Why We Sleep by Matthew Walker

Why We Sleep Book Review by Ishan Shanavas

Book Notes – In this series, I share my insights, ideas, and reviews of my favourite books, whose topics are wide-ranging.

Rating – 9/10

Rating: 4 out of 5.

Amazon Link

Book Compressed into 3 Points

  • Our sleep quality and quantity affects all spheres of our lives. Good sleep is a key to better immunity, fitness and lifespan.
  • Adequate sleep increases longevity, enhances memory and creativity, keeps you slim and lowers food cravings. It reduces the risk of cancer, dementia, flu, heart attacks and strokes.
  • Establishing a sleep routine is one of the simplest tasks we can do to boost our wellbeing.

Who is it for?

  • Those who’d like to understand the science behind sleep.
  • Those who’d like to improve the quality of their sleep and lives.
  • Those striving to better their cognitive and physical abilities.

3 Favourite Quotes

  • Sleep is the single most effective thing we can do to reset our brain and body each day—Mother Nature’s best effort yet at contra-death.
  • We sleep for a rich litany of functions, plural— an abundant constellation of nighttime benefits that service both our brains and our bodies. There does not seem to be one major organ within the body, or process within the brain, that isn’t optimally enhanced by sleep(and detrimentally impaired when we don’t get enough).
  • I believe it is time for us to reclaim our right to a full night’s sleep, without embarrassment or the damaging stigma of laziness. In doing so, we can be reunited with that most powerful elixir of wellness and vitality, dispensed through every conceivable biological pathway. Then we may remember what it feels like to be truly awake during the day, infused with the very deepest plentitude of being


  • Sleep is a universal phenomenon. All animal species sleep or engage in activities similar to sleep. Until very recently, the science of sleep was unknown, as were its benefits and effect on our lives. 
  • On its face, sleep seems to provide no objective value to our lives. Evolutionary sleep seems counterintuitive, for why you sleep, you cannot eat, nurture your offspring or reproduce. Furthermore, you are entirely vulnerable while sleeping. 
  • So since evolution has not weeded out sleep from our lives, it must have some tangible benefit to our lives despite these apparent drawbacks.
  • Sleep has far-reaching effects on all our major body parts. It affects our ability to learn, memorise, and make decisions. It resets the immune system for the day, fights malignancy, prevents infection, restores our metabolism and hormonal levels. It controls our appetite and body weight, gut bacteria numbers, blood pressure and cardiovascular system health.
  • Melatonin regulates the time when sleep occurs. That is why passengers travelling across time zones face jet lag- their melatonin levels are disturbed as their biological clock adapts to the new timezone.
  • The two factors that determine sleep timings are:-
  1.  Your circadian rhythm: Your internally generated body clock influences your daily moods, emotions, core body temperature, metabolic rate, hormonal levels.
  2. Sleep Pressure: A chemical called adenosine accumulates in the brain throughout the day. Higher the concentration, the greater the desire to sleep. It peaks after 12-16 hours of being awake (an irresistible urge to sleep).
  • The drug caffeine (found in coffee, tea, chocolate etc.) binds to the adenosine receptors, making it harder to sleep. Thus you feel awake despite high levels of adenosine in the brain. Caffeine stays in the bloodstream long after consumed, thus altering sleep patterns.
  • Despite caffeine being one of the most addictive drugs, it is present in many aspects of our daily life. It is a drug we readily give children. 
  • The circadian rhythm is like a wave—sometimes during the day, you feel very alert( Eg: from 7 am to 11 pm), whereas, at other times, you feel the urge to sleep (Eg: 11 pm to 7 am).
  • While sleeping, even though your sensory organs still function, the senses are not heeded by the brain.
  • While you consciously don’t feel time pass in your sleep, your brain non-consciously counts it. That is why when you need to wake up in the morning at a specific time, you sometimes wake up early by a few minutes, unassisted.
  • Sleep activity is studied by recording two parameters.
  1. Brainwave activity
  2. Eye movement
  3. Muscle activity
  • There are two stages of sleep with defining ocular features-
  1.  NREM- Non-Rapid Eye Movement
  2. REM – Rapid Eye Movement

These two stages occur alternatively throughout the night at 90-minute intervals.

