What is the circadian rhythm?

Among the few things that are really certain is the understanding that a night is followed by a day and vice versa. All living beings have to adjust to this precept, because the physiological processes in the body have to be coordinated with the day-night rhythm, whether in a mimosa or a modern human being. It is worth knowing this rhythm. If you live in harmony with your health, you can improve your health on the spot. We explain why.

In a nutshell-the circadian rhythm

The circadian rhythm

The word circadian is derived from the Latin phrase 'circa diem' and means as much as extending over a period of 24 hours [1]. Circadian rhythm describes an internal rhythm that can be understood as an internal clock. The best known circadian rhythm is the wake-sleep rhythm. This large internal clock can be detected down to individual cells. In 2017, three U.S. researchers were awarded the Nobel Prize in Medicine and Physiology for deciphering this rhythm using molecular mechanisms. [2]

It is helpful to know your circadian rhythm. If you live in harmony with it, you sleep restfully. If your habits are not in harmony with this rhythm, the result can be less restful sleep or even insomnia. It is worthwhile to deal with one's circadian rhythm, because this rhythm functions relatively independently of external factors. All living beings need such a rhythm to coordinate the periodic functions of the body - eating, sleeping, reproduction. Humans who lived in bunkers independent of daylight or clocks also settled after some time to a rhythm of about 25 hours. [2]

Before describing how this rhythm is often disrupted in contemporary society, we briefly explain what happens in the body when it adapts to its environment.

How the body adapts to external conditions

The body must continuously adapt to its environment, this begins via light perception via photoreceptors in the outer granular layer of the retina. These photoreceptors report light perception to the nucleus suprachiasmaticus. This nucleus suprachiasmaticus can be considered the command center for the circadian rhythm and controls some essential body functions:

Body temperature
Hormone secretion
Blood pressure fluctuations
Heart rate
Urine production [3]

Since many essential bodily functions are controlled in this rhythm, it is obvious that a disturbance could also have significant health consequences.

Health consequences of mismatch

Life in contemporary societies now places special demands on this inner clock: the typical jet lag that results from flying to another time zone occurs because the body has to adjust to a different day-night rhythm for a short time and eventually reacts to this with exhaustion. [3] So it's not good if the body's ability to adapt is overly stressed. Many habits of modern people are now not in harmony with their inner rhythm, this is continuously disturbed and the body has to adapt again and again.

The health consequences of a maladjustment of the circadian rhythm can be seen, for example, in the accumulation of heart attacks in the early morning hours. [3] Since sleep is more or less voluntarily reduced in many people nowadays and one is on one's feet more or less around the clock, one's own sleep habits respect the natural day-night rhythm less and less and chronic cardiovascular diseases accumulate.

When you align your lifestyle habits with your circadian rhythm, the positive results for your health are obvious, because the risk of many diseases of civilization decreases: Cardiovascular disease, diabetes, cancer and many mental illnesses decreases when one avoids these stresses on the body. [4]

What are the circadian rhythm disorders?

A number of circadian rhythm disorders can be identified, the most common being: [6]

Jet lag: The disturbances of the circadian rhythm have already been mentioned. A disturbance of the internal clock on intercontinental flights is typical. Until one's own body has become accustomed to the new day-night rhythm, the body reacts with sleep disturbances and exhaustion.
Shift work upsets one's day-night rhythm. After working a night is less restful and often much shorter. Why this is so is obvious, because the sleep times are opposite to the natural sleep times.
Advanced sleep phase disorder (ASPD): ASPD occurs when you feel tired and fall asleep in the early evening hours, but suffer from insomnia in the early morning hours. Even though these people want to stay awake in the late evening hours, they cannot.
Sleep phase syndrome or delayed sleep phase syndrome affects the so-called night owls: Those who fall asleep relatively late, but sleep relatively quietly through the night, suffer from this sleep disorder.
Non-24: This circadian rhythm disorder occurs mainly in people with complete blindness, because they have no light perception and the coordination of the inner day with the outer day may cause delays if the inner day is longer or shorter than the outer day. Without light perception, the body has no way to adapt to external conditions and responds with insomnia and daytime exhaustion.[5]
Irregular sleep-wake rhythm disorder: This sleep disorder occurs in mental illnesses, e.g. dementia, and is characterized by the fact that several sleep phases can be detected irregularly distributed over a 24-hour period.

The disturbances of the circadian rhythm can therefore be manifold, e.g. due to physiological impairment or personal habits or the working conditions, which you can sometimes do little about, for example as a nurse, you cannot avoid night shifts. In the following, we give some tips on how you can live in harmony with your circadian rhythm.

Living in harmony with the circadian rhythm

Even though you cannot influence all the factors according to which the circadian rhythm adjusts, there are some tips that can help you live better in harmony with your internal clock.

Get enough sun: Especially in the morning hours it is helpful to get natural light. Therefore, plan time in the sun!
Sleep at fixed times: If you go to bed and get up at widely varying times, you make it harder for your body to settle into a fixed circadian rhythm. A fixed routine for sleeping requires less adaptation from the body.
Reduce your caffeine intake: Caffeine stimulates the body and can therefore upset the body's rest-activity phases.
Everyone reacts differently to stimulating substances, but you should avoid coffee, tea or cola after lunchtime if you have sleep problems.
Reduce the light in the bedroom: Even the presence of a small light can reduce your rest. Therefore, it is worthwhile to darken your home in the evening hours before sleep and to do without electronic devices, especially in the bedroom.
Take short rest periods in the early afternoon. If you have trouble getting tired early in the evening, it can be helpful to take a short sleep period in the early afternoon.

These are a few tips on how to get your sleep used to your body clock more quickly. If you experience sleep problems over a longer period of time, it is worth asking your family doctor for advice, as further examinations may be necessary to clarify your sleep problems.

Sources:

[1] Duden | circadian | spelling, meaning, definition, origin duden.de
[2] Nobel Prizes 2017: Nobel Prize in Medicine for the internal clock - Spektrum der Wissenschaft spektrum.de
[3] Circadian rhythm - DocCheck Flexikon flexikon.doccheck.com
[4] The circadian rhythm determines health hogrefe.com
[5] Information platform on the cyclic sleep-wake rhythm disorder in totally blind people non-24.de.
[6] Circadian sleep-wake rhythm disorders - Encyclopedia of sleep medicine - eMedpedia springermedizin.de.