Best Summary: Why We Sleep, by Matthew Walker

Best Summary: Why We Sleep, by Matthew Walker

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.

  • True low-sleepers (people who can chronically sleep < 6 hours per night, without impairment of function) are incredibly rare, at less than 1% of the population. Everyone else is disguising their sleep deprivation with caffeine and sleeping pills.
  • Insidiously, you’re very bad at objectively assessing your decrease in performance under sleep deprivation. When sleep-deprived, you think you’re performing better than you really are.
  • Fasting and starvation does lower sleep, which is why hunter-gatherer tribes show 6.5 hours of sleep. This fact is then inappropriately picked up by popular media as evidence that it’s natural. But when resources are plenty, your body naturally wants to sleep more.

Sleep has two general types – NREM and REM.

  • NREM occurs earlier in the sleep phase, while REM is concentrated later.
  • NREM is slow (~2Hz) (like billions of neurons singing in synchrony) while REM is fast (50Hz) and looks like being awake.
  • NREM is responsible for pruning memories, transferring short-term memory to long-term memory, gaining “muscle memory,” growth hormone secretion, and parasympathetic nervous system activation.
  • REM is responsible for forming new neural connections, problem solving, dreaming, blunting emotional responses to painful memories, reading other people’s facial emotions, and neonatal synaptogenesis.
  • Both are generally necessary – depriving a person of either one leads to different problems.

Sleep deprivation shows consistently bad outcomes. Nothing is reported to be beneficial from sleep deprivation.

  • Sleep deprivation is associated with more severe disease: higher mortality, risk of cancer, heart disease, weight gain, rate of infection, Alzheimer’s, irritability, inflammation.
  • Sleep deprivation lowers performance: lower productivity, social fluidity, rational decision-making, memory recall, emotional control, testosterone, immune system function, response to flu vaccine.
  • In the extreme, chronic sleep deprivation causes death.
  • Even if you think you’re gaining time by sleeping less, it’s compensated for with lower productivity and creativity.

Checklist for improving your sleep:

  • Set a sleep schedule: sleep and wake up at the same times every day. Don’t sleep procrastinate, and don’t think that you can just sleep in on weekends (it makes it harder to wake up Monday morning)
  • Don’t use alarms if you can help it. Alarms cause a huge stress reaction on waking. And snoozing causes repeated stress traumas every morning.
  • Wake up with the sun or use very bright lights. This sets your circadian rhythm.
  • Avoid all caffeine and nicotine if possible. But if you have to have caffeine, avoid it in the afternoon, since it takes over 10 hours to wear off fully.
  • Exercise regularly, but not within 3 hours of sleep.
  • Don’t nap after 3PM – they make it harder to sleep at night.
  • Don’t drink alcohol unless it is completely metabolized by sleep time (including the aldehydes produced).
  • Avoid large meals and drinks late at night. Large meals can cause indigestion; too many fluids cause frequent urinations.
  • Reduce light before sleep. Blue light is the most harmful, but even bedside lamps cause issues.
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