By Anna Cave-Bigley
When I first began breastfeeding, I was dealing with the opposite of what so many mothers fear. I wasn’t worried about not making enough milk, I was drowning in too much of it. Engorgement, painful leaking through the night, constant fullness: my body felt out of sync with my baby’s needs.
At first, I thought it was just bad luck. But as I began investigating the biology of lactation, I learned that breastmilk isn’t produced on a flat line. It follows circadian rhythms, 24-hour hormonal cycles that influence not only how much milk we make, but also what’s in it.
That discovery changed everything for me as both a mother and as the product co-developer of Our Breastfeeding Herbata. It reframed my 2 a.m. resentment into something else: an understanding that those difficult night feeds were biologically programmed, not just for supply, but for my baby’s sleep, brain development, and immune system.
Prolactin: The Hormone That Peaks at Night
Milk production depends on prolactin, a hormone secreted in pulses by the pituitary gland. Prolactin levels aren’t constant, they surge most strongly in the evening and early morning hours, particularly between midnight and 4 a.m. (Neville et al., 2001).
This means night feeds aren’t just a chore: they are biologically strategic. Nursing during these peak windows reinforces prolactin surges, helping to maintain or even increase supply long-term. By contrast, consistently skipping night feeds can flatten prolactin patterns and lead to reduced production over weeks.
When I struggled with overproduction, I eventually realised that my engorgement wasn’t random, it was tied to these hormonal rhythms. My body was making milk on a circadian schedule, and by understanding that, I could work with the rhythm instead of fighting it. For mothers with low supply, the same principle applies: night feeds are one of the body’s strongest natural drivers of milk synthesis.
Melatonin and Night Milk: Sleep in a Bottle
Breastmilk is “time-stamped.” Its composition changes across 24 hours, with night milk carrying higher concentrations of melatonin, the hormone that regulates sleep. Melatonin in human milk peaks at night and is nearly absent during the day.
Why does this matter? Babies don’t reliably produce their own melatonin until about 3 months old. Until then, they rely on external cues to shape their circadian rhythm. Night milk provides melatonin, along with tryptophan, a precursor to serotonin and melatonin, which helps infants consolidate sleep and adapt to day–night cycles.
There’s also evidence that melatonin in breastmilk carries antioxidant and anti-inflammatory properties, potentially protecting the infant gut and immune system during vulnerable nighttime hours.
For me, this explained why my baby often settled more easily after those exhausting night feeds than during the day. My milk itself was carrying sleep signals her body didn’t yet know how to produce.
Cortisol and Morning Milk: Alertness on Cue
If night milk is designed to soothe, day milk is designed to stimulate. Cortisol, a hormone associated with alertness and metabolism, is naturally higher in morning breastmilk. One study found that infants whose mothers had higher daytime milk cortisol were more active and wakeful in the day, while those with lower levels were more sluggish.
This cortisol rhythm helps synchronise the infant with daylight activity. It may also play a role in early immune programming, as cortisol influences inflammation and stress responses.
Together, these daily variations show that breastmilk isn’t just food. It’s a circadian map, providing babies with hormonal guidance to align their physiology with the outside world.
What Happens When the Rhythm is Disrupted?
In modern parenting, it’s common to express milk and feed it later. While this is often necessary, it may blur the circadian “signals” embedded in milk. Research suggests that giving infants night milk during the day (or vice versa) can confuse these cues, potentially affecting sleep patterns and feeding behaviours.
Some experts recommend labelling expressed milk as “day” or “night,” so babies receive it in sync with their body clocks. While this research is still emerging, it highlights an important point: breastfeeding is not just about quantity, but about timing.
Supporting Mothers Through the Night
Knowing the biology doesn’t erase the exhaustion. Night feeds are still brutal, I remember the bone-deep fatigue, the resentment of never having a stretch of sleep. But understanding the science gave me a sense of purpose: those hours weren’t wasted, they were essential.
It also shaped how we think at The SABI. Our Breastfeeding Herbata was formulated with this reality in mind. Blending mineral-rich nettle and oat straw with calming herbs like tulsi and vervain, it’s safe to drink at night, replenishes hydration lost through milk-making, and helps calm the nervous system when cortisol is already too high. Because supporting supply is about more than hormones, it’s about protecting the mother’s body in the hours when she needs it most.
Rethinking Night Feeds
We often frame night feeds as unnecessary or unfair, but the science tells us they are among the most important parts of breastfeeding. They:
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Synchronise supply with circadian prolactin peaks.
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Deliver melatonin and tryptophan to help babies consolidate sleep.
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Provide cortisol and other signals in morning milk that align infants with daytime rhythms.
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Carry antioxidant and immune factors that may protect babies during critical development windows.
For me, the shift was recognising that the rhythms of milk aren’t mistakes of biology. They’re built-in programming, connecting mother and baby, night after night, until the baby’s own internal clock can take over.
HORMONAL & PROUD
Created as a brand to help women navigate the toughest moments in pregnancy, childbirth, postpartum — and practically every stage of life –– The SABI is changing the narrative around our hormones from one of taboo, embarrassment, and loneliness to awareness and even, pride. As more than a wellness brand, The SABI offers a carefully-crafted line of products to carry you through your hormonal journey, including rituals, supportive tools, and ancient herbal remedies that have been tested time and time again by women and now come backed by medicine. The SABI is a blend of science and nature conceived by women who have experienced the joys and deep struggles of bringing a child into the world, the pains of a heavy, difficult period, miscarriage, and difficulty conceiving.
We invite you to get to know your body and its cycles better –– to really understand what is going on inside. Learn to use your hormones to your advantage no matter your stage of life, and know that you can support and balance your hormone levels. We are here to help with the information, understanding and natural tools to support your body and the emotional process along with it.
ABOUT ANNA
Anna is a Co-founder of The SABI and has spent the past 13 years working in or for governments, senior businessmen and politicians around the world. Living in Bogota, Colombia, she recently renovated one of Colombia’s oldest and most iconