Sleep is universal in animals (even in insects and worms). These deep biological roots suggest a vital function and that it isn’t simply a vestigial byproduct of evolution.
Humans in today’s nutrient-rich environment need 8 hours of sleep to function optimally.
Sleep has two general types - NREM and REM.
Sleep deprivation shows consistently bad outcomes. Nothing is reported to be beneficial from sleep deprivation.
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(Chapter 1 is just an introduction, so we’re skipping it.)
Sleep is universal in animals, even in insects and worms, despite its apparent drawbacks (vulnerability to predators, loss of time for productivity). When a biological feature is preserved deep in evolutionary history, it is usually a critical function. This must mean sleep is a critical function, and it’s important to understand why it’s important.
Sleep is regulated by two mechanisms:
These two mechanisms interact as shown in this graph:
Notice that sleep naturally happens when the difference between curves is greatest - you feel the greatest sleep pressure from adenosine, and the least “wake drive” from your circadian rhythm.
This explains an odd phenomenon: if you’ve ever had to pull an all-nighter, you might have noticed yourself getting a second wind in the morning, oddly feeling more awake at 8AM than at 3AM. This happens because the circadian rhythm “wake drive” is starting up again, and reduces the adenosine-circadian gap.
Circadian rhythms vary from person to person, depending on when they naturally wake up and have maximum energy. The idea of “morning people” and “night owls” is real.
Now that you understand how sleep rhythm works, you can better understand common disruptions to sleep.
Caffeine blocks adenosine receptors, thus reducing how much you feel the “sleep pressure.” If you ever drink coffee and then feel a crash later, this comes from caffeine wearing off while adenosine keeps increasing throughout the day.
Jetlag disrupts your circadian rhythm.
**How do you know if you have a...
Now you understand how your sleep rhythm gives a regular schedule of sleep from night to night. Next, we’ll look into how, within a single night of sleep, your brain cycles between different types of phases of sleep. This is important to understanding the function of sleep for your brain.
In summary, your brain switches between two types of sleep - REM (rapid eye movement) and non-REM (NREM) sleep. The two types of sleep have different functions - simplistically:
In total for a single night, there’s about an 80/20 split between NREM/REM sleep.
When you sleep, your brain goes through sleep cycles that each last about 90 minutes. Each sleep cycle generally begins with NREM sleep, then ends with REM sleep. As one cycle ends, the next begins. You can see this in a sleep graph here:
A deeper line means going deeper into NREM sleep.
Notice that not all sleep cycles look the same. As the sleep progresses through the night, a greater fraction of each cycle is spent in REM sleep.
Why would the sleep cycles be unbalanced in this way? Why not just have all sleep cycles look the same, with 80% in NREM and 20% in REM?
The author hypothesizes that it’s like making a sculpture out of a mass of clay. Earlier in the night, more NREM is needed to clear out junk memories that aren’t useful anymore. Then once only the useful stuff remains, REM strengthens what’s left.
(Shortform note: One way to think about this is that an animal might be interrupted in the middle of the night. So if an animal could only sleep 3 hours in one night, it’d make sense for the more critical functions to be performed first, with the later functions being a luxury if the animal could sleep a full night. This may suggest that NREM performs a more vital function for survival.)
Also, beware of what this means for cutting your sleep short. If you normally sleep 8 hours, and one night you have to cut sleep to 6 hours, then you’re not just losing 25% of sleep - you might be losing 60-90% of your REM sleep!
Likewise, going to sleep later than usual might cut short your NREM sleep.
REM and NREM are distinguishable by measuring electrical activity in the brain. NREM is characterized by slow (3-4 Hz) waves that propagate far from the frontal cortex to the back of the brain. REM is characterized by faster (30-40 Hz), frenetic activity that looks the same as being awake.
Wakeful thought looks frenetic because many different neural signals are occurring at once throughout the brain. An analogy: it’s like a microphone picking up a football stadium full of distinct conversations. The summation of all the conversations just looks like noise.
