Circadian Rhythm: Consequences, Improvements, Functions, Physiology And Types

This word comes from the Latin circa and means “around” and dies , which means “day.” In biology they are said to be “oscillations of biological variables” at regular intervals of time.

These oscillations are really mental, physical and behavioral changes that have a cycle of one day (24 hours) and are responses to stimuli such as light, darkness and temperature that are in the environment of an organism. All living things, whether plants, animals or microbes have physiological rhythmic variations. For example, heat production, flowering and metabolic rate, all associated with environmental changes.

The study of these circadian rhythms is known as chronobiology and these biological rhythms are defined by three elements: the endogenous oscillator or pacemaker, the afferent pathways to the pacemaker and the efferent pathways from the pacemaker to the effectors.

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Physiology of the circadian rhythm

The functioning of the circadian rhythm and sleep work under these elements located in the body:

  • Nervous System (SN): helps the body or organism to respond to all internal or external changes, in addition to controlling various activities of the body.
  • Neuron : it is the main and functional unit of the SN and works with fast communications.
  • Neurotransmitters : are those chemical substances released by neurons, which among their functions can excite or inhibit others.
  • Central Nervous System : made up of the brain and spinal cord. Coordinate nerve signals.
  • Peripheral Nervous System : cell bodies that carry impulses to the CNS.
  • Brain : it can be said that it is the skull in its entirety and is composed of the brain, brainstem, cerebellum and diencephalon.
  • Brain : who oversees the entire nervous system is the brain, which is divided into two hemispheres.
  • Midbrain : eye and facial movements are controlled by it.
  • Medulla oblongata : handles all cardiac, vasoconstrictor, respiratory and reflex activities.
  • Medulla : all the control of cardiac and pulmonary functions is given here.
  • Spinal Cord : carries messages from the brain to the rest of the body.
  • Thalamus : in charge of receiving both sensory and motor signals to the cerebral cortex.
  • Hypothalamus : its fundamental and essential function is homeostasis.

There are areas and structures that are connected with sleep and sleep, these are: the cerebral cortex, the thalamus, the hypothalamus, the brain stem and the reticular formation.

On the other hand, there are also substances that maintain wakefulness such as adrenaline, norepinephrine and dopamine.

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Functions of the circadian rhythm

One of its peculiarities is that it has an endogenous nature . What does this mean? They function under dependence on an internal pacemaker clock that produces autonomous rhythmic activities that are genetically determined.

Ability to be synchronized: if in the external environment there is no presence of signals from there, the circadian rhythms are also maintained. At times considered normal and stable, the period of the sleep / wake rhythm is 24 hours, but if there are signals from the environment, these circadian rhythms are synchronized in periods other than that of the endogenous pacemaker.

Circadian rhythm of blood pressure

We must start this topic by indicating that blood pressure is not the same, nor is it constant, and during the day and night it suffers from various changes. For example, if you have high levels of stress or do physical exercise, there will be sharp variations. However, the common denominator is that blood pressure drops during sleep .

This blood pressure maintains a circadian rhythm, with lower levels at night due to physical inactivity and changes in sleeping posture , which means that the time of day has nothing to do with these changes. On the other hand, when waking up, these systolic and diastolic values ​​increase and the heart rate varies markedly.

If you are in the presence of a lack of adequate nighttime lowering of blood pressure, this can have negative consequences, usually in people who suffer from diabetes or hypertension.

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What is the altered circadian rhythm?

There are a number of ways in which the circadian rhythm can be altered. Among which are:

Night work

These types of jobs in which the working hours are at night or require constant shift changes and rotations produce insomnia or drowsiness. This occurs because the body is prepared to rest and sleep in the hours of the night when sleep generally occurs.

Rapid time zone change syndrome

It is also called jet lag and its explanation is simple. The body and the sleep-wake cycle are out of adjustment because there is a difference between the geophysical schedule from the place from where you leave to the destination to arrive. An example of them are transoceanic trips by plane. So the biological clock has to adapt to the new geophysical cycle.

