The Relevance of "Biological Clocks" for Modern Humans: Chronotype in the Age of Artificial Light

The concept of "biological clocks" has ceased to be a metaphor and has become a strict scientific concept in chronobiology — the science of the temporal organization of living systems. For modern humans living under conditions of round-the-clock access to light, information, and work, understanding and respecting their circadian rhythms is not just a matter of well-being but a question of long-term health, productivity, and psychological resilience.

Scientific Foundations: From Genes to Hormones

Biological clocks are a hierarchical system. Their central "rhythm driver" is located in the suprachiasmatic nucleus (SCN) of the hypothalamus of the brain. This cluster of about 20,000 neurons synchronizes the work of peripheral clocks, located in virtually every cell of the body.

Molecular Mechanism. The basis lies in a transcriptional-translational feedback loop. Genes "clocks" (such as Clock and Bmal1) initiate the production of proteins that, upon accumulation, suppress their own activity. This cycle lasts about 24 hours.

Synchronizer No. 1 — light. The SCN receives information about light directly from special light-sensitive cells of the retina that react to the blue part of the spectrum. In the morning, light suppresses the production of the hormone melatonin (a sleep signal) and stimulates the release of cortisol (a hormone of awakening and activity).

Impact on Physiology. These clocks regulate not only sleep and wakefulness but also the peak secretion of hormones, peristalsis of the intestines, immune system function, body temperature, cognitive functions, and even cell division.

The Main Challenge of Modernity: Desynchronization

Civilization has created a powerful factor disrupting the functioning of biological clocks — artificial lighting, especially in the blue spectrum (gadget screens, LED lamps), and a flexible, often round-the-clock, work schedule. This has led to a mass phenomenon of social jetlag (desynchronization) — a mismatch between a person's internal clocks and external social demands.

Consequences of Chronic Desynchronization:

• Metabolic Disorders. Disrupted clocks affect the production of insulin, leptin (a satiety hormone), and ghrelin (a hunger hormone). This is a direct path to obesity, metabolic syndrome, and type 2 diabetes. Experiments on mice with knocked-out clock genes demonstrate a tendency to obesity even on a normal diet.
• Cardiovascular Risk. An incorrect sleep-wake schedule is associated with increased blood pressure, dyslipidemia, and an increased risk of heart attacks and strokes. The famous study on "changing the clocks" for daylight saving time showed a short-term but statistically significant increase in the number of heart attacks in the first week after the clocks were changed.
• Immune Dysfunction. Immune cells also have their circadian rhythms. Their activity, such as the production of cytokines, reaches a peak at night. Desynchronization suppresses the immune response and increases the risk of inflammatory and infectious diseases. There is evidence that the effectiveness of vaccination depends on the time of day.
• Mental Disorders. A consistent link has been found between the disruption of circadian rhythms and the development of depression, bipolar disorder, and anxiety. Melatonin and serotonin are key players in the regulation of mood and sleep.
• Cancer Risk. The World Health Organization classifies working night shifts as a probable carcinogen (group 2A). It is believed that the suppression of the nocturnal peak of melatonin (a powerful antioxidant and regulator of estrogens) and the disruption of the cell division cycle may contribute to the development of breast and prostate cancer.

Practical Relevance: From Chronopharmacology to Sleep Hygiene

The understanding of biological clocks has given rise to new approaches in medicine and personal effectiveness.

Chronopharmacology. Taking medications at a specific time of day can multiply their effectiveness and reduce toxicity. For example:

Statins (cholesterol-lowering drugs) are more effective to take in the evening, as the liver's synthesis of cholesterol is most active at night.

Chemotherapy at certain hours can be less toxic to healthy cells and more destructive to tumor cells.

Old-generation antihistamines, causing drowsiness, logically should be taken at night, turning a side effect into a therapeutic effect.

Management of Productivity. Knowing one's chronotype ("early bird," "night owl," "dove") allows for planning peaks of intellectual and physical activity. It is meaningless to assign important negotiations at 8 a.m. to "night owls," and at 8 p.m. to "early birds." Cognitive abilities, such as concentration and creativity, also follow circadian rhythms.

Circadian Rhythm Hygiene. This is a set of practices for synchronizing internal clocks:

Bright light in the morning (solar or special lamp) and limiting blue light in the evening (filters on gadgets, glasses with blue light blocking).

A strict sleep-wake schedule, even on weekends.

Regular meal times. Late dinners disrupt peripheral clocks in the liver and pancreas, disrupting metabolism.

Interesting Facts and Examples

The 2017 Nobel Prize was awarded to Jeffrey Hall, Michael Rosbash, and Michael Young for their discovery of the molecular mechanisms controlling circadian rhythms, confirming the fundamental importance of the topic.

Experiment in the Cave. In the 1960s, French speleologist Michel Siffre spent two months in a deep cave without any time indicators. His "days" stretched to about 25 hours, revealing the endogenous nature of our clocks and their tendency to small discrepancies with the 24-hour solar day.

Time for Surgical Operations. Studies show that the risk of complications after open-heart surgery is lower if it is performed in the second half of the day. This is associated with the peak activity of genes responsible for tissue repair and stress resistance at this time of day.

"Night Owls" and Risks. Large-scale studies show that people with a pronounced evening chronotype ("night owls"), forced to live in an early-morning world, have statistically higher risks of depression, diabetes, and cardiovascular diseases simply due to chronic social jetlag.

Conclusion

The relevance of biological clocks for modern humans is colossal. In an era when technological progress allows us to ignore the change of day and night, we pay for it with epidemics of non-communicable diseases and a decline in the quality of life. Understanding one's circadian rhythms is no longer the province of scientists and is becoming a crucial skill of self-regulation and prevention. This is not a call to renounce the benefits of civilization but a guide to conscious synchronization with ancient rhythms encoded in our DNA. To listen to our biological clocks means not just to sleep better but to invest in long-term health, efficiency, and psycho-emotional well-being in a world that is not going to stop. This is the science of how to live in harmony with the time within us.

Permanent link to this publication: