Why We Sleep - Matthew Walker
One-Sentence Summary:
It’s the one book everyone in the world should read, especially those in positions of power. It will make you live longer, perform better and make society better.
Rating On Time Of Review:
10/10. This book should be required reading in every school, for every adult…. It’s a travesty that it isn’t.
Book notes below. My thoughts are in italics. Opinions are mine during the time of review.
Date Reviewed: August 6, 2020
Chapter 1
Sleep <6-7 hours doubles risk of cancer. It also increases likelihood of developing Alzheimer’s. It kills your immune system and contributes to depression, anxiety and suicidality. Also, weight gain.
Dieting with insufficient sleep = loss of lean muscle mass, not fat.
12-18 months of no sleep = death
“..sleep is the single most effective thing we can do to reset our brain and body health each day.” / if you have to focus on ONE THING, it’s sleep.
Chapter 2
Circadian rhythms are approx 1 day in length but not exactly. It’s also not entirely dependent on sunlight. We can develop our own in absence of light.
One can depict the circadian cycle from the increase and decrease in core body temperature. The average person will see peak core body temperature at ~4pm. I think this may lead to the supporting literature on mid afternoons being optimal training periods for strength athletes. Body temp then drops to lowest point at ~1am.
**Morning types are 40%, evening types are 30% and remaining 30% are in between with a tilt towards evening. This can be known by observing when you have most energy, when you feel tired, when you naturally wake up. Despite waking up at 5am for most of my early professional life…. I realized from this book that I am actually tilted to the evening and naturally wake up between 8am and 9:30am… falling asleep past 12am. Night owls are apparently incapable of falling asleep early at night, no matter how hard they try…. Though that’s not me… it has been a painful enough experience.
Chronotypes (morning lark/night owl type) is genetics. You can’t change it. It just so happens that a CEO who wakes up at 430am is a morning lark. Doesn’t make morning larks naturally successful. It’s just that the world supports that style because of some weird societal belief system.
**Night owl types have higher rates of depression, anxiety, diabetes, cancer, heart attack and stroke because they are forced to work on a morning lark’s schedule.
The test: night owl sleep at 1-2am and wake up at 9-10am. Morning larks sleep at 9pm and wake up at 5am.
Melatonin signals to the brain when you should be sleeping. It starts releasing in greater quantities as of ~6pm.
Jet lag explains how circadian rhythms run irrespective of sunlight. Sunlight suppresses melatonin release but it’s one of many contributing factors.
**Jet lag math = 1 time zone is 1 day of adjustment. So 6 hour difference will require 6 days to adjust. Harder when flying east rather than west because you are forced to sleep earlier when you go east. Going east shortens your day… when your circadian rhythm is already slightly longer than 24 hours… so that’s why it’s harder…. Whereas when you go westward, you have lengthened your day.
Short-term memory was impaired for people who frequently change time zones. Parts of brain responsible for learning/memory shrank as well.
**Adenosine is the other trigger that works with melatonin to tell your body it’s time to sleep. It’s something that builds up the moment you wake up. It usually peaks 12-16 hours after waking up. Caffeine mutes adenosine, hence why coffee keeps you up.
**Caffeine has half life of 5-7 hours for body to cleanse.
Ice cream, chocolate and pop all have caffeine. Decaf also has 15-30% of caffeine of normal coffee.
Caffeine is degraded by enzymes in the liver. The speed also depends on genetics. Speed slows with age too. Just don’t take any caffeine after 2pm.
If you can fall asleep midmorning, then that’s a sign the quality of your sleep was poor. You need to sleep more. If sufficient sleep, the first few hours of the morning is when you are most awake.
Two key questions to test for sufficient sleep: 1) can you fall back asleep at 10/11 am? 2) can you function without caffeine before noon? A yes to 1) and no to 2) means you are not getting enough sleep.
Chapter 3 - Defining and Generating Sleep
There is REM and 4 stages of NREM (non-REM). Stage 3 & 4 of NREM are slow wave sleep and are commonly referred to “deep sleep”. Throughout the sleep period, we go through ~5 cycles of REM to NREM to REM sleep. We have more NREM sleep in the beginning and more REM later.
**Sleeping later than you should means missing out on NREM deep sleep and waking up too early means missing out on REM sleep. You think sleeping only 6 instead of the required 8 means you just get 25% less NREM and REM…. But because of the cyclical/fluctuating nature…. By waking up too early and only getting 6 hours… you end up killing 60-90% of your REM sleep. Not an equal distribution of REM and NREM.
