I just finished reading Why We Sleep by Matthew Walker, PhD. It was an excellent
book. Before reading I knew that sleep was vital to ones well-being. But I was unaware of
how large an impact it has on EVERY aspect of ones life. The top three most important
things are sleep, exercise and diet. I am starting to think it may be in that order as
well.
I hope you learn something from my notes and I highly encourage everyone to read this
book. Enjoy.
My Notes
Part 1
To Sleep... (Ch.1)
Routinely getting less than six hours of sleep can lead to all sorts of horrible things such as weakening your immune system, increase cancer risk, Alzheimers disease (large increase in risk), disrupts blood sugar levels, CVD and mental health problems such as depression. Also it makes you feel hungrier.
"The shorter your sleep, the shorter your lifespan"
The fact that sleep survived throughout evolution means that is must be extremely important as it has numerous downsides
"...sleep is the single most effective thing we can do to reset our brain and body health each day..."
Caffeine, Jet lag, and Melatonin (Ch.2)
Our circadian rhythm is not exactly 24 hours in length, slightly more. It can be a bit inaccurate, but each day the sunlight helps reset it close to 24 hours
Our internal clock is called the suprachiasmatic nucleus (located in our brain)
We have a sleep genetic sleep chronotype. The classic "morning larks" vs "night owls"
Melatonin is released by the pineal gland as instructedby the suprachiasmatic nucleus. It is our biological command to sleep
Melatonin ONLY signals that sleep should start/occur. It itself does not participate in generating sleep. It is just an instruction to other brain regions to sleep
There is little effect of melatonin, but there is a massive placebo effect
Melatonin is released throughout the night by the pineal gland. Once sunlight enters our brain through our eyes this is halted. It then starts up again once the sun goes down
This is one of the reasons getting sunlight in the morning is important
A chemical builds up in our brain throughout the day called adenosine. This builds up what we call "sleep pressure". As it builds up this pressure increasees which will cause the desire to sleep
Caffeine binds to and blocks the signal from adenosine receptors. Therefore muting the sleep signal/pressure
Some people are more sensitive to caffeine. It is broken down by an enzyme in the liver and for some, this enzyme is strong while others it is weaker
Aging also weakens this enzyme
Caffeine is an addictive drug and should be used with caution
There are some questions to ask yourself to see if you get enough sleep:
Could I fall back asleep at 10/11 am?
Can I function optimally without caffeine before noon?
If I didn't set an alarm clock, would I sleep past that time? (for me the answer is almost always yes)
Defining and Generating Sleep (Ch.3)
More NREM sleep happens in the beginning of the night and REM happens more towards the end. So if you go to sleep later than normal, you will miss NREM, if you wake up earlier than normal, you miss REM. So just losing a couple hours of sleep can actually cause losing the majority of one of these types of sleep
NREM sleep is where memories are stored. The waves are lower frequency, therefore they can travel further. They transfer information from short term to long term memory.
Wake state is like reception (experiencing and learning), NREM is like reflection (storing and strengthening from wake state) and REM is like integration (interconnecting these experiences)
Ape Beds, Dinosaurs and Napping with Half a Brain (Ch.4)
Humans naturally sleep biphasically. Monophasic sleep is a result of modernity. This has been shown in hunter-gatherer tribes who are untouched by electricity. The main chunk of sleep is still 7-8 hours with a 30-60 minute nap
Humans have a hardwired dip in alertness in midafternoon called post-prandial alertness dip.
A study in Greece showed that there was a 37% increase in risk of death from heart disease over a 6 year period for those that abondoned the natural biphasic sleep schedule that was also very common in Greece.
