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slug: sleep-circadian
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# Sleep and Circadian Health

Sleep stages, sleep architecture, circadian-rhythm interventions, and chronotype-sensitive protocols. The single biggest healthspan lever the field still under-treats.

Start with [Sleep Architecture](sleep-architecture.md): the map of N1, N2, N3, REM, sleep cycles, fragmentation, and why total sleep time is necessary but incomplete. Then use [Circadian Light Hygiene](circadian-light-hygiene.md) for the bright-day, dim-evening timing signal that lets the night unfold. [Sleep Consistency](sleep-consistency.md) keeps that signal attached to a repeatable schedule, while [Caffeine Half-Life and Adenosine](caffeine-adenosine-cycle.md) separates stimulant kinetics from bedtime willpower. [Sleep Tracking Anxiety](sleep-tracking-anxiety.md) names the failure mode that appears when stage estimates become nightly verdicts.

Read straight through, or land on a specific entry and follow its outgoing links into the rest of the book.

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- [Next: Sleep Architecture](sleep-architecture.md)
- [Previous: Single-Biomarker Tunnel Vision](single-biomarker-tunnel.md)