The notes below are designed to give prospective readers an idea of what to expect from the book, and to aid in making a decision on whether to buy it.
Why We Sleep, Dr Matthew Walker.
How much does one need?
7.5 hours is advised a desired minimum – to get that, one typically needs an 8 hour sleep opportunity. The adverse consequences of regularly getting less than this are covered later.
Performance
Humans sleep for just 8 hours vs 10-15 hours for all other primates. But REM is a much higher %. Evolution made humans sleep less but more efficient as we were the first ground sleepers.
Roger Federer organizes his routine around 10-11 hours of sleep per night. Usain Bolt had only been awake for 35 minutes when he broke his 100m record – he’d had a quick nap beforehand. Many professional sports teams are turning towards sleep for legal performance enhancement.
Humans react significantly worse to negative stimuli when sleep deprived. The buffer between type 1 and 2 thinking (chimp vs human) is suppressed so we react rather than act.
Learning when well rested is also far more efficient. The Head of Human Resources at Accenture can be seen on YouTube quoting the same research on this.
Sleeping moves information from your short-term memory into your long-term memory, helping both free up space to ingest more information and consolidate information already absorbed.
Somebody who has been awake for 19 hours shows the same concentration and reaction time as somebody at the legal alcohol limit. The tipping point seems to be 15 hours for rapid deterioration. This is an exponential effect, such that someone who has had four hours sleep is 11x as likely to be involved in an accident.
“Elderly adults needing less sleep is a myth” because of the “floor effect”. Their performance doesn’t suffer as much when deprived of sleep because their performance is already lower, often due to lack of sleep. Tips for elderly to rebuild their sleep appetite are outside of scope of the book – but they exist if you are interested.
Aetna – a firm adept at crunching large amounts of data on population health, awards employees up to $500 bonuses for getting 20 sequential 7 hour night sleeps. They’re aware of the added benefit of well rested employees. Those with insomnia are rewarded for receiving treatment. Google and Nike facilitate afternoon naps, and encourage ‘hitting sleep minimums’.
Health
If the benefits of sleep were injectable or available in pill form, everyone would take it given the health benefits. But people seem very unwilling to self-prescribe sleep.
Deep sleep manages blood pressure, specifically in the brain where it reduces.
Impairment in the immune system becomes apparent when regular sleep thresholds drop below 6-7 hours. Long term, the author asserts a much higher risk of developing cancer risk (ceteris paribus).
Studies also point to increased risk of Alzheimer’s, heart attack & suicide.
“There are no mental disorders when sleep is affected”. Sleep is probably not a panacea, but we do not fully understand the interactivity between cause and effect and the role of sleep may be under-discussed.
Daylight savings changes result in a big spike in heart attacks (in the at-risk population) and a big drop when they go back (the night when you get a bonus hour).
Alzheimer’s causes lack of sleep and is also made worse by lack of sleep - a vicious cycle (of building amyloid plaque on neurons). Reagan and Thatcher both boasted about lack of sleep, but both developed the disease.
Sleep deprivation also flips both Leptin (which makes you feel full) and ghrelin which (makes you feel hungry) in the wrong directions. It contributes to a needless lack of satiation.
Sleep is very important in fertility and pregnancy.
The author contends that a large proportion of ADHD diagnoses in children are mis-diagnoses of a sleep disorder.
If you combine dieting with sleep deprivation the body becomes fat-sparing and the weight reduction accrues disproportionately to the loss of lean muscle mass.
One long-term study showed adults who sleep 6-7 hours a night are 3x more likely to have a heart attack than those sleeping 7-8 hours.
Sleep is the single most effective thing we can do to reset our brain and body health each day.
Tips for getting more and better sleep
For each of us there’s an unseen trade-off between being productive right before bedtime and being productive all of the next day. I’m trying to manage this by restricting evening reading to print outs. Some period of disengagement and quieting the mind is also helpful for sleep prep.
Many households have switched to LED lighting in recent years which is a new source of blue light and can reduce melatonin. Dimmers on these lights is a good tip, as well as generally making the house darker in the evening. Same logic with black-out blinds. “We are a darkness deprived society…”
Caffeine blocks the receptors that allow you to feel tired. The author advises avoiding caffeine after around 10am.
Coffee and most teas contain caffeine. De-caff coffee only has ~80% of the caffeine removed.
The author points out the incompatibility of alcohol in the evening and proper sleep (damn!). The sedation effect of alcohol can aid sleep onset, but it harms overall sleep patterns and the last 4 hours of sleep usually become much lower in quality. In some instances, alcohol intake reduces the number of rapid-eye-movement cycles that demark each discrete sleep cycle from 5 (in a 7.5hour session) to only 1.
Your core body temperature drops by 2 degrees around the onset of sleep. Those that struggle with sleep onset can ‘hack’ this with a hot shower or bath before bed, which pushes heat to the extremities and dumps core body heat.
Sleep fragmentation is also an issue, especially in people with weaker bladders, so limiting fluids at night should help.
Having sugar near bedtime is not ideal. Your pancreas has already started to make less insulin to mop it up near bedtime – i.e. don’t jolt your organs out of their wind-down routine.
Sleeping pills are not a long-term solution. SEDATION IS NOT SLEEP. Doesn’t bathe the brain in the same healing brainwaves or remove waste products in the same way.
If you do suffer from poor sleep efficiency / insomnia etc. the author advises seeking the advice from a sleep doctor. The leading treatment is Cognitive Behavioral Therapy (CBT: sequence of take-home sleep exercises) – the author reports very high efficacy with these techniques.
For those not in the insomnia camp but seeking some sleep improvement from CBT, there is an app called Sleepio that you can follow along with at home. Obviously practice a couple of hours before bed as this is still screen time.
A gene “DEC2” which is very rare, allows some people to have just 5-6 hours a night. But it is less than 1% of population. It’s not good to simply pre-suppose that you are part of this group. As probabilistic thinkers, it is impossible to conceive that we would have several of this geno-type in the same investment team.
If you’ve made it this far without nodding off, then thanks - hopefully this can help.
Thanks, Ryan Brown, for these terrific notes!