In biology, circadian rhythms are defined as oscillations of the physiological variables of an organism at regular time intervals. All living beings, from bacteria to humans, present oscillations in our parameters depending on environmental conditions, which usually change rhythmically and in time 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 light-dark variation, since for human beings, the night involves rest and repair, while the day involves a peak of physiological and neuronal activity. As you can imagine, not all living beings respond in the same way to the light-dark cycle, nor do they interpret other environmental parameters such as dryness, heat, rain and many more in the same way.
Circadian cycles are essential for the health of humans and all animals, no matter how independent we may seem from nature in an increasingly anthropized Earth. If you want to know how our species’ circadian cycles influence health, keep reading.
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 inside ourselves to regulate the cycle of circadian rhythms.
In mammals, The biological clock is located in a specific area of the brain, the suprachiasmatic nucleus This consists of a group of about 20,000 neurons in the medial hypothalamus, which integrate the cycles based on the concentration of the CLOCK and BMAL1 proteins, among other things. We will not go into complex terminology, since it is enough for us to know that the genes that encode these proteins allow their dimerization, which activates genes such as period (per) and timeless (tim), essential in the mechanisms included here.
How do these cycles influence health?
We have seen a few glimpses of the biological clock of living beings, but this mechanism stands out for its complexity and nuances. Next, we explore the effects of imbalance and maintenance of circadian rhythms on health.
1. The relationship of the circadian rhythm with diet
As we have seen previously, the biological clock tends to match the rhythms of light and darkness in the environment. Multiple sources establish that Nutrient intake can modulate the expression of certain genes that regulate the circadian rhythm, which alter feeding behavior in the hypothalamus These concepts fall into the field of epigenetics, that is, the existence of changes in the expression/inhibition of genes without disrupting the genome itself, but rather taking into account environmental factors.
An interesting article that investigates these correlations is Impact of nutrients on circadian rhythmicitypublished in 2015 in the scientific journal Regulatory, integrative and comparative physiology. This review article cites that, indeed, diets high in fat and sugar can lead to alterations in genes that modulate our biological clock, which translates into effects on peripheral tissue and the central nervous system (CNS).
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, since 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 times of darkness, sends a signal to the pineal gland to produce melatonin. The increase in the concentration of circulating melatonin tells us, subconsciously, that it is time to go to sleep.
Today, it has been shown that exposure to bright lights at night prevents the secretion of melatonin, which delays normal circadian cycles. The study Self-luminous mechanisms and melatonin suppression in adolescents He demonstrates it in a simple way. In this research, a group of teenagers were put on special glasses (that cancel out the light from electronic devices) before going to sleep, while others maintained their normal routine without glasses. Melatonin levels were measured in both experimental sectors throughout the night.
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 cell phone before going to sleep can delay sleep for more than an hour
3. Circadian cycles and body temperature
Circadian rhythms and the biological clock also determine the temperature we present inside our body throughout the day. Individual body temperature decreases during the night (time of reduced metabolism), reaching its minimum at 3 in the morning and its maximum at 6 in the afternoon Thus, between 6 in the morning and 6:00 p.m., an increase of approximately 0.5 degrees is expected.
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 drops below 35 degrees is considered hypothermia, of greater or lesser severity depending on each case.
Summary
As you can see, circadian cycles modulate our hunger and desire to eat, our body temperature, sleep rhythm and many more things. Although the biological clock is encoded in our genetic imprint, there are a series of factors and habits that can tilt its functioning to a more positive and natural balance. The amount of circulating melatonin and exposure to screens are a clear example of this.
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