What is the circadian rhythm?

One of the few things that is really certain is the realization that a day follows a night and vice versa. All living beings have to adapt to this 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 'extending over a period of 24 hours' [1]. The 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 in individual cells. In 2017, three US 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 worth taking a closer look at your circadian rhythm, as this rhythm functions relatively independently of external factors. All living beings need such a rhythm in order to coordinate the periodic functions of the body - eating, sleeping, reproduction. People who lived in bunkers independent of daylight or clocks also settled into a rhythm of around 25 hours after a while. [2]

Before we describe how this rhythm is often disturbed 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, starting with the perception of light via photoreceptors in the outer granular layer of the retina. These photoreceptors report the perception of light to the suprachiasmatic nucleus. This suprachiasmatic nucleus can be regarded as the command center for the circadian rhythm and controls some essential bodily functions:

Body temperature
hormone secretion
Blood pressure fluctuations
heart rate
Urine production [3]

As many essential bodily functions are controlled by this rhythm, it is obvious that a disruption could also have significant health consequences.

Health consequences of a mismatch

Life in today's societies places particular demands on this internal clock: the typical jet lag that occurs when flying to a different time zone arises because the body has to adjust to a different day-night rhythm at short notice and ultimately reacts with exhaustion. [3] It is therefore not good if the body's ability to adapt is overstretched. Many of modern people's lifestyles are not in harmony with their internal rhythm, which is constantly disrupted and the body has to constantly readjust.

The health consequences of a misalignment of the circadian rhythm can be seen, for example, in the high incidence of heart attacks in the early hours of the morning. [3] As many people nowadays reduce their sleep more or less voluntarily and are on their feet more or less around the clock, their own sleeping habits respect the natural day-night rhythm less and less and chronic cardiovascular diseases are on the increase.

If you harmonize your lifestyle habits with your circadian rhythm, the positive results for your health are obvious, as the risk of many diseases of civilization decreases: Cardiovascular disease, diabetes, cancer and many mental illnesses decrease when you avoid these stresses on the body. [4]

What disorders of the circadian rhythm are there?

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

Jet lag: Circadian rhythm disorders have already been mentioned. A disruption of the internal clock on intercontinental flights is typical. Until the body has adjusted to the new day-night rhythm, the body reacts with sleep disturbances and exhaustion.
Shift work disrupts your own day-night rhythm. After a night's work, sleep is less restful and often much shorter. It is obvious why this is the case, because the sleep times are the opposite of the natural sleep times.
Advanced sleep phase disorder (ASPD): ASPD occurs when a person feels tired and falls asleep in the early evening hours, but suffers from insomnia in the early morning hours. Even if these people want to stay awake in the late evening hours, they cannot.
Sleep phase syndrome or delayed sleep phase syndrome affects so-called night owls: Anyone who falls asleep relatively late but sleeps relatively soundly through the night suffers from this sleep disorder.
Non-24: This circadian rhythm disorder mainly occurs in people with complete blindness, as they have no perception of light and the coordination of the inner day with the outer day can lead to delays if the inner day is longer or shorter than the outer day. Without light perception, the body has no way of adapting to external conditions and reacts with insomnia and exhaustion during the day[5].
Irregular sleep-wake rhythm disorder: This sleep disorder occurs in mental illnesses, e.g. dementia, and is characterized by the irregular distribution of several sleep phases over a 24-hour period.

The circadian rhythm disorders can therefore be manifold, e.g. due to physiological impairment or personal habits or working conditions, which can sometimes be difficult to change, for example as a care worker, there is no getting around night shifts. Here are some tips on how you can live in harmony with your circadian rhythm.

Living in harmony with the circadian rhythm

Even if you can't influence all the factors according to which your circadian rhythm adjusts, there are some tips that can help you to live more in tune with your internal clock.

Get enough sun: It is particularly helpful to get natural light in the morning hours. So plan some time in the sun!
Sleep at set times: If you go to bed and get up at widely varying times, you make it more difficult for your body to settle into a fixed circadian rhythm. A fixed sleep routine requires less adjustment from the body.
Reduce your caffeine intake: Caffeine stimulates the body and can therefore disrupt the body's rest-activity phases.
Everyone reacts differently to stimulants, but you should avoid coffee, tea or cola after lunchtime if you have trouble sleeping.
Reduce the light in your bedroom: Even the presence of a small light can reduce your rest. It is therefore worth darkening your home in the evening hours before going to sleep and avoiding electronic devices, especially in the bedroom.
Take short rest periods in the early afternoon. If you have problems getting tired early in the evening, it can be helpful to introduce a short sleep phase in the early afternoon.

These are a few tips on how to get your sleep used to your internal clock more quickly. If you experience sleep problems over a longer period of time, it is worth asking your GP 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 circadian 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 cyclical sleep-wake rhythm disorder in completely blind people non-24.de
[6] Circadian Sleep-Wake Rhythm Disorders - Encyclopedia of Sleep Medicine - eMedpedia springermedicine.com