PDF Summary:Why We Sleep, by Matthew Walker
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1-Page PDF Summary of Why We Sleep
You’re probably getting less sleep than you should be. Many people are more chronically sleep-deprived than they realize, and the punishments for this are severe—reduced productivity and happiness, and an increased risk of a panel of diseases. In Why We Sleep, “sleep diplomat” Matthew Walker, Ph.D. unlocks some of the mysteries of sleep based on research from both in and outside his Center for Human Sleep Science.
In this guide, we’ll explore how sleep happens, its major benefits, and the best ways to get better sleep. We’ll also discuss sleep research from other experts as well as new findings that emerged after the book was published.
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2. Sleep deprivation worsens emotional control. Walker says that when you’re sleep deprived, your amygdala (the part of your brain that controls emotion) can run amok, leading to 60% more emotional reactivity. Sleep disruption is a common symptom of all mood disorders. However, sleep deprivation actually makes one-third of depression patients feel better. (Shortform note: Guzey notes that Walker downplays the benefits of sleep deprivation—studies suggest that it’s beneficial to about 45-50% of patients with depression. Walker clarifies that these findings emerged after the book was written.)
3. Sleep deprivation may contribute to Alzheimer’s. Sleep loss may disrupt memory formation as well as the glymphatic cleanup system, which clears out Alzheimer’s-associated plaques. (Shortform note: A study suggests that sleeping on your side can help decrease the chances of developing Alzheimer’s and other neurological diseases.)
Diseases Linked to Sleep Deprivation
In addition to the damage it causes the brain, sleep deprivation disrupts the normal function of many physiological processes, likely contributing to the following:
- Heart disease
- Diabetes
- Obesity and weight gain
- Reduced reproduction (by affecting hormones and attractiveness)
- Some cancers
- Aging
- Reduced athletic performance
- Death
A Note on the Studies in Why We Sleep
Many of the population studies cited in Why We Sleep are correlational—for example, their results show that people who sleep less are more likely to have heart disease, after controlling for many other factors. But the causation of these results is unclear—some other factors that predispose people to heart disease (like a high baseline level of stress) could also reduce sleep.
To address this, the experimental studies Walker cites attempt to link lack of sleep to a middle physiological state, which itself is causative for the disease. For instance, a lack of sleep increases blood pressure, which the medical consensus believes is causative for heart disease.
Ideally, the “smoking gun” experiment would be to randomize people into normal-sleep and low-sleep groups for years, then observe the rate of disease. However, this is impractical (it’s hard to run very long studies like this and impossible to double-blind) and likely unethical (if low sleep is already believed to cause severe disease).
Part 3: The Science of Dreams
Most vivid dreaming happens during REM sleep. Walker says that your visual, motor, memory, and emotional areas of the brain are active. Your prefrontal cortex (governing rationality) is muted. Some people are even capable of lucid dreaming, meaning they’re able to voluntarily control their actions within their dream. (Shortform note: One study found that you can increase your chances of having lucid dreams by combining three techniques: reality testing, breaking up your sleep, and mnemonic induction of lucid dreams.)
Benefits of Dreaming and REM Sleep
Walker says there are three ways dreaming and REM sleep are good for you:
- REM dreaming blunts emotional pain from memories—the brain seems to reprocess upsetting memories and emotional themes in a way that retains the useful lessons while lessening the visceral emotional pain. (Shortform note: Walker attributes this only to REM sleep, but neuroscientist Rebecca Spencer posits that NREM sleep also plays a role.)
- REM sleep increases your understanding of other people’s emotions—sleep-deprived people more often interpret faces as hostile and aggressive. (Shortform note: This works both ways: While sleep-deprived individuals view other people more negatively, other people also view sleep-deprived people as more unpleasant.)
- REM sleep creates novel connections and a higher-level comprehension of ideas, and increases your ability to solve creative problems. (Shortform note: In fact, it may be possible to manipulate your brain to solve problems during sleep.)
Part 4: The Current State of Sleep
Walker finishes by covering sleep disorders, sleep disruptors, and ways to get better sleep.
Sleep Disorders
He explains that there are three sleep disorders that people commonly experience:
1. Somnambulism (sleepwalking)—the act of walking and performing other behaviors while asleep. It happens during NREM sleep. (Shortform note: A 2021 study suggests that men who sleepwalk may have a higher risk of developing Parkinson’s disease. The two share a common neural pathway and both involve involuntary movements, confusion, and amnesia.)
2. Insomnia—defined as making enough time for sleeping, but having insufficient sleep quantity or quality, for more than three months. The most common triggers are emotional concerns or distress. (Shortform note: Researchers suggest that physical and emotional stress—from discrimination in the workplace and financial pressure due to unemployment, for example—may be the reason behind the sleep disparity between people of color and white people.)
3. Narcolepsy—a not-awake, not-asleep state marked by three symptoms: sudden bouts of extreme sleepiness, sleep paralysis (waking up in REM sleep during muscle atonia), and cataplexy (sudden loss of muscle control while awake). (Shortform note: It can be hard to diagnose narcolepsy because its symptoms overlap with the symptoms of depression, hypothyroidism, sleep apnea, and epilepsy, among other conditions.)
