Sleep is vital to our lives, yet it's often undervalued and misunderstood. Dr. Matthew Walker, a renowned sleep expert, shares the science behind sleep and practical tips to improve the quality of our sleep, lives, and learning in his book Why We Sleep.
“The best bridge between despair and hope is a good night’s sleep.”
Matthew Walker (1973- )
The Importance of Sleep
1. Zero Tolerance for Sleep Deprivation: No one can function optimally with less than 7 hours of sleep. Typically, people consider 8 hours a whole night’s sleep, but that can vary by the individual. Even with just missing out on an hour, there are noticeable differences in performance. Sleep deficits affect performance, mood, and overall health.
There is a myth that people need less sleep as they age; adults will always require 8 hours of sleep no matter the age. Older people are constantly waking up and going to their early bird specials or gardening at odd hours, but many fail to consider when they go to bed. Older people tend to wake up earlier because they go to sleep earlier. They don’t need less sleep; their circadian rhythms have slightly shifted from the norm.
2. Hunter-Gatherer Sleep Patterns: Without modern distractions and artificial lighting, hunter-gatherer communities experience little to no sleep problems, suggesting that modern lifestyles disrupt natural sleep patterns.
3. Real Beauty Sleep: People who sleep more look better. Adequate sleep significantly affects our appearance and physical health. Lack of sleep can make us look less attractive, impacting social and professional opportunities.
4. Cognitive Impact: The prefrontal cortex, which governs decision-making and self-control, is severely impaired by lack of sleep, leading to poor emotional and behavioral regulation. If we don’t sleep, we lose our ability to regulate our emotions, actions, responses, discipline, and planning for the future.
5. Emotional Sensitivity and Impulsivity: Sleep deprivation increases sensitivity to negative emotions and impulsive behavior, making it challenging to resist immediate gratification. Again, this is because of the lower activity in our prefrontal cortex.
Sleep Mechanics
6. Memory Consolidation: Sleep serves as a critical period where short-term memories transition to long-term storage, enhancing learning and retention.
Moving information from short-term memory to our long-term memory happens during sleep and is known as consolidation. We need to consolidate because holding information in our short-term memory uses cognitive load, which can be thought of as our brain’s physical processing power. Sleeping is what resets our cognitive load. As our days go on, we take in more and more information and store it in our short-term memory – this is known as acquisition. When we sleep, we move all that information into our long-term memory, clearing space in our short-term memory.
7. Sleep Stages: Simply moving information from short-term memory to long-term memory is a massive oversimplification of the actual process.
Only certain kinds of information get consolidated during certain stages of sleep. There are four stages of sleep, and they happen in a cycle. Throughout the night, we experience these four stages over and over until we wake up. An entire sleep cycle lasts about 90-120 minutes.
Stage 1—This is when someone moves back and forth between consciousness and sleep. On an EEG, they exhibit alpha waves. They look pretty drowsy at this point. This only lasts about 5-10 minutes. If we wake up during stage 1, we will feel well-rested and ready to take on the day. The best way to wake up in stage 1 is to avoid alarm clocks. Our body will naturally wake up in stage 1 when it is ready.
Stage 2—This is when we really start to sleep. Our body releases chemicals that make it difficult to wake up. Our heart rate and body temperature start to decrease. On an EEG, we’d notice k-complexes and sleep spindles. This lasts about 20 minutes.
Stage 3—At this point, we are in a pretty deep sleep. We can have dreams at this stage, but the brain isn’t as active on an EEG. The brain would be giving off delta waves. This is also when information consolidation happens, but not all information is moved to long-term memory.
In stage 3, only a certain kind of declarative memory is moved from short-term to long-term. Declarative Memory holds information regarding facts, things that we “know”, or things that can be “declared as known,” are consolidated and saved for later. Keep in mind that this process just saves the neural pathway; strengthening them requires practice. Declarative memory consolidation occurs in NREM (non-REM) sleep if the information is emotionally neural or straightforward. Once the declarative information is emotionally charged or complex, our brain uses REM sleep to consolidate that information.
REM Sleep—This is the deepest stage of sleep, yet our brain is the most active on an EEG. REM stands for Rapid Eye Movement because our eyes move so much during this phase.
We do our most intense dreaming here, and if we’re woken up during this phase, we’ll feel groggy and disoriented.
REM sleep is necessary for the body and mind to function correctly. REM sleep allows our cardiovascular systems to reset by lowering heart rate and blood pressure and restocks our immune systems. Most of the benefits from sleep come during REM sleep, so don’t be fooled into thinking short naps are a replacement for long, deep sleep.
