circadian

adj

1. (not-comparable)Of, relating to, or showing rhythmic behaviour with a period of approximately 24 hours; especially of a biological process.

   “The circadian clock is involved in the regulation of the diurnal sleep-wake cycle, […].”

   “To summarize, the circadian system, particularly the SCN, controls the circadian pattern of melatonin release in mammals.”

   “The most obvious circadian rhythm is the daily cycle of sleep and activity.”

   “Circadian clocks developed early in evolution in single-celled organisms, before the animal and plant kingdom split from one another. The original clocks probably functioned to protect the cells from damage induced by high UV radiation.”

   “In addition, the truck driver’s schedule involved sleeping at irregular times, including times when the body’s circadian rhythms are geared toward being awake. He was also awake at times when his circadian rhythms were geared toward being asleep. The time of the crash, about 1:36 a.m., is when sleepiness tends to be greater and performance capabilities are lower.”