Phase delay syndrome

They are adolescents and young people (usually) in which their levels of creativity, alertness and productivity are activated at night. So they delay their sleep by starting the sleep routine after midnight. In general, if this happens and they get up in the early hours of the morning they can become drowsy throughout the day.

Phase advance syndrome

It happens to older people who get used to sleeping early, even from 6 in the afternoon, but wake up in the early morning hours.


Although people report that they get a good night’s sleep, they have high levels of daytime sleepiness during the day.

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Circadian rhythm for weight loss?

It is based on eating according to how the biological rhythm works, to stimulate the metabolic process that helps to lose weight quickly, but always being healthy.

This theory indicates that the body during the day consumes different levels of energy that you obtain from meals and food and this is due to the biological rhythm. In this way, the diet proposes to distribute the food in this way: for breakfast consume protein (milk, egg, yogurt), for lunch also protein and also carbohydrates (fish, meat, beans).

If coffee is consumed, it should be done after 4 pm as caffeine alters circadian rhythms. For its part, fruits are recommended at night and whole to enjoy fiber.

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Biological clock and circadian rhythm

These terms are not the same, but they are related. In this case, the biological clock is a set of cells found in the body that control circadian rhythms. It works like a main clock and influences hunger, sleep or sexual activity.

Circadian rhythm of sleep and wakefulness

When the biological pacemaker is not synchronized with the external elements, basically the light is the one who plays a fundamental role, a sleep-wake cycle of more than 24 hours occurs, which causes a delay of at least 2 hours a day to go to bed and stand up.

In general, this is suffered by blind people, who suffer from dementia or healthy people but with some brain damage. And it is quite uncomfortable because sleep is present in blocks of three hours and is very variable and the period of time in which they sleep is usually never the same.

Circadian rhythm of cortisol

It usually appears at an early age, between 3 and 8 years, and after it is established, it is usually maintained over time at times such as fasting or when sleep deprived for several days. In order for the secretion of cortisol to occur, the adrenocorticotropic hormone (in the circadian rhythm) plays a fundamental role. After several hours of sleep, the body needs energy that is translated into glucose, which is why cortisol increases in the morning when waking up and also at the end of the afternoon , as there is a bit of stress. Its half-life is 60 to 90 minutes but increases considerably if you suffer from hyperthyroidism, stress or liver failure.

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How is the circadian rhythm of body temperature?

For a long time (centuries inclusive) it has been shown that body temperature has a 24-hour circadian rhythm , with a peak occurring during the day and a drop at night. This helped humans of those times to save that energy that they could not use when they slept, but it had a disadvantage and that is that it became difficult for the body to adapt to variations in the temperature of the environment, regardless of the time of day.

Studies currently carried out revealed that five in the morning is when it has the greatest capacity to withstand high cold temperatures.

Body temperature is considered a fairly stable and useful endogenous marker for studying circadian alterations. This maintains the 24-hour synchrony and begins to decrease when the sleep period begins and increases at the beginning of the day.

In children, what is the circadian rhythm like?

It has been shown that from early stages of birth the circadian system of children is very sensitive to light and the clock can be adjusted thanks to low intensity lighting. Placing a premature baby in light-dark cycles may be able to quickly establish activity / rest patterns.

On the other hand, they also expose a direct relationship between the rhythm of the sleep cycle – watch out for the need to feed children, in this case babies.

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Heart rate and circadian rhythm

Another of the physiological systems influenced by circadian variations is the cardiovascular or heart rate. Proving in a safe and confirmed way that there is a greater possibility of incidence in cardiac events or stages in the morning hours and there are mechanisms that influence this variation throughout the day. This is because sympathetic activity increases when people wake up in the morning. However, in hypertensive people, the heart rate varies during the day.

In this way, as we mentioned before, the heart rate increases sharply in the morning and reaches its peak at noon, decreasing progressively and at 4 AM it finds its lowest level, then upon waking it begins to increase and the cycle repeats. .

Hormonal circadian rhythm

The body performs its functions in the endocrine system through hormones that are substances expelled by different organs, hence the importance of keeping the body stable free of alterations.

