Rock Around the Clock by Bill Haley & His Comets became a worldwide hit in the 1960s. Around the same time, science coined the term circadian rhythm. Coincidence? Most likely – but there is one commonality: It’s all about clocks.
While humans have been measuring time with sundials for millennia, the history of biological timekeepers goes back even further. Our body also follows such an internal clock, the circadian rhythm: A complex interplay of genes, proteins and hormones helps to synchronize numerous biological processes in a rhythm of approximately 24 hours. How this internal clock works, what influences it, and what happens when it gets out of sync, you will learn in this article.
What does circadian mean?
The adjective "circadian" is derived from Latin: circa means "approximately," which stands for "day."A circadian rhythm thus describes a biological rhythm with a period duration of approximately 24 hours. Throughout the day, various conditions of our environment change – primarily light and darkness, but also temperature and the availability of food. For living beings, it can be advantageous to time their biological processes to these regularly recurring changes.
In this context, we do not possess just a single internal clock. Practically every cell in our body has its own molecular timekeepers that need to be coordinated. A central role in this synchronization is played by the overarching internal clock in the brain. It helps to provide numerous biological processes with a temporal framework – after all, not all processes in the body need to be on the agenda at the same time. Similar to how a large broadcasting station does not air its blockbusters on all channels simultaneously.
In addition to the circadian rhythm, there are other biological rhythms that follow different temporal patterns. Infradian rhythms have a period duration of more than 24 hours. Ultradian rhythms, on the other hand, repeat several times within a day. This includes various sleep phases as well as certain rhythmic processes such as breathing and heartbeat.
Jetlag: When the circadian rhythm is out of sync
What some people find soothing drives others crazy: the periodic "tick-tock" of an analog clock. Fortunately, this is not an issue with our biological timekeeper – we do not hear our internal clock ticking. We are usually unaware of the complex regulatory processes happening in the background. Until our internal clock suddenly no longer aligns with external time.
This can happen during long-haul flights across multiple time zones.Our internal clock is initially still set to the usual daily rhythm and must first adjust to the new local time. This temporary discrepancy between circadian rhythm and new time zone is known to us as jet lag . Typical complaints can include sleep disturbances, fatigue, reduced performance, or general malaise . The direction of travel also plays a role: traveling east is often tolerated worse than traveling west.
To facilitate the adjustment to the new time zone, some general measures can be helpful:
- try to follow the daily rhythm at the destination as closely as possible
- expose yourself to natural daylight intentionally
- pay attention to getting enough sleep
Because light is one of the most important external time cues for our circadian rhythm.Until our internal clock is back in the right rhythm, it needs some time.
Did you know?
Melatonin helps to alleviate the subjective jet lag sensation .
The positive effect occurs when at least 0.5 mg of melatonin is taken on the first travel day shortly before going to sleep and on the first days after arrival at the destination.
The melatonin tablets from MOLEQLAR are divisible for two dosage levels: 1 mg or 0.5 mg of melatonin.
The Aschoff Rule: How light influences the internal clock
What happens to the internal clock when an important external time cue like light is missing or changes permanently? This question was addressed by behavioral physiologist Jürgen Aschoff in his studies on circadian rhythms.
It was shown that: In diurnal animals, the period duration of the internal clock is shortened under artificial constant light, while it is prolonged in constant darkness. In nocturnal animals, the situation is reversed. This relationship between light conditions and circadian rhythm is known as the Aschoff rule.
Lights off, internal clock on?
Sleep masks reduce the light entering the eyes and can thus create a darker sleep environment. Since light is an important Zeitgeber for the circadian rhythm, the light environment also plays a significant role in our sleep-wake rhythm.
What consequences can a disturbed circadian rhythm have?
Our circadian rhythm is fundamentally generated by endogenous processes but can be adjusted to the 24-hour day by external signals.Such signals are referred to as Zeitgeber, the process itself as synchronization. The most important Zeitgeber for our internal clock is light. Other external factors can also contribute to temporal coordination.
Light stimuli are perceived through specialized cells in the retina and transmitted to the suprachiasmatic nucleus (SCN) in the hypothalamus. It is considered the central control center of the internal clock and coordinates numerous time-dependent processes in the body as well as other peripheral clocks. Also, melatonin, which is primarily produced in the pineal gland, plays an important role in regulating the sleep-wake rhythm.
At the molecular level, the circadian rhythm is controlled by several clock genes and the proteins they produce. This results in complex feedback loops of transcription and translation: Genetic information is first transcribed into RNA and then translated into proteins.These, in turn, influence the activity of the involved genes – a recurring regulatory mechanism that spans approximately 24 hours. Sounds complicated? It is. However, for understanding our internal clock, one thing is primarily important at this point: It arises from a finely tuned interplay of molecular processes.
Why is the circadian rhythm so important for us?
Our circadian rhythm is not only relevant for our daily lives but has even been worthy of a Nobel Prize since 2017. At that time, Jeffrey C. Hall, Michael Rosbash, and Michael W. Young received the Nobel Prize in Physiology or Medicine for their discoveries of the molecular mechanisms that control the circadian rhythm. Their fundamental findings were gained by the researchers through studies on fruit flies.
But what happens when our internal clock goes out of sync in the long term? Disruptions of the circadian rhythm are associated in research with various health changes and diseases. Among other things, connections with metabolic disorders, depression, and other mental illnesses as well as certain cancers are being investigated. It is important to note: An observed correlation does not automatically mean that a disrupted circadian rhythm causes the respective disease. The underlying mechanisms and interactions are the subject of current research.
Our internal clock coordinates numerous biological processes and is oriented, among other things, by external time cues such as light.If this finely tuned system gets out of sync, it can manifest, for example, in jet lag – long-term disruptions of the circadian rhythm are also being intensively studied for their health significance.
Rock Around the Clock is therefore better left as music in our ears – while our body follows its own rhythm.
