can dream about beating the daylights out of your enemy, and you’ll wake up feeling released from the grip of your rage, better able to handle interpersonal conflict. In one study, professionals who got inadequate sleep were rated by their peers and their employees as having lower emotional intelligence.12 Marital satisfaction, too, is linked to sleep quality.13 Recent lack of sleep not only worsens conflict between spouses, it also heightens each person’s inflammatory immune response to conflict, a biological marker paralleling each partner’s heightened reactivity to their spouse’s complaint.14 If you’re not getting adequate sleep, better avoid talking to other humans.
Did we say this yet? Sleep is important.
We are built to oscillate between wakefulness and sleep, because we require the things our brain does on its own during sleep to make us fully functional while we’re awake.
And at its most extreme, sleep deprivation is a form of torture.15 You can quite literally die of sleep deprivation—by physiological deprivation akin to starvation.16 When researchers deprive rats of sleep for two weeks, the rats’ immune systems become so impaired their blood becomes infected with their own gut bacteria and they die of septicemia.
“When you are broken, go to bed,” goes the French proverb. You are not complete without sleep.
And what are the costs of inadequate sleep?
Inadequate sleep damages your physical health: chronic sleep deprivation—short sleep and disturbed sleep—is a causal factor in 20 percent of serious car accidents,17 and in every common cause of death, including heart disease, cancer, diabetes, hypertension, Alzheimer’s, and immune dysfunction, increasing risk by up to 45 percent.18 Poor sleep is a better predictor of developing type 2 diabetes than lack of physical activity, but when was the last time anyone told you to get enough sleep to prevent diabetes?19
Inadequate sleep impairs brain functioning, including working memory and long-term memory, attention, decision-making, hand-eye coordination, calculation accuracy, logical reasoning, and creativity.20 People who’ve been awake for nineteen hours (say, woke up at 7 A.M. and now it’s 2 A.M.) are as impaired in their cognitive and motor functioning as a person who is legally intoxicated.21 People who’ve slept just four hours the previous night are similarly impaired, as are those who’ve slept six or fewer hours every night for the last two weeks. Anything you wouldn’t do drunk—drive, lead a work meeting, raise a child—don’t try it if you’ve been awake for nineteen hours, slept only four hours the previous night, or slept fewer than six hours every night for two weeks.
Your social life is also affected by lack of sleep: team communication in the workplace and group decision-making are impaired, while hostility and even unethical workplace behavior increase.22 Your emotional life is impacted, too: depression and sleep difficulties are closely intertwined, each exacerbating the other,23 and insomnia predicts suicidal thoughts, even in people without depression.24 Anxiety and sleep, too, are closely related and mutually causal.25 If you struggle with depression, anxiety, or other mental health issues—which more than twice as many women as men do (a conservative estimate is about one in five women in their lifetime26)—sleep is medicine for you.
This is not an area of research where there’s any reasonable debate; the medical opinion is in: Sleep is good for you, and not sleeping is bad for you in every way—dangerous and potentially lethal. Three recent meta-analyses, comprising millions of research participants, found overall around a 12 percent greater risk of all-cause mortality among those who slept fewer than five or six hours a night.27 If you make only one change in your life after reading this book, let it be getting more sleep.
CAN YOU GET “TOO MUCH” SLEEP?
“But naps make me feel worse!” you may say.
When we’re sleep deprived, our bodies try to compensate by activating the stress response—doses of adrenaline and cortisol to help us survive the temporary stressor of too little sleep—which masks the fatigue and impairment. The result is that sleep deprivation can act a little like alcohol; just as a person who has been drinking may be too impaired to know how impaired they are (“I’m fine, gimme the keys!”), a person who isn’t rested may be too sleep deprived to be aware of how sleep deprived they are.
The counterintuitive result is that when we eventually sleep, the stress response reduces, so when we’re actually better rested, we may feel less rested. Adrenaline is no longer masking our fatigue. And we groan, “Ugh, I slept too much,” the way we’d groan after a huge meal, “Ugh, I ate too much.”
Can you actually sleep “too much”?
The general rule is: If you’re sleeping more than nine hours out of every twenty-four, and you still don’t feel rested, that could be a sign of an underlying issue, and it would be good to talk with a medical provider.28
One day Emily said this to a group of students and one raised her hand and said, “But I’ve been sleeping, like, ten hours a night and I’m exhausted.” Lots of people in the group had an opinion about what might be causing her exhaustion—everything from depression to narcolepsy to laziness—but Emily said, “If you’re sleeping more than nine hours every night and don’t feel rested, what do you do?”
“Talk to a doctor?” the student parroted back.
“Right.”
Six months later, that student approached Emily and said, “Hey, you probably don’t remember, but I’m the one who was sleeping ten—”
“Oh, I remember,” Emily said.
“Well, I actually did go to the doctor and I did a sleep study, and it turned out I had really severe sleep apnea. Over the summer I had my tonsils and adenoids removed and now I sleep with a mask, and it has completely changed my life. I had no idea how sleep-deprived I was my whole life.”
Bottom line: If you’re sleeping more than nine hours a day and don’t feel rested, talk to a medical provider.29 And if you’re thinking, “But Emily and Amelia, I’m trying. I give myself an eight-hour window of opportunity to sleep and the sleep doesn’t happen! I literally can’t get the sleep I need,” talk to a medical provider. Do a sleep study. It could change your life. Maybe even save it.
An “Invisible Workplace”