Book Synopsis: "Why We Sleep" by Matthew Walker

Last updated Feb. 27, 2019, 6:18 p.m. by Author

Tags: gym health fitness book synopsis


The following post is the first one in a (hopefully) longer series of reviews and synopses of the books I have read and found worthy of putting some time and effort to extract the most important findings and gather them here.

The summary does not strive to be as comprehensive as possible but it rather sums up some of the more interesting point made in the book. That said it is recommended to read the whole book because it is much more comprehensive than what you can read below and because it is really worth it - at least the first four chapters which describe what is sleep and why we need to sleep.


So the first and the most important finding of the book is that you sleep too few hours a night. If you routinely sleep less than 7 hours per night, you should increase it to around 8 hours and this is non negotiable.

Sleeping less than necessary causes a plethora of health issues and has a devastating influence on your body and mind, which in turn lower your quality of life, make you live shorter, age faster, decrease your productivity, make you earn less money and (to put it bluntly) become stupid.

Moving on to some details, there are two factors that determine when you want to sleep and when you want to be awake. The first factor is a signal beamed out from your internal twenty-four-hour clock located deep within your brain. The clock creates a cycling, day-night rhythm that makes you feel tired or alert at regular times of night and day, respectively. The second factor is a chemical substance that builds up in your brain and creates a “sleep pressure.” The longer you’ve been awake, the more that chemical sleep pressure accumulates, and consequentially, the sleepier you feel. It is the balance between these two factors that dictates how alert and attentive you are during the day, when you will feel tired and ready for bed at night, and, in part, how well you will sleep.

Everyone has his own circadian (daily) rhythm - a biological clock which looks like this:


Source: "Why We Sleep" by Matthew Walker

Everyone has a different one, but the one thing is common across all of people: it continues to works this way whether or not you have slept. This also explains why after a sleepless night you may feel quite ok during the day - your circadian rhythm increases your body temperature and makes you more attentive.

Based on the above one can conclude that the common wisdom claiming that there are 'night owls' and 'morning larks' is true. It one would be right. The evening types make about 30% of population, the morning types make about 40% of population, and the remaining 30% is somewhere between those two types.

By trying to suppress your personal rhythm you hurt yourself, both physically and mentally. That's why it is important to determine your own rhythm and try to stick to it if possible.

The other factor is melatonin, and its blood level during a day looks like this:


Source: "Why We Sleep" by Matthew Walker

Melatonin helps regulate the timing of when sleep occurs by systemically signaling darkness throughout the organism. That is why it is very important to sleep in a dark room and to avoid blue light sources before going to sleep.

There are two phases of sleep: REM (rapid eye movements) and NREM (non REM), each of them having its own purpose and each of them being necessary to remain healthy. The sleep cycle looks like this:


Source: "Why We Sleep" by Matthew Walker

A key function of deep NREM sleep, which predominates early in the night, is to do the work of weeding out and removing unnecessary neural connections. In contrast, the dreaming stage of REM sleep, which prevails later in the night, plays a role in strengthening those connections.

In the context of injury, there is no better risk-mitigating insurance policy for these investments than sleep. Described in a research study of competitive young athletes in 2014, you can see that a chronic lack of sleep across the season predicted a massively higher risk of injury:


Source: "Why We Sleep" by Matthew Walker

The relationship between decreasing hours of sleep and increasing mortality risk of an accident is not linear, but instead exponentially mushrooms:


Source: "Why We Sleep" by Matthew Walker

Epidemiological studies have established that people who sleep less are the same individuals who are more likely to be overweight or obese. Indeed, if you simply plot the reduction in sleep time (dotted line) over the past fifty years on the same graph as the rise in obesity rates across the same time period (solid line) the relationship is clear:


Source: "Why We Sleep" by Matthew Walker

Evidence suggests that the relationship between sleep and mortality risk is not linear, such that the more and more sleep you get, the lower and lower your death risk (and vice versa). Rather, there is an upward hook in death risk once the average sleep amount passes nine hours, resulting in a tilted backward J shape. One point is important to bear in mind - usually the people who are sick sleep more because of their immune system that activates more sleep.

