Book Review - Why we sleep
Book review - ‘Why We Sleep’ by Matthew Walker
Once in a while you read a book that has a profound impact on you. This was one of those books for me. I liked that I learned things that I didn't know. I also came to realise that some of the challenges I face day to day or the changes that i’ve seen in myself are the result of not enough sleep. Looking ahead was a bit bleak and I have been inspired to take action as a result.
Bold statements!
As someone with a scientific mind, I really like that the book was based on fact. By fact I don’t mean anecdote or examples here and there, but on solid scientific facts based on formal trials. When the truths were not as I might have wanted them to be, it was impossible to just squirm away from them and dismiss them as not convenient or choose to not believe them. The facts are irrefutable!
In this review I simply share my highlights. Bear in mind that we all filter the information that we come across based on our own needs and experiences. So you may read this book (and I would highly recommend it to everyone) and learn something different than me.
I’ll start with some of the facts that I found most interesting and then focus in on the pertinent points that relate to athletes and then to the workplace. Finally, I look at general health & wellbeing considerations not covered elsewhere, how to tell if you’re under-sleeping and tips for getting good sleep.
Facts about sleep
The book opens with some bold statements in the first chapter:
Routinely sleeping less than six or seven hours a night (that’s me) demolishes your immune system, more than doubling your risk of cancer
Insufficient sleep is a key lifestyle factor determining whether or not you will develop Alzheimer’s disease.
Inadequate sleep - even moderate reductions for just one week - disrupts blood sugar levels so profoundly that you would be classified as pre-diabetic.
Short sleeping increases the likelihood of your coronary arteries becoming blocked and brittle, setting you on a path toward cardiovascular disease, stroke, and congestive heart failure.
Sleep disruption further contributes to all major psychiatric conditions, including depression, anxiety, and suicidaility.
Increased desire to eat and associated weight gain.
OK, so that may have got your attention, it did mine. I’ve already had a brush with cancer and have several auto-immune disorders. My aunt has Alzheimer’s, my family is riddled with diabetes, my Dad had a heart attack in his 40s and I’ve battled weight my entire life. All a bit close to home.
Why do we feel the need to sleep?
Some basics
There are two main factors that influence when you want to sleep and when you are awake:
Circadian rhythm which is approximately (but not exactly) 24 hours, peaking around mid-afternoon. This doesn’t just impact our sleep cycles but numerous other things like when we eat & drink, mood, body temperature and metabolic rate. There really are two groups of people, morning types (morning larks) and evening types (night owls). Employment often forces night owls into an unnatural sleep-awake rhythm. Work performance is generally poorer in the mornings for night owls. Night owls are often chronically sleep-deprived as they have to wake up with the larks but are unable to fall asleep until late. This has a knock on impact on health.
Melatonin is a hormone that is released at night and by doing so it helps regulate the timing of when sleep occurs, in itself it doesn’t actually help you sleep. Once sleep is underway, melatonin slowly decreases in concentration throughout the night and into the morning. When sunlight enters the brain through the eyes (even when closed), melatonin release stops.
Sleep pressure
The Circadian rhythm is the first of two factors determining when you wake and when you fall asleep. The second is the sleep pressure caused by the chemical adenosine. It builds up during the waking hours and degrades while you sleep.
Caffeine
Caffeine masks the impact of adenosine tricking you into feeling alert and awake when otherwise you would feel a desire to sleep. It takes about 30 minutes to take effect but then lingers. You will still have half of it impacting you 5-7 hours later. If you use caffeine to try and stay awake late into the night you should also expect a caffeine crash - your energy levels will plummet rapidly and you’ll find it difficult to function and concentrate with a strong sense of sleepiness. The reason for this is that the whole time that caffeine is in your system, the adenosine chemical continues to build up but it is blocked by the caffeine. Once that caffeine block is removed you feel a strong backlash - the sleepiness that you had taken the caffeine to avoid plus all the adenosine that has accumulated in the meantime.
Bringing it all together
The circadian rhythm and sleep pressure caused by adenosine are independent of each other, though usually neatly aligned.
The book goes on to explain why you sometimes get a ‘second wind’ if you stay awake throughout the night - useful for any ultra endurance athletes. Though a second night awake would be extremely difficult.
