Melatonin in Breastmilk
by Anne Eglash MD, IBCLC, FABM
Melatonin is a hormone secreted by the pineal gland, which sits in the back portion of the brain. Often referred to as our ‘third eye’, the pineal gland secretes melatonin in response to light exposure. Monkeying with light exposure, such as bedtime reading of screens that emit blue light, can disturb our rhythmic melatonin secretion, contributing to sleep problems. Getting up each morning and bathing oneself in sunshine helps to regulate our melatonin, and thereby our sleep/wake cycle.
Melatonin, present in breastmilk, contributes time-of-day information to infants by varying its concentration throughout the 24 hours. Other compounds in breastmilk also play a role in the circadian rhythm of infants, such as cortisol, tryptophan, leptin and others.
The researchers for this week’s CQW article sought to determine if freezing/thawing of expressed breastmilk has an effect on the concentration of melatonin in breastmilk. They studied melatonin concentrations in the expressed breastmilk from 13 women after the milk was frozen and defrosted. Measurements were taken at 1,2,3,4, and 24 hours after defrosting. They found that melatonin levels are stable for at least 4 hours and up to 24 hours after defrosting.
But, there are some other interesting things to know about melatonin, so go ahead and test yourself below.
- The level of melatonin in breastmilk peaks at 11 pm.
- Melatonin is at its lowest level in breastmilk at 7 am.
- Melatonin synthesis in healthy term infants begins at 6-8 weeks of life.
- Melatonin treatment has been shown to have an analgesic effect in infants.
See the Answer
Melatonin is an antioxidant, a circadian pacemaker, and an immune system stimulator. Studies have demonstrated beneficial effects of melatonin on various conditions in neonates. Melatonin is secreted in breast milk in circadian rhythm, but its half-life and stability in this medium and in real-life conditions of freezing and defrosting is unknown. The objective of this feasibility study was to evaluate stability of melatonin in breast milk after freezing and defrosting.
Methods and Results
Breast milk samples of nocturnal milk and daytime milk were collected from 13 healthy breastfeeding mothers and were immediately frozen. Samples were defrosted in room temperature and were sampled for melatonin immediately and every hour for 4 hours and at 24 hours after defrosting. Melatonin levels were measured with Melatonin direct Saliva ELISA kit (IBL International).There was no statistically significant difference between levels at the different time points (p = 0.696). Melatonin levels in daytime milk were significantly lower than night-time levels (p = 0.028).
Melatonin is stable in human milk for at least 4 hours after defrosting and even up to 24 hours. Further research of the therapeutic potential of night breast milk high in melatonin is needed.
Breastmilk melatonin peaks at 3 am, which clinically appears to be associated with that 3am-7am blissful sleep among neonates during the first few weeks of life. Melatonin secretion in breastmilk is lowest at 10am-noon, and at that point is nearly undetectable, until it gradually rises before night time sleep, peaking in the early morning hours.
According to the authors of this study, melatonin treatment has been shown to improve respiratory distress syndrome, reduce inflammation from neonatal sepsis, and have an analgesic effect on infants.
The big question is whether giving breastmilk expressed at a time of day that is not congruent with when the infant takes the milk has an effect on infant circadian rhythm. A recent article on 'chrononutrition' explains that other substances in breastmilk also may contribute to time-of-day information to infants. Tryptophan levels in the evening play a role in promoting sleep and relaxation, and higher levels of breastmilk cortisol occur in the morning, as do activity-promoting amino acids, to aid in energizing infants during awakefulness. There is also preliminary evidence that the breastmilk leptin level, an appetite suppressive hormone, is higher at night.
There are no clinical trials showing infant health effects of mistimed feedings. Until we know more, it may be reasonable for mothers to label the time of day of the expressed breastmilk and try to match this with the time of feeding.