221 ‒ Understanding sleep and how to improve it

KEYPOINTS

• 01

  Modern society has cut sleep sharply in an evolutionary blink.

  Walker argues evolution spent millions of years establishing an eight-hour night of sleep, and in about 70 years we've lopped off roughly 20–25% of it. He compares it to deciding to lower everyone's oxygen saturation by 20–25% for a century — no one would think that a good idea. Sleep deprivation likely degrades health faster than not eating or not exercising; Guinness stopped accepting sleep-deprivation record attempts.

• 02

  Sleep cycles every 90 minutes, but the mix changes across the night.

  You descend from stage 1 through stages 2, 3 and 4 (deep, slow-wave sleep), rise back after about 70 minutes, then enter REM — repeating roughly every 90 minutes. Early cycles are dominated by deep non-REM sleep; later cycles by REM. Sleep is scored in 30-second epochs, using criteria in place for 60–70 years.

• 03

  Cutting sleep short disproportionately costs REM.

  Someone sleeping six hours instead of eight loses 25% of total sleep but may lose up to 70% of their REM, because REM concentrates in the final hours. Waking at 5:30 to 'get a jump start' has a steeper price than it seems.

• 04

  Brainwaves slow dramatically as sleep deepens.

  Awake, brain activity oscillates around 50–60 times per second; relaxing in bed, it drops toward 10 cycles per second; theta around 6–7. Stage 2 features sleep spindles of 10–15 cycles per second. Deep sleep's slow, high-amplitude waves looked so coma-like that it had a bad reputation for 20–30 years.

• 05

  Chronotype is largely genetic and shifts with age.

  About 25–30% of people are morning types, 25–30% evening types, the rest in between; companies like 23andMe estimate it from genes. Teenagers' chronotype moves later, so a 15-year-old in bed at 10:30 for a 5:30 bus can't fall asleep — biology, not laziness. It drifts back in adulthood and earlier again in old age, hence Florida's early-bird dinner specials.

• 06

  Sleep efficiency means you need more time in bed than sleep.

  A healthy person in their 40s has about 90% sleep efficiency. To get eight hours (480 minutes) of actual sleep, they need roughly 8 hours and 50 minutes in bed. Walker's 7–9 hour recommendation refers to sleep, not time in bed.

• 07

  Counterintuitively, insomnia is treated by restricting time in bed.

  Compressing the sleep window builds sleep pressure and re-teaches the brain that bed is for sleep. Don't lie awake: after about 20 minutes, get up and return only when sleepy, to avoid a learned association between bed and wakefulness.

• 08

  Naps are a double-edged sword.

  For people sleeping well, naps can be fine — hunter-gatherer tribes often nap in summer afternoons and sleep around 8:30–9 p.m. But for insomniacs, a late-afternoon nap releases sleep pressure needed at night.

• 09

  Cool room, warm bath.

  Current data suggest about 65–67°F is optimal. A hot bath or shower helps not because you're toasty but because blood rushes to the skin and core temperature then plummets. A smart thermostat can warm the room in the final 15–20 minutes before waking.

• 10

  Walker has softened on blue light.

  His book cited a Harvard study in which an hour of iPad reading delayed melatonin, reduced REM and impaired sleep for days. Work by Michael Gradisar at Flinders University changed his mind: he's less convinced device harm comes from blue light, though he believes it has some effect; engagement and displaced sleep matter too.

• 11

  Coffee's benefits may come from antioxidants, not caffeine.

  A 2017 review found decaffeinated coffee — same antioxidants, no caffeine — shares many health associations. For Americans eating poor diets, morning coffee may be a main antioxidant source. Walker still advises avoiding caffeine in the afternoon.

• 12

  Sleeping pills carry real risk; CBT-I is first line.

  The FDA updated mortality warnings on sleeping pills. Dan Kripke's research found even three to 18 pills per year associated with statistically significant mortality increases. In 2016 the American College of Physicians said pills shouldn't be first line for insomnia; cognitive behavioural therapy for insomnia (CBT-I) should.