Stages & patterns of sleep
Research has shown the various stages of sleep play out in a recurring cycle which lasts about 90 minutes for each cycle. Both Rapid Eye Movement (REM) sleep and Non-REM (NREM) fulfil different purposes and neither are more important hence why we don’t prioritise one type over the other and instead cycle through the sleep stages.
Naturally, we have two bouts of sleep in a day - one longer bout of sleep at night followed by a shorter nap mid-afternoon. Interestingly, where this practice continues (siestas), the average lifespan is longer.
Towards the end of this review, I show a graph overlaying a typical night’s sleep and try to establish which bit(s) are most important.
Changes in sleep across the lifespan
The circadian rhythm of a young child runs on an earlier schedule than an adult - they become sleepier earlier and wake up earlier. During puberty it changes again and rather than lagging behind parents, it passes ahead of them. After that it slowly goes back to the schedule you adopt as an adult. With advanced age the circadian rhythm shifts again to an earlier and earlier bedtime.
Poor sleep is one of the most under-appreciated factors contributing to cognitive and medical ill health in the elderly, including issues of diabetes, depression, chronic pain, stroke, cardiovascular disease, and Alzheimer’s disease.
Athletes
In this section, I share the areas I picked up on that seem to be particularly relevant to athletes.
Fitness & energy
Studies have shown that whilst exercise doesn’t directly create better sleep, generally increasing exercise does trend towards increasingly better sleep.
Good sleep does improve exercise. Levels of physical physical exertion are powerfully maximised the day after good sleep.
Sleep boosts fitness and energy, setting in motion a positive, self-sustaining cycle of improved physical activity (and mental health).
Motor skills
Motor skills benefit from sleep. Your brain will continue to improve skill memories in the absence of any further practice due to sleep. Practice does not make perfect. It is practice followed by a night of sleep that leads to perfection. This ability seems to be linked to stage 2 NREM - in the last two hours of eight hours of sleep. Daytime naps can also offer significant motor skill memory improvement, together with a restoring benefit on perceived energy and reduced muscle fatigue.
Exhaustion & muscular strength
Obtain anything less than eight hours of sleep a night, and especially less than six hours a night, and the time to physical exhaustion drops by 10 to 30% and aerobic output is significantly reduced. Similar impairments are observed in limb extension force and vertical jump height, together with decreases in peak and sustained muscle strength. Add to this marked impairments in cardiovascular, metabolic, and respiratory capabilities that hamper an under-slept body, including faster rates of lactic acid buildup, reductions in blood oxygen saturation, and increases in carbon dioxide. Even the ability of the body to cool itself during physical exertion through sweating is impaired by sleep loss.
Injury risk
A chronic lack of sleep across the season leads to a significantly higher risk of injury. The chart below shows the dramatic increase in injury risk with lower levels of sleep.
Sleep Loss and Sports Injury
Recovery
Sleep is as important after an event or major training session as it is before. Post performance sleep accelerates physical recovery from common inflammation, stimulates muscle repair, and helps restore cellular energy in the form of glucose and glycogen.
Sleep and employment
In this section I share the areas I picked up on that seem to be particularly relevant to productivity in the workplace.
Sleep deprivation degrades many of the key faculties required for most forms of employment. Why, then, do employers overvalue employees that undervalue sleep and stretch the working day at both ends, sacrificing sleep?
A study across four large US companies found that insufficient sleep cost almost $2,000 per employee per year in lost productivity. That rose to $3,500 per employee in those suffering the most serious lack of sleep. It amounted to $54 million annually.
Individuals who sleep fewer than 7 hours a night on average cause fiscal cost to their country, compared to employees who sleep more than eight hours each night. For the UK that amounts to $40 billion a year. Numerous employee traits determine these measures, but commonly they include: creativity, intelligence, motivation, effort, efficiency, effectiveness when working in groups, as well as emotionally stability, sociability, and honesty. All of these are systematically dismantled by insufficient sleep.
The irony that employees miss is that when you are not getting enough sleep, you work less productively and thus need to work longer to accomplish a goal. This means you often must work longer and later into the evening, arrive home later, go to bed later, and need to wake up earlier, creating a negative feedback loop. Interestingly, people do not perceive themselves to be applying less effort to the work challenge or being less effective when they are sleep deprived, despite both being true.
Employees like their jobs less when sleep-deprived.
Employees who sleep six hours or less are more likely to lie the following day than those who sleep six hours or more. The less an individual sleeps, the more likely they are to create fake receipts and reimbursement claims. Under-slept employees are more likely to blame other people in the workplace for their own mistakes, and even try to take credit for other people’s successful work.
Underslept managers and CEOs are less charismatic and have a harder time infusing their teams with inspiration and drive. Unfortunately for bosses, a sleep deprived employee will erroneously perceive a well-rested leader as being significantly less inspiring and charismatic than they truly are. The implications if both boss and teams are under-slept must be significant.
Sleep the night before learning
Sleep before learning refreshes our ability to initially make new memories. This is related to stage 2 NREM.
Sleep the night after learning
Sleep protects newly acquired information, affording immunity against forgetting: an operation called consolidation. Specifically, it is early night deep NREM sleep that makes the difference. Not only does sleep maintain those memories that you have successfully learned before bed, it will also salvage those that appeared to have been lost soon after learning.
Sleep to forget
Just as much as it is useful to remember things that you’ve learned, it’s also important to be able to forget (e.g. forgetting where you parked the car last week so that you can remember today’s spot; removing cravings; or painful experiences). Forgetting is not just useful to delete stored information that we no longer need, it also lowers the brain resources required for retrieving those memories that we want to retain. Sleep helps you retain everything that you need and nothing that you don’t. Sleep accomplishes this by using meaningful tags on these memories when they are learned or potentially during sleep itself. This happens during NREM sleep.
Sleep for creativity
The sleeping brain fuses together disparate sets of knowledge that foster impressive problem-solving abilities. This happens during the REM phases.
Concentration
With just four hours of sleep for six nights, concentration will be just as bad as someone who has not slept for 24 hours straight - a 400% increase in the number of ‘micro sleeps’ where you completely fail to respond. After 11 days of this level of sleep deprivation and concentration will match someone who had pulled two back-to-back all-nighters, going without sleep for 48 hours.
Ten days of 6 hours sleep a night equates to the same impact on concentration as going without sleep for 24 hours and this would continue to degrade the longer it goes on.
The most worrying factor is that those people who are sleep deprived in this way do not recognise it and consistently under estimate the degree of performance degradation.
With chronic sleep deprivation over months or years, an individual will acclimatise to their impaired performance, lower alertness and reduced energy levels. The low-level exhaustion becomes the accepted norm. What follows is a slow accumulation of ill-health, but the individual rarely makes the connection.
People who are sleep deprived are as cognitively impaired as those who are legally drunk. Operating on less than 5 hours of sleep, your risk of a car crash increases threefold. After 4 hours or less and you are 11.5 times more likely to be involved in a car accident.
Humans need more than 7 hours of sleep a night to maintain cognitive performance. After 10 days of 7 hours of sleep, the brain is as dysfunctional as it would be after going without sleep for 24 hours. Three full nights of recovery sleep are insufficient to restore the performance back to normal levels after a week of short sleeping.
Emotional irrationality
Sleep deprivation leads to over 60% increase in emotional reactivity. Those individuals produce unmetered, inappropriate emotional reactions and are unable to place events into a broader or considered context. The under slept brain swings excessively to both extremes of emotions - positive and negative. There are links to suicidal tendencies. Sleep deprivation has also been linked to aggression, bullying and behavioural problems.
Insufficient sleep also determines relapse rates in addiction disorders. Insufficient sleep in childhood significantly predicts early onset of drug or alcohol use.
Tired and forgetful
There is a 40% deficit in the ability of sleep-deprived people to cram new facts into the brain relative to those who are not sleep deprived. Similar impacts are found when people lack the deep NREM phase of sleeping. Furthermore, memories formed without sleep are weaker memories which disappear quicker.
When you sleep is also important. Sleeping the night after learning is vital to consolidate what has been learned. If you miss that night’s sleep you can’t catch up on it.
Dreaming to enable reading of expressions
REM sleep enables us to read emotions in others’ facial expressions. Those individuals who are deprived of REM sleep can no longer distinguish one emotion from another with accuracy. With the absence of such emotional acuity, sleep deprived individuals slip into a fear bias, believing even gentle- or somewhat friendly looking faces are menacing. The outside world becomes a more threatening and aversive place. Reality and perceived reality are no longer the same. By not having sufficient REM sleep you remove the ability to read the social world around you.
Creative problem solving
As we enter REM sleep and dreaming takes hold, no longer are we constrained to see the most typical and plainly obvious connections between memory units, instead the brain becomes actively biased towards seeking out the most distant, non-obvious links between sets of information. Answers to complex problems can be solved overnight if you feed the waking brain with the ingredients of a problem before sleep and actually dream about the problem whilst asleep. ‘Sleep on it’ is very good advice.
General health & wellbeing considerations
Cardiovascular system
Progressively shorter sleep is associated with a 45% increased risk of developing and / or dying from coronary heart disease. Adults who are 45 years or older who sleep fewer than 6 hours a night are 200% more likely to have a heart attack or stroke during their lifetime, as opposed to those sleeping 7-8 hours a night.
One night of modest sleep reduction, even by just one or two hours, speeds up the contracting rate of a person’s heart, hour upon hour, and significantly increases the systolic blood pressure.
People who obtain 5-6 hours of sleep each night are 200-300% more likely to suffer calcification of their coronary arteries over the next five years compared to those who sleep 7-8 hours, significantly increasing the risk of a coronary heart attack.
Sleep deprivation leads to an over reaction of the sympathetic nervous system leaving the body in the fight or flight state. This can lead to a catalogue of issues.
Sleep loss and metabolism: diabetes & weight gain
Short sleep will increase increase hunger and appetite, compromise impulse control within the brain, increase food consumption (especially high calorie foods), decrease feelings of satisfaction after eating, and prevent effective weight loss when dieting.
Sleep loss and the immune system
Sleep fights against infection and sickness by deploying all manner of immune responses. When you do fall ill, the immune system actively stimulates the sleep system, demanding more bed rest to help reinforce the effort. Reduce sleep even for a single night and immune resilience is removed. You also can’t catch up on lost sleep when it comes to your immunity.
It doesn’t take many nights of short sleeping before the body is rendered immunologically weak, and there the issue of cancer becomes relevant. Not getting enough sleep when battling cancer is particularly concerning.
Sleep loss, genes and DNA
Chronic sleep loss erodes the genetic code and the structures that encapsulate it.
After just one week of sleep reduced to 6 hours a night the activities 711 genes have been shown to be distorted, either upwards or downwards. The genes that were increased included those linked to chronic inflammation, cellular stress, and various factors that cause cardiovascular disease. Among those turned down were genes that help maintain stable metabolism and optimal immune responses. Short sleeping also impacts the genes that regulate cholesterol, particularly HDLs.
Two individuals of the same chronological age would not appear to be the same biological age if one was sleeping 5 hours a night and the other 7 hours. The later would appear younger, whilst the former would have artificially aged far beyond their calendar years.
Dreaming as an overnight therapy
REM sleep is the only time during the 24 hours of a day when your brain is completely shut off from noradrenaline - a key stress-related chemical. The process of REM dreaming accomplishes two critical goals: (1) sleeping to remember the details of those valuable, salient experiences, integrating them with existing knowledge and putting them into autobiographical perspective, yet (2) sleeping to forget, or dissolve, the visceral, painful emotional charge that had previously been wrapped around those memories.
Think back to your childhood and try to recall some of the strongest memories that you have. What you will notice is that almost all of them will be memories of an emotional nature: perhaps a particularly frightening nature of being separated from your parents, or almost being hit by a car on the street. Also notice, however, that your recall of these detailed memories is not longer accompanied by the same degree of emotion that was present at the time of the experience. You have not forgotten the memory but have cast off the emotional charge, or at least a significant amount of it.
Modern light
Sunset and the onset of darkness is a natural indication that it is approaching the time to sleep. The body releases melatonin. The challenge with modern light is that this trigger is missed and this can make it much more difficult to fall asleep at a reasonable time. A subtly lit living room will use about 200 lux which although is only 1-2% of the strength of daylight it can have 50% of the melatonin-suppressing influence within the brain. Blue LED light is even worse. LED-powered laptop screens, smartphones, and tablets are a problem. Using an iPad for two hours before bedtime blocks melatonin by 23%. This doesn’t just impact the night in question, it can impact you for several days afterwards too.
Using LED devices at night impacts our natural sleep rhythms, the quality of our sleep, and how alert we feel during the day.
