2025.09.07 – Hormones, Light Exposure, and Sleep Regulation

Learning objective

The objective is to analyze cortisol (cortisol – hormona del estrés), melatonin (melatonina – hormona del sueño), serotonin (serotonina – hormona de la calma y el bienestar), and oxytocin (oxitocina – hormona del amor), including their roles in circadian rhythms, stress, digestion, and bonding, while integrating factors such as blue light (luz azul – rango visible de 450–495 nm), ultraviolet light (luz ultravioleta – radiación electromagnética invisible al ojo humano), ethnocentrism (etnocentrismo – valoración excesiva del propio grupo), Amazon Audible (Amazon Audible – servicio de audiolibros), smartphone use, bug zappers, and relevant institutions and researchers.

CONCEPTUAL FOUNDATIONS

[F1] Cortisol (cortisol – hormona del estrés) is a glucocorticoid produced by the adrenal cortex that follows a circadian rhythm. Levels peak in the early morning, facilitating wakefulness, energy mobilization, and cognitive readiness. Although chronic elevation associates with stress-related disorders, normal fluctuations are essential for survival. Cortisol also regulates metabolism, immune activity, and cardiovascular function. Its complexity illustrates a dual role of adaptation and risk.

[F2] Melatonin (melatonina – hormona del sueño) is secreted by the pineal gland primarily in response to darkness. Its nocturnal rise signals biological night and prepares the organism for sleep. Suppression occurs under exposure to blue light, particularly within the 460–480 nanometer range, mediated by melanopsin-containing retinal cells. Unlike cortisol, melatonin follows a nightly peak pattern. Its modulation by environmental lighting underscores its sensitivity to technology use.

[F3] Serotonin (serotonina – hormona de la calma y el bienestar) is synthesized predominantly in the gastrointestinal tract, accounting for approximately 90% of the body’s total. Central serotonin regulates mood, cognition, and appetite, while peripheral serotonin influences digestion and intestinal motility. This duality explains the bidirectional gut-brain axis linking digestive health and emotional states. Disruptions in serotonin balance are implicated in depression, anxiety, and gastrointestinal disorders.

[F4] Oxytocin (oxitocina – hormona del amor) is a hypothalamic peptide secreted by the posterior pituitary. Traditionally associated with childbirth and lactation, it also modulates bonding, trust, and social attachment. Research demonstrates ambivalence: it can enhance in-group trust but also intensify jealousy and exclusion. Its role in ethnocentrism reveals the hormone’s capacity to promote group cohesion while discouraging openness toward outsiders, expanding its social significance.

[F5] Ultraviolet light (luz ultravioleta – radiación electromagnética invisible al ojo humano) has wavelengths shorter than visible violet, typically 100–400 nanometers. Bug zappers emit UVA around 350–370 nanometers to attract insects. Although these devices appear bluish-violet, the emission does not activate melanopsin pathways responsible for melatonin suppression. Therefore, their circadian effect is negligible compared to visible blue light from digital devices.

[F6] Blue light (luz azul – rango visible de 450–495 nm) is the most potent circadian regulator due to its direct interaction with intrinsically photosensitive retinal ganglion cells. Exposure at night delays melatonin secretion and shifts circadian rhythms. Smartphones, tablets, and LED lamps are dominant sources. In contrast, placing a smartphone face down while playing audio eliminates most circadian disruption, separating photic from auditory influences on sleep.

APPLICATIONS AND CONTROVERSIES

[A1] Cortisol as a biological alarm clock is supported by evidence showing morning peaks that prepare the body for daily activity. However, studies on light exposure report variable effects, with some findings indicating enhanced cortisol awakening responses and others showing suppression. Institutions such as Johns Hopkins Medicine emphasize cortisol’s role in circadian regulation but caution against oversimplified interpretations. The hormone’s complexity requires balanced understanding.

[A2] Melatonin is consistently validated as sensitive to visible light, especially blue light. Screen exposure at night suppresses secretion and delays sleep onset. By contrast, ultraviolet emissions from bug zappers do not significantly affect melatonin levels. Research from the National Institutes of Health confirms that circadian suppression is wavelength-specific. The distinction highlights the importance of differentiating between apparent violet glow and true blue light.

[A3] Serotonin’s dual origin provides insight into digestive and emotional health. Clinical studies reveal that irritable bowel syndrome often co-occurs with anxiety and depression, supporting the gut-brain axis concept. References from Nature Reviews Gastroenterology & Hepatology emphasize serotonin’s systemic roles. This challenges the outdated idea of serotonin as a purely cerebral “happiness molecule” and redefines its importance in both gastroenterology and psychiatry.

[A4] Oxytocin demonstrates paradoxical outcomes. Research by Carsten De Dreu in Proceedings of the National Academy of Sciences (2011) showed that intranasal administration increases in-group trust while also promoting ethnocentrism. This duality complicates the image of oxytocin as the universal “love hormone.” The Endocrine Society notes its capacity to foster cooperation and exclusion simultaneously, requiring careful contextualization in social neuroscience.

[A5] Audio platforms such as Amazon Audible illustrate the separation between photic and auditory stimulation. When a smartphone is placed face down, blue light emission toward the eyes is minimal, reducing circadian impact. Sleep quality then depends on content type, emotional arousal, and listening duration. The American Academy of Sleep Medicine advises caution with stimulating content but does not classify audio playback as a circadian disruptor.

[A6] Bug zappers, despite their bluish glow, function through ultraviolet radiation that primarily affects insects, not circadian photoreceptors in humans. Concerns about melatonin suppression from such devices are unfounded, though other issues such as ecological disruption and ozone generation may arise. The National Sleep Foundation underscores that the main environmental threat to sleep quality is visible screen light, not ultraviolet emissions from insect traps.

Sources

• De Dreu, C. K. W., et al. “Oxytocin promotes human ethnocentrism.” Proceedings of the National Academy of Sciences, 2011, research article.
• Brainard, G. C., et al. “Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor.” Journal of Neuroscience, 2001, research article.
• Thapan, K., et al. “An action spectrum for melatonin suppression in humans.” Journal of Physiology, 2001, research article.
• Gershon, M. D. “Serotonin is a fundamental molecule for gut development and function.” Nature Reviews Gastroenterology & Hepatology, 2013, review.
• Carter, C. S. “Oxytocin pathways and the evolution of human behavior.” Annual Review of Psychology, 2014, review.
• Johns Hopkins Medicine. “Sleep and wake cycles.” Institutional resource.
• National Sleep Foundation. “Technology use and sleep.” Institutional resource.
• American Academy of Sleep Medicine. “Sleep hygiene recommendations.” Institutional guideline.
• Endocrine Society. “Hormones and endocrine function: Brain hormones.” Institutional resource.