Why We Sleep


Physical Copy:

By: Matthew Walker

Rating: A

This book was an absolutely fascinating dive into sleep. There were so many related ailments that I had never considered. More than anything it made me want to prioritize good quality sleep for the long-term health benefits. You have to check this one out!

Random tidbit. The book stated that autistic children don’t need as much sleep as non-autistic. When I read that, I thought of Elon Musk for some reason. I read his biography a while back and I enjoy reading articles about him. But he has made wild claims about how much he works and how he doesn’t need as much sleep as the average person. Then a few weeks later, Elon made an appearance on Saturday Night Live and told the audience that he was a high-functioning austistic. That blew my mind and made total sense. Wow!


Part 1 – This Thing Called Sleep

Chapter 1 – To Sleep . . .

The shorter your sleep, the shorter your life span. Sleep is the most effective thing we can do to reset our brain and bodily health each day.

Chapter 2 – Caffeine, Jet Lag, and Melatonin

Circadian Rhythm: One of two factors determining wake and sleep. Melatonin helps regulate the timing of when sleep occurs by signalling darkness throughout the organism, but has little influence on the generation of sleep itself.

Sleep pressure: The second factor affecting sleepiness. Sleep pressure is caused by a buildup of the chemical adenosine in your brain.

Caffeine works by blocking the receptors that adenosine affects (after about 30 minutes) and lasts for several hours.

Chapter 3 – Defining and Generating Sleep

The different stages of wake and sleep states have different purposes for your brain and body and how you process information.

Awake State: Reception (experiencing and constantly learning the world around you). 

NREM Sleep: Reflection (storing and strengthening those raw ingredients of new facts and skills).

REM Sleep: Integration (interconnecting these raw ingredients with each other, with all past experiences, and, in doing so, building an ever more accurate model of how the world works, including innovative insights and problem-solving abilities). REM sleep recalibrates and fine-tunes the emotional circuits of the human brain while also fueling creativity.

Alcohol is one of the most powerful suppressors of REM sleep that we know of.

Chapter 4 – Ape Beds, Dinosaurs, and Napping with Half a Brain

How Should We Sleep?

In developed nations, most adults sleep in monophasic patterns, or one single bout of slumber at night with an average duration of just under 7 hours.

Cultures untouched by electricity sleep differently. Hunter-gatherer tribes in undeveloped nations sleep in a biphasic pattern. Their sleep is made up of a long sleep at night (seven to eight hours) followed by a thirty- to sixty-minute nap in the afternoon.

Interesting that in the small enclaves of Greece where siestas still remain intact, men are nearly four times as likely to reach the age of ninety as American males.

Chapter 5 – Changes in Sleep Across the LifeSpan

Childhood Sleep

The changes in deep NREM sleep always precede the cognitive and developmental milestones within the brain by several weeks or months, implying a direction of influence: deep sleep may be a driving force of brain maturation, not the other way around.

A strong case can already be made for defending sleep time in our adolescent youth, rather than denigrating sleep as a sign of laziness.

Sleep in Midlife and Old Age

Myth: Older adults need less sleep. 

Older adults appear to need just as much sleep as they do in midlife, but are simply less able to generate sleep.

A hallmark of altered sleep as we age is fragmentation. The older we get, the more frequently we wake up throughout the night.

Any individual, no matter what age, will exhibit physical ailments, mental health instability, reduced alertness, and impaired memory if their sleep is chronically disrupted.

Part 2 – Why Should You Sleep?

Chapter 6 – Your Mother and Shakespeare Knew

The Benefits of Sleep for the Brain

Sleep has proven itself time and again as a memory aid. 

Sleep Before Learning: prepares your brain for initially making new memories. 

Sleep After Learning: cement memories and prevent forgetting.

Stage 2 NREM sleep, especially the last 2 hours of an 8 hour night of sleep are responsible for motor-skill enhancement. Your brain is reinforcing those motor-skill connections.

Get less than eight hours of sleep a night (especially less than 6 hours) and the following happens: 

  • time to physical exhaustion drops by 10 to 30 percent 
  • aerobic output is significantly reduced
  • impairments  in limb extension force and vertical jump height 
  • decreases in peak and sustained muscle strength
  • marked impairments in cardiovascular, metabolic, and respiratory capabilities 
  • faster rates of lactic acid buildup, 
  • reductions in blood oxygen saturation 
  • increases in blood carbon dioxide
  • impaired ability of the body to cool itself during physical exertion through sweating

Post-performance sleep accelerates physical recovery from common inflammation, stimulates muscle repair, and helps restock cellular energy in the form of glucose and glycogen.

Sleep for Creativity: A final benefit of sleep for memory is arguably the most remarkable of all: creativity.

Chapter 7 – Too Extreme for the Guinness Book of World Records

Sleep loss inflicts devastating effects on the brain, linking it to numerous neurological and psychiatric conditions (e.g., Alzheimer’s disease, anxiety, depression, bipolar disorder, suicide, stroke, and chronic pain), and on every physiological system of the body, further contributing to countless disorders and disease (e.g., cancer, diabetes, heart attacks, infertility, weight gain, obesity, and immune deficiency). No facet of the human body is spared the crippling, noxious harm of sleep loss.

