Melatonin is the primary hormone that regulates the sleep-wake cycle, acting as an internal signal for the onset of darkness and rest. Produced by the pineal gland, this hormone governs the body’s 24-hour internal clock, known as the circadian rhythm. When light levels drop, melatonin production increases, inducing drowsiness. While this rhythmic process is established early in life, it is not active from birth, which explains the erratic sleep patterns of newborns.
The Timing of Melatonin Production
Newborns do not produce significant amounts of their own melatonin because the pineal gland, responsible for its synthesis, is not yet mature enough to establish a rhythmic secretion pattern. Their disorganized sleep results from this lack of internal regulation, causing them to sleep in short, irregular bursts. The appearance of a distinct, 24-hour melatonin rhythm in full-term infants typically begins around 9 to 12 weeks of age.
This onset of endogenous production marks the start of a more predictable sleep schedule, though the process is gradual. A stable, measurable melatonin rhythm becomes reliably established around three to four months of age. Even at six months, an infant’s total melatonin excretion is only about 25% of adult levels, showing the system continues to mature throughout the first year.
Maternal Transfer and Breast Milk Supply
Before the infant’s pineal gland develops its own rhythm, the baby receives melatonin passively from the mother. During late-stage pregnancy, maternal melatonin crosses the placenta, providing the fetus with a daily rhythm signal. This placental transfer ceases abruptly at birth, but the supply continues for breastfed infants through breast milk.
Breast milk contains melatonin, and its concentration fluctuates over a 24-hour period, mirroring the mother’s circadian rhythm. The concentration is considerably higher in milk collected at night compared to milk collected during the day. This difference provides a natural, passive sleep cue that helps with the initial entrainment of the infant’s developing circadian system.
Establishing the Infant Circadian Rhythm
Establishing a regular sleep cycle requires a robust circadian rhythm, primarily regulated by environmental light exposure. The brain’s internal clock is sensitive to light, which suppresses melatonin production and signals wakefulness. Conversely, darkness signals the pineal gland to release the hormone.
Parents can support the calibration of the infant’s natural timing mechanism by managing environmental cues. Exposing the baby to bright, natural light in the morning signals the start of the day and suppresses residual sleep hormone. Maintaining a dark environment for nighttime sleep and naps helps stimulate the developing pineal gland to produce melatonin at appropriate times.
Melatonin Supplements for Infants
Given the challenges of infant sleep, some parents consider giving their baby a melatonin supplement. However, the use of exogenous melatonin in infants is not recommended due to a lack of long-term safety data. Melatonin is regulated as a supplement, not a medication, meaning its quality and dosage are not strictly controlled. Sleep issues in infants are typically related to environmental or behavioral factors, not a hormone deficiency. Parents should always consult with a pediatrician before considering any supplement for sleep difficulties in their baby.