The Circadian Cycle, your internal biological clock

Chronobiology is a science that interests more and more researchers to better understand the rhythms of our internal biological clock. In 2017, 3 American geneticists got a Nobel Prize in Medicine for their work on chronobiology.

The circadian cycle is your natural biological cycle set according to the rhythm of the Earth's day-night alternation. The retinal cells receive information on the intensity of the light and then will transmit it to the hypothalamus synchronizing all the organic functions. In the absence of sunlightThe regularity of the cycle is maintained for a certain period of time until it is extended to 25 hours instead of 24 hours.

"circadian" comes from the Latin circa, "around" and dies, "the day"

The circadian cycle is thus an alternation of phases of peak (acrophase), trough (nadir) and average rhythm (mesor) over 24 hours.

All living organisms, bacteria included, are regulated by this internal biological clock. The effects are manifested on: blood pressure, sleep/wake cycle, digestion, body temperature, hormone secretion, etc...

Circadian cycle in humans: several phases.

From the moment sunlight begins to occur, the hypothalamus sends a signal to the adrenals to secrete cortisol. This hormone is produced towards the end of the night and its peak secretion is just before the alarm clock. Cortisol plays a primary role in starting up our bodies: it wakes us up and begins to trigger intestinal peristalsis preparing us fordigestion.

In the evening, as soon as night falls, melatonin is secreted by the epiphysis or pineal gland. Its peak is between 2 and 4 o'clock in the morning. This hormone is the one that causes sleep and the slowing down of our organism: lowering of the body temperature, slowing down of the organic functions including the intestinal peristalsis.

It is also at beginning of the night, during slow and deep sleep that the growth hormone is produced which, as its name indicates, allows the growth of bone and muscle tissue in children and adolescents and in adults it plays a role in metabolism (fat-burning effect, protein synthesis...)

Unbalancing factors.

Exposure tolight late in the day pushes back the biological clock, whereas early exposure advances it.

The intensity of an artificial light affects the circadian rhythm. A few years ago, it was thought that 1000 lux was needed to disrupt the biological clock, whereas 10 lux is enough to stop the secretion of melatonin . 10 lux is the light of a candle!

The photoreceptor cells ofthe retina, the menalopsin ganglion cells, are sensitive toblue light. It is this same blue light that is found in screens and urban lighting greatly disrupting the secretions ofmelatonin and thus making it difficult to fall asleep.

Night work exposes people to desynchronization of their internal clocks as well as a debt of sleep. Studies have highlighted the health risks that this rhythm implies: sleep disorders, high blood pressure, risk of obesity, alteration of cognitive functions (concentration, reflection, attention...) .... A team from INSERM showed that "non-menopausal women who work at least 3 hours between midnight and 5 a.m. have a 26% increased risk of breast cancer and this risk increases with the frequency of nights worked and the duration of the job. "

Phototherapy to restore a regular cycle

This technique involves exposing the subject sufferingfrom circadian rhythm shift to high intensity light for 30 minutes to 1 hour at a particular time depending on the problem.

The Circadian Cycle

Melatonin in supplementation.

Increasingly prescribed or recommended, melatonin is beginning to dethrone famous sleeping pills. It is still wise to create an adequate visual and sound environment for this treatment to be beneficial. Indeed, as we have seen above, melatonin is secreted as soon as the intensity of light decreases and, conversely, blue light short-circuits it. Taking melatonin and sitting in front of the TV with all the lights in the living room on is nonsense...

Chronotherapyis a technique of increasing interest to researchers. Its principles are based on administering a treatment at an optimal time according to the body's natural biological rhythms. Currently, studies are underway to determine the best time to administer anti-inflammatory or anti-cholesterol drugs(source: INSERM). These principles are found in naturopathy where certain food supplements, infusions, foods will be taken at appropriate times according to needs and issues.

Alexia Bernard 26 March, 2019
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