The circadian rhythm is a fundamental component of life on Earth, regulating the biological cycles of many organisms, including humans. This internal biological rhythm of approximately 24 hours is crucial to maintain optimal physiological balance. But how does it work? And what is its impact on overall health?
What is circadian rhythm?
The term "circadian" comes from the Latin "circa diem", meaning "about a day", which reflects the cyclical nature of this biological phenomenon. Every living thing, from simple single-celled organisms to complex mammals like humans, is affected by this rhythm. It is primarily regulated by an internal biological clock located in the brain, specifically in a region called the suprachiasmatic nucleus (SCN) of the hypothalamus.
The circadian rhythm is influenced by external environmental factors such as daylight, temperature and dietary habits. Light, in particular, plays a crucial role in synchronizing our internal clock with the day-night cycle of the environment. Light receptors located in the retina send signals to the SCN, which in turn regulates the secretion of various hormones and neurotransmitters, thereby influencing our physiological and behavioral functions.
How does the circadian rhythm work?
At the heart of how the circadian rhythm works is a complex biochemical feedback loop involving multiple genes and proteins. So-called “clock” genes are activated or deactivated at specific times of the day , which triggers the production of different proteins regulating the biological rhythm.
A key protein in this feedback loop is period protein (PER), which accumulates in cells over time and inhibits the activity of clock genes. When PER levels decrease, clock genes are activated again, resulting in the production of new PER proteins, and so on. This process takes place continuously over approximately 24 hours, ensuring that the circadian rhythm is maintained.
Although the internal clock naturally tends to oscillate between 11:30 p.m. and 24:30 p.m., it is constantly resynchronized to a 24-hour cycle by external stimuli . This rhythm can, however, be disrupted by factors such as time zone changes, irregular sleep schedules, night work and other environmental disruptions.
Impact on health
A regular circadian rhythm is essential for maintaining health and well-being , as demonstrated by various studies which have highlighted the harmful effects of disruptions to this rhythm on several aspects of health, including sleep, cognition, metabolism and the risk of chronic diseases.
Virtually all bodily functions , including those of the cardiovascular system, immune system, body temperature, blood pressure, hormone production, and heart rate, are influenced by the circadian rhythm.
The sleep
The circadian rhythm plays a crucial role in regulating sleep. It controls sleep-wake cycles by influencing the secretion of melatonin , a hormone that promotes sleep. A disrupted circadian rhythm can therefore lead to sleep disorders such as insomnia or excessive daytime sleepiness.
The metabolism
Studies have also shown that the circadian rhythm influences body metabolism, including the regulation of blood sugar, lipid metabolism, and appetite . Circadian rhythm disruptions may contribute to the development of obesity, type 2 diabetes, and other metabolic disorders.
Mental health
Circadian rhythm is also closely linked to mental health. Circadian rhythm disruptions have been linked to an increased risk of mood disorders such as depression and anxiety. Indeed, this can lead to alterations in the secretion of essential neurotransmitters involved in mood regulation such as serotonin and dopamine.
Additionally, sleep disruptions associated with circadian rhythm changes may affect emotional stability and the ability to cope with daily stress, thereby increasing vulnerability to mood disorders.
How to maintain a healthy circadian rhythm?
Fortunately, there are easy strategies to adopt to maintain a healthy circadian rhythm and support our overall well-being.
Exposure to light
The regulation of the biological clock depends mainly on light . External light intensity can influence melatonin production, thus delaying the biological clock and the process of falling asleep during late exposure to light in the evening.
To maintain proper synchronization with the day-night cycle, it is recommended to expose your body to natural daylight during the day and limit exposure to artificial light at night. In some cases, light therapy can also be beneficial in regulating the circadian rhythm.
Sleep routine
Establishing a regular sleep routine is also essential for maintaining a healthy circadian rhythm and improving sleep quality. By going to bed and getting up at the same time every day, our body gets used to a regular cycle, which promotes better synchronization of the internal clock.
This regularity allows the body to anticipate the moment of rest and awakening, thus making it easier to fall asleep and reducing difficulty waking up in the morning. Additionally, a stable sleep routine helps stabilize levels of sleep-regulating hormones like melatonin, promoting deeper, more restful sleep.
Diet and exercise
Adopting a healthy lifestyle, including balanced eating habits and regular exercise, can also promote an optimal circadian rhythm by positively influencing metabolic and hormonal functions.
Although its impact is less significant than that of light, physical activity also plays a role in synchronizing the biological clock. Likewise, the rhythm of meals directly impacts health and can contribute either to synchronizing the circadian rhythm or to disrupting it.
In short, the circadian rhythm is much more than just a biological clock; it significantly impacts our health and well-being. Its disruption can therefore have harmful consequences on sleep, metabolism and even mental health. However, by adopting healthy lifestyle habits such as appropriate exposure to light, a regular sleep routine and a balanced diet, it is possible to effectively support our circadian rhythm. Furthermore, a better understanding of these cycles is essential for medical research, particularly in the field of chronopharmacology, which aims to adjust drug treatments to individual biological rhythms for optimization of therapeutic effects.
References :
Inserm. (June 13, 2017). Chronobiology – the 24 hours of the body.
Richard J. Schwab, MD, University of Pennsylvania, Division of Sleep Medicine. (Revised May 2022). Circadian rhythm disorders.
