Why We Sleep by Matthew Walker: A Review

Sleeping is underrated.

Sleep is not just a necessity; it’s the foundation of our well-being. To function effectively, to learn, to remember, to avoid illness—sleep is central. If I had to describe Why We Sleep by Matthew Walker in just two words, they would be game-changer.

Why This Book Matters

“Sleep is the most effective thing we can do to reset our brain and body health each day,” Walker declares. This idea resonates deeply throughout his book. Walker, a neuroscientist and Professor of Neuroscience and Psychology at the University of California, Berkeley, has spent decades studying the science of sleep. I stumbled upon his work after watching his 13-million-view TED Talk, Sleep Is Your Superpower (highly recommended at 19:19 minutes). That video alone inspired me to quit coffee.

The book goes further, equipping you with knowledge and actionable steps to avoid sleep deprivation and improve your mental and physical health. Walker’s scientific rigor is matched by his ability to communicate complex ideas simply, making his research accessible to all.

The Key Takeaways

Sleep isn’t just rest—it’s an intricate process that shapes every aspect of our lives. Walker explains this in detail, breaking the book into six main parts:

How Sleep Works
The Benefits of Sleep
The Consequences of Sleep Deprivation
How to Sleep Well
What Disrupts Sleep
Dreams and Their Role

Let’s dive into each.

1. How Sleep Works

The ideal sleep pattern is biphasic: 7–8 hours at night, plus a 30–60-minute nap in the afternoon. Sleep consists of two primary phases:

NREM (Non-Rapid Eye Movement): Deep, restorative sleep where your brain categorizes and stores daily experiences.
REM (Rapid Eye Movement): Dreaming sleep, where your brain builds connections, combines new and old information, and enhances creativity.

These phases are essential. During REM sleep, brain scans show activity similar to being awake, yet the body is paralyzed—a paradoxical state. This is why we often say, “Sleep on it” before making a big decision; REM sleep fuels problem-solving and insight.

Your body also operates on a circadian rhythm, a natural 24-hour cycle tied to Earth’s rotation. This rhythm governs your sleep, body temperature, and hormones. Even without external cues like clocks or sunlight, your body instinctively follows this rhythm.

2. The Benefits of Sleep

Walker doesn’t just make the case for more sleep—he quantifies it. Research shows that a good night’s sleep:

Improves memory retention by 20–40%.
Helps your brain selectively preserve important information.
Boosts emotional regulation and the ability to read facial expressions.

Sleep also enhances your physical health. It lowers the risk of cancer, heart disease, stroke, and dementia while strengthening your immune system. Even your attractiveness improves!

3. The Consequences of Sleep Deprivation

Not sleeping enough is catastrophic for your body and mind. Here’s a quick test:

Do you need coffee to function before noon?
Could you nap easily by 11:00 AM?
Do you struggle to focus or need an alarm to wake up?

If you answered “yes” to most of these, you’re likely sleep-deprived. The effects are severe:

After 16 hours awake, brain performance declines.
After 22 hours awake, your cognitive abilities mirror those of someone intoxicated.
Even a two-hour sleep loss cuts 60–90% of your REM sleep.

Chronic sleep deprivation increases the risk of anxiety, depression, obesity, diabetes, and even car accidents due to microsleep episodes.

4. How to Sleep Well

Improving sleep quality is about consistency, not just duration. Here are Walker’s tips:

Stick to a regular sleep schedule.
Avoid screens before bed.
Keep your room dark and cool (around 18.3°C).
Avoid caffeine and alcohol.
Take a warm shower before sleeping.
Don’t hit snooze—wake up naturally if possible.

Remember, you can’t “catch up” on lost sleep.

5. What Disrupts Sleep

The main culprits? Caffeine, alcohol, and screens.

Caffeine: A psychoactive stimulant that blocks adenosine, the chemical that makes you feel sleepy. Its effects linger for hours, disrupting your natural rhythms.
Alcohol: Suppresses REM sleep, impairing your ability to recover mentally and physically.
Screens and light exposure: Interfere with your circadian rhythm, making it harder to fall asleep.

Different drug effects on web spider (NASA - Noever, R., J. Cronise, and R. A. Relwani. 1995. Using spider-web patterns to determine toxicity. NASA Tech Briefs 19(4):82. Published in New Scientist magazine, 29 April 1995. http://www.caffeineweb.com/?p=15, Public Domain.)

Jet lag and night shifts are equally harmful, destroying brain cells and impairing memory.

6. Dreams and Their Role

Dreams are not meaningless—they play a therapeutic role. During REM sleep, the brain processes emotional concerns, offering a form of overnight therapy. This helps heal emotional wounds, solve problems, and spark creativity.

Interestingly, REM sleep is the only time your body’s stress chemical, noradrenaline, is absent, allowing your brain to reset emotionally.

Final Thoughts

Sleep is non-negotiable. It is the bedrock of your health, affecting your lifespan, memory, creativity, and emotional stability. After reading Why We Sleep, I had a simple realization: I need to sleep.