Why we sleep poorly, biologically
Sleep is not a switch we flip. It is a hormonal cascade that starts in the late afternoon, as soon as light dims. The begins to release .
This cascade is fragile. Blue light at 10pm (screen, cold LED ceiling light) delays melatonin release by tens of minutes. A high evening , typical of chronic stress or late coffee, does the same. Cortisol and melatonin are sworn enemies.
, the kind that physically repairs us, clusters in the first half of the night. dominates the second half. Going to bed at 1am mostly costs deep sleep.
Waking at 4am unable to fall back asleep often signals a premature cortisol spike. Sleeping well is about respecting internal signals: light, temperature, cortisol, .
HPA axis, adenosine, sleep architecture
The HPA axis, conductor
The governs cortisol. In health: morning peak, evening trough. Chronic stress flips it: flat in the morning, wired at night. Restoring sleep starts with this axis: slow breathing, morning daylight, fewer stimulants after 2pm.
Adenosine, your sleep debt
Every waking hour the brain builds . blocks its receptors: it masks fatigue, doesn't erase it. When caffeine wears off, the built-up adenosine hits all at once. Hence the 5pm crash.
90-minute cycles
A night runs through 4 to 6 . Each cycle moves through light, deep, REM. Deep dominates early, REM late. Waking mid-cycle feels groggy. Waking at cycle end feels fresh, even with fewer hours.
Plants and micronutrition
, , , , : these levers don't create sleep, they remove brakes.
Quiz: the 5 sleep myths
Melatonin, caffeine, alcohol, chronotype: watch out, there are traps
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This tool is not medical advice. It does not provide dosing, personal protocols, or replace a healthcare professional. For any clinical question, see our terms.
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