What is the Circadian Rhythm (Part II)?

By Sheila Kun RN, BSN, MS, CPN, FCCP

Discovery of the Circadian Rhythm

A long time ago, people noticed humans, plants, and animals have daily cycles of hunger and sleep. The first known written record is from a 13th-century Chinese medical textbook. In the year 1729, a French scientist Jean-Jacques d’Ortous de Mairan recorded observations about circadian rhythm as he watched a plant “wake” and “sleep” over 24 hours, even when kept in darkness. It wasn’t until 1977 that the scientific community agreed on the term we use today and exactly what this meant. Joseph Takahashi first discovery gene coding for the circadian rhythm in 1994 by studying the DNA of mice.

The Wide Reach of the Circadian Rhythm

The circadian clock affects more than when we feel sleepy. So far, scientists have discovered 35 conditions it affects:

  Blood pressure is lowest at three am, during deep sleep, and highest when we wake up, meaning risks for heart attacks and stroke are highest between 8 am and midday.

  Asthma attacks are worse during daylight because the body creates a natural anti-inflammatory during night time.

  Cells grow and repair more quickly during daylight hours.

Research into circadian rhythms has led to a new field of medicine, chronotherapy; doctors use this knowledge to administer medicine at the times it will be most effective.

The Brain Controls the Circadian Cycle

A section of the brain called the hypothalamus controls the circadian rhythm of animals. At night the brain releases melatonin, which makes you feel tired. Although the circadian rhythm is built-in and can work without exposure to daylight, it can be altered by outside conditions. If you have ever experienced jet-lag, you know what it feels like when the circadian rhythm tries to acclimatize to new conditions. Travel affects the circadian rhythm because darkness encourages the brain to release the sleep hormone melatonin, while daylight releases cortisol to wake the brain.

Your homework from the Care Ministry this week: explain to a friend what Circadian rhythm is.

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