Health
by Matthew Walker
What is sleep actually for?
Matthew Walker is a neuroscientist who runs a sleep lab at Berkeley in California. He argues that almost every part of the brain and body works better with sleep and worse without. Why We Sleep sets out what sleep does, and why he thinks most of us get too little.
Hear a sample · read by Laura
Walker describes two systems. Sleep pressure builds all day as a chemical called adenosine collects in the brain. Separately, a 24-hour body clock decides when you feel alert. Caffeine works by blocking adenosine, so it hides tiredness without clearing it.
Deep non-REM sleep, which fills more of the early night, helps move the day's memories into long-term storage. REM sleep, which fills more of the early morning, is when most vivid dreaming happens. Walker calls REM overnight therapy, because he thinks it takes the sting out of painful memories.
Walker links short sleep to heart disease, cancer, Alzheimer's and early death. Other scientists have said some of his figures are overstated, and that many rest on correlations rather than proof of cause. Few doubt his broader point that chronic short sleep is bad for health.
Alcohol sedates you, and sedation feels like sleep. Walker says it breaks your sleep up through the night and holds back REM. Bright screens late in the evening delay melatonin, the hormone that tells your body it's night, so sleep comes later.
Enough
Adults need seven to nine hours. Regularly getting less harms nearly every part of the body.
Memory
Sleep after learning locks the new memories in. Sleep before learning makes room for more.
Caffeine
Caffeine hides sleepiness for hours. An afternoon coffee can still be in you at bedtime.
Dreams
Dreaming sleep softens painful memories, so they hurt less the next day.
Alcohol
A drink before bed knocks you out but ruins your dreaming sleep.
A story from the book
Walker describes a study where volunteers were allowed six hours in bed a night. After ten days, their attention was as poor as that of people kept awake for twenty-four hours straight. Yet when asked, they felt only a little affected.
Hot take · true or myth?
A nightcap helps you sleep better.
Myth. Walker says alcohol is a sedative, and sedation isn't natural sleep. It wakes you more often in the night and cuts down REM sleep, when most dreaming happens.
One thing to try
For the next seven days, get up at the same time every morning, weekends included. It's the first tip on Walker's list. If you snore heavily, or feel sleepy all day however long you sleep, talk to a doctor.
Knotd has the key ideas from 250+ non-fiction books, each in a few minutes, in plain words. Why We Sleep comes with a Hot Take round to make it stick.
Get the whole book on KnotdOpen in the appWhat is sleep actually for? Matthew Walker is a neuroscientist who runs a sleep lab at Berkeley in California. He argues that almost every part of the brain and body works better with sleep and worse without. Why We Sleep sets out what sleep does, and why he thinks most of us get too little.
Two forces run your night; Two kinds of sleep; Where critics push back; Nightcaps and late screens.
For the next seven days, get up at the same time every morning, weekends included. It's the first tip on Walker's list. If you snore heavily, or feel sleepy all day however long you sleep, talk to a doctor.
Yes. Knotd has the key ideas from Why We Sleep in a few minutes, in plain words, plus a Hot Take round to test them. It's one of 250+ non-fiction books in the app.
