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DID YOU KNOW that we have an Internal Clock?

By: Samantha Palacios, Winthrop Undergraduate Student

What are Circadian Rhythms?

Have you ever wondered why we get sleepy when the sun goes down? The answer lies in the definition of the circadian rhythm. The term "circadian" comes from the Latin "circa," which means around, and "diem," which means day as a whole, "around the day." This happens in 24 hours and is directed by light and darkness. So the circadian rhythm is an internal clock that regulates metabolic, hormonal, physical, and behavioral functions influenced by external factors. This interplay of light and dark causes the circadian rhythm to promote the sleep cycle.

How does Circadian Rhythm affect the organism?

The circadian rhythm, also known as the "control center," is located in the hypothalamus, where many functions are regulated. For this reason, the circadian rhythm is of utmost importance to maintain the proper functioning of the systems of the human body.

  • When the sun goes down, our body increases the secretion of Melatonin, a hormone that promotes sleep and keeps sending signals that keep us asleep throughout the night.

  • The circadian rhythm can also alter metabolism, body weight, and digestion.

  • The circadian rhythm also influences mental health, and its malfunction can result in psychiatric and neurodegenerative diseases. (depression, bipolarity, dementia, schizophrenia)

  • The immune system can also be affected by a malfunction of the circadian rhythm as it influences the DNA repair process, which helps prevent cancer.

Circadian Rhythm and Nutrition

  • Dietary intake can impact the circadian rhythm. Nutrients can often modulate the expression of certain genes, which can alter food behavior in the hypothalamus. Eating frequency can upset digestion and disrupt the circadian rhythm and normal bowel functions. The circadian rhythm occurs at the central level and in every cell in the body. Each organ has its clock. Eating food shortly before bedtime can cause changes or alterations in our sleep cycle. The intestinal function generally happens during the day as it absorbs nutrients better since the digestive system lowers its activity at night.

  • On the other hand, we have two hormones that regulate the cycles of hunger and satiety; these are leptin and ghrelin, which are closely related to the circadian rhythm and sleep. Sleep disturbances can result in decreased leptin levels, which is the hormone responsible for satiety, and lead to overweight or obesity. The ghrelin hormone is also affected when we do not sleep well, and this alteration causes the person's hunger to increase. The imbalance of these two hormones can result in overweight or obesity in people. In a study, it was found that people who work nights have more obesity problems as a result of lack of sleep and nutrition.

What can disrupt Circadian Rhythm?

  • When we travel to countries like Europe, we may suffer from Jet Lag, a disorder that can be modified quickly as an adaptation to the new schedules.

  • The work schedule can also disrupt the circadian rhythm.

  • Sleep disorders can be caused by genetics, underlying physical conditions, and a person's behavior.

Recommendations for a Healthy Circadian Rhythm

  • Get daily sunlight to have a healthy and strong circadian rhythm

  • Have a sleep routine

  • Being physically active daily will help you fall asleep more easily

  • Avoid caffeine or stimulants. (this varies from person to person)

  • At night avoid exposure to artificial light

Let’s work on creating good sleep and eating habits to maintain a balance in our circadian rhythm as it regulates and assists each cell in our body with the central and peripheral clock!


“What Is Circadian Rhythm?” Sleep Foundation, 25 Sept. 2020, Accessed 14 June 2023.

National Institute of General Medical Sciences. “Circadian Rhythms.”, 4 May 2022,

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