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We, humans, spend one-third of our life sleeping; it is the single biggest investment of our time. For such a significant investment of our time, our understanding of sleep and its benefits is abysmal.
This article (second of the two), part of my Personal Growth Framework, focuses on health effects of sleep deprivation and dreaming.
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Why We Sleep by Matthew Walker – Book Summary Part 2
This article is a summary of the book Why We Sleep by Matthew Walker.
Sleep is the universal health care provider.
Given the volume of takeaways from this book, I am splitting the summary into two parts.
Part 1 is published in the article Why We Sleep focused on improving our understanding of sleep.
Part 2 covered by this article focuses on the health effects of sleep deprivation and dreaming.
I hope you find the summary useful.
I strongly recommend you read the book as a lot of what I have summarized is in a context that’s beautifully articulated in the book.
Health Effects of Sleep Deprivation
Humans need more than seven hours of sleep each night to maintain cognitive performance.
The recycle rate of a human being is around sixteen hours.
After sixteen hours of being awake, the brain begins to fail.
Individuals fail to recognize how their perpetual state of sleep deficiency compromises their mental aptitude and physical vitality, including the slow accumulation of ill health.
- Three full nights of recovery sleep (i.e., more nights than a weekend) is insufficient to restore performance to normal levels after a week of short sleeping.
- After ten days of just seven hours of sleep, the brain is as dysfunctional as it would be after going without sleep for twenty-four hours.
Sleep deprivation is –
(i) having the adequate ability to sleep; yet
(ii) giving oneself an inadequate opportunity to sleep.
When deprived of sleep following happens:
- Sleep duration is far longer on the recovery night, technically called as sleep rebound.
- NREM sleep rebounds harder. The brain will consume a far larger portion of deep NREM sleep than of REM sleep on the first night after total sleep deprivation, expressing a lopsided hunger.
- Should you keep recording sleep across a second, third, and even fourth recovery night, there’s a reversal. Now REM sleep becomes the primary dish of choice with each returning visit to the recovery buffet table, with a side of NREM sleep added.
- The brain never comes close to getting back all the sleep it has lost.
Obtain anything less than eight hours of sleep a night, and especially less than six hours a night, and the following happens:
- Time to physical exhaustion drops by 10 to 30 percent, and aerobic output is significantly reduced.
- Impairments are observed in limb extension force and vertical jump height, together with decreases in peak and sustained muscle strength.
- There are impairments in cardiovascular, metabolic, and respiratory capabilities hampering an underslept body. This includes faster rates of lactic acid buildup, reductions in blood oxygen saturation, and converse increases in blood carbon dioxide, due in part to a reduction in the amount of air that the lungs can exhale.
- Even the ability of the body to cool itself during physical exertion through sweating – a critical part of peak performance – is impaired by sleep loss.
- Post-performance sleep accelerates physical recovery from common inflammation, stimulates muscle repair, and helps restock cellular energy in the form of glucose and glycogen.
Learning and Sleep
Forgetting is the price we pay for remembering.
Sleep helps us retain everything we need and nothing that we don’t, improving the ease of memory recollection.
Sleep before learning refreshes our ability to make new memories initially. Those who napped did markedly better and improved in their capacity to memorize facts.
Sleep after learning protects newly acquired information, affording immunity against forgetting: an operation called consolidation.
- A memory retention benefit of between 20 and 40 percent being offered by sleep, compared to the same amount of time awake.
- Even daytime naps as short as twenty minutes can offer a memory consolidation advantage, so long as they contain enough NREM sleep.
- At every stage of human life, the relationship between NREM sleep and memory solidification is observed.
- Following a night of sleep, you regain access to memories that you could not retrieve before sleep.
Memories formed without sleep are weaker memories, evaporating rapidly.
- The most elemental units of the learning process – the production of proteins that form the building blocks of memories within these synapses – are stunted by the state of sleep loss.
- If you don’t sleep the very first night after learning, you lose the chance to consolidate those memories, even if you get lots of ‘catch-up’ sleep after that.
Theories, beliefs, and practices die one generation at a time.
Margaret Thatcher and Ronald Reagan – two heads of state that were very vocal, if not proud, about sleeping only four to five hours a night – both went on to develop Alzheimer’s disease.
Exercise and Sleep
Practice does not make perfect.
It is practice, followed by a night of sleep, that leads to perfection.
Training and strengthening muscles can help you better execute a skilled memory routine. The routine itself resides firmly and exclusively within the brain.
- Your brain will continue to improve skill memories in the absence of any further practice.
- That delayed “offline” learning occurs exclusively across a period of sleep.
- Motor memories get shifted over to brain circuits that operate below the level of consciousness. As a result, those skill actions were now instinctual habits.
- Sleep helped the brain automate the movement routines, making them second nature – effortless.
- The increases in speed and accuracy, underpinned by efficient automaticity, were directly related to the amount of stage 2 NREM, especially in the last two hours of an eight-hour night of sleep.
The 100-meter sprint superstar Usain Bolt has, on many occasions, taken naps in the hours before breaking the world record, and before Olympic finals in which he won gold.
If you don’t snooze, you lose.
Attention and Sleep
One brain function that buckles under even the smallest dose of sleep deprivation is concentration.
There are two main culprits of drowsy-driving accidents – people falling asleep at the wheel and microsleep.
People falling asleep at the wheel
This happens infrequently and usually requires an individual to be acutely sleep-deprived, having gone without sleep for twenty-plus hours.
Microsleep
A more common cause of drowsy-driving accidents is a momentary lapse in concentration, called a microsleep, lasting for just a few seconds.
Microsleep usually affects chronically sleep-restricted individuals, defined as getting less than seven hours of sleep a night on a routine basis.
During microsleep, the brain becomes blind to the outside world for a brief moment – and not just the visual domain, but in all channels of perception.
Results from research studies
- Those individuals who slept eight hours every night maintained a stable, near-perfect performance across the two weeks.
- After the first night of no sleep at all, their lapses in concentration (missed responses) increased by over 400 percent.
- After four hours of sleep for six nights, participants’ performance was just as bad as those who had not slept for twenty-four hours straight.
- Ten days of six hours of sleep a night was all it took to become as impaired in performance as going without sleep for twenty-four hours straight.
- The three-night total sleep deprivation group suffered catastrophic impairment.
- After being awake for nineteen hours, sleep-deprived people were as cognitively impaired as those who were legally drunk.
- Operating on less than five hours of sleep, your risk of a car crash increases threefold. With less than four hours of sleep, the risk increases 11.5 times.
- Four hours of sleep plus the effect of alcohol, people drove off the road almost thirty times more than the well-rested, sober group.
Emotional Reactions and Sleep
The prefrontal cortex – the region of the brain that sits just above your eyeballs; is most developed in humans, relative to other primates; and is associated with rational, logical thought and decision-making.
After a full night of sleep, the prefrontal cortex was strongly coupled to the amygdala, regulating this deep emotional brain center with inhibitory control.
Without sleep, however, the strong coupling between these two brain regions is lost.
- The under-slept brain swings excessively to both extremes of emotional valence, positive and negative.
- Insufficient sleep has been linked to aggression, bullying, and behavioural problems in children across a range of ages.
- The relationship between a lack of sleep and violence has been observed in adult prison populations.
- Insufficient sleep also determines relapse rates in numerous addiction disorders.
- Insufficient sleep during childhood significantly predicts the early onset of drug and alcohol use in that same child during their later adolescent years.
- There is no major psychiatric condition in which sleep is normal – depression, anxiety, post-traumatic stress disorder (PTSD), schizophrenia, and bipolar disorder (once known as manic depression).
By improving sleep quantity, quality, and regularity, a research team systematically demonstrated the healing abilities of sleep for the minds of numerous psychiatric populations.
The best bridge between despair and hope is a good night’s sleep.
– E. Joseph Cossman
Cardiovascular System and Sleep
One night of modest sleep reduction – even just one or two hours – will speed the contracting rate of a person’s heart, hour upon hour, and significantly increase the systolic blood pressure within their vasculature.
- A lack of sleep erodes the fabric of strained blood vessels, especially those that feed the heart itself, called the coronary arteries.
- Individuals obtaining just five to six hours each night or less were 200 to 300 percent more likely to suffer calcification of your coronary arteries over the next five years.
Every experiment investigating the impact of insufficient sleep on the human body has observed an overactive sympathetic nervous system.
- A chronic increase in a stress hormone called cortisol, which is triggered by the overactive sympathetic nervous system.
- One undesirable consequence of the sustained deluge of cortisol is the constriction of those blood vessels, triggering an even more significant increase in blood pressure.
- Growth hormone – a great healer of the body – which usually surges at night, is shut off by the state of sleep deprivation.
- Deep sleep prevents an escalation of this physiological stress that is synonymous with increased blood pressure, heart attack, heart failure, and stroke.
Think of your deep NREM sleep as a natural form of nighttime blood-pressure management – one that averts hypertension and stroke.
In the Northern Hemisphere, the switch to daylight savings time in March results in most people losing an hour of sleep opportunity.
- Should you tabulate millions of daily hospital records, as researchers have done, you discover that this seemingly slight sleep reduction comes with a frightening spike in heart attacks the following day.
- When the clocks move back, and we gain an hour of sleep opportunity time, rates of heart attacks plummet the day after.
A similar effect is observed for driving accidents.
Obesity and Weight Gain
The less you sleep, the more you are likely to eat.
Your body becomes unable to manage those calories effectively, especially the concentrations of sugar in your blood.
Results of research studies –
- Individuals were far more hungry when sleeping four to five hours a night, despite being given the same amount of food and being similarly active.
- Inadequate sleep decreased concentrations of the satiety-signaling hormone leptin and increased levels of the hunger-instigating hormone ghrelin.
- From a metabolic perspective, the sleep-restricted participants had lost their hunger control.
- High-calorie foods became significantly more desirable in the eyes of the participants when sleep-deprived.
- Sleep makes your gut happier. It improves the bacterial community, known as your microbiome. Insufficient sleep will prevent the meaningful absorption of all food nutrients and cause gastrointestinal problems.
- When given just five and a half hours of sleep opportunity, more than 70 percent of the pounds lost came from lean body mass – muscle, not fat. The group offered eight and a half hours in bed each night, and a far more desirable outcome was observed, with well over 50 percent of weight loss coming from fat while preserving muscle.
Diabetes and Sleep
In a research study, participants were limited to sleeping four hours a night for just six nights.
- By the end of that week, these (formerly healthy) participants were 40 percent less effective at absorbing a standard dose of glucose, compared to when fully rested.
- If the researchers showed those blood sugar readings to an unwitting family doctor, the GP would immediately classify that individual as being pre-diabetic.
Reproductive System and Sleep
Men suffering from sleep disorders, especially sleep apnea associated with snoring, have significantly lower levels of testosterone than those of similar ages and backgrounds but who do not suffer from a sleep condition.
- Males with low testosterone often feel tired and fatigued throughout the day.
- They find it difficult to concentrate on work tasks, as testosterone has a sharpening effect on the brain’s ability to focus.
- They have a dulled libido, making an active, fulfilling, and healthy sex life more challenging.
Routinely sleeping less than six hours a night results in a 20 percent drop in follicular-releasing hormone in women – a critical female reproductive element that peaks just before ovulation and necessary for conception.
Immune System and Sleep
When you do fall ill, the immune system actively stimulates the sleep system, demanding more bed rest to help reinforce the war effort.
Volunteers in a research study were infected with the common cold virus, and the results were –
- In those sleeping five hours on average, the infection rate was almost 50 percent.
- In those sleeping seven hours or more a night in the week prior, the infection rate was just 18 percent.
- A single night of four hours of sleep – such as going to bed at three a.m. and waking up at seven a.m. – swept away 70 percent of the natural killer cells circulating in the immune system.
- Ramping up the body’s level of sympathetic nervous activity will provoke an unnecessary and sustained inflammation response from the immune system.
- Cancers are known to use the inflammation response to their advantage. Inflammatory factors associated with sleep deprivation may be used to physically shear some of the tumors from its local moorings, allowing cancer to spread to other parts of the body. It is a state called metastasis.
Sleep-deprived mice suffered a 200 percent increase in the speed and size of cancer growth, relative to the well-rested group.
World Health Organization has officially classified nighttime shift work as a ‘probable carcinogen.’
Insomnia
Insomnia is:
(i) suffering from an inadequate ability to generate sleep, despite
(ii) allowing oneself the adequate opportunity to get sleep.
Billy Crystal has said when describing his battles with insomnia, ‘I sleep like a baby—I wake up every hour.’
The two most common triggers of chronic insomnia are psychological:
- Emotional concerns, or worry, and
- Emotional distress, or anxiety
Cognitive Behavioural Therapy for Insomnia (CBT-I)
Patients must –
- Establish a regular bedtime and wake-up time, even on weekends
- Go to bed only when sleepy and avoid sleeping on the couch early/mid-evenings
- Never lie awake in bed for a significant time; instead, get out of bed and do something quiet and relaxing until the urge to sleep returns
- Avoid daytime napping if you are having difficulty sleeping at night
- Reduce anxiety-provoking thoughts and worries by learning to decelerate before bed mentally, and
- Remove visible clockfaces from view in the bedroom, preventing clock-watching anxiety at night.
Longevity and Sleep
Any adult sleeping an average of 6.75 hours a night is = predicted to live only into their early sixties.
- There is an upward hook in death risk once the average sleep amount passes nine hours.
- The causes of death in individuals sleeping nine hours or longer include infection (e.g., pneumonia) and immune-activating cancers. Sickness, especially sickness that activates a powerful immune response, enables more sleep.
Health Effects of Dreaming
Dreaming
REM sleep is a state characterized by strong activation in visual, motor, emotional, and autobiographical memory regions of the brain, yet a relative deactivation in areas that control rational thought.
There is a spike in the following activity when someone starts dreaming in REM sleep:
- The visuospatial regions at the back of the brain, which enable complex visual perception
- The motor cortex, which instigates movement;
- The hippocampus and surrounding areas that we have spoken about before, which support your autobiographical memory; and
- The deep emotional centers of the brain – the amygdala and the cingulate cortex – both of which help generate and process emotions.
Perhaps it was not time that heals all wounds, but rather time spent in dream sleep.
REM-sleep dreaming offers a form of overnight therapy.
- REM-sleep dreaming takes the painful sting out of difficult, even traumatic, emotional episodes you have experienced during the day, offering emotional resolution when you awake the next morning.
- Concentrations of a critical stress-related chemical called noradrenaline are entirely shut off within your brain when you enter this dreaming sleep state. REM sleep is the only time during the twenty-four-hour period when your brain is entirely devoid of this anxiety-triggering molecule.
It postulated that the process of REM-sleep dreaming accomplishes two critical goals:
- Sleeping to remember the details of those valuable, salient experiences, integrating them with existing knowledge and putting them into autobiographical perspective, yet
- Sleeping to forget, or dissolve, the visceral, painful emotional charge that had previously been wrapped around those memories. Sleep, and specifically REM sleep, was needed for us to heal emotional wounds.
Through its therapeutic work at night, REM sleep performed the elegant trick of divorcing the bitter emotional rind from the information-rich fruit.
It was only patients, expressly dreaming about the painful experiences around the time of the events, who went on to gain clinical resolution from their despair, mentally recovering a year later as clinically determined by having no identifiable depression.
To sleep, perchance to heal.
Creativity
Sleep provides a nighttime theater in which our brain tests out and builds connections between vast stores of information. This task accomplished using a bizarre algorithm biased towards seeking out the most distant, non-obvious associations, thus resulting in creativity.
During the dreaming sleep state, your brain will cogitate vast swaths of acquired knowledge, and then extract overarching rules and commonalities – the gist.
We awake with a revised “Mind Wide Web” that is capable of divining solutions to previously impenetrable problems.
Problem-solving abilities rocketed up, with participants solving 15 to 35 percent more puzzles when emerging from REM sleep compared with awakenings from NREM sleep or during daytime waking performance!
I saw in a dream a table where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper. Only in one place did a correction later seem necessary.
Dmitri Mendeleev, Discoverer of the Periodic Table
As we enter REM sleep and dreaming takes hold, an inspired form of memory mixology begins to occur.
- No longer are we constrained to see the most typical and apparent connections between memory units. On the contrary, the brain becomes actively biased toward seeking out the most distant, nonobvious links between sets of information.
- If we feed a waking brain with the individual ingredients of a problem, novel connections and problem solutions should preferentially emerge after time spent in the REM dreaming state, relative to an equivalent amount of logical thinking time spent awake.
It is both the act of dreaming and the associated content of those dreams that determine creative success.
A problem difficult at night is resolved in the morning after the committee of sleep has worked on it.
– John Steinbeck
Recommended Reading
Why We Sleep by Matthew Walker
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Very informative and usefull. Thanks to this for i was able to realize my bad habit of sleeping 4 to 5 hours a night and without naps at day time.