During REM, we consolidate a different type of information – Procedural Memory. This includes the knowledge of how to do things, typically with motor skills. REM sleep is essential for learning how to play an instrument or a sport, anything that requires a knowledge of moving ourselves in a certain way. When we’re in REM, we can brain run through the procedures (fire the specific neural pathways) 30-40 times during one night’s sleep. The study titled "Practice with Sleep Makes Perfect: Sleep-Dependent Motor Skill Learning" by Walker et al. (2002) found that people are about 20-30% better at a skill after a night of proper sleep without extra practice.
When I first learned the guitar, I always had trouble playing a song in one sitting. I could never get it perfectly right, but I knew I could do it if I went to sleep the next day. I thought it was my superpower, but after reading a little about skill acquisition, I know now that my brain was practicing those procedures repeatedly in my sleep. No wonder I was so much better the next day!
REM sleep is beneficial for memory consolidation and critical for emotional regulation and information processing.
“Dreaming suggesting that EMDR was related to rapid eye movement (REM) sleep—the phase of sleep in which dreaming occurs. Research had already shown that sleep, and dream sleep in particular, plays a major role in mood regulation. As the article in Dreaming pointed out, the eyes move rapidly back and forth in REM sleep, just as they do in EMDR. Increasing our time in REM sleep reduces depression, while the less REM sleep we get, the more likely we are to become depressed.”
Bessel van der Kolk, M.D. (The Body Keeps the Score)
“In a series of elegant studies Stickgold and his colleagues showed that the sleeping brain can even make sense out of information whose relevance is unclear while we are awake and integrate it into the larger memory system.”
Bessel van der Kolk, M.D. (The Body Keeps the Score)
Health Connections
8. Neurological Maintenance: Our body has this system known as the Glymphatic System, which is responsible for cleaning the brain during sleep. It’s similar to the more commonly known, lymphatic system, which cleans the body. The glymphatic system washes away beta-amyloid, a protein that builds up in our brains while awake. Too much of this beta-amyloid in our brains will prevent us from firing our neural pathways correctly. It is the main component of the plaque found in Alzheimer’s patients.
Living is hard work; our brains are doing a lot, and if we don’t give them a break, we can’t expect them to work well over the long term. If you know that you have a family history of Alzheimer’s, then I highly recommend taking your sleep seriously.
9. Sleep and Testosterone: Men's reproductive health is directly linked to sleep, with inadequate sleep leading to lower testosterone levels and smaller testicle size.
Men who sleep 5 hours or less per night have smaller testicles than men who sleep seven or more hours per night. Men who sleep less than 5 hours per night also produce as much testosterone as someone ten years older than them.
10. Fertility Issues: Insufficient sleep can adversely affect both men's and women's fertility. If you are trying for kids, make sure you are well rested.
11. Cardiovascular Health: Heart attack, stroke, and high blood pressure increase by 24% the day after daylight savings, but in the fall, when we gain an hour of sleep, we only get a 21% increase. There is a similar profile for car accidents, suicide rates, and federal judge sentencing severity as well. Just a single hour of sleep can have a significant influence. Maintaining a consistent sleeping schedule is crucial to a healthy cardiovascular system.
Societal Impacts
12. Sleep and Education: Just like older folks, teenagers have a shifted circadian rhythm, which causes them to sleep and wake later than the average person typically. After I learned this, I was so surprised that my entire high school education started class at 7:30 am. My brain never really woke up until 3rd period, and now I know why. If education is about the children, we must change schools to adapt to our bodies. High schools shouldn’t start until at least 10 am.
13. Dangers of Sleep Deprivation: Driving or performing any attention-heavy tasks without enough sleep can be more dangerous than being under the influence of alcohol.
Sleep depravity lowers our IQ more than alcohol intoxication, so we are dumber when we don’t sleep. Additionally, drivers under the influence have slowed reflexes, but sleep-deprived drivers have no reflexes.
14. Cultural Misconceptions: Societal undervaluation of sleep often leads to disregard for the health impacts of sleep deprivation. The inconvenient truth is that we live in a society that does not value sleep as much as it deserves. People who sleep are often labeled as lazy and shamed if they need or ask for more sleep. People flaunt their sleeplessness as badges of honor as if it is something to be coveted.
If we want to control our sleep as a society, we must start rewarding people for sleeping adequately. I try to encourage everyone I know to sleep as much as they need to and shame them for skipping sleep. It’s the opposite of what most people do, and I see many people think I’m crazy, but sleeping correctly is more important than others’ poorly informed opinions.
