What is circadian rhythm?

Everyone has a biological, internal, clock called a circadian rhythm (yes, even men can say they have a biological clock). It’s the patterns of repeated activity associated with the environmental cycles of day and night—rhythms that repeat roughly every twenty-four hours. Examples include the sleep-wake cycle, the ebb and flow of hormones, the rise and fall of body temperature, and other subtle rhythms that mesh with the twenty-four-hour solar day. When our rhythm is not in sync with the twenty-four hour solar day, you will feel (and probably look) it. Anyone who has traveled across time zones and felt off-kilter for a few days can understand this.

From The Mind-Beauty Connection: 9 Days to Less Stress, Gorgeous Skin, and a Whole New You by Amy Wechsler.

Circadian rhythms -- our own internal biological "clock" -- govern our sleep-wake cycle and several other daily rhythms of the body. It's a complicated and finely tuned system of hormonal and bio-chemical reactions that helps us live in rhythm with the 24-hour day, waking in the morning and remaining alert throughout the daylight hours, then sleeping and rejuvenating at night. A key component of our circadian system is the timed release of the "sleep hormone" melatonin. When our circadian clocks are functioning properly, melatonin levels rise during the nighttime hours, promoting sleep. Melatonin levels are suppressed during daytime hours, as other hormones such as cortisol rise, helping to provide the alertness and energy we need to navigate our waking day.
Marjorie Nolan Cohn
Nutrition & Dietetics

Circadian rhythms are physical, mental and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism’s environment. They are found in most living things, including animals, plants and many tiny microbes. The study of circadian rhythms is called chronobiology. They are produced by natural factors within the body, but they are also affected by signals from the environment. Light is the main cue influencing circadian rhythms, turning on or turning off genes that control an organism’s internal clocks.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.