Tagesrhythmen

Tagesrhythmen describe the regular daily cycles observed in biological systems. They correspond to roughly 24 hours and are sustained by endogenous circadian clocks that are synchronized by environmental cues, or zeitgebers, such as light-dark cycles.

In humans, the essential Tagesrhythmen include the sleep–wake cycle, fluctuations in core body temperature, hormone release (such as cortisol and melatonin), and variations in alertness and cognitive performance. Light exposure is the dominant zeitgeber, but temperature, feeding schedules, and social cues also shape the rhythm. At the molecular level, a network of clock genes in the brain and in peripheral tissues generates these rhythms and coordinates physiological processes across the body.

The concept applies broadly: many plants exhibit diurnal patterns such as stomatal opening and leaf movement; animals adjust activity and feeding to the time of day; metabolic processes in tissues follow daily gene-expression cycles. These rhythms help optimize energy use, metabolism, and behavior in line with the environment.

Disruption of Tagesrhythmen, for example through shift work or rapid time-zone changes, can contribute to sleep disorders, metabolic disturbances, and mood problems. Chronobiology seeks to align daily activities and medical treatments with the body's rhythms, an approach known as chronotherapy or chrononutrition.

Researchers measure Tagesrhythmen with methods such as actigraphy, monitoring melatonin onset, core body temperature, and hormone profiles to determine the phase and amplitude of rhythms. Etymologically, Tagesrhythmen combines Tages (day) with rhythms, and the term is widely used in German-language chronobiology to refer to diurnal cycles, closely related to the broader concept of circadian rhythms.