Hormonal circadian rhythm is called the variation in the secretion of these hormones that change day and night. For example: at dawn and in the morning the body is alert thanks to adrenaline, norepinephrine, cortisol and insulin and the consumption of food will keep these hormones working.

For its part, at night the serotonin is increased, which provides tranquility and sleep, but if sugar is consumed before going to sleep, this hormone loses its function and there is a risk of increasing fat levels.

How does it work on growth hormone?

The secretion of this hormone is stimulated by the so-called periods of slow wave sleep (phase III and IV or Delta phase of sleep) that is moderated by the periods of sleep and wakefulness.

It is proven that the highest level time when this growth hormone is secreted is in the deep sleep phase, approximately 20 minutes after starting the sleep cycle.

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What is the infradian and ultradian circadian rhythm?

The infradian rhythm is that greater than 24 hours, which means that it happens practically less than once a day. Several types can be differentiated: those that follow the variations of the tide (also called the circa-tidal rhythm), the lunar phases (or circalunar rhythm) and those that follow variations according to the terrestrial translational movement (circa-annual or seasonal rhythm ). We can also include here the menstrual cycle in women that occurs every 28 days.

Contrary to this, the ultradiano rhythm occurs in 20 hours or less and refers to physiological cycles. The release of hormones, heart rate, lung ventilation, thermoregulation and appetite are some examples of this ultradian rhythm. That is, everything that has to do with feeding, copulation, learning, etc.

Organs, what is the circadian rhythm like?

There are cells and organs that also have circadian rhythms and some of these respond to factors such as light. These cells that have their own rhythm are also called peripheral oscillators and are defined by rhythms of eating and fasting. Let’s see some examples of these organs and their operating hours:

  • 11 pm – 1 am: Gallbladder
  • 1 am – 3 am: liver
  • 03 am – 05 am: Lung
  • 05 am – 07 am: Large Intestine
  • 07 am – 09 am: Stomach
  • 09 am – 11 am: Spleen
  • 11 am – 13 pm: Heart
  • 13 pm – 15 pm: Small Intestine
  • 15 pm – 17 pm: Bladder
  • 17 pm – 19 pm: Kidney
  • 19 pm – 21 pm: Pericardium
  • 21 pm – 23 pm: Circulation, blood cells, lymphatic cells and hormones.

Circadian respiratory rhythm, what does it consist of?

The airways are covered by cells that have their own biological clock, this is how they somehow manage time so that when an affectation arises, the lungs can become inflamed.

For example, pneumonia and asthma (belonging to the respiratory system) perform their performance based on this biological clock and the applications of medicines and treatments to cure these diseases will be dependent on this factor.

Which leads to the conclusion that if there is a loss of regulatory capacity this will be caused by the biological clock.

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Recommendations for not altering the circadian rhythm

We will leave you some tips so that you can sleep and rest better, in order to keep your circadian rhythm stable:

  • Technology: although it seems incredible, it can cause alterations in biological signals. For example: the light emitted by TV screens, computers and telephones produces certain artificial signals and this makes the body unable to detect the cyclical rhythm of light. The same happens with heating, preventing recognition of the drop in temperature.
  • Exercise: it is a good option to contribute to good sleep habits, preferably if they are done in the morning and afternoon, but not at night.
  • Coffee and alcohol: you should avoid consuming them as they collide with REM sleep.
  • Close the curtains or blinds: what happens is that even though the eyes are closed, the light that enters through the window is recognized by the retina. So the biological clock of the brain sends species of signals so that the whole body becomes alert and it is possible that you unintentionally wake up.
  • Stress and anxiety: both high levels of these factors will make the mere act of sleeping a complicated situation because your brain is constantly working, they also significantly increase the chances of waking up in the middle of the night due to not reaching deep sleep.

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Kathie Sand always saw the world of beauty as the terrain on which to build her professional career, a goal that was clear to her when she was only 15 years old. Her great concern to expand knowledge led her to settle in Paris where she studied hand in hand with the best beauty professionals and with the most advanced techniques for skin care.

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