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Diurnal Variation

Meaning

Diurnal Variation, in endocrinology, describes the predictable, rhythmic fluctuation in the concentration of a hormone or other physiological parameter that occurs over a 24-hour period, intrinsically linked to the sleep-wake cycle and light exposure. This biological rhythm is a manifestation of the body’s internal circadian clock, which anticipates and adapts the internal environment to the external day-night cycle. Cortisol, Melatonin, and Growth Hormone are among the most clinically significant hormones exhibiting this pronounced cyclical pattern.