Research
Hormonal
The intrinsic human circadian period averages 24.1 to 24.2 hours, not 25 hours as previously estimated in older studies.
Your body clock is naturally slightly longer than 24 hours. To stay aligned with the day, you need to manage light exposure, especially in the evening, to prevent your clock from drifting later.
StrongRefutesVERY_HIGH confidence
reevaluation of the circadian period under these controlled conditions has revealed that the intrinsic circadian period in sighted humans averages between 24.1 and 24.2 hours... and that the intrinsic period remains stable with age in healthy adults.
Why this rating
Based on forced desynchrony protocols which control for light exposure.
Source
Sleep and Circadian Rhythms in Humans
Charles A. Czeisler et al. · Cold Spring Harbor Symposia on Quantitative Biology · 2007
DOI 10.1101/sqb.2007.72.064
narrative_reviewCited 403×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
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