**NREM clean out the gunk in our brains and REM strengthens the remaining connections. So, you clean up the mind’s memory bank and REM puts in the details and connects various models together. NREM saves the memories. It decides what to keep and kill by moving memories from short term to long term storage.
Muscle activity is disabled in REM sleep. This prevents you from acting out your dreams. The brain paralyzes the body for safe dreaming.
Chapter 4 - Ape Beds, Dinosaurs, and Napping with Half a Brain
**REM sleep inspires creativity and leads to higher EQ. Maybe this is why traders are such assholes… they have failed to develop EQ…. Possibly the same for robotic CEOs who tout the virtues of waking up at 5am.
**Biphasic sleep = nap + night sleep = better health. Naps are ideally 30min and before 3pm.
Societies that gave up the siesta culture saw 37% increase in risk of death from heart disease over 6-year period. Mortality of workingmen increased 60%. People wth siesta/biphasic sleep cultures are seen to live longer. Incorporate this to a healthy diet to live longer.
REM sleep is key to compounding knowledge, so companies are better off not having any morning meetings so employees can get ample REM sleep.
When sleep deprived, one will need 10-12 hours of sleep to recoup but it takes several days (depending on how severe the debt is) for brain to recoup both REM + NREM. Both are required.
Dolphins need to swim while they sleep. But if REM sleep paralyzes the body, the dolphins will die…. So they’ve evolved to be able to put half the brain to sleep while the other half keeps the dolphin alive and then it will switch.
Fasting/excessive-dieting will lead to less sleep as brain will put foraging for food as priority as it will think food has become scarce. Hence, focus on eating food that will keep you satiated throughout the night. Aka, no sugary/simple carb foods for dinner.
Most people will get drowsy mid-afternoon… avoid that time slot for presentations.. and maybe interviews as well.
Chapter 5 - Changes in Sleep Across the Life Span
NREM cements new learning + memories. Not enough leads to risk of schizophrenia.
REM is reduced significantly by alcohol. Not enough REM leads to autism in children (i.e. alcohol during pregnancy = autism risk). REM is essential for sharpening the details in learnings by refining them.
**Children run on a different circadian rhythm than adults. Children become sleepy earlier and wake up earlier than adults. But, this shifts drastically in their teenage/adolescent years. Teens will have cycles of sleeping past their parents bed time and will need to wake up much later. This means that high schools (which start earlier than work times for adults) are contributing to killing off NREM and REM sleep for students. School systems are destroying students ability to actually learn and also contributing to psychiatric disorders.
Telling a teen to sleep at 10pm is like telling an adult to sleep at 7pm.
Sleep efficiency = actual time slept / total time in bed. Teens should have 90%+ efficiency and this declines as one ages. 70-80% efficiency is being awake for 1-1.5hr of every 8 hour period…. Which means my efficiency is at about 80%.
Low sleep efficiency = higher mortality risk, worse physical health, likely to suffer from depression, low cognitive function, forgetful, less energy…..
Seeing daylight in late afternoon will push release of melatonin…. So basking in the sun can act as a coffee.
Chapter 6 - Your Mother and Shakespeare Knew
NREM = helps memory retention from hippocampus (short-term memory storage). More sleep means more transfer
Napping will help with learning as memory is transferred during this period to free up space in the hippocampus as well. The reverse is true. Not getting enough sleep and staying up (even all nighters) led to accelerating forgetting. Ironic how students pull all nighters…. They are ruining their chances with each hour they stay up.
Muscle memory = brain memory. The brain tells the muscles to execute a routine pattern. A routine that is part of a memory program. Practice WITH sleep makes perfect. NREM sleep is what will make practice an instinctual habit.
No sleep => Greater risk of sports injury. At minimum you need 8 hours. Ideal is 9 hours. Reminds me of what my powerlifting coach used to tell me. 9 hours of sleep being essential for athletes.
Sleep helps with recovery from inflammation, stimulates muscle repair, restocks energy cells, etc,…
Chapter 7 - Too Extreme for the Guinness Book of World Records
No sleep also leads to increased risk of being bi-polar, depressed and to become risk-seeking.
“After four hours of sleep for six nights, participants’ performance was just as bad as those who had not slept for twenty-four hours straight.” / no matter what, try to sleep for 8 hours! Not sleeping enough is as bad as pulling all nighters. Better to do it right than to half ass.
