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Circadian Rhythm

Reviewed by Psychology Today Staff

Circadian rhythms are the cycles that tell the body when to sleep, wake, and eat—the biological and psychological processes that oscillate in predictable patterns each day. This internal clock is influenced by external cues, like sunlight and temperature, which help determine whether one feels energized or exhausted at different times of the day.

What Is Circadian Rhythm?
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Circadian rhythms are governed by a master clock, a group of neurons called the suprachiasmatic nucleus, located in a region of the brain called the hypothalamus. This master clock translates cues from the environment into directives for the body. For example, receptors in the eyes detect darkness and pass that signal along to the suprachiasmatic nucleus, which then stimulates the production of melatonin, the hormone that causes sleepiness.

Why is circadian rhythm important?

Circadian rhythms have been critical throughout evolution, allowing animals to prepare for upcoming changes to their environment. Today, research is charting the harms of a disrupted circadian rhythm, such as sleep disorders, obesity, diabetes, depression, and bipolar disorder—not to mention difficulties concentrating and staying productive.

What happens when my circadian rhythm is out of whack?

Due to frequent travel and shift work, many people today experience disturbances to their circadian clock. These disruptions can lead to difficulty sleeping, difficulty staying awake during the day, or clinical insomnia. More rarely, individuals may develop circadian rhythm disorders such as Delayed Sleep Phase Syndrome or Advanced Sleep Phase Disorder.

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How to Get Better Sleep
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An individual's biological clock can be set earlier or later, but keeping cues that influence circadian rhythm steady can help everyone maintain their routine. Waking up and going to sleep at the same time each day—and exposing oneself to sunlight and darkness at those times—supports steady melatonin production. Avoiding screens in the evening is therefore an important change that can benefit those hoping for better sleep.

Sometimes these changes are outside of one's control, as in the case of travel. Jet lag occurs when the internal clock and external cues become misaligned, which can result in fatigue or irritability before the two forces realign.

How can I improve my circadian rhythm?

Most people can reset their body clock by keeping a regular schedule and exposing themselves to natural light in the morning. But if you have Delayed Sleep Phase Disorder, you may want to explore melatonin, chronotherapy, or bright light therapy. 

How can I protect my circadian rhythm from screen time?

Decrease the brightness of screens at all times, and keep screens out of the bedroom altogether. Increase your exposure to sunlight and nature, incorporate more exercise into your day, and maintain a regular routine. These tips and others can offset the chance that screens disrupt your circadian rhythms.

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