What Stops You From Getting Good Sleep
Walker names jet lag as an increasingly common sleep disruptor. It affects travelers by disturbing the circadian rhythm. He says it can take you up to 10 days to readjust to a 10-hour time difference. (Shortform note: There are several ways to minimize the effects of jet lag, such as hydrating adequately and exposing yourself to natural light at your destination.)
He says that even those who aren’t traveling face five major influences that have drastically changed how we sleep:
1. Caffeine—blocks adenosine receptors, thus reducing how much you feel the desire to sleep. (Shortform note: If you can’t shake the habit of drinking a hot beverage late in the afternoon or evening, try herbal teas that may help promote sleep and relaxation.)
2. Light—nowadays, artificial light constantly fills our homes and disrupts our circadian rhythm. Blue light is most problematic, suppressing melatonin at twice the levels of warm light. (Shortform note: Blue light may have an even bigger impact on children, as they’re more sensitive to light and have bigger pupils.)
3. Constant temperature—in modern times, thermostats homogenize temperatures, suppressing the biological systems that use temperature changes throughout the day as sleep cues. (Shortform note: If it’s too hot and you have no access to air-conditioning, cool your body temperature by avoiding exercising at night, avoiding anything spicy, and stashing your pillowcases in the fridge.)
4. Alcohol—a sedative that causes what appears to be sleep but is really more like anesthesia. It causes you to wake up throughout the night and prevents you from getting REM sleep. Walker encourages total abstinence from alcohol. (Shortform note: A less puritanical approach comes from The Sleep Foundation, who recommend that you stop drinking alcohol at least four hours before bedtime.)
5. Alarms—cause acute stress responses when you wake up, spiking your cortisol levels, heart rate, and blood pressure. (Shortform note: One study suggests that changing your alarm from a jarring sound to an upbeat song can help combat sleep inertia, that disoriented state you’re in upon waking up.)
How to Get Better Sleep
Walker provides a number of tips on how you can start getting better, less interrupted sleep.
- Keep the same waking and sleeping time each day. Erratic sleep schedules disrupt sleep quality.
- Practice sleep hygiene—lower bedroom temperature, reduce noise, reduce light.
- Avoid alcohol, caffeine, exercise, or long naps before sleep.
- Get some exercise, which may increase total sleep time and increase quality of sleep. Exercising has more of a chronic effect, meaning it helps in the long run and doesn’t take effect on a day-to-day scale—exercise on one day doesn’t necessarily lead to better sleep that night. But worse sleep on one night does lead to worse exercise the following day.
- Eat a normal diet (not severe caloric restriction of below 800 calories per day). Avoid very high carb diets (>70% of calories) since this decreases NREM and increases awakenings.
- Avoid sleeping pills—they’re no better than a placebo.
- For those with insomnia, try cognitive behavioral therapy, which has been shown to be more effective than sleeping pills.
More Tips to Help You Sleep
In The Sleep Revolution: Transforming Your Life, One Night at a Time, Arianna Huffington devotes a chapter to sleep tips, tools, and techniques. While there are many overlaps with While We Sleep (such as limiting blue light, avoiding alcohol, and getting the temperature right), she offers some additional tips that Walker doesn’t mention:
Try acupuncture. According to a study, this centuries-old practice had a positive effect on 93% of insomnia patients.
Sip (or sniff) some lavender. Studies suggest that the herb has a relaxing effect, which can set the stage for a good night’s sleep. Huffington writes that in Germany, lavender tea is an approved treatment for insomnia. You can also try spritzing some lavender onto your pajamas or sheets.
Empty your mind. To help you reduce anxiety-producing thoughts, try doing a “mind dump” before bed: Write down your to-do list for the next day so that your thoughts won’t keep you up at night.
Improving Sleep in Society
Walker argues that sleep deprivation goes far beyond individual sleep practices. He says that our society has structurally locked in sleep deprivation in two ways: First, work schedules disrupt sleep. Companies associate hours worked with productivity and tend to see sleep as an indulgence of the weak. Second, school schedules disrupt sleep: Early start times disrupt children’s circadian rhythms. Walker offers ways to improve sleep quality in society:
- Employers should focus less on hours worked and instead implement flexible hours to suit personal circadian rhythms. They can even incentivize sleep with vacation days or bonuses.
- Use sleep technology to improve sleep tracking and help you adjust your circadian rhythm when needed.
- Educate the general public about the importance of sleep, in the same way schools have educational programs about diet and drugs.
- Promote sleep hygiene for hospital patients—hospitals can replace their harsh lighting and find ways to minimize beeping noises at night.
(Shortform note: The sleep landscape continues to change with technological advancements that we can use to improve our sleep. In 2021, the FDA approved SleepCogni for medical use. Clinical trials have shown that SleepCogni, a data-supported device, can reduce insomnia in just seven days. In the hospitality industry, where sleep is an essential part of a hotel guest’s stay, a scientist predicts some ways in which the experience of sleep will change, including bed covers and sheets made of high-tech thermal regulation fabrics and pillows that can detect sleep activity.)
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