In contrast, NREM sleep is a slow, pulsing wave that’s noticeably different from REM sleep. Continuing the analogy, it’s like a stadium full of voices singing in synchronization. That billions of neurons can do this together is awe-inspiring.
What’s the function of these slow NREM waves? By being lower frequency, slow NREM waves can propagate further without attenuation, like AM radio waves. The author suggests this is useful in transferring memories far across the brain, from temporary memory stores toward more permanent storage. It also allows communication across the brain for different sections to collaborate on their shared experience.
REM sleep looks like awake activity, and it’s where dreams happen. A few odd things happen during REM sleep:
If REM sleep looks like wakefulness, how can an observer...
Sleep is present in all animal species, even invertebrates. And bacteria that survive for longer than 24 hours have circadian-like rhythms. As we’ve said before, this suggests that it’s universally critical for survival.
We ask all the time why we sleep. One researcher posed an interesting inversion of the question - if wakefulness is damaging to the body and sleep recovers it, why did life ever bother to wake up? (Shortform note: of course, you can’t be productive and reproduce when sleeping, so sleeping too much would be evolutionarily disadvantageous.)
The amount of sleep per day varies from 4 hours in elephants to 19 hours in bats. There are no strong correlations between animal characteristics and amount of sleep, though within animals of a similar size, a more complex brain increases sleep.
Among animals, REM sleep occurs only in birds and mammals. Because REM evolved independently in these two distant evolutionary trees, REM likely performs a critical function that NREM cannot accomplish, or that REM is more efficient at accomplishing.
Interesting animal sleep patterns
What’s the ideal human sleep pattern? Native pre-industrial tribes show a biphasic sleep pattern, with 7-8 hours at night and a 30-60 minute nap in the afternoon. At night, they sleep 2-3 hours after sunset, awaking around dawn.
What about supposed historical styles of sleeping, like segmented sleep (two periods of sleep at night, separated by a few hours of wakefulness)? The author argues this is mostly a cultural artifact, and not a natural way to sleep. No evidence suggests a biological desire to wake up for a few hours in the middle of the night
Relative to great apes, humans sleep less (8 hours in humans vs 10-15 hours in apes) and have more intense REM sleep (20% in humans vs 9% in apes). Matthew Walker hypothesizes this evolved as follows:
Fetuses spend almost all of the time in a sleep-like state. It doesn’t yet have the part of the brain that causes muscle-atonia during sleep, thus explaining why babies in the womb kick and punch.
During the last 2 weeks of pregnancy, REM sleep in fetuses ramps up to 12 hours a day. This causes rapid synaptogenesis and building of neural pathways throughout the brain. In experiments with rat fetuses, disturbing REM sleep stalls construction of the cerebral cortex.
Alcohol impedes REM sleep in fetuses and babies, causing abnormal synaptogenesis. Once disrupted, a fetal brain may never fully regain normal function.
Because REM sleep is involved in emotional recognition and social interaction, disrupting REM sleep in utero might contribute to the autism spectrum.
While starting with very irregular sleep, babies eventually show more regular sleep patterns starting at 4 months, as their suprachiasmatic nucleus and circadian rhythm develop.
With age, total time sleeping decreases, and the fraction of REM sleep decreases. Now that the synaptogenesis of REM tapers off, NREM plays a larger role in brain refinement, pruning the associations that are most valuable unique to that child’s life.
Consider NREM to actually cause cognitive development - changes in deep NREM sleep precede cognitive milestones, and the last maturation is in the frontal lobe, dealing with rationality.
Caffeine exposure during childhood could reduce NREM sleep, delaying brain maturation and learning.
In puberty, teens develop a later biological clock than adults, preferring to stay up later and wake later. This isn’t just teens being rebellious - it’s in their biological nature. Asking teens to sleep at 10PM is like asking adults to sleep at 7PM.
