Circadian rhythm

circadian adj. Designating physiological activity which occurs approximately every twenty-four hours, or the rhythm of such activity. 1959 F. HALBERG in Zeitschr. f. Vitamin- Hormon- & Fermentforschung X. 235 ‘Circadian’ might be applied to all ‘24 hour’ rhythms, whether or not their periods..are different from 24 hours, longer or shorter, by a few minutes or hours. 1963 J. LEITH tr. Fraisse's Psychol. of Time i. 20 Circadian rhythms in animals, unlike plants, are almost always acquired. 1964 Perceptual & Motor Skills XIX. 211 (heading) Circadian activity and noise comparisons of two confined groups with or without reference to clock time. Ibid., Both measures revealed highly positive correlations between the mean circadian patterns of the two groups. [f. L. circa about + dies day + -AN.]

The circadian rhythm is the 24-hour cycle by which we live our lives, usually driven - from our perspective - by the need to sleep for approximately 8 hours each day. But it is this rhythm of biochemical, physiological, or behavioural processes that drives our sleep cycle and not vice versa. Circadian rhythm is endogenous, but can be adjusted to environmental cues like daylight. Here are some of the things that follow a circadian rhythm:

• sleep
• core body temperature
• thought processing
• hormone production
• cell regeneration
• immune response
• blood pressure
• blood viscosity
• salivation
• tooth growth

Following the circadian rhythm can increase the effectiveness of medical treatment, such as chemotherapy. Total blindness may affect the circadian rhythm. Disturbances to the circadian rhythm can cause sleep disorders, seasonal affective disorder, jet lag, and bipolar disorder. New research on circadian rhythm in humans and other living organisms is being conducted all the time and the findings are reported in the Journal of Circadian Rhythms and other biological and physiological journals. Scientists have now identified a genetic component of circadian rhythm. Most understandable to us laypeople is the determination of whether we are morning people or night owls.