“You do not know how sleep-deprived you are when you are sleep-deprived.”
No-one can function on 5 hours of sleep. It is a truly small number but the likelihood I will meet that person is also just as small. So, better to awesome not possible at all because nothing to be gained from the opposite.
Awake for 19 hours => same cognitive impairment as being legally drunk. Not sleeping will kill plenty of people in car crashes like alcohol.
Sleep deprived people can’t regain performance by sleeping it back. Lost sleep means lost memory and deteriorated health.
10 days of 7 hour sleep = 24 hours of no sleep in one day. 3 nights of recovery sleep will not restore performance from 1 week of short sleeping. So, a weekends worth of sleeping will not make up for a poor weekday.
Naps/Caffeine can’t salvage the deterioration in core functions like learning, memory, emotional stability, decision making and complex reasoning.
Per a learning experiment, those who pulled all-nighters had a 40% deficit in ability to cram new facts into their brains when compared to well rested groups.
As Walker notes, the idea of final exams for an entire semester of university is an asinine decision because it forces the dumb behaviour of cramming, all nighters etc…. Given the typical human tendency to procrastinate. You’d think academics would think about this a little more.
NREM cleans out the build up of amyloid protein. It’s toxic debris and when it builds up, it leads to Alzheimers. The built up amyloid plaques will also degrade brain’s ability to go into deep sleep…. A sort of vicious cycle.
Chapter 8 - Cancer, Heart Attacks, and a Shorter Life
**Insufficient sleep leads to = more inflammation, more cholesterol, risk of type 2 diabetes, weight gain (increases appetite, sugar cravings, no feeling of satiation), muscle loss (body kills lean mass for energy as fight/flight state), cancer (agents that kill it die + agents that promote it grow….a double whammy), telomeres die (the measurement of biological aging), overall immune system weakens so you get sick easily.
“Adults forty-five years or older who sleep fewer than six hours a night are 200 percent more likely to have a heart attack or stroke during their lifetime, as compared with those sleeping seven to eight hours a night.” / shorter sleep = shorter life
When sleep deprived, heart beats faster and it will increase production of cortisol (stress hormone). It will also suppress (even shut off) production of growth hormone (healer of the body) at night. The heart beats faster = strains blood vessel = no growth hormone to repair the vessels = vessels shred/implode = heart attack/stroke
Leptin = signals sense of feeling full. Ghrelin = signals of hunger. Sleep deprivation decreases leptin and increases ghrelin.
Sleep deprivation also makes one insensitive to insulin. Cells cease to absorb glucose, making one hyperglycaemic.
Sleep = helps with discipline.
“Three year olds sleeping just ten and a half hours or less have a 45 percent increased risk of being obese by age seven than those who get twelve hours of sleep a night.” / kids need to sleep.
No sleep = smaller testicles, less testosterone, dulled sex-drive
Chapter 11 - Dream Creativity and Dream Control
REM sleep allows for latticework of mental models to form. Kill the alarm clock and allow for late morning slumbers. It may also be an advisable strategy to journal out problems you’d like to think through before sleeping so the brain can process it while you sleep.
“…learning versus comprehension. REM sleep allows your brain to move beyond the former and truly grasp the latter.” / wisdom requires REM
Edison’s story of holding ball bearings, letting himself go to sleep and as he entered the creative components of REM sleep, the body would be paralyzed… leading to dropping of the ball bearings… which would wake him up and he would be in that state of connective creativity. Fascinating story… though I imagine the continued use of the technique might be damaging if used for night sleep but highly effective for the 60-90min afternoon naps.
Chapter 12 - Things That Go Bump in the Night
Starvation = puts you on alert. Be satiated.
**High core body temp = difficulty sleeping = possible insomnia. Anxiety + stress (cortisol) raises core body temp and wakes the body as the fight/flight system is up and running.
Sleep walking/talking happen during NREM not REM. Referred to as somnambulism. Children have it more than adults, many grow out of it. One explanation is that kids have 80/20 distribution of NREM to REM and this distribution equals out as they grow older. So just statistics. Unsure why they have it though,
Test for insomnia = if you lie in bed for 7-9 hrs but you can’t fall asleep. Conditions need to be present for several months. Difficulty sleeping for several nights is normal.
