Nighttime Breastmilk - how it is different
Breastfeeding is a relationship between a baby and their mother. But it is also a relationship between a baby and the breasts. A complex system of hormones guides your baby in many ways which might surprise you.
Nighttime milk is different to daytime!
Your baby is born without an independent circadian rhythm, the day/night clock which regulates our sleep/wake cycle in sync with the sun. While the maternal body clock supports the infant in the womb, their own system only begins to function from around 3 months.
Cortisol is a hormone our bodies increase as the sun rises and our brains respond to light. It wakes us up and keeps us alert. Breastmilk levels of cortisol are higher in the morning than at night. This signals to your baby it is time to wake up and start the day.
“Morning levels are approximately 4 times higher than levels present in breast milk produced in the evening (around 6pm). And they are about twice as high as levels present in milk expressed during the night (Pundir et al 2017; Italianer et al 2020).”
Melatonin is the hormone our body relies on to wind down for sleep at the end of the day, as the sun sets and darkness sets in. In breastmilk it begins to rise in the evening and peaks at midnight.
It is possible the infant brain is guided to develop their own circadian rhythm through natural cycles of these hormones.
“Researchers in China have documented dramatic changes across a 24-hour period.
Yishi Qin and her team tested the breast milk of 98 lactating mothers, and compared milk melatonin levels at 3pm, 9pm., and 3am (Qin et al 2019).
On average, melatonin levels at 9pm were nearly 3 times as high as melatonin levels at 3pm. And the breast milk pumped in the middle of the night? At 3am?
That’s when melatonin concentrations were at their peak — nearly 10 times higher than melatonin levels in milk collected during the afternoon.”
How does this impact expressed breastmilk?
We don’t know as the research is yet to be done. But if your baby is exclusively fed expressed breastmilk you might like to label the time of day you pumped and try to feed your baby that milk at the corresponding time of day.
It is worth noting that cluster feeding is most common in the late afternoon/early evening. That corresponds with the decrease of cortisol and increase of melatonin. This is probably no coincidence. The shorter the time between feeds then the higher the fat content is in your breastmilk. Evening breastfeeds are usually lower in volume but higher in fat, preparing your baby for nighttime sleep.
Nighttime breastmilk is a bedtime drink
Tryptophan, an amino acid which helps us fall to sleep for the night, is also found in breastmilk. Adults and children benefit from tryptophan in foods which help make us sleepy and breastfed babies are just the same. Trypotophan is also necessary to synthesise melatonin and serotonin. Ingestion of tryptophan in infancy leads to more serotonin development, creating the potential for life-long well-being.
“Tryptophan is a precursor to serotonin, a vital hormone for brain function and development. In early life, tryptophan ingestion leads to more serotonin receptor development (Hibberd, Brooke, Carter, Haug, & Harzer, 1981). Nighttime breastmilk also has amino acids that promote serotonin synthesis (Delgado, 2006; Goldman, 1983; Lien, 2003). Serotonin makes the brain work better, keeps one in a good mood, and helps with sleep-wake cycles (Somer, 2009). So it may be especially important for children to have evening or night breastmilk because it has tryptophan in it, for reasons beyond getting them to sleep.”
Nighttime breastfeeding matters
In the 20th century, feeding babies during the night was treated like a behavioral problem by many. An inconvenient habit needing to be stopped by parents refusing to attend to their infant’s feeding cues and signals. “Sleeping through the night” was seen as a desirable milestone.
It is confronting then to discover that not only is breastfeeding through the night normal and natural but babies actually rely on those feeds for around 20% of their daily milk intake. Nighttime breastmilk is naturally higher in fat, important for growth and development. Denying babies the breastfeeds they need during the night might lead to low milk supply and poor weight gains. When babies are left to cry their cortisol levels increase and remain high even when they cease calling for their mother. Cortisol is also a stress hormone.
Night feeding is important for milk production
Not only are the hormones important for circadian rhythm different at night but the hormone prolactin which drives milk production is too. Prolactin peaks in the early morning hours around 2-5 a.m., while the lowest prolactin levels happen in the late afternoon to early evening. Just in time to be boosted by that cluster feeding. By morning, your breasts might feel fuller and you notice a higher volume of milk if you express, though this milk is lower in fat than it was 12 hours before.
Breastfeeding helps babies AND mothers return to sleep quickly.
Breastmilk contains a wonderful hormone called cholecystokinin (CCK). CCK induces sleepiness, both in the baby and the mother. When the baby sucks, CCK is released within the mother to help her rest and relax. While mothers sometimes describe breastfeeding as making them tired, what they are experiencing during a feed is sleepiness. This is why lying down to breastfeed and breastsleeping work so well to help mothers get the sleep they need. Mothers who breastfeed during the night get more sleep than formula feeding mothers, who can take up to an hour to fall back to sleep after getting up to prepare and give their baby a bottle.
Breastfeeding to sleep is a natural part of an infants sleep behaviour. CCK release is caused by sucking and when food, especially fat, enters the stomach. There are actually two CCK peaks, one at the end of a feed, and the other higher peak between 30 and 60 minutes after the feed. This is why babies often wake after the first 40 minute cycle of sleep and return to the breast before having a longer sleep period.
Breastsleeping is nature's way of packaging all this so that mothers and babies maximise milk production and sleep during the dark hours. The baby feeds most frequently around sunset and in the hours mother and baby would naturally spend lying together in the night. Frequent removal of milk from the breast stimulates production and the baby takes nearly a quarter of their daily nourishment while the baby sleeps.
Nighttime breastfeeding helps suppress fertility and aids natural child spacing.
Raising a human infant takes dedicated care around the clock. Conceiving another pregnancy while still tending a dependent infant is risky for all involved. Babies born too close together compete with each other for care and put a high demand on the mother both physically and emotionally. So nature put some protective barriers in place against premature conception by suppressing fertility.
When a infant has unrestricted access to the breast day and night a woman’s return to ovulation and menstruation typically occurs after her baby begins eating family foods in the second six months. Some families practice The Lactational Amenorrhea Method (LAM) for postpartum contraception. This is not infallible and mothers can conceive while exclusively breastfeeding.
Typical child spacing in humans is 3-4 years, allowing the infant to wean before a new pregnancy. Similar age gaps are also seen in gorillas and chimpanzees, who parent in community like humans. Orang-utan mothers, who live solitary lives with their young, breastfeed each for around 8 years before they separate and she is ready to breed again.
Babies and breasts work together around the clock to maximise infant growth and brain development. Night waking is normal in the first years of life and nighttime breastfeeding helps babies AND mothers.
