Cortisol, melatonin and circadian rhythm: understanding sleep regulation

The circadian cycle is an approximately 24-hour system of biological regulation responsible for organising multiple physiological processes, including sleep, wakefulness, metabolism and the response to the sun. stress. Among its main modulators are cortisol and melatonin, two hormones with complementary functions in the body's adaptation to the different periods of the day and night.

Cortisol, often referred to as the hormone of stress, has a well-defined circadian pattern. Its levels tend to be highest in the early hours of the morning, contributing to an increase in alertness, energy mobilisation and the ability to respond to the demands of the day. Over the course of the day, cortisol levels progressively decrease, participating in the regulation of metabolism, the inflammatory response and the hydroelectrolytic balance, i.e. the proper regulation of water and mineral salts in the body.

Melatonin, on the other hand, is associated with the transition to rest. Its production increases with a decrease in ambient light, especially at the end of the day, signalling to the body that the rest period is approaching. This hormone is involved in reducing core body temperature, decreasing muscle tone and facilitating the mechanisms that promote the induction and maintenance of sleep. Melatonin therefore plays a central role in the organisation of sleep and in the processes of physiological recovery during the night.

The relationship between cortisol and melatonin can be understood as a dynamic system of alternation and balance, essential for an adequate transition between the states of wakefulness and rest. When this balance is preserved, the body tends to adapt more efficiently to daily rhythms. On the other hand, states of stress chronic, persistent changes in routines or inadequate patterns of light exposure can interfere with this regulation, leading to sleep disturbances and changes in overall well-being.

Strategies that can support circadian balance and sleep quality

Some everyday behaviours can contribute to a more consistent organisation of the circadian rhythm:

• Regular exposure to natural light in the morning, which acts as a signal for the biological clock, favouring daytime activation and the regulation of melatonin at night.
• Maintaining relatively consistent sleeping and waking times, supporting the predictability of hormonal cycles
• The value of an adequate night's rest in terms of duration and regularity, since sleep deprivation can interfere with hormone secretion.
• A balanced diet, including foods that provide precursors involved in neurotransmitter synthesis, such as tryptophan
• Moderation in the consumption of stimulants, particularly in the afternoon and evening
• Opting for lighter meals at the end of the day, reducing digestive interference in the process of falling asleep
• The regular practice of physical activity, preferably during the day, respecting the individual response
• Reducing exposure to bright artificial light at night, especially blue light emitted by electronic devices
• The creation of a sleep environment with little light, silence and reduced stimuli, associating the bedroom primarily with rest.

Circadian rhythm: an approach in Clinical Psychoneuroimmunology

In Integrative Osteopathy, with a framework in Clinical Psychoneuroimmunology, sleep and circadian rhythm are evaluated as central regulatory processes, and not just as isolated phenomena. The clinical assessment considers how factors such as stress, persistent body tension, nervous system activation patterns, exposure to light, irregular schedules and emotional demands may be interfering with the organisation of the cortisol-melatonin axis.

From this integrative perspective, it is understood that alterations in sleep or circadian rhythm are not just the result of a “sleep problem”, but may reflect states of compromised adaptation between the nervous, endocrine and immune systems. Musculoskeletal tension, difficulty switching off, frequent nocturnal awakenings or a feeling of tiredness that doesn't improve with rest are often analysed in the light of these regulatory mechanisms.

Integrative Osteopathy can be integrated into this context by addressing, through assessment and manual intervention, factors related to mobility, the tone of the autonomic nervous system and body perception. Clinical Psychoneuroimmunology makes it possible to fit the elements identified in the assessment into a broader functional model, considering the impact of stress, of sleep and biological rhythms in overall health, also allowing individualised recommendations to be made in terms of daily habits, such as exposure to light, organisation of rest, management of the stress and activity patterns.

Understanding the circadian rhythm from an integrative perspective

The organisation of the circadian rhythm depends not only on the time of going to bed, but on the way the body is exposed to stimuli throughout the day. Regular exposure to natural light in the morning, maintaining relatively consistent sleep schedules, managing the body's stress, adequate physical activity and reduced exposure to bright artificial light at night are factors often taken into account in clinical assessment.

Understanding the interaction between cortisol, melatonin and circadian rhythm allows us to frame sleep as an active process of regulation and adaptation, influenced by multiple biological and contextual factors. In an integrated approach, this understanding contributes to a more complete assessment and the definition of strategies adjusted to the needs and individual context of each person, respecting biological variability and the clinical moment.