The circadian rhythm problem: what it's like to have a body that asks you to sleep during the day and keeps you awake all night

The circadian rhythm determines the physiological functioning of our body. But, far from being homogeneous, there are some interesting differences between people. Among them the existence of morning and evening people.

This refers to people who feel more active during the day or at night, respectively. It is not just a matter of customs, but has a genetic and physical background. What's more, it also has a series of important consequences for our health.

Owls and larks: evening and morning people

Yes, there is a difference between people who feel more active at night and those who feel more active during the day. So much so that there is a colloquial term to differentiate them: larks and owls. There is also a more technical one: morning and evening. While the former are more active in the morning, the latter do so when the day falls.

Morning people often wake up easily in the morning and begin their activity freely, quickly. As the day goes by, their performance decreases. Under normal circumstances, they fall asleep easily at night, and they often feel tired with lack of sun.

By contrast, evening people need more effort to fully wake up, feeling lazy and awkward in the morning. As the day progresses, they feel more lucid and mentally agile. At bedtime, at night, they remain more active times and it may take them to fall asleep, although this is not decisive.

In general, these two habits obey two chronotypes. A chronotype is what is called a specific circadian cycle, attached to a specific rhythm. Chronotypes determine many behavioral aspects, in addition to physiological (everything is related, after all). These are not static and depend on our own circadian cycle.

The internal clock that determines everything

All living beings have an internal clock that determines the circadian functioning, that is, around 24h that a day has. This clock marks the daily rhythms, but also in the long term. This watch has an internal function, to a certain extent independent, but it is adjusted every day by means of certain stimuli. Chief among them is sunlight.

In order to function, the circadian rhythm activates a cascade of activities that affect different organs in different ways. For example, the pancreas secretes more insulin during daylight hours, which should be when we eat, and works more slowly at night, when we should have no need to eat.

The protagonist piece of the circadian rhythm is melatonin, a hormone in charge of controlling these metabolic cascades we were talking about or, in other words, controlling how our bodies behave. This also affects our attitude and our spirits, of course.

What happens when our rhythm goes awry?

How is a chronotype acquired? In general, our circadian rhythm is adaptive. This means that we can mold it according to our needs. How? Forcing us at certain times. It is not an easy task, as we will see now, but over time this biological rhythm adapts and shifts. Thus, a morning person can become evening. Melatonin segregation will change your schedule and adjustments will be made for other types of stimuli.

The sun, which inhibits the secretion of this hormone, can cause an adaptation problem, but we have measures to avoid daylight in our homes. In short, we can adapt this rhythm almost without complications, beyond spending an adaptation period. And what happens during that adaptation period? Or, in other words, what happens when a circadian rhythm goes awry?

In the short term, people with a mismatched chronotype experience symptoms of tiredness and clumsiness, rash and poorly thought-out decision making. In its most acute stages there are mood swings and early depression may occur. Another more important question, as we can imagine, appears at the physiological level. Indeed, not following our circadian rhythm can affect metabolism in various ways.

Among other things, it affects various inflammatory diseases or metabolic problems of all kinds, including diabetes, fat accumulation, coronary heart disease or metabolic syndrome. In animals, we know that disrupting the circadian rhythm results in a fatal outcome. For humans, the answers are no better. Sure, this brings us to the question we started with: Not everyone has the same chronotype.

The difference between night and daytime

Some studies, such as this one carried out by the University of Granada, indicate that it is not right to force people with a certain chronotype to work outside their "natural" hours. As we said, this can affect your ability to make decisions, due to a lack of cognitive control that causes impulsivity, to give just one example. But, if people can choose their moment of activity, adapting your circadian rhythm, why would this be a problem?

Because, in reality, it is not always possible to adapt easily. First, like the whiting tail, there are differences in personality between morning and evening people, and these promote a habit, as this study by the Complutense de Madrid shows. What came first the chicken or the egg? The answer is not so important because, in the end, what really matters is the behavior that people adopt.

On the other hand, there is also another question of a genetic nature. The CLOCK gene, from Circadian Locomotor Output Cycles Kaput, encodes a protein involved in the regulation of circadian rhythms and was identified by the group of Joseph Takahashi in 1997. Interestingly, a mutation was found associated with this gene in 2008, the effect of which manifests itself in the person's personality, which is more docile and accommodating.

The CLOCK gene predisposes our chronotype to morning and evening. It does not mean that we cannot adapt to another rhythm, but that we have a certain tendency. This gene has also been linked to cognitive development problems, obesity, and other metabolic issues. In conclusion, it is clear that our circadian rhythm is much more than a series of adjustable behaviors. There are a series of predefined patterns that make us tend towards one or another phase of the day. And, much more importantly, these characteristics are undoubtedly linked to our health.

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