**Base case is that 2/3 people will have one night per week where they have difficulty sleeping. It’s normal.
“..based on epidemiological data, any adult sleeping an average of 6.75 hours a night would be predicted to live only into their early sixties…” / sleep 8 hours… which probably requires being in bed for about 9 hours
Chapter 13 - iPads, Factory, Whistles, and Nightcaps
Artificial light suppresses melatonin. Keep the home dark as night comes and/or wear glasses that block blue light. Blue LED lights are most potent in suppressing melatonin (~about 50% suppression at night).
**Alcohol is a sedative that puts one to sleep similar anesthesia. It is not a restorative sleep. It’s a sleep where you will wake frequently throughout. Alcohol is most powerful suppressor of REM sleep. Metabolizing alcohol produces aldehydes and they suppress brain’s ability to generate REM sleep.
Abstinence is best to limit sleep disruption. If required, alcohol consumption during the day might be better to give liver/kidney ample time to degrade/excrete it.
Cooling body temp => warm hands/feet help your body’s core cool = sleep quickly/efficiently. Ideal bedroom temp is 18.3 degrees celsius. 65 Fahrenheit.
**Hot baths before bed = radiates out inner heat, core body temp plummets, faster sleep and possibly longer NREM sleep. This makes me wonder if that is why I get tired coming back home after a hot day out… and makes me wonder if that is why hot places have a Siesta culture.
Alarms = forced wake-ups spike blood pressure = creates more stress/cortisol = attacks the heart viciously
Chapter 14 - Hurting and Helping Your Sleep
Sugar rich and low fiber diets = less deep sleep + more awake. Cut the high simple carbs!
Exercise = deeper sleep leading to more recovery for more energy for the next training session. Just don’t exercise 2-3 hours before bed time.
Go to bed when you get sleepy/tired. Don’t force it. Follow your natural cycle.
If you can’t fall asleep while lying in bed, don’t lie there. Get back up and do some relaxing activities until you get tired to try again.
Don’t take sleeping pills.
Chapter 15 - Sleep and Society
Schools should start late = increase performance for students + decrease death of kids in car crash. 5am to a teenager is the adult equivalent of 3am. We all have different biological clocks. Turns out, children who sleep longer (at least 45min+) will develop higher IQs. The ROI is insane per the studies in the chapter.
No sleep = generates symptoms of ADHD. ADHD drugs suppress sleep further. You are literally killing your children.
Work should start late for most adults as well.
**Hospitals should let doctors sleep = less patient deaths = doctor error is 3rd largest case of death. The modern hospital shift schedule of having sleep-deprived residents working 72 hour shifts was set up by William Halsted of Johns Hopkins Hospital…. And he based it on his own ability to do it for 72 hours…. Which he managed as a cocaine addict… he later became addicted to cocaine and morphine as well. Residents make 460%+ more mistakes after a 36 hr shift. 1/20 residents will kill a patient due to lack of sleep. Further negligence and fatheadedness by medical community referenced in the book. It’s truly disgusting.
22 hours of no sleep = same level of impairment as someone who is drunk.
Sleep will also decrease major disasters like Chenobyl.
**“Brain can never recover all the sleep it has been deprived of.” / Fix your habits ASAP. Don’t let the errors compound.
**Costs to companies of insufficient sleep = $2K per employee per year for lost productivity, ~$54M annually in lost capital. Sleep deprived employees are less productive and are less able to generate creative solutions to problems. It’s a negative feedback loop problem to have employees work more and sleep less.
**“Under-slept employees are not only less productive, less motivated, less creative, less happy, and lazier, but they are also more unethical.” / reminds me of professional services like banking, consulting, law and accounting.
Same applies for leaders of organizations. A worthwhile question to ask CEOs would be how much sleep they get.
People in the west coast get less sleep as sun sets later in day.
**Appendix - 12 tips for healthy sleep
Avoid caffeine/alcohol/nicotine
Avoid large meals at night = indigestion = bad sleep
Avoid lot’s of fluids at night
Relax before bed + hot shower/bath
30 minutes of sunlight each day to regulate pattern…. An hour of morning sunlight I best.
Disclaimer - I’m writing this for myself. For my past, present and future self. Much of what I write is my opinion. If it somehow ignites agreement in you then great, I’d love to hear about it. If it sparks disagreement in you, don’t reach out because I don’t care for it. There always are obvious exceptions and the flawed person in me hasn’t considered them all.