Modern / Health Science · 2017
Why We Sleep
Matthew Walker
Sleep sits under hormones, mood, skin, memory and grit. Short sleep is not stamina.
What sleep does
Walker's survey of the research shows sleep is not downtime: it consolidates memory, regulates appetite hormones, clears metabolic waste from the brain, tunes emotional reactivity and maintains immune function.
NREM and REM
Deep NREM, weighted to the first half of the night, does physical repair and memory transfer. REM, weighted to the last hours, handles emotional processing and creative recombination. Cutting sleep short at either end removes a different faculty.
The cost of six hours
Repeated short sleep produces measurable deficits in attention, glucose regulation, immune response and mood — and, crucially, subjective adaptation. You stop noticing the impairment while it continues.
Alcohol, caffeine and light
Caffeine's half-life keeps a mid-afternoon coffee active at bedtime. Alcohol sedates and then fragments REM. Evening light delays melatonin release. These three are the most common and most fixable causes of poor sleep.
The practical protocol
Fixed wake time, cool dark room, no caffeine after early afternoon, no alcohol as a sleep aid, morning daylight. Regularity matters more than duration on any single night.
What to take from it
Fix wake time first. Everything else in the routine hangs off that anchor.
Lines to keep
- “You stop noticing the impairment while it continues.”
- “Regularity beats any single long night.”
- “Alcohol sedates; it does not put you to sleep.”
Practice
- · Set one wake time and hold it for fourteen days, weekends included.
- · Move your last caffeine to before 1pm.