How do circadian cycles affect health?

In biology, circadian rhythms are defined as oscillations of the physiological variables of an organism at regular intervals of time. All living beings, from bacteria to humans, present oscillations in our parameters depending on environmental conditions, which tend to change rhythmically and in rhythm with our Body.

In our species, circadian rhythms encompass physical, mental, and behavioral changes that follow a 24-hour rhythm. Most of these mechanisms are based on the variation of light-dark, because for human beings, the night implies rest and repair, while the day implies a peak of physiological activity and neuronal. As you can imagine, not all living beings respond in the same way to the light-dark cycle, just like nor do they interpret other environmental parameters in the same way, such as dryness, heat, rain and many more.

Circadian cycles are essential for the health of humans and all animals, independent as we may seem from nature on an increasingly anthropized Earth. If you want to know how the circadian cycles of our species influence health, read on.

• Related article: "Endocrine system: anatomy, parts and functions"

Circadian rhythms and the biological clock

Although biological clock and circadian rhythm / cycle are widely linked terms, they do not mean the same thing. in no case. Rhythms are physical, mental and behavioral changes that we carry out cyclically every 24 hours, while biological clocks are the mechanisms that we present within us to regulate the cycle of rhythms circadians.

In mammals, the biological clock is located in a specific area of ​​the brain, the suprachiasmatic nucleus. This consists of a grouping of about 20,000 neurons of the medial hypothalamus, which integrate the cycles based on the concentration of the CLOCK and BMAL1 proteins, among other things. We will not enter into complex terminology, since it is enough for us to know that the genes that encode these proteins allow its dimerization, which activates genes such as period (per) and timeless (tim), essential in the mechanisms here encompassed.

How do these cycles affect health?

We have seen some brushstrokes on the biological clock of living beings, but this mechanism stands out for its complexity and nuances. Next, we explore the effects of circadian rhythm imbalance and maintenance on health.

1. The relationship of the circadian rhythm with diet

As we have seen previously, the biological clock tends to keep pace with the rhythms of light and darkness of the environment. Multiple sources state that the intake of nutrients can modulate the expression of certain genes that regulate the circadian rhythm, which alter feeding behavior in the hypothalamus. These concepts fall within the field of epigenetics, that is, the existence of changes in the expression / inhibition of genes without disrupting the genome itself, but taking into account factors of the environment.

An interesting article investigating these correlations is Impact of nutrients on circadian rhythmicity, published in 2015 in the scientific journal Regulatory, integrative and comparative physiology. This review article cites that diets high in fat and sugar can indeed lead to disturbances. of genes that modulate our biological clock, which translates into effects on peripheral tissue and the central nervous system (SNC).

In any case, certain sources argue that, to reset the biological clock, the total amount of nutrients (energy) is more important than their nature. Much research is still required, as we are in the infancy of epigenetics.

2. Melatonin and sleep

Melatonin is the most important hormone in living beings when it comes to regulating the sleep-wake cycle. The suprachiasmatic nucleus receives information from the outside light from the eyes and, in moments of darkness, sends the signal to the pineal gland that it should produce melatonin. The increased concentration of circulating melatonin tells us, subconsciously, that it is time to go to sleep.

To this day, exposure to bright lights at night has been shown to prevent the secretion of melatonin, delaying normal circadian cycles. The study Self-luminous devices and melatonin suppression in adolescents It demonstrates it simply. In this investigation, special glasses were put on them (which canceled out the incidence of light from the electronic devices) to a group of adolescents before going to sleep, while others maintained their normal routine without glasses. Melatonin levels were measured in both experimental sectors throughout the nights.

The boys who did not wear glasses had 28% less circulating melatonin than those who did after an hour of exposure to a screen before going to sleep. Based on data like these, it has been calculated that prolonged exposure to a tablet or mobile before sleeping can delay sleep for more than an hour.

• You may be interested in: "Melatonin: the hormone that controls sleep and seasonal rhythms"

3. Circadian cycles and body temperature

Circadian rhythms and the biological clock also determine the temperature that we present inside our body throughout the day. The individual body temperature decreases during the night (moment of reduced metabolism), reaching its minimum at 3 in the morning and its maximum at 6 in the afternoon. Thus, between 6 a.m. and 6 p.m., an increase of 0.5 degrees is expected, approximately.

Therefore, a person should not worry if they have a lower than normal body temperature at night, especially between 2 and 4 in the morning. Even so, any temperature that falls below 35 degrees is considered hypothermia, of greater or lesser severity depending on the case.

Resume

As you can see, circadian cycles modulate our hunger and desire to eat, our body temperature, the rhythm of sleep and many other things. Despite the fact that the biological clock is encoded in our genetic imprint, there are a series of factors and habits that can incline its functioning to a more positive and natural scale. The amount of circulating melatonin and exposure to screens are a clear example of this.

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Bibliographic references:

• Figueiro, M., & Overington, D. (2016). Self-luminous devices and melatonin suppression in adolescents. Lighting Research & Technology, 48 (8), 966-975.
• Oosterman, J. E., Kalsbeek, A., la Fleur, S. E., & Belsham, D. D. (2015). Impact of nutrients on circadian rhythmicity. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 308 (5), R337-R350.
• Reddy, S., Reddy, V., & Sharma, S. (2020). Physiology, circadian rhythm. StatPearls [Internet].