The author theorizes that this is evolutionarily helpful for teens to gain independence from their parents (having time to be awake while their parents are sleeping). Moreover, teens do so collectively, and so they get private time to socialize.
Unfortunately, in the modern day, schools start at a very early hour (largely to match the circadian rhythms of adult parents). It’s far out of sync with the natural circadian rhythm of teens, so they tend to sleep late and wake up far earlier than they naturally would.
Considering all this, if you’re a parent, there’s no need to get frustrated at your teenage kid for seemingly being lazy and sleeping too much, when the environment is heavily geared against their biological tendencies.
Sleep quality starts deteriorating in the late 20s, with deep NREM sleep becoming impaired in length and power. In your late 40s, you’ll have lost 70% of deep sleep as a teenager; by 70, you’ll have lost 90% of deep sleep. Unfortunately, less NREM sleep worsens the ability to cement new memories in older people.
You often hear of the elderly sleeping little at night, so the natural conclusion is that the elderly just need less sleep. But this could be a myth. The elderly might be sleeping less because they’re unable to sleep for as long. This means they could still benefit from more sleep.
Seniors have three things going against them: 1) they sleep less, 2) they have less efficient sleep, and 3) they want to sleep earlier. This is caused by:
Exacerbating this are a few factors:
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Getting good sleep improves your brain in these ways:
1) Sleep improves long-term factual recall
Your brain stories different memories in different places. The hippocampus stores short-term memory with a limited capacity; the cortex stores long-term memory in a large storage bank.
The slow-wave, pulsating NREM sleep moves facts from the hippocampus to the cortex. This has two positive effects: 1) it secure memories for the long term, and 2) it clears out short-term memory to make room for new information and improves future learning.
Have you ever woken up recalling facts that you couldn’t have recalled before sleeping? Sleep may make corrupted memories accessible again.
While good sleep improves memory, sleep deprivation can prevent new memories from being formed. In part, this might be because the hippocampus becomes less functional with less sleep, partially because lack of NREM sleep prevents solidifying of new memories.
Unfortunately, making up a sleep deficit later doesn’t help recover a previous days’ memory - if you lost it, you’ve lost it.
2) Sleep prunes memories worth forgetting
Sleep doesn’t preserve all memories equally strongly - somehow, the brain knows which memories are useful and worth preserving, and which ones are useless and OK discarding.
Experimentally, this has been shown in experiments where subjects are given a list of words and instructed which words to remember and which to forget. Students who get to take a nap show stronger memories for the appropriate words, compared to students who don’t nap.
3) Sleep increases “muscle memory” or motor task proficiency
You might struggle with a motor task (like playing a tough sequence on piano), but after sleeping, be able to play it flawlessly. Sleep seems to transfer motor memories to subconscious habits.
Sleep deprivation also worsens general athletic performance: getting less sleep decreases your aerobic capacity, time to exhaustion, and recovery; and it increases the risk of injury and lactic acid generation.
The above benefits generally occur in NREM sleep, which is concentrated in the beginning of sleep. In experiments, participants who have NREM sleep disrupted perform worse than those who have REM sleep disrupted.
A few last scientific details:
Now that we understand the impact of sleep on the brain, imagine how we can apply this knowledge into useful therapies:
While getting great sleep is good for the brain, sleep deprivation is unambiguously harmful to the brain. We’ll show damage in three ways: to attention, to emotion control, and for Alzheimer’s Disease.
Sleep deficits are very bad for attention and concentration. This is especially harmful during high-risk activities, like driving.
Here are some ways to put the risk into perspective:
Sleep deficits add up over time, and performance progressively worsens with greater sleep deficit. Having 10 nights of 6-hour sleep is equal in damage to one all-nighter, as is 6 nights of 4-hour sleep.
Why does sleep cause more accidents? Part of it is delayed reaction time. Another part is a “microsleep,” where your eyelids shut for just a few seconds and you go unconscious and lose motor control. If you’re in a car going 60 mph, falling asleep for just a few seconds could result in a terrible accident.
Sleep deprivation is an insidious problem because when you’re sleep-deprived, you don’t know how poorly you’re performing. (This is like being drunk and thinking you’re far more capable of doing things than you actually are). And if you’re chronically sleep-deprived, your low performance becomes a new normal baseline, so it’s hard for you to see just how badly you’re performing.
Think you can do just fine on 6 hours of sleep? Chances are, you can’t. Less than 1% of the population is able to get six hours of sleep and show no impairment (this is largely genetic and relates to the BHLHE41 gene). Everyone else is just fooling themselves and propping up their energy with caffeine.
And think you can get by with power naps? They only get you partway there - power naps are most effective at the onset of fatigue, not when you’re already sleep-deprived.
A baby that doesn’t get its nap time tends to get cranky. Adults are the same way.
The amygdala is the part of your brain responsible for emotions like fear and anxiety. Normally, it’s held in check by your prefrontal cortex (the rational part of your brain). But when you’re sleep-deprived, this suppression is weakened, and your amygdala can run amok, leading to 60% more emotional reactivity. The highs can be higher, and the lows lower.
On the other side of fear and anxiety, positive rewards and dopamine may be amplified by sleep deprivation too. Therefore, sleep deprivation can intensify sensation-seeking, risk-taking, and addiction.
More gravely, sleep may play an important role in mental illness. Here’s suggestive evidence:
While no definitive causal link has been shown yet, sleep losses may contribute to Alzheimer’s through a few mechanisms:
In addition to the damage it causes to the brain, sleep deprivation disrupts the normal function of many physiological processes, likely contributing to chronic diseases. In this chapter, we’ll cover a bevy of health issues associated with sleep deprivation.
At a high level, sleep deprivation of even just 1-2 hours triggers the sympathetic nervous system (fight or flight response) and disrupts hormonal balances. This also implies that sleep is necessary for the normal maintenance of physiology.
Many of the population studies cited in Why We Sleep are correlational - e.g. people who sleep less are more likely to have heart disease, after controlling for many other factors. But the causation is unclear - some other factors that predispose people to get heart disease (like a high baseline level of stress) could also reduce sleep.
To address this, the experimental studies cited attempt to link lack of sleep to a middle physiological state, which itself is causative for the disease. For instance, lack of sleep increases blood pressure, which the medical consensus believes is causative for heart disease.
Ideally, the “smoking gun” experiment would be to randomize people into normal-sleep and low-sleep groups for years, then observe the rate of disease. However, this is impractical (it’s hard to run very long studies like this and impossible to double-blind) and likely unethical (if low sleep is already believed to cause severe disease).
Sleep deprivation has a number of effects related to cardiovascular disease:
A population study showed that shorter sleep was associated with a 45% increased risk of developing heart disease.
An interesting finding: daylight savings time is a natural sleep experiment that typically increases or decreases sleep by 1 hour. When the clock moves forward and the population gets 1 less hour of sleep, there is a significant spike in heart attacks and traffic accidents.
Sleep deprivation reduces insulin responsiveness, which causes hyperglycemia.
In a population study, those sleeping < 6 hours a night showed higher rates of T2D (after controlling for body weight, alcohol, smoking, and other factors).
As it relates to weight, sleep deprivation:
In an experiment, subjects were randomized into a normal 8-hr sleep group, and a low 4-hr sleep group. Both groups were carefully monitored and controlled for physical activity.
One might argue that decreased sleep naturally causes more calorie burn, but an all-nighter actually consumes only 147 more calories than sleeping. Sleep is metabolically more intense than you might guess.
Finally, if you’re losing weight and under sleep deprivation, the shift of where you lose the weight from differs. When sleep-deprived, 70% of weight loss comes from lean body mass like muscles, compared to under 50% with plentiful sleep.
In males, sleep deprivation decreases testosterone, testicle size, and sperm count.
In females, sleep deprivation reduces follicular-releasing hormone (necessary for conception), increases abnormal menstrual cycles, and causes more issues with infertility.
Your face is rated as less attractive and less healthy after one night of short sleep. So there might be something to the idea of “beauty sleep.”
Sleep deprivation reduces your ability to ward off infectious disease:
Sleep deprivation increases inflammation, which increases cancer severity:
Dreaming is a bizarre sensation. You’re unconscious, but you perceive intense vivid sensations and hallucinate things that aren’t there. You feel like you’re moving in the world, but your muscles have been forced to be limp. You remember faces and memories that you haven’t thought about for years, maybe decades. You had no control over your emotions, swinging from intense rage and jealousy to exuberance. Finally, when you woke up, you promptly forgot everything. If you experienced all of this while awake, you’d think you had a psychosis episode!
It’s not surprising then that dreaming has had a complicated history. In the ancient past, Egyptians and Greeks wondered if dreams were divine gifts from gods.
Freud helped dispel this, firmly centering it within the human brain. He considered dreams as expressions of repressed desires, and he built a psychological movement around interpreting dreams as such.
Most vivid dreaming happens during REM sleep (though NREM sleep has some vague non-vivid dreaming, like “I was thinking about clouds”).
During REM dreaming, your visual, motor, memory, and emotional areas of the brain are active. Your prefrontal cortex (governing rationality) is muted.
Interesting: it may be possible to predict what you’re dreaming about through fMRI.
We often think about the meanings of our dreams. Do dreams merely replay events of the day, or do they reflect our emotional concerns?
We’ll now discuss three benefits of dreaming and REM sleep.
REM dreaming reduces pain from difficult emotional experiences. The brain seems to reprocess upsetting memories and emotional themes, retaining the useful lessons while blunting the visceral emotional pain. This might be why we can look back at painful memories without feeling the original full emotional intensity.
Interestingly, dreaming about the upsetting content itself, or its emotional themes, is necessary to have this emotional blunting effect. REM sleep by itself does not.
How might this happen? In REM sleep, the stress hormone norepinephrine in your brain is reduced to zero, which possibly allows the brain to process upsetting memories in a “safe” brain environment. In fact, REM sleep is the only time that norepinephrine is absent from your brain.
Sleep deprivation reduces your ability to interpret subtle facial expressions. Sleep-deprived people more often interpret faces as hostile and aggressive.
Suggestive evidence: people on the autism spectrum have disrupted REM sleep. They also have issues reading people’s facial expressions
This function seems to begin in adolescence, when kids have to start navigating the social world independently.
Imagine the mistakes sleep-deprived professionals can make - police, medical staff, parents - if they mistake faces for aggression.
REM sleep creates novel associations between ideas, increasing creativity and problem-solving.
Informally, imagine the brain asking: “how can I connect what I’ve recently learned with what I already know, thus discovering insightful revelations? What have I done in the past that might be useful in solving this new problem?”
Thomas Edison knew the power of dreams. Reportedly, he would fall asleep holding metal ball bearings, releasing them just as he entered REM sleep. The noise would wake him up, just in time for him to write down his dreams before he forgot them.
These experiments showed a bevy of positive effects on creativity:
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We’ve talked before about how sleep deprivation causes disease. Now we’ll discuss sleep disorders, or primary issues with abnormal sleep, and their consequences.
Sleepwalking is the act of walking and performing other behaviors while asleep. Automatic, nonconscious routines are executed, like brushing teeth or opening the refrigerator.
Sleepwalking happens during NREM sleep, and not REM dreaming sleep (like some think). Neurologically, sleepwalking is accompanied by an unexpected spike in nervous system activity, causing the person to be stuck somewhere between sleep and wakefulness.
Sleepwalking is more common in children than adults, for unknown reasons - possibly because kids spend more time in NREM sleep than adults do.
In one of the most extreme cases, a sleepwalker drove 14 miles to an in-laws’ home, stabbed the mother-in-law to death, and strangled the father-in-law (who survived). This person was later acquitted as not being control of his actions. This defense has been tried in later cases (most unsuccessfully).