"When we are cleaved from the innate practice of biphasic sleep, our lives are shortened"
Changes in Sleep Across the Life Span (Ch.5)
Alcohol is one of the most powerful suppressors of REM sleep
Fetuses who do not get sufficient REM sleep can have many issues, including autism
Mothers who drink even a small amount of alcohol when pregnant can cause REM sleep disruption in their child
Also the alcohol content of a mothers breastmilk is roughly the same as their BACS. This also causes the childs sleep to be disrupted
Sleep in children and teenagers is a significant factor for them to achieve mature thinking and the ability to reason
NREM sleep in adolecents does "brain pruning". Basically we all start with a generic brain and it is pruned based on our experiences over time
Many psychiatric issues including schitzophrenia may be a result of a lack of NREM sleep in the teenage years
As people age from a young child to teenager, their circadian rhythm shifts. This is why children fall asleep early but teenagers want to stay up late, even later than their parents
Older adults needing less sleep is a myth. They are just sometimes unable to get as much as they need (which is the same amount of it was in their midlife)
REM sleep stays intact. But NREM starts declining by early 30's. By mid 40's 60-70% is gone and by 70 80-90% is gone (gone as in compared to "youthful sleep")
The lower an older individuals sleep efficiency score, the higher their mortality risk, worse physical health, more likely to have depression, less energy and less cognitive function (especially forgetfullness)
Part 2
Your Mother and Shakespeare Knew (Ch.6)
The hippocampus is like our brains RAM, short term and limited storage. Sleep is what causes us to flush this RAM into more long term storage (cortex). Even a mid-day nap after learning information causes this and allows one to retain more information
Sleep flushes the contents of the hippocampus to the cortex
Walker mentions that they noticed a current pulsing between the hippocampus and cortex every 100-200ms. It just seems wild to me that our brains work in such an amazing way.
Stage 2 NREM sleep and sleep spindles have to do with this flushing of the hippocampus
late-morning hours of sleep are rich in these NREM sleep spindles. So sleeping say six or less hours robs you of a lot of the benefit
The more deep NREM sleep, the one more one will remember the next day
The brain continues to improve skill memories while sleeping, even in the absense of further practice
Practice followed by a night of sleep makes perfect
This information gets transfered to parts of the brain below consciousness instead of long term storage during sleep
Stage 2 NREM especially in the last two hours of an eight-hour sleep were most effective for this, because of the sleep spindles (they are most abundant during this time). They are linked with the "offline memory boost"
Too Extreme for the Guinness Book of World Records (Ch.7)
People are not able to accurately determine if they are sleep deprived. Many think they are functioning just fine but in reality they are not living up to their potential
Being awake for nineteen hours has the same cognitive impairment of someone who is legally drunk
Drowsy driving is extremely dangerous. Sleep deprivation and risk of crashing is an exponential relationship. DO NOT DRIVE WHEN DROWSY
A lack of sleep increases sensitivity to both positive and negative emotions. The positive side though is hedonic, therefore it is bad as well. It can lead to addiction/addictive behaviors
When sleep deprived, it seems that the hippocampus does not work properly. It kind of shuts down and just does not want to accept new information
Even just disrupting ones NREM sleep (preventing deep sleep) causes similar deficits
Memories formed without sufficient sleep are weaker memories and will fade quickly
If you don't get quality sleep the night of learning something you lose the chance of consolidating that memory, catchup sleep does NOT help
Alzheimer's disease is associated with the buildup of beta-amyloid. This is poisonous to neurons and kills them
This does not affect all areas of the brain
Beta-amyloid does not affect the hippocampus. But people with more beta-amyloid buildup have their deep sleep disrupted, this is the reason for the forgetfullness in Alzheimer's patients
A structure called the glymphatic system exists within the brain. This is responsible for cleaning up metabolic contaminants generated by neurons
This system works a bit during the day, but at night during NREM sleep it has a ten to twenty fold increase. This is where the real work happens
It is for this reason that a lack of NREM sleep causes beta-amyloid buildup
Therefore, getting little sleep over ones life significantly increases their risk for Alzheimer's disease
Cancer, Heart Attacks, and a Shorter Life (Ch.8)
SLEEP LOSS AND THE CARDIOVASCULAR SYSTEM
Every major system and organ in your body suffers from a lack of sleep, the shorter your sleep, the shorter your life
Lack of sleep leads to a 45% greater risk of heart disease. Sleeping less than 6 hours also has 3x greater risk of cardiovascular or coronary event than those that sleep 7 to 8 hours a night
Note that these results stuck even when controlling for other cardiac risk factors. This means that unhealthy sleep, unhealthy heart
Even one night of poor sleep can cause increase in heart rate and blood pressure in healthy people
This is because of disruptions to the sympathetic nervous system
Those that slept 5 to 6 hours each night were 200-300% more likely to suffer calcification of the coronary arteries over the next five years
Growth hormone which is used in healing within the body surges at night, sleep deprivation results in a lack of growth hormone.
Growth hormone is important in keeping the endothelium healthy. If it is not, one is more prone to atherosclerosis
SLEEP LOSS AND METABOLISM: DIABETES AND WEIGHT GAIN
One study had participants sleep 4 hours a night for 6 nights. After this the healthy people were 40% less effective at absorbing a normal amount of glucose compared to before
Our cells are less responsive to insulin when sleep deprived
Inadequate sleep leads to decreased levels of leptin and increased levels of ghrelin
Basically this means one will not feel satisfied from the food they are eating and will want to eat more
Also sleep loss leads to an increase in endocannabinoids which as you may have assumed, stimulate appetite
SLEEP LOSS AND THE REPRODUCTIVE SYSTEM
Men who sleep five hours a night for a week have their testosterone drop below their normal baseline. The drop is so large that it "ages" them by 10-15 years in terms of their testosterone levels
It is shown that because of this, those that have sleep disorders, especially sleep apnea, have significantly lower testosterone levels compared to others their age.
SLEEP LOSS AND THE IMMUNE SYSTEM
Even one night of four hours of sleep reduces the natural killer immune cells cirulating in someone by 70%
This is a reason that nighttime shift workers have increased odds of developing cancer
Lack of sleep can also increase cancer risk because of the inflammation that is caused from having ones sympathetic nervous system in overdrive. Cancers can use this inflammation response to their advantage
Therefore, sleep disruption can increase the risk of developing cancer as well as allow cancer to spread and grow more rapidly if it is already there
SLEEP LOSS, GENES, AND DNA
Short sleeping can damage telomeres. This damage can be significant, similar to the damage from Aging
Part 3 How and Why We Dream
Dreaming as Overnight Therapy (Ch.10)
Dreaming state of REM sleep helps with emotional resolution
Dreaming about the emotional themes is what has been shown to resolve emotional trauma/issues
Dream Creativity and Dream Control (Ch.11)
During REM sleep ones brain ignores obvious links and common logic and will attempt to connect distantly related concepts. These are nonobvious and possible bizzare links that our aware brain or brain in NREM sleep would never be able to see
One can "go to bed with disparate pieces of the jigsaw and wake up with a complete puzzle"
REM sleep allows comprehension versus learning, piecing together what one has learned to deeply understand it
Part 4 From Sleeping Pills to Society Transformed
iPads, Factory Whistles, and Nightcaps (Ch.13)
The main factors disrupting our sleep in modernity are:
Artificial light:
Even low strength artificial light tricks our suprachiasmatic nucleus into beleiving that it is still day, inhibits the reactivation of the pineal gland which results in no melatonin production
This artificial light is also shown to affect our sleep quality (including amount of REM sleep) and how we feel in the morning
Alcohol:
Not related to sleep but still interesting: Alcohol is a sedative, it binds to receptors in the brain and prevents neurons from firing. The reason that is "loosens people up" is because the prefrontal cortex is that part that it affects first
But, sedtation is not sleep. Alcohol sedates you but does not induce natural sleep
Alcohol also fragments sleep and suppresses REM sleep
Temperature:
To initiate sleep there needs to be a drop of ~2-3 degrees F or 1 degree C. Regularized room temperature can interfere with this
There are cells in the hypothalamus that send a signal to the suprachiasmatic nucleus upon detecting the temperature drop. Therefore its not just natural light that initiates the release of melatonin, it is also the temperature drop (that would naturally come with the sun setting)
A room temp of ~65 degrees F is recommended for quality sleep
Forceful awakening:
Having an alarm go off can increase blood pressure and heart rate. Doing this repeatedly in the same morning and over ones lifetime can put strain on our hearts
The reason that we even need these alarm clocks in the first place is because of all the other factors impacting our sleep, the ideal scenario is to get good quality sleep so that we do not have to force ourselves awake
Hurting and Helping Your Sleep (Ch.14)
Sleeping pills do not induce natural sleep, they are sedatives that target the same receptors that alcohol does that stop your neurons from firing
In numerous studies, users of sleeping pills were shown to die at a 3.6-5.3x higher rate than the control group over a period of a few years
Heart disease, stroke and cancer risks all increase when taking these sleeping pills