  • NREM is associated with “deep” sleep when it is hard to wake up an individual. In contrast, REM sleep is when brain activity almost resembles awake people. It is the stage associated with dreaming.
  • Both these stages are vital for a good night’s sleep.
  • We, as a species, are geared to have a biphasic sleep pattern—in 2 periods during the day. Due to our industrialised world, we are forced to sleep in a monophasic pattern, with jobs requiring us to work during the day, giving us the night to sleep.
  • The cognitive intelligence of our species, which made us the most dominant piece on the planet, can be attributed to the disproportionate amount of REM sleep.
  • Our emotional IQ(ability to regulate emotions) can be traced to the amount of REM sleep received. It is also what influences our creativity.
  • A growing foetus spends most of its time sleeping in the REM state. Insufficient REM sleep at this stage can have cognitive disorders (like autism). Drinking alcohol during pregnancy can have the same effect.
  • Insufficient sleep can result in a higher mortality risk, a higher likelihood of depression, lower cognitive function, and forgetfulness.
  • Sleeping before and after bouts of learning significantly helps solidify information in the brain and body— be that intellectual or physical learning.
  • Sleep deprivation is linked to numerous neurological and psychological disorders like Alzheimer’s disease, anxiety, depression, bipolar disorder, suicide, stroke etc. It affects your attention spans, memory and emotions.
  • The functioning of body systems, be that immunity, cardiovascular, neurological, muscular, metabolism are all intrinsically linked to sleep. Sleep deprivation drastically affects all of them.
  • Dreams have an evolutionary purpose— to nurse our emotional and mental health and stimulate our creative spirits.
  • Somnambulism (movement in sleep), insomnia(lack of good sleep quality/quantity), narcolepsy, and fatal insomnia are some disorders related to sleep.
  • Modern lighting, especially blue light from devices, disrupts the circadian rhythm, affecting sleep cycles. This, along with alcohol and temperature fluctuations, are common factors affecting sleep patterns globally.
  •  Using sleep pills is highly not recommended because it dramatically affects the regularity of the sleep pattern, inducing a cycle of shortened constant sleep and insomnia.
  • Studies have shown that underperformance in the workplace due to lack of sleep results in substantial economic losses for countries. Similarly, early school timings have a comparable effect on students, degrading their performance in their academics. A more flexible schedule accommodating people with varying sleep patterns will help mitigate this.
  • At an individual level, we must strive to better our sleep habits. Only then will systemic changes take place. It starts with educational and organisational change—tearing down society’s wrong notions around sleep.
  • Methods of obtaining good sleep
  1.  Sticking to a sleep schedule
  2. Exercising at least 3 hours before bedtime
  3. Avoiding caffeine and nicotine
  4. Avoiding alcohol before bed
  5. Avoiding large meals at night
  6. Avoid medicines that delay or disrupt sleep (if possible)
  7. Don’t take naps after 3 pm.
  8. Relax and unwind before going to bed
  9. Take a hot bath before bed.
  10. Sleep in a dark, cool, gadget-free bedroom
  11. Have the correct sunlight exposure in the day
  12. Don’t lie awake in bed if you’re not getting sleep. Get up and do some activity until you feel sleepy.


A personal favourite, this well-written book is suitable for all ages. It explains scientific concepts in a manner that anyone can understand. It offers actionable advice on improving sleep hygiene. It is a reasonable length and will take a few weeks to finish. This book gave me a proper sleep routine, opening my eyes to caffeine and technology’s disastrous effects on sleep. After reading it, I have established a proper night time detox routine, vital for my wellbeing. 

If you found this insightful, please subscribe. It encourages me to produce new content regularly.

Enter your email ID below. You will receive an email asking you to confirm your subscription. Once you confirm, sit back and enjoy content delivered right into your inbox. It’s free!

Subscribe here!

Published by Ishan Shanavas

I am a young adult, interested in nature, photography, art and culture. An aspiring polymath, I share my learnings through my blog. I also include insights from my favourite books.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: