Matthew Walker’s “Why We Sleep” Is Riddled with Scientific and Factual Errors. I like Matthew Walker’s book since I learned a lot about sleep from the book. I don’t know which side is correct, but it’s more important to give both sides.
2018 has been a good year in terms of great books. Great reads so far this year include Sapiens, Messy Middle, The Courage to be disliked, Subscribed, to name a few. I wrote quickly about some of them on this blog. However, none is more important than Why we sleep.
Here are a few things I learned:
Sleep isn’t like money in the bank. If you over-spend this month, saving up a little more next month will make up the difference. If you lose one quality sleep one night, that ship has already sailed. There is no getting it back. Hence, the notion of staying up late on the weekdays just to make it up on the weekends is false
Without sufficient sleep, amyloid plaques (poisonous to neurons, killing the surrounding brain cells and associated with Alzheimer’s disease) build up in the brain, especially in deep-sleep-generating regions, attacking and degrading them. The loss of deep NREM sleep caused by this assault therefore lessens the ability to remove amyloid from the brain at night, resulting in greater amyloid deposition. More amyloid, less deep sleep, less deep sleep, more amyloid, and so on and so forth
At fault were the two characters, leptin and ghrelin. Inadequate sleep decreased concentrations of the satiety-signaling hormone leptin and increased levels of the hunger-instigating hormone ghrelin. It was a classic case of physiological double jeopardy: participants were being punished twice for the same offense of short sleeping: once by having the “I’m full” signal removed from their system and once by gaining the “I’m still hungry” feeling being amplified. As a result, participants just didn’t feel satisfied by food when they were short sleeping.
When given just five and a half hours of sleep opportunity, more than 70% of the pounds lost came from lean body mass – muscle, not fat. Switch to the group offered eight and a half hours’ time in bed each night and a far more desirable outcome was observed, with well over 50% of weight loss coming from fat while preserving muscle
With a genuine lack of malice, I proceed to inform them that men who report sleeping too little or having poor-quality sleep have a 29% lower sperm count than those obtaining a full and restful night of sleep, and the sperm themselves have more deformities.
Routinely sleeping less than 6 hours a nigh results in a 20% drop in follicular-releasing hormone in women – a critical female reproductive element that peaks just prior to ovulation and is necessary for conception.
One such foreign entity that natural killer cells will target are malignant (cancerous) tumor cells. Natural killer cells will effectively punch a hole in the outer space of these cancerous cells and inject a protein that can destroy the malignancy.
Examining a healthy young men, Irwin demonstrated that a single night of four hours of sleep – such as going to bed at 3AM and waking up at 7AM – swept away 70% of the natural killer cells circulating in the immune system, relative to a full 8-hour night of sleep.
A large European study of almost 25,000 individuals demonstrated that sleeping 6 hours or less was associated with a 40% increased risk of developing cancer.
A chemical called melatonin helps regulate the timing of when sleep occurs. It governs when the race (sleep) begins, but does not participate in it. Our distractions by modern technology and LED lights suppress and delay the rise of melatonin, meaning that our body is told that sleep should start late. Throw in the enforced awakening by virtue of the industrial culture (alarm clock) and we have a recipe for inadequate sleep.
Memories remain perilously vulnerable to any disruption of sleep (including that from alcohol) even up to three nights of learning, despite two full nights of natural sleep prior.
Selectively warming the feet and hands by just a small amount (0.5 Celsius degrees) caused a local swell of blood to these regions, thereby charming heat out of the body’s core, where it had been trapped. The result of all this ingenuity: sleep took hold of the participants in a significantly shorter time, allowing them to fall asleep 20% faster than was usual, even though these were already young, healthy and fast-sleeping individuals
Most controversial and alarming are those highlighted by Dr Daniel Kripke, a physician at the University of California, San Diego. Kripke discovered that individuals using prescription sleep medications are significantly more likely to die and to develop cancer than those who do not
Saying that alcohol is a sedative often confuses people, as alcohol in moderate doses helps individuals liven up and become more social. How can a sedative enliven you? The answer comes down to the fact that your increased sociability is caused by sedation of one part of the brain, the prefrontal cortex, early in the timeline of alcohol’s creeping effects. As we have discussed, this frontal lobe region of the human brain helps control our impulses and restrains our behavior. Alcohol immobilizes that part of our brain first. As a result, we “loosen up”, becoming less controlled and more extroverted.
Your desire and ability to remain conscious are decreasing and you can let go of consciousness more easily. I am very deliberately avoiding the term “sleep”, however, because sedation is not sleep. Alcohol sedates you out of wakefulness, but it does not induce natural sleep.
I have mixed feelings from reading this book. On one hand, I am glad to be enlightened by all the scientific findings on sleep. On the other, I am a bit horrified by what I have done to my body. Nonetheless, I am determined to prioritize sleep more in 2019 and beyond or at least to limit the hard done to my body.
Above are just a few of many great insights that the book offers. I am not doing the book justice, but I hope you spend some time reading this book and gifting it to friends or beloved ones. (I have no connection whatsoever with the author or the publisher. Just a big fan who wants as many to learn about the science of sleep as possible)
This piece will be my summary of the first two chapters of a wonderful book called “Why we sleep”. I feel a mixed feeling of concern and excitement after reading these two chapters, and would like to share what I learned. The two chapters use science to describe the two primary factors influencing our sleep and the consequences of our normal behavior nowadays, including the effect of caffeine. Knowing these consequences helps a person make better decisions to improve his/her sleep and health.
I highly recommend the book to anyone who cares about sleep and his or her health. All the good findings are from the book. All the clumsy explanations and communication are mine.
Melatonin & circadian rhythm
Everyone has a 24-hour rhythm called a circadian rhythm. The internal 24-hour clock in our brain communicates the circadian rhythm to every area of the brain and part of the body. When the sun sets, our body starts to release a chemical called Melatonin. Melatonin signals to our body that “it’s getting dark, it’s getting dark” and that the time for sleep is close. As we sleep, the chemical starts to wear off. As soon as the sun rises and interacts with our eyes, our brain knows that it’s time to stop pumping Melatonin into our bloodstream. Once the chemical stops circulating, the brain and body know that it’s time to wake up. The rhythm continues in the same way every day regardless of our lifestyle.
It’s worth noting that Melatonin has little effect on why we feel sleepy. It is just a signaling chemical released by our body to trigger a certain action. In this case, it’s a) knowing that it’s dark b) getting up now.
Adenosine and the sleep process
As we are awake, our body constantly produces a chemical called Adenosine. The more Adenosine is accumulated, the sleepier we feel. It is because the concentration of Adenosine will trigger the sleep-inducing part of our brain and mute the wake-promoting region. The production of Adenosine happens only when we are awake and stops when we are sleeping.
The diagram below will explain why the urge to sleep is the biggest at 11pm or midnight. The blue line is our sleep process which represents the level of Adenosine. It rises from 7am to 11pm and decreases when we are asleep. The black line represents our circadian process. It doesn’t change because of our lifestyle. On the other hand, the blue line can certainly does
What will happen if we pull an all-nighter?
As we stay awake during the night, the level of Adenosine continues to rise. Around 4-5 am in the morning, we will feel particularly sleepy since the level of Adenosine is the highest at that moment so far (the orange line). We will feel better in the morning, especially at the peak of our circadian rhythm. However, the level of Adenosine continues to accumulate and later in the evening, we will be hit by a wave of sleepiness that is even harder to resist. To remove the extra sleep pressure from an all-nighter, we will have to sleep longer in the morning. However, who can have the luxury of sleeping till 10am in the morning during the weekdays? As a result, we become sleep-deprived to some extent. There is always a residue of Adenosine from the previous day in our body and it will keep us sleepy, unproductive and listless.
The same happens when we party, go out or binge-watch series late at night. Instead of going to bed around 10-11 pm, we stay up late till 2-3am. Our body has only 4 hours of sleep. There will be plenty of Adenosine left to be carried over to the following day. If the behavior repeats, it will accumulate and we will constantly feel lethargic and sleepy. After a while, even longer sleeps on the weekends may not be enough to remove all the lingering Adenosine. And would you want to sleep in the whole weekends when the weather is nice outside? With family obligations, will there be enough time for sleep on the weekends?
Additionally, our sleep process and circadian rhythm can help explain why we feel easier to sleep when travelling Westward than when travelling Eastward.
When we travel East, we are forced to sleep earlier (the orange line) than we normally do. On the other hand, as we travel Westward and are tied up with business or social obligations, we would tend to sleep later when we normally do (the purple line).
To fight back against the urge to sleep, we tend to rely on caffeine. Caffeine does make us feel more awake and less prone to falling asleep. How does it do that?
Caffeine blocks Adenosine from interacting with the receptors in our brain, an interaction that would cause sleep-inducing effects. While being blocked from caffeine, the sleep-inducing chemical will keep increasing while we are awake. On other hand, caffeine is worn off gradually by our body. Eventually, caffeine in our body will disappear and Adenosine will be free to interact with the brain’s receptors, this time in an accumulated amount.
If we drink coffee late at night to stay awake and our body doesn’t remove caffeine fast enough, we can stay up later. Once the caffeine disappears, Adenosine in an increased quantity will attack our receptors and the urge to sleep is even bigger than it normally is (the purple line)
According to the book “Why we sleep”, it takes our body on average five to seven hours to remove 50% of the caffeine consumed, meaning that if a person has a cup of coffee at 8pm, it’s like that 50% of the caffeine is still in that person’s body by 1am. Of course, each body is different in how fast it can wear the caffeine off. That’s why some people don’t seem to be much affected by caffeine while others are more prone to the chemical’s effect. Plus, the older we are, the more slowly the caffeine-removing process takes place.
As a result, keep in mind the effect of Caffeine before you decide to sip that hot and delicious cup of coffee or tea at night.
Consequences of sleep deprivation
- Diminished immune system
- Higher risk of cancer
- Higher risk of Alzheimer
- Higher exposure to diabetes
- You feel hungry despite being full. Hence, you’ll be more susceptible to gaining weights
H. Keong. (2015). Vulnerability to Sleep Deprivation: A Drift Diffusion Model Perspective.
M. Walker. (2017). Why We Sleep: Unlocking the Power of Sleep and Dreams