Why we sleep

Book review: Why We Sleep (Matthew Walker)

If you are a subscriber to my newsletter, you know this week is Sleep Awareness Week. One of the factors driving negative health outcomes is lack of sleep. Among the people leading research on this topic is Professor Matthew Walker. Here, I review his bestselling book Why We Sleep: The New Science of Sleep and Dreams.

The author

Matthew Walker is a British scientist and academic with a degree in neuroscience and a PhD in neurophysiology. He is currently a Professor of Neuroscience and Psychology at the University of California, as well as the founder and director of the Center for Human Sleep Science.

He has published numerous papers on the impact of sleep on health, but today I’m focusing on his excellent book Why We Sleep.

Prof Walker is also an outstanding speaker. You will find a link to his TED talk at the bottom of this article. I have enjoyed listening to many podcast interviews. In fact, it was a podcast that introduced me to him and his work. I was mildly disappointed to see that he did not narrate the audio version of his book, but it is a great listen regardless.

The book

This book is a rounded exploration of sleep, including what happens when we sleep, what aspects of health are impacted by insufficient sleep and how we can leverage technology to help us sleep more and better.

Part 1

This section deals with the basics: what is sleep, who sleeps, how much, how human beings should sleep, and how sleep changes throughout the lifespan. Topics include how caffeine works, why jet lag messes up with our circadian rhythm and how to determine if you are getting enough sleep.

This is where the types of sleep (REM and NREM) are introduced. REM sleep resets our emotional state and makes associations between bits of information; NREM sleep helps transfer recent memories into long-term memory.

Another important distinction described in this part of the book is that of circadian rhythm shifts across the lifespan. For example, the fact that adolescents are wired to wake up and stay up later, while older people’s rhythm is shifted earlier.

A few other interesting facts:

  1. Autistic children sleep less, especially REM sleep
  2. Alcohol is one of the most powerful suppressors of REM sleep that we know of
  3. Alcohol readily crosses the placenta and affects brain electric activity of the child, and it’s also readily absorbed in the mother’s milk
  4. Sleep disruption contributes to dementia in mid and later life

Part 2

The second part of the book deals with the good, the bad and deathly of sleep, as well as how and why lack of sleep causes health issues.

This section explains the role of sleep in consolidating memories and perfecting motor skills. Regarding the latter, Prof Walker rightly remarks “muscle memory is, in fact, brain memory”.

Another important issue related to lack of sleep is drowsy driving, which is the cause of many car crashes. Note that the author talks about crashes and not accidents, because their cause is preventable. Two more concerning facts are that the risk of getting into a car accident increases exponentially with sleep deprivation and our brains cannot tell how sleep deprived they are while sleep deprived.

Finally, lack of sleep has been linked to several health ailments, including dementia, cancer, cardiovascular disease, metabolic dysregulation and diabetes. On the metabolism topic, insufficient sleep is associated with increased food intake, undesirable food choices and impaired blood sugar control. Our immunity is also affected by lack of sleep; an example is the fact that the flu shot is more effective if you are not sleep deprived.

Part 3

This part of the book attempts to explain the often misunderstood realm of dreams. Despite the popular belief that dreams have a specific meaning, it seems that they act more as an emotional cleanse and a creativity boost.

It is also known now that dreams come from REM sleep, which happens later during the night.

Part 4

The final section deals with sleep disorders including insomnia and the rather rare fatal familial insomnia. Other topics include sleeping pills and why they are a bad idea, as well as non-drug therapies for better sleep. Finally, it examines the impact of insufficient sleep on education, healthcare and business.

One interesting takeaway from this part is that alcohol intake doesn’t only affect sleep, but also learning as our brain doesn’t get the same chance to consolidate memories. In addition, the author identifies the relationship between food intake and sleep, e.g.:

  1. Severe caloric restriction (e.g. 800 kcal/day for 1 month) = difficulty sleeping and reduced NREM sleep
  2. High carbohydrate + low fat = decreased deep NREM sleep and increased REM sleep
  3. High sugar + low fibre = decreased deep NREM sleep and increased number of awakenings at night

On the topic of mental health, the author notes that long periods of sleep deprivation cause more suicidal thoughts and that symptoms of ADHD are nearly identical to those caused by lack of sleep.

Lack of sleep decreases self control, work engagement and productivity at work. Moreover, shift workers should note that 22 hours of sleep deprivation is cognitively equivalent to being legally drunk.

Why We Sleep tips for better sleep

The book wraps up with 12 actionable items that will help you achieve better sleep:

  1. Go to bed and wake up at the same time every day
  2. Exercise but not too close to 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 sleep (e.g. asthma/cough medications)
  7. Don’t take naps after 3pm
  8. Relax before bed
  9. Take a hot bath before bed (to cool down core temperature)
  10. Keep your bedroom dark, cool and gadget-free
  11. Get sunlight exposure during the morning and turn down lights before bedtime
  12. Don’t lay awake in bed

More information

Head to Prof Walker’s website Sleep Diplomat and also take some time to watch his TED talk below.

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