Il ciclo circadiano del neonato

What is the circadian rhythm?

The circadian rhythm is an endogenous system that regulates biological processes over a period of approximately 24 hours. It influences essential physiological functions such as sleep, body temperature, hormone secretion, and feeding.

In newborns, this system is still immature at birth, but it develops rapidly during the first months of life. The maturation of the circadian rhythm plays a crucial role in the infant’s well-being and neurophysiological development.

How does it work?

The circadian rhythm is governed by a “central biological clock” located in the suprachiasmatic nucleus (SCN) of the hypothalamus. This center receives information mainly from environmental light and synchronizes bodily rhythms with external stimuli such as the light-dark cycle.

At birth, the SCN is morphologically formed but still functionally immature, which explains the seemingly random distribution of sleep and wakefulness across the 24 hours in newborns.

Two key hormones involved in circadian regulation are:

• Melatonin, secreted by the pineal gland during the dark hours, with a sleep-promoting effect.
• Cortisol, produced by the adrenal glands, with a peak in the early morning, promoting wakefulness.

In newborns, autonomous melatonin production begins around the 8th to 12th week of life, while cortisol develops a more defined circadian rhythm around 2 to 3 months.

Characteristics of the circadian rhythm in newborns

The maturation of the newborn’s circadian rhythm depends on a combination of genetic, environmental, and behavioral factors. Among these, exposure to natural light is the main external synchronizer (zeitgeber), while breastfeeding and daily routines (such as feeding and a nighttime bath) contribute to transmitting time cues that support sleep regulation.

Key characteristics of this process include:

• Lack of light-dark differentiation: in the first days of life, the newborn does not yet respond significantly to environmental light as a time cue.
• Polyphasic sleep pattern: newborns sleep in short cycles spread throughout the 24-hour period, with a predominance of REM sleep.
• Progressive maturation: from around the 6th to 8th week of life, a differentiation between daytime and nighttime sleep begins to emerge, thanks to SCN maturation and synchronization with environmental signals.

Proper circadian regulation positively impacts several aspects of neonatal health:

• Improves sleep quality and nighttime continuity.
• Supports neurological and cognitive development.
• Contributes to metabolic balance.
• Reduces the risk of infant sleep disorders.

However, circadian rhythm development may be hindered by factors such as prematurity, limited exposure to natural light, and lack of consistent routines.