If you have a good sleep rhythm, you feel fitter and healthier.” This wisdom doesn’t come from nowhere. Sleep is an important tool for our body to recover, clean up and regenerate. But regularity and rhythm are also crucial and our body has many more processes that are subject to oscillation, which is essential for the functioning of our body. There are ultradian rhythms that last less than 24 hours and include, for example, the heartbeat. The sleep rhythm is one of the circadian rhythms and periods of more than 24 hours are referred to as infradian rhythms – this includes, for example, the menstrual cycle. In our series of articles on the Hallmarks of Health Let's take a closer look at this topic.
Rhythmic oscillations
Oscillations are regular vibrations that are omnipresent in our body. A noticeable example of this is rhythmically fluctuating hormone levels. But let's start on a small level - in our nerve cells. Perhaps you have already had an electroencephalogram (EEG)? This is a test that is used primarily in neurology to measure and display electrical activity in the brain. The display of brain activity looks very rhythmic and regular. The speed of the oscillation in the brain changes depending on the activity.
The speed of our heartbeat also changes depending on physical activity. The heartbeat is one of the ultradian oscillations and, as you can imagine, is vital, just like the oscillation of brain activity. A slightly longer ultradian rhythm is the cell cycle, i.e. the division of our cells. Our cells divide and renew themselves again and again to repair possible damage and keep the body's machinery running.
Infradian rhythms play a much greater role in the animal and plant world than in humans, for example in the flowering times of certain plants or the shedding of fur in mammals. An important infradian oscillation in humans is the menstrual cycle or the associated rhythm of the sex hormones.
Mechanism of the circadian clock
The best studied rhythm of the human body is the circadian rhythm, which lasts approximately 24 hours. The heart of this "clock" is the suprachiasmatic nucleus (SCN), a part of the brain in the hypothalamus that lies directly above the intersection of our optic nerves. Various genes in the SCN are expressed or inhibited in an interplay using light/dark information from the retina - the genes are therefore "active" or "inactive". These genes then activate or inhibit many other processes in our body, such as sleep, digestion, hormone balance and much more. More than half of the genes are subject to these circadian oscillations in at least one tissue or organ.
Stem cell regulation
As the central clock mechanism of the body, the circadian clock influences many processes that run rhythmically - for example, blood formation, the cycle of hair and skin formation, neurogenesis and bone formation. In these processes, tissue is made from stem Cells rebuilt. When the stem cells differentiate into specialized cells, there is always a certain risk of mutations and DNA damage due to increased cell division.
As we all know from sunburns and the resulting increased risk of skin cancer, sunlight damages our cells. Therefore, there is a mechanism under the influence of the circadian clock that causes differentiation (i.e. the formation of specialized cells) to occur primarily at night. This minimizes the risk of damage from sunlight.
Function of mitochondria
mitochondria – they are known as the “powerhouse of the cell” because they produce the energy for our body. Depending on how much energy is needed, mitochondria fuse or divide into several power plants. More mitochondria can generate more energy for the body. Over the course of the day, we need different amounts of energy, and therefore different numbers of mitochondria. It only makes sense that energy production is also controlled by our body's time control center. The number of mitochondria, or their division or fusion, is also regulated by the mechanisms of the circadian clock.
Microbiota
We now know that the intestinal flora (microbiota) has a major influence on our health. An unbalanced and disturbed microbiome (dysbiosis) promotes an imbalance in the body and can be the cause of various diseases. Researchers have discovered that the composition of the microbiome is also subject to daily fluctuations. Adapting this composition to other fluctuating processes in our body is therefore important so that all the gears can mesh correctly. Frequently changing meal times can have an effect on the intestinal flora and thus on the overall rhythm. Conversely, the body's rhythm has an influence on how well our digestion and microbiome can handle food.
In harmony with the oscillation
Whether it's sleep or our meal times: a constant rhythm in life and our activities significantly promotes the continuity of physiological processes and thus our health. It is therefore not surprising and nothing new that shift work, frequent changes between different time zones, jet lag and changing meal times throw our bodies off track and out of rhythm in different ways.
Sources
Literature:
López-Otín, Carlos, and Guido Kroemer. “Hallmarks of health.”Cell 184.1 (2021): 33-63. https://pubmed.ncbi.nlm.nih.gov/33340459/
Images:
The images were purchased under license from Shutterstock or Canva and are marked accordingly.