Sleep is typically the first thing people choose to sacrifice when they get busy.
I know many people live their lives this way because things get complicated.
It’s easy to believe that sleep is optional and sacrificing a little bit won’t hurt anyone except maybe ourselves, but the opposite is true.
Sleep is essential because our bodies will work against us if they aren’t properly maintained. People have time for what they prioritize, but sleep needs to be a main priority. Sacrifice something else to achieve your goals; don’t be quick to think that trading sleeping for anything is an even exchange. Sleep debt is difficult to pay back, and Nature will always collect what she is owed.
Practical Tips
15. Managing Sleep Environment: Control light exposure—especially blue light—as it can disrupt sleep timing and degrade sleep quality.
The blue light from our devices delays melatonin (the hormone that gets us ready to sleep) release by 3 hours and cuts its concentration by 50%. Something as simple as exposing ourselves to blue lights will delay our sleep onset by 3 hours.
For example, we are trying to sleep at 10, so we stop using our phones and turn off all the lights. Our bodies won’t release melatonin for another 3 hours! We won’t be able to start feeling tired until about 1 a.m. Those blue frequencies tell our brain that the sun is still out, and we should still be up. On top of the later onset of sleep, our REM sleep is of lower quality when exposed to these blue lights during the evening hours.
Many of us know this, and many devices have a night mode setting to block out the blue frequencies so we don’t mess with our neural biochemistry too much, but I’m not so sure that night mode works well enough.
Additionally, artificial lighting in our homes can interfere with proper sleep.
It’s not just blue light that we are sensitive to (although it affects our sleep tremendously); it’s all light. Keeping lights dim at night signals our body that it’s nighttime, and we should start physiologically preparing for sleep. This lowers our blood pressure, keeps our circadian rhythms in their most natural states, and improves the quality of our sleep.
16. Diet and Sleep: Avoid stimulants like caffeine and depressants like alcohol close to bedtime, as they can severely impact sleep quality and duration.
Some people like to call alcohol in the evening a “nightcap” to help them go to sleep, but the truth is alcohol doesn’t help us sleep. Alcohol may knock us unconscious, but that is not the same as sleep if we are looking at it from a physiological perspective. Alcohol blocks REM sleep and fragments our sleep throughout the night. The frequent interruptions keep us sleeping in the first two stages of the sleep cycle, and even if we stay asleep, REM is blocked, and that is where most of the benefits from sleep are. This is usually why we wake up exhausted after a night of drinking. Alcohol doesn’t induce sleep; it sedates us.
Caffeine has a half-life of 6 hours, so it takes the body 6 hours to process half the concentration of the caffeine out of the body.
Let me put it this way: if we drink a coffee at 6 am, half of that caffeine is still circulating in my body at noon, and a quarter of it will be there at 6 pm. But most of us don’t just have one coffee, we’ll have one in the morning then one at lunch to get us through that afternoon slump. Let’s say we drink that coffee at 2 pm, which means that half of that 2nd cup of coffee is still in our system by 8 pm and a quarter of it is at 2 am.
We may feel tired, but our brains still physically deal with caffeine, and studies have shown that it interferes with sleeping correctly.
The bottom line is that coffee stay in the brain hours after we drink it, if we don’t want our coffee to mess with our sleep, Dr. Walker suggests drinking coffee 14 hours before bed. Even if we manage to fall asleep with the caffeine in our brains, we will experience a 20% reduction in sleep quality, which is equivalent to aging our brains 20 years.
17. Optimal Sleep Conditions: Lowering body temperature before bedtime can facilitate quicker and deeper sleep; consider a warm bath followed by a cool bedroom.
The body needs to drop by about 1°C to start sleeping. There are many ways to make this happen. My favorite is to take a super hot shower before bed. The hot water will make the heat radiate from us when the shower is over, and our bodies are way more primed for sleeping. Keeping the room cool when we try to sleep is a great way to help us get to sleep faster while increasing sleep quality. This makes sense if we think about it: it gets colder when the sun goes down, and it’s time to sleep. It’s no wonder we get tired when we lower the temperature just slightly.
Additionally, when our bodies need to wake up, the core temperature rises by about 1°C. If you have the means, consider heating the room when you need to wake up to make that process easier.
Sleep isn't just a passive state but a dynamic activity crucial for our physical, emotional, and cognitive health. By understanding and applying the lessons from sleep science, particularly those highlighted by Dr. Walker, we can improve our sleep quality and overall quality of life.