Insomnia is defined as making enough time for sleeping, but having insufficient sleep quantity or quality, for more than 3 months. Symptoms include difficulty falling asleep, waking up in the middle of the night, and feeling unrefreshed in the morning.
When they do sleep, insomniacs have more fragmented REM sleep and shallower brainwaves in NREM.
1 out of 9 people suffers from insomnia. It’s twice as common in women than men, and more common in blacks/Hispanics than whites, for unknown reasons.
The most common triggers of insomnia are emotional concerns or distress. The biological cause is linked to an overactive sympathetic nervous system, which raises body temperature and levels of cortisol/epinephrine. In turn, the thalamus, hippocampus, and amygdala all remain more active than in normal sleeping patients
Given the complex physiology of insomnia, it’s unlikely blunt instruments like sleeping pills will fix the root cause.
People with narcolepsy show sudden bouts of extreme sleepiness during the day. Some people who are chronically sleep-deprived mistakenly think they’re narcoleptic. The severity of feeling for narcolepsy is far more severe, equivalent to the feeling after 3 consecutive all-nighters. Narcolepsy occurs in just 1 out of 2,000 people
Narcoleptics also suffer other symptoms:
How does narcolepsy arise? It’s a disruption in a normal process. Normally, wakefulness is signaled by the neurotransmitter orexin in the hypothalamus; in sleep, this is shut off.
There are no current effective treatments for narcolepsy.
Gravely, sleep deprivation can directly cause death.
In rodent studies, REM sleep deprivation causes death over the same period as food deprivation - about 15 days.
In humans, sleep deprivation leading to death is uncommon (possibly since the natural urge to sleep is so strong). But lack of sleep could contribute to more acute causes of death like seizures, and thus be misreported.
The strongest evidence that humans can die from sleep deprivation comes with a very rare inherited condition, fatal familial insomnia. In this disease, prion proteins cause the thalamus to be destroyed, and the patient is totally unable to sleep, even with heavy sedatives. Severe disability sets in (dementia, speech disorders), and death occurs within 10 months. There are no treatments or preventions.
Let’s return to the question of normal sleep amounts.
On the lower end, you may have seen reports of hunter-gatherer tribes who sleep just 6.5 hours, leading to assertions that this is a universally “natural” state for all humans. They also are rarely obese.
But this is a misguided conclusion. In reality, the hunter-gatherer tribes are basically perpetually starving, since food is never abundant for long periods of time. Starvation naturally induces less sleep, so that animals stay awake...
Five influences have drastically changed how we sleep: caffeine, light, temperature, alcohol, and alarms.
This was already discussed in chapter 2. The tips, for good measure:
Light is a signal for the suprachiasmatic nucleus to regulate the circadian rhythm (by signaling to the pineal gland to secrete melatonin). In the natural world, when the sun goes down, there’s little light. But nowadays, artificial light bathes our homes and disrupts our circadian rhythm.
Any light is disruptive to the circadian rhythm. Electric light delays your 24-hour circadian rhythm by 2-3 hours each evening.
Blue light is most problematic, suppressing melatonin at twice the levels of warm light. Blue light is most strongly emitted by digital screens like TVs, computer monitors, and smartphones.
In natural environments, the temperature rises and falls with the day. This is used by the hypothalamus, along with light, to set the circadian rhythm. Our bodies react in kind -- before sleep, the body cools, ejecting heat through densely perfused areas like hands, feet, and face.
But in modern days, we use thermostats to homogenize our temperatures, suppressing the highs in the day and raising the lows with pajamas and blankets. Our brain doesn’t get the same signal about the day’s cycle that it used to.
Cooling body temperatures improves sleep. In an experimental treatment, people wear a bodysuit that circulates cool water. Among insomniacs and the elderly, this reduces time to sleep and increases the quality of NREM sleep.
