Biorhythms: following the biological clock

Living beings have internal time regulation mechanisms that organise multiple physiological functions. These systems are largely synchronised with the natural rhythms of planet Earth, such as the alternation of day and night and the succession of seasons.

The study of these mechanisms, known as chronobiology, has become increasingly important in the field of health. In 2017, this area gained particular prominence with the award of the Nobel Prize for Medicine to Jeffrey C. Hall, Michael Rosbash and Michael W. Young, for their contribution to understanding the molecular mechanisms involved in regulating circadian rhythm. As Michael Rosbash said after the prize was announced, even before the Earth's atmosphere had its current composition, the cycle of light and darkness already had an influence on the beginning of life on the planet.

Chronobiology studies cell rhythms, hormonal cycles and the relationship between sleep and wakefulness. As the human being is a multi-cellular organism, made up of multiple interdependent systems, it is necessary for organs and functions to be coordinated in time. Without this organisation, processes such as hunger, sleep or metabolic activity would tend to occur less efficiently.

The central biological clock

The central biological clock corresponds anatomically to the suprachiasmatic nucleus, a small cluster of neurons located in the hypothalamus. This nucleus acts as a synchronisation centre, integrating environmental signals and helping to coordinate the body's internal rhythms.

The suprachiasmatic nucleus receives information about light intensity from specific cells in the retina, the photoreceptor ganglion cells. This functional link helps explain the importance of light exposure in regulating biological rhythms.

Circadian rhythm and biological regulation

The circadian rhythm participates in the regulation of numerous biological processes and is significantly influenced by the cycle of light and darkness. Sunlight acts as one of the main environmental signals associated with states of alertness and rest. In general, greater exposure to light is associated with greater activation, while reduced luminosity favours states of less activity and rest.

To transmit this information to the body, the central nervous system uses hormonal mediators such as cortisol and melatonin, as well as catecholamines such as adrenaline and noradrenaline. These substances take part in the temporal signalling that guides awakening, physical and mental activity and preparation for sleep.

During the day, for example, the digestive system tends to increase enzyme production in line with the usual meal times, while the endocrine system adjusts hormone release to the body's energy needs.

Clinical expressions of circadian rhythm

Circadian rhythms contribute to understanding various phenomena observed in clinical and epidemiological practice. Spontaneous births occur more frequently during the night and early morning, a phenomenon associated with the hormonal release characteristic of this period. From an evolutionary point of view, this organisation may have reduced the vulnerability of both mother and newborn.

On the other hand, cardiovascular events such as myocardial infarction or stroke have a higher incidence in the morning. This pattern is related to variations in blood pressure throughout the night, which tends to reach lower values in the early hours of the morning and progressively increase as the body wakes up and becomes more upright.

People with chronic pain often report greater intensity of symptoms on waking, which may be associated with lower nocturnal production of cortisol, an anti-inflammatory hormone.

A widely recognised example of a circadian rhythm mismatch is the jet lag, resulting from the abrupt change of time zone.

Zeitgebersexternal regulators of biorhythms

Although the biological clock functions autonomously, it needs external stimuli to maintain its synchronisation. These stimuli are called Zeitgebers, a German term meaning “time givers”.

Among the main Zeitgebers The following stand out:

• Light, the most powerful regulator of the circadian rhythm
• Food, both the type of food and the timing of meals
• Physical activity and the time of day when it occurs
• Environmental temperature variations
• Social interactions

Cortisol, melatonin and the organisation of the day

From an evolutionary point of view, human genes were selected in environments close to the equator, characterised by a relatively constant cycle of around 12 hours of light and 12 hours of darkness. This pattern may have influenced the organisation of hormonal rhythms.

Cortisol usually peaks in the early hours of the morning, favouring awakening and physical and cognitive activity. Throughout the day, its production tends to decrease, allowing for a progressive increase in melatonin in the late afternoon and early evening, signalling to the body that the rest period is approaching.

This hormonal balance contributes to the organisation of the sleep-wake cycle.

What biology tends to favour

Simply put, biological functioning tends to be organised more efficiently when certain principles are respected:

• Progressive awakening, ideally without abrupt stimuli
• Exposure to natural light in the morning
• Adequate overnight fasting periods
• Greater intensity of physical activity during the day
• Progressive reduction in light and food stimulation at the end of the day
• Dark, quiet and cool environments at night

Circadian maladjustment in modern life

Modern lifestyles often make it difficult to respect these rhythms. It's common to wake up with an alarm clock, spend most of the day indoors with artificial light, maintain exposure to blue light at the end of the day, eat late and use electronic devices until close to bedtime.

This pattern can create a mismatch between the expected biological rhythm and the rhythm imposed by everyday life, generating a state comparable to a jet lag chronic.

Dysregulation of the circadian rhythm has been associated with hormonal, metabolic, immune and cardiovascular changes, and can be manifested by persistent fatigue, mood swings, anxiety, difficulty concentrating, digestive disorders and weight variations.

Understanding biorhythms from an integrative perspective

In Integrative Osteopathy, with a framework in Clinical Psychoneuroimmunology, biorhythms and sleep are considered central regulatory processes, closely linked to the way the body adapts to internal and external demands. The organisation of biological rhythms reflects the continuous interaction between the nervous, endocrine and immune systems, influencing the ability to recover, the response to stress and overall functional balance.

The clinical assessment of biorhythms goes beyond analysing sleep schedules alone. It integrates resting and waking habits, exposure to natural and artificial light throughout the day, eating times and patterns, levels and timing of physical activity, the state of activation of the autonomic nervous system and the person's life context, including emotional, professional and social factors. This approach makes it possible to understand how the body is managing its activation and rest cycles.

From this perspective, alterations in biorhythms are understood as possible manifestations of broader dysregulation, which may involve:

• Circadian rhythm maladjustments associated with irregular schedules
• Changes in the balance between cortisol and melatonin
• Persistent states of hyperactivation of the nervous system
• Increased load stress maintained over time
• Difficulty transitioning between alert and resting states

Biorhythms are thus seen as a relevant indicator of the body's functional organisation and adaptive capacity. An integrated clinical reading makes it possible to identify patterns that contribute to dysregulation, without reducing the situation to a single symptom or isolated cause.

Respecting the biological rhythm does not imply returning to unattainable ideal conditions, but rather developing a greater awareness of the body's signals and reducing, wherever possible, the factors that interfere with its regulation mechanisms. This framework favours a clinical approach aligned with human physiology, adjusted to the individuality of each person and their life context, contributing to a more coherent understanding of the processes that sustain the body's balance and self-regulation.