Circadian Variation
- Biological processes follow a roughly 24-hour pattern driven by the body’s internal clock.
- Common manifestations include the sleep–wake cycle, daily fluctuations in body temperature, metabolic rate and appetite, and time-of-day differences in cognitive performance.
- Environmental cues such as light and temperature influence these rhythms, and hormones (melatonin, cortisol, thyroxine, ghrelin) mediate many effects.
Definition
Section titled “Definition”Circadian variation refers to the natural changes in an individual’s physiological and behavioral processes that occur on a daily basis. These changes are regulated by the body’s internal clock and are influenced by environmental cues such as light and temperature.
Explanation
Section titled “Explanation”The body’s internal clock coordinates daily (circadian) fluctuations across multiple systems. Hormonal signals and environmental inputs shape when and how these changes appear. For example, hormones like melatonin and cortisol help time sleepiness and energy levels; thyroxine affects body temperature patterns; and ghrelin influences appetite timing. Together, these mechanisms align physiology and behavior with day–night cycles.
Examples
Section titled “Examples”Sleep–wake cycle
Section titled “Sleep–wake cycle”Most individuals experience increased fatigue and a desire to sleep at night and greater alertness during the day. This pattern is associated with the release of melatonin, which promotes sleep, and a decrease in cortisol, which helps regulate energy levels.
Body temperature
Section titled “Body temperature”Body temperature typically decreases during the night and increases during the day, reaching its peak in the late afternoon. This pattern is influenced by the hormone thyroxine, which helps regulate body temperature.
Metabolism and appetite
Section titled “Metabolism and appetite”Metabolism generally slows at night, reducing energy expenditure and increasing hunger. This effect is related to the release of ghrelin, which stimulates appetite.
Cognitive function
Section titled “Cognitive function”Performance on tasks requiring attention and memory tends to be better during the day, while tasks involving creativity and problem-solving tend to show better performance at night. These variations are influenced by hormones such as cortisol and melatonin affecting brain function.
Related terms
Section titled “Related terms”- Internal clock
- Environmental cues (light, temperature)
- Melatonin
- Cortisol
- Thyroxine
- Ghrelin
- Sleep–wake cycle