Alcohol is a sedative, causing what appears to be sleep but is really more like anesthesia. It disrupts sleep by suppressing REM sleep and causing waking throughout the night. This is caused by aldehydes from alcohol metabolism.
Alcoholics are so sleep-deprived that their brain imposes REM-like behavior during wakefulness, such as hallucinations and scattered thinking. (Shortform note: an unfortunate vicious cycle can result here -- alcohol disrupts sleep, which causes more fatigue and less behavior control when awake, which prompts more alcohol.)
By disrupting REM sleep, alcohol disrupts the normal processes of learning and complex knowledge.
Alarms cause acute stress...
In addition to avoiding all the problems from the last chapter (eg caffeine, alarms), here are more tips:
Sleeping pills are typically sedatives that put the body into a state that doesn’t fully resemble sleep (similar to alcohol). The sleep looks different electrophysiologically -- the deepest brainwaves are lacking.
They don’t even really work. Sleeping pills are no better than placebo at reducing the time to fall asleep (even though self-reported satisfaction is higher). The lower quality of sleep causes daytime sleepiness.
Sleeping pills can kick off a heavily medicated vicious cycle:
Population studies show that sleeping pills increase mortality in a dose-dependent way. Suggestive causes, possibly with a root cause of abnormal sleep:
Cognitive behavioral therapy (CBT) is a common non-pharmacological method for changing behavior. It’s commonly applied to depression, but there are variants for insomnia.
CBT has been shown to be more effective than sleeping pills.
A big part of alleviating insomnia is redeveloping confidence around the ability to sleep. Thus, some practices force insomniacs to restrict their time in bed, maybe even to 6 hours or less. This builds up stronger sleep pressure, and so patients fall asleep faster and regain psychological confidence.
Sleep deprivation goes far beyond our individual sleep practices. Our society has structurally locked in sleep deprivation in 4 ways.
The ethos at many companies sees sleep as an indulgence for the weak. They lionize the road warrior who fearlessly crosses time zones on tiny amounts of sleep and answers emails at 1AM. In their minds, more hours worked = more productivity.
This is short-sighted. The effects of sleep deprivation are costly to employers:
Another vicious cycle: people sleep less because of the amount of work they have to do, but their low sleep reduces their productivity and increases the work remaining.
Solutions for employers:
To match parent’s schedules, primary/secondary school often begins at 8AM, sometimes 7AM. Kids who need to catch a long bus ride have to wake at 5:30AM or earlier.
Remember that children have delayed circadian rhythms. This is akin to forcibly waking adults at 3:30AM everyday. Kids these days are sleeping two hours less per night, compared to children a century ago.
Kids with lower sleep show lower motivation, academic performance, test scores, IQ, as well as greater irritability, distraction, anxiety, substance abuse, and risk of traffic accidents.
Unfortunately, kids from poorer families are less likely to be driven to school, so they need to wake up even earlier.
Many kids diagnosed with ADHD may actually have sleep disorders (the author estimates >50% are misdiagnosed). Unfortunately, they’re treated with amphetamine (Adderall), causing even worse sleep problems.
Society should push to change school schedules to better match the circadian rhythm of kids.
The medical residency training system began with a cocaine-addicted surgeon (William Halsted) in New York in the 1880s. Viewing sleep as the enemy, he instituted 30-hour shifts.
Sleep-deprived residents show a greater risk of medical errors, surgical errors, misdiagnoses, and careless deaths. (Recall that after 22 hours without sleep, performance is impaired to the same level as being legally drunk.)
First-year residents are now limited to 24-hour shifts and 80-hour weeks. Later-year residents have no such restriction, since the ACGME claims the medical error studies were done only on first-year residents.
Structurally, the medical system resists change for fear of limiting training volume. Also, older doctors may fear this encourages laziness, relative to what the attending...
We’ve seen chronic sleep deprivation caused by a variety of factors, from the individual scaling up to the societal. The book ends with the author’s musings on how to improve sleep quality systemically: