The importance of sleep continuity in the newborn: the role of melatonin and growth hormone

Neonatal sleep is not merely a period of inactivity but acts as a crucial biological mechanism, orchestrated to promote growth, neurocognitive maturation, endocrine regulation, and immune system stability.

During the first months of life, sleep continuity becomes a determining factor for the secretion of melatonin and growth hormone (GH), two fundamental physiological pillars for the harmonious development of the newborn, as well as for the establishment of circadian rhythms, which regulate physiology, behavior, and metabolism.

Neonatal Sleep Architecture and Physiological Significance

In newborns, sleep cycles are shorter than in adults, lasting approximately 50–60 minutes, with a predominance of REM sleep, which is essential for cerebral plasticity and the maturation of neuronal networks. Although less represented, NREM sleep provides the optimal context for maximal GH secretion, which is crucial for somatic growth, musculoskeletal development, and tissue regeneration.
Sleep continuity allows the completion of physiological sleep cycles and the optimization of endocrine processes; conversely, frequent interruptions may impair hormonal secretion and negatively affect growth and the regulation of neonatal circadian rhythms.

Melatonin: Origin, Function, and Mechanisms

Melatonin is a hormone primarily produced by the pineal gland, located in the epithalamic region of the brain. Its synthesis follows a circadian rhythm regulated by light exposure: light inhibits melatonin production, while darkness promotes its secretion. In the newborn, melatonin performs several key functions:

• Regulates circadian rhythms, facilitating sleep onset and maintenance;
• Exerts antioxidant effects, protecting cells from oxidative stress;
• Modulates vagal tone and neuroendocrine activity, contributing to neurological maturation and physiological stability;
• Synchronizes metabolic and immune rhythms, essential for growth and well-being.

In newborns, melatonin levels are initially very low and become rhythmic only after several weeks of life, as exposure to light–dark cycles increases and the circadian system matures.

Circadian Rhythms and the Neonatal Brain

1. Synaptic plasticity: during REM sleep, neuronal networks exhibit desynchronized electrical oscillations that promote synapse formation and consolidation, essential for early cognitive and sensory development.
2. Myelination and cortical development: deep NREM sleep allows pulsatile GH production, promoting myelination, neuronal growth, and maturation of brain tissues.
3. Neuroendocrine regulation: circadian activity of the SCN modulates the hypothalamus and pituitary gland, controlling melatonin secretion from the pineal gland and GH release from the anterior pituitary, supporting somatic growth, metabolism, and physiological stability.
4. Neurotransmission development: alternation between wakefulness and sleep regulates the release of key neurotransmitters such as serotonin, dopamine, and GABA, essential for neurological balance and future mood and anxiety regulation.
5. Peripheral synchronization: the brain sends signals to peripheral circadian clocks (liver, gut, immune system), contributing to metabolic maturation and regulation of digestion, enzyme secretion, and immune response.

Growth Hormone (GH) and Growth

Growth hormone is secreted by the anterior pituitary in a pulsatile manner, with peaks occurring mainly during deep NREM sleep (stages 3 and 4 of slow-wave sleep). This pulsatile secretion is regulated by a complex neuroendocrine system involving the hypothalamic arcuate nucleus, somatostatin, growth hormone–releasing hormone (GHRH), and metabolic feedback from peripheral factors such as IGF-1, blood glucose, and amino acid levels.
In newborns, the pulsatile pattern of GH secretion is essential for coordinating somatic and neuroendocrine development.

Regular GH secretion supports:

• Harmonious linear and weight growth, by stimulating proliferation and differentiation of epiphyseal chondrocytes;
• Organ and tissue maturation, promoting functional development of the liver, heart, kidneys, and lungs;
• Cellular repair and energy metabolism, enhancing lipolysis, preserving glycemia, and supporting protein synthesis;
• Musculoskeletal development, stimulating muscle mass formation and bone mineralization.

Sleep continuity is a fundamental prerequisite for optimal GH secretion. Fragmented or interrupted sleep reduces nocturnal GH peaks, impairing growth regulation and altering neuroendocrine balance. In particular, deprivation of deep NREM sleep may lead to delayed growth, impaired protein synthesis, and alterations in energy homeostasis, with potentially long-lasting metabolic and neurocognitive consequences.

GH interacts closely with other endocrine mediators, such as melatonin and oxytocin, coordinating growth processes with emerging circadian rhythms. Melatonin facilitates deep sleep onset and consequently enhances nocturnal GH pulsatility, creating a synergistic neuroendocrine cycle essential for harmonious brain and body development.

Interactions Between Melatonin, GH, and Sleep Continuity

Melatonin and GH act synergistically: melatonin promotes deep, continuous sleep, which is indispensable for pulsatile GH secretion. This endocrine mechanism underpins growth, neurological development, and overall neonatal health, with long-term effects on metabolic regulation and physiological well-being.

Key message:

• Sleep continuity is essential for neonatal growth and neuroendocrine maturation.
• Melatonin and GH act complementarily to optimize sleep, growth, and brain development.
• Circadian rhythms mature gradually from birth through early infancy; environment and routines play a decisive role.
• Early parental education (sleep routines, light and noise management, recognition of sleep cues) supports neonatal health.
• Continuous sleep in early months improves cerebral oxygenation, hormonal regulation, and immune function, positively influencing physical and emotional development.

Approaches and Practices to Promote Well-being and Sleep Continuity in the Newborn

Promoting high-quality sleep in the newborn requires the adoption of environmental and behavioral strategies consistent with the physiology of developing circadian rhythms.

• Establish consistent routines while respecting the infant’s sleep cues, in order to provide stable temporal references that support circadian system maturation and reduce episodes of fragmented wakefulness.
• Expose the newborn to natural daylight through daily walks and outdoor activities, promoting circadian synchronization and regulation of the sleep–wake cycle.
• Avoid waking the newborn or infant during sleep, preserving sleep continuity and the proper release cycle of growth hormone, which is essential for somatic growth, brain maturation, and metabolic regulation.
• Minimize stimuli and interruptions during the night by avoiding sudden noises, bright lights, or sensory overstimulation, in order to protect nocturnal peaks of melatonin and growth hormone.
• Encourage moments of relaxation and physical contact with the mother, such as cuddling, gentle touch, and breastfeeding, strengthening bonding, stimulating maternal and infant oxytocin release, and positively modulating stress through reduced cortisol levels.
• Integrate daily walks and gentle movement, which support the physiological maturation of circadian rhythms, promote overall infant well-being, and improve the quality of nocturnal sleep.
• Monitor and correct potential sleep-disrupting factors, such as overstimulation or environmental noise, creating a safe and predictable context that consolidates emerging circadian rhythms.

Continuous sleep in newborns acts as a fundamental preventive biological intervention for growth, neurological maturation, and overall health. Melatonin, through circadian rhythm regulation, and growth hormone, through tissue growth and regeneration, are the primary mediators of this process. Promoting appropriate routines, supportive environments, and targeted educational behaviors allows optimization of neonatal outcomes and supports harmonious, long-term physiological development.