A circadian rhythm, or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism and responds to the environment. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in animals, plants, fungi and cyanobacteria. The term circadian comes from the Latin circa, meaning "approximately", and dies, meaning "day". Processes with 24-hour cycles are more generally called diurnal rhythms; diurnal rhythms should not be called circadian rhythms unless they can be confirmed as endogenous, and not environmental. Although circadian rhythms are endogenous, they are adjusted to the local environment by external cues called zeitgebers, which include light, temperature and redox cycles. In clinical settings, an abnormal circadian rhythm in humans is known as a circadian rhythm sleep disorder.

Read more in the app

Mimicking an enigmatic property of circadian rhythms through an artificial chemical clock

Circadian clock controls sunflower blooms, optimizing for pollinators

Pancreatic cancer linked to disrupted circadian clocks in cells

Cells' circadian clock keeps ticking over even during starvation

New study on the circadian clock of the fruit fly

5 Ways To Regulate Your Circadian Rhythm

What Happens if Your Body Clock Is Out of Whack? Disrupted Circadian Rhythms Linked to Cancer

What happens if your circadian rhythms are out of whack?

The surprising link between circadian disruption and cancer may have to do with temperature

New clues into how the circadian clock helps the brain recover after injury

Diabetes: When circadian lipid rhythms go wrong

Circadian rhythm disruption found to be common among mental health disorders

Research Reveals the Circadian Clock Influences Cell Growth, Metabolism and Cancer Progression

New research reveals the circadian clock influences cell growth, metabolism and tumor progression

Circadian clocks play a key role in fat cell growth

Circadian rhythm in cognitive and physical health

Researchers decode retinal circuits for circadian rhythm, pupillary light response

Prostate Cancer Hijacks Tumor Cells’ Circadian Rhythm To Evade Hormone Therapy

Chronobiologists identify key circadian clock mechanism in cyanobacteria

What Drives the Circadian Rhythms: Unlocking Complex Workings of the Biological Clock