Hormonal Causes of Daytime Sleepiness: Understanding the Endocrine Influence on Wakefulness

By SWA

Excessive daytime sleepiness (EDS) is a multifactorial condition that may significantly impair cognitive function, productivity, and overall quality of life. While sleep hygiene and neurological conditions are commonly examined, the role of endocrine function is equally critical. Hormonal imbalances can disrupt the sleep-wake cycle and contribute to persistent fatigue. This article outlines the primary hormones involved in sleep regulation and their potential contributions to daytime somnolence.

Melatonin: Regulator of Circadian Rhythm

Melatonin is a neurohormone synthesized by the pineal gland in response to darkness. It plays a central role in regulating the circadian rhythm, promoting sleep onset and maintenance. Its secretion typically increases in the evening and peaks during the night, then declines in the early morning.

  • Excessive melatonin levels during daytime hours—whether due to circadian rhythm disorders, irregular sleep schedules, or exogenous supplementation—can result in residual drowsiness and impaired alertness.

  • Insufficient nocturnal melatonin secretion may lead to fragmented sleep or insomnia, ultimately causing EDS.

Cortisol: Mediator of Wakefulness and Stress Response

Cortisol, a glucocorticoid produced by the adrenal cortex, follows a diurnal secretion pattern, with peak levels occurring in the early morning to support arousal and wakefulness. Levels gradually decline throughout the day, reaching a nadir at night.

  • Hypocortisolism, as seen in adrenal insufficiency or prolonged stress, may cause fatigue, poor concentration, and difficulty waking.

  • Disrupted cortisol rhythms, including elevated evening levels, can interfere with sleep initiation and maintenance, contributing to next-day sleepiness.

Thyroid Hormones (T3 and T4): Modulators of Metabolism and Energy

Thyroxine (T4) and triiodothyronine (T3) are essential thyroid hormones that regulate basal metabolic rate and energy homeostasis.

  • Hypothyroidism is frequently associated with lethargy, cognitive slowing, and hypersomnia due to diminished metabolic activity.

  • Hyperthyroidism, conversely, often presents with insomnia, restlessness, and non-restorative sleep, potentially leading to fatigue despite adequate sleep duration.

Estrogen and Progesterone: Hormonal Fluctuations and Sleep Architecture

In women, estrogen and progesterone levels fluctuate during the menstrual cycle, pregnancy, and menopause—each of which can impact sleep quality.

  • Progesterone has sedative properties, but its abrupt withdrawal (e.g., premenstrually or postpartum) can lead to sleep disturbances.

  • Estrogen modulates serotonin and other neurotransmitters that influence sleep regulation; low levels during menopause are often associated with insomnia and night awakenings, contributing to EDS.

Growth Hormone (GH): Role in Sleep Quality and Recovery

Growth hormone, primarily secreted during slow-wave sleep, supports tissue repair, cellular regeneration, and metabolic function.

  • GH deficiency, particularly in adults with hypopituitarism, is associated with reduced sleep efficiency, poor sleep quality, and increased fatigue.

  • Impairment in slow-wave sleep, whether due to aging or sleep disorders, may disrupt GH secretion and the restorative functions of sleep.

Additional Considerations in Daytime Sleepiness

While hormonal dysregulation is a significant contributor to EDS, other etiologies must be considered:

  • Primary sleep disorders such as obstructive sleep apnea, narcolepsy, and insomnia

  • Chronic medical conditions, including anemia, depression, and chronic fatigue syndrome

  • Pharmacological agents that affect hormone levels or interfere with sleep architecture

A comprehensive clinical evaluation—including hormonal panels, sleep studies, and a detailed medical history—is essential for accurate diagnosis and targeted treatment.

Conclusion

Daytime sleepiness is a complex symptom that may stem from or be exacerbated by hormonal imbalances. Melatonin and cortisol are central to circadian regulation, while thyroid hormones, reproductive hormones, and growth hormone also influence sleep quality and daytime alertness. Recognizing and addressing endocrine factors can be crucial in the effective management of EDS.

Individuals experiencing persistent fatigue despite adequate rest should seek evaluation from a healthcare provider to investigate potential hormonal or systemic causes.

References:

On the Interactions of the Hypothalamic-Pituitary-Adrenal (HPA) Axis and Sleep: Normal HPA Axis Activity and Circadian Rhythm, Exemplary Sleep Disorders
https://academic.oup.com/jcem/article-abstract/90/5/3106/2837129?redirectedFrom=fulltext&login=false

Hypothyroidism (Underactive) https://www.thyroid.org/hypothyroidism/

Sleep and metabolic function https://link.springer.com/article/10.1007/s00424-011-1053-z



© 2000-2025 Sieglinde W. Alexander. All writings by Sieglinde W. Alexander have a fife year copy right. Library of Congress Card Number: LCN 00-192742

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