In a study of 10,000 patients taking sleeping pills, the vast majority of whom were taking zolpidem (brand name Ambien), though some were taking temazepam (brand name Restoril), which were contrasted them with 20,000 very well matched individuals of similar age, race, gender, and background, but who were not taking sleeping pills the following resulted:


Source: "Why We Sleep" by Matthew Walker

Twelve Tips for Healthy Sleep:

  • Stick to a sleep schedule. Go to bed and wake up at the same time each day. As creatures of habit, people have a hard time adjusting to changes in sleep patterns. Sleeping later on weekends won't fully make up for a lack of sleep during the week and will make it harder to wake up early on Monday morning. Ths is the most important of the tips presented here.
  • Exercise is great, but not too late in the day. Try to exercise at least 30 minutes on most days but not later than 2—3 hours before your bedtime.
  • Avoid caffeine and nicotine. Coffee, colas, certain teas, and chocolate contain the stimulant caffeine, and its effects can take as long as 8 hours to wear off fully. Therefore, a cup of coffee in the late afternoon can make it hard for you to fall asleep at night. Nicotine is also a stimulant, often causing smokers to sleep only very lightly. In addition, smokers often wake up too early in the morning because of nicotine withdrawal.
  • Avoid alcoholic drinks before bed. Having a "nightcap" or alcoholic beverage before sleep may help you relax, but heavy use robs you of deep sleep and REM sleep, keeping you in the lighter stages of sleep. Heavy alcohol ingestion also may contribute to impairment in breathing at night. You also tend to wake up in the middle of the night when the effects of the alcohol have worn off.
  • Avoid large meals and beverages late at night. A light snack is okay, but a large meal can cause indigestion that interferes with sleep. Drinking too many fluids at night can cause frequent awakenings to urinate.
  • If possible, avoid medicines that delay or disrupt your sleep. Some commonly prescribed heart, blood pressure, or asthma medications, as well as some over-the-counter and herbal remedies for coughs, colds, or allergies, can disrupt sleep patterns. If you have trouble sleeping, talk to your healthcare provider or pharmacist to see whether any drugs you're taking might be contributing to your insomnia and ask whether they can be taken at other times during the day or early in the evening.
  • Don't take naps after 3 p.m. Naps can help make up for lost sleep, but late afternoon naps can make it harder to fall asleep at night.
  • Relax before bed. Don't overschedule your day so that no time is left for unwinding. A relaxing activity, such as reading or listening to music, should be part of your bedtime ritual.
  • Take a hot bath before bed. The drop in body temperature after getting out of the bath may help you feel sleepy, and the bath can help you relax and slow down so you're more ready to sleep.
  • Have a good sleeping environment. Get rid of anything in your bedroom that might distract you from sleep, such as noises, bright lights, an uncomfortable bed, or warm temperatures. You sleep better if the temperature in the room is kept on the cool side. A TV, cell phone, or computer in the bedroom can be a distraction and deprive you of needed sleep. Having a comfortable mattress and pillow can help promote a good night's sleep. Individuals who have insomnia often watch the clock. Turn the clock's face out of view so you don't worry about the time while trying to fall asleep.
  • Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside in natural sunlight for at least 30 minutes each day. If possible, wake up with the sun or use very bright lights in the morning. Sleep experts recommend that, if you have problems falling asleep, you should get an hour of exposure to morning sunlight and turn down the lights before bedtime.
  • Don't lie in bed awake. If you find yourself still awake after staying in bed for more than 20 minutes or if you are starting to feel anxious or worried, get up and do some relaxing activity until you feel sleepy. The anxiety of not being able to sleep can make it harder to fall asleep.
  • See a health professional if you continue to have trouble sleeping. If you consistently find it difficult to fall or stay asleep and/or feel tired or not well rested during the day despite spending enough time in bed at night, you may have a sleep disorder. Your family healthcare provider or a sleep specialist should be able to help you, and it is important to rule out other health or emotional problems that may be disturbing your sleep.

Source: https://medlineplus.gov/magazine/issues/summer12/articles/summer12pg20.html


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