Alcohol
Alcohol can sedate you out of wakefulness but it does not induce natural sleep. Also, alcohol fragments sleep, littering the night with brief awakenings, most of which go unnoticed by the person themselves. Alcohol is also one of the most powerful suppressors of REM sleep known. People drinking even moderate amounts of alcohol in the afternoon and / or evening will deprive themselves of the important REM quality sleep. It also impacts the learning process that relies on REM sleep.
Body temperature
To successfully initiate sleep, your core temperature needs to decrease by about 1 degree Celsius. Most thermic work is performed by three parts of your body: hands, feet and head. Industrialised cultures have impacted this natural ability due to central heating, bedcovers and pyjamas, we have architected a minimally varying or constant thermal range in our bedrooms. Without the natural drop in evening temperature, our brains do not receive the cooling instruction in the brain that facilitates a naturally timed release of melatonin.
A luxury for many is to draw a hot bath in the evening and soak the body before bedtime. We feel it helps us fall to sleep more quickly, which it can. You don’t fall asleep because you’re all toasty and warm, instead the bath brings blood to the surface of your skin. The resulting dilated blood vessels on the surface quickly help radiate out inner heat and a quick reduction of body temperature. Hot baths before bed can also induce 10-15% more deep NREM sleep in healthy adults.
Alarm clocks
When you are artificially woken from sleep you will suffer a spike in blood pressure and a shock acceleration in heart rate caused by an explosive burst of activity from the fight or flight part of the nervous system. Using the snooze button makes this happen multiple times within a short space of time. Avoid using the snooze button!
Waking up at the same time of day, every day, no matter if it is the week or weekend is a good recommendation for maintaining a stable sleep schedule you are having difficulty with sleep.
Sleeping tablets
No past or current sleeping medications induce natural sleep. The sleep induced lacks the largest, deepest brainwaves. As well as this the side effects can impact the next day with grogginess, daytime forgetfulness and slowed reactions. The waking grogginess can lead people to reach for caffeine, making sleeping the next night even more difficult leading to increased doses of sleeping tablets, amplifying the grogginess the next day and even greater consumption of caffeine. A downward spiral.
Rebound insomnia can also be an issue when individuals stop taking the sleeping tablets. This can often be worse than the poor sleep that led them to take sleeping tablets.
Sleeping tablets also weaken the brain-cell connections originally formed during learning leading to memory loss rather than memory consolidation usually associated with sleep.
More worryingly, mortality risk is increased with sleeping tablet use.
Bringing it all together
I thought it might be useful to bring together a typical sleep pattern chart and overlay which part of sleep are most important.
The architecture of sleep over-layed with key benefits
Not surprisingly, from all that I read, it’s all important. Miss any one part and there will be consequences.
If you’re not giving yourself 7-8.5 hours of sleep opportunity each night, you really should have a think about how you can change that. If you’re an athlete it will improve your sporting performance. If you work, your work performance will improve. Over and above all of this, your health with thank you.
How can you tell if you’re getting enough sleep?
A simple rule of thumb:
After waking up in the morning, could you fall back asleep at 10-11am? If the answer is yes, you are probably not getting enough sleep quantity and/or quality.
Can you function optimally without caffeine before noon? If the answer is ‘no’ you are likely self-medicating your state of chronic sleep deprivation.
Other signs:
If you didn’t set an alarm clock, would you sleep beyond that time?
Do you find yourself at your computer screen reading and re-reading the same sentence?
Twelve tips for healthy sleep
Stick to a sleep schedule. Go to bed and wake up at the same time each day, including weekends. Set an alarm to go to bed.
Exercise is great, but not too late in the day. Try to exercise at least 30 minutes on most days but not later than two to three hours before your bedtime.
Avoid caffeine & nicotine.
Reduce alcohol intake, especially before bed.
Avoid large meals and beverages late at night.
If possible, avoid medicines that delay or disrupt your sleep.
Don’t take naps after 3pm. Naps can make up for lost sleep, but late afternoon naps can make it harder to fall asleep at night.
Relax before bed. Don’t over schedule 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.
Dark, cool, gadget free bedroom.
Have the right sunlight exposure. Daylight is key to regulating daily sleep patterns. Try to get outside into natural light for at least 30 minutes each day. If possible, wake up with the sun or use very bright lights in the morning.
Never lie awake in bed for a significant time period; rather, get out of bed and do something quiet and relaxing until the urge to sleep returns