Attention and Concentration

  • One brain function that buckles under even the smallest dose of sleep deprivation is concentration. 
  • Every hour, someone dies in a traffic accident in the US due to a fatigue-related error.
  • Humans need more than seven hours of sleep each night to maintain cognitive performance. After ten days of just seven hours of sleep, the brain is as dysfunctional as it would be after going without sleep for twenty-four hours.

Can Naps Help?

  • Power naps may momentarily increase basic concentration under conditions of sleep deprivation, as can caffeine up to a certain dose. Neither naps nor caffeine can salvage more complex functions of the brain, including learning, memory, emotional stability, complex reasoning, or decision-making.

Tired and Forgetful?

  • If you don’t sleep the very first night after learning, you lose the chance to consolidate those memories via high quality REM sleep. The best thing to do the night before a test is to get a good night’s sleep.

Chapter 8 – Cancer, Heart Attacks, and a Shorter Life

Sleep Deprivation and the Body

  • There are more than 20 large-scale epidemiological studies that have tracked millions of people over many decades, all of which report the same clear relationship: the shorter your sleep, the shorter your life. 
  • The leading causes of disease and death in developed nations (heart disease, obesity, dementia, diabetes, and cancer) all have recognized causal links to a lack of sleep.

Weight Gain and Obesity

  • Short sleep increases hunger and appetite, compromises impulse control within the brain, increases food consumption, decreases feelings of food satisfaction after eating, and prevents effective weight loss when dieting.

Sleep Loss and the Immune System

  • Sleep deprivation vastly increases your likelihood of infection, and reduces your response to flu vaccine.

Part 3 – How and Why We Dream

Chapter 10 – Dreaming as Overnight Therapy

Dreaming – The Soothing Balm

  • REM sleep is the only time during the 24 hour period when your brain is completely devoid of noradrenaline. Noradrenaline is the brain equivalent to a body chemical adrenaline.

Chapter 11 – Dream Creativity and Dream Control

Dreaming: The Creative Incubator

  • Deep NREM sleep strengthens individual memories. But REM sleep offers the complementary benefit of fusing and blending those elemental ingredients together, in abstract and highly novel ways.

Part 4 – From Sleeping Pills to Society Transformed

Chapter 13 – iPads, Factory Whistles, and Nightcaps

What’s Stopping You from Sleeping?

  • (1) constant electric light as well as LED light, 
  • (2) regularized temperature, 
  • (3) caffeine (discussed in chapter 2), 
  • (4) alcohol, and 
  • (5) a legacy of punching time cards.

Turning Down the Nightcap – Alcohol

  • Alcohol fragments sleep, littering the night with brief awakenings. Alcohol-infused sleep is therefore not continuous and, as a result, not restorative. 
  • Alcohol is one of the most powerful suppressors of REM sleep that we know of.

Get the Nighttime Chills

  • A bedroom temperature of around 65 degrees Fahrenheit (18.3°C) is ideal for the sleep of most people, assuming standard bedding and clothing.
  • A hot bath in the evening before bedtime can be a fantastic sleep aid but not for the reason most people imagine. You do not fall asleep faster because you are toasty and warm to the core. Instead, the hot bath invites blood to the surface of your skin. When you get out of the bath, those dilated blood vessels on the surface quickly help radiate out inner heat, and your core body temperature plummets. Consequently, you fall asleep more quickly because your core is colder. Hot baths prior to bed can also induce 10 to 15 percent more deep NREM sleep in healthy adults.

Chapter 15 – Sleep and Society: What Medicine and Education Are Doing Wrong; What Google and NASA Are Doing Right

  • Studies on changing school start times to an hour later have shown higher GPAs following the change, increased life expectancy due to lower traffic accidents, and increased attendance.
  • The residency system was developed by a doctor who later turned out to be a cocaine addict, Dr. William Halsted.
  • The number of errors vastly increase when residents and doctors are deprived of sleep.
  • You should ask your doctor how much sleep they have had before undergoing any serious surgery.

Twelve Tips for Healthy Sleep

  1. Stick to a sleep schedule
  2. Exercise is great, but not too late in the day. Try to exercise at least thirty minutes on most days but not later than two to three hours before your bedtime.
  3. Avoid caffeine and nicotine.
  4. Avoid alcoholic drinks before bed.
  5. Avoid large meals and beverages late at night.
  6. If possible, avoid medicines that delay or disrupt your sleep.
  7. Don’t take naps after 3 p.m.
  8. Relax before bed. Don’t overschedule your day so that no time is left for unwinding. A relaxing activity, such as reading or listening to music, should be part of your bedtime ritual.
  9. Take a hot bath before bed.
  10. Dark bedroom, cool bedroom, gadget-free bedroom.
  11. Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside in natural sunlight for at least thirty minutes each day. If possible, wake up with the sun or use very bright lights in the morning.
  12. Don’t lie in bed awake.

Next Actions:

Use all of the 12 tips for healthy sleep!

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