The sleep-duration curve is U-shaped. Your night is still noisy.

Population studies often show higher risk at short and long sleep durations. That does not make one isolated night a diagnosis.

Topic: sleep duration Study type: systematic review and meta-analysis Published: 2019

Study

A meta-analysis published in the Journal of the American Heart Association reviewed sleep duration and mortality literature, describing a U-shaped relationship around a lower risk middle range.

Reference: Systematic review and meta-analysis in Journal of the American Heart Association. DOI: 10.1161/JAHA.119.014587.

What Was Observed

Both short and long reported sleep durations were associated with higher all-cause mortality risk in the reviewed literature. The useful observation is the curve shape, not a precise personal threshold.

What It Does Not Prove

Long sleep can reflect recovery, illness, measurement error, schedule debt, or underlying conditions. Short sleep can mean restriction, fragmented sleep, shift work, stress, or simply one unusual night.

Signal vs Noise

Single-night duration is noisy. Seven-day consistency, wake time stability, sleep timing, subjective recovery, alcohol, late meals, stress, and exercise provide better context.

How Entropy Would Track It

Sleep duration and wake time consistency.
Late meals, alcohol, stress, and exercise on the same day.
Subjective recovery, not only device score.
Weekly trend before single-night judgment.

Discussion Prompt

For a 7-day ledger, which sleep signal would you trust more: duration, timing consistency, subjective recovery, or device score?