What Circadian Rhythms Are
A Primer on the Body's Timekeeping System
Ben Harrison, Chief Innovation Officer & Chief Scientist, Korrus · June 2026
A circadian rhythm is an endogenous, body-wide timing system: self-sustaining cellular clocks in nearly every tissue, coordinated by a master pacemaker in the brain, set to the external day by environmental cues. This paper makes that picture available to a reader without a chronobiology background, and shows why it is the alignment of the system, not the mere presence of a rhythm, that underwrites normal sleep, alertness, hormone release, and metabolism.
Key insights
A circadian rhythm is generated inside the body and persists even without time cues from the environment.
The timing system runs throughout the body, coordinated by a master pacemaker, the suprachiasmatic nucleus (SCN), in the brain.
What matters for everyday function is whether the many internal clocks hold their normal phase relationships with each other and with the external day.
Sleep, cognition, metabolism, hormone release, and immune function are all shaped by the timing system; misalignment can degrade them.
What the paper covers
- 01What a circadian rhythm actually is
- 02The clock is in every cell
- 03The hierarchy: a master pacemaker for many local clocks
- 04Why an internal clock needs external time cues
- 05What an aligned system looks like
- 06Alignment is the most actionable everyday variable
- 07What disruption looks like, and what it costs
- 08Counterarguments and clarifications
Want the full argument, figures and references? Read the complete white paper.
Read the PDFPublished by Korrus, the photonics company behind OIO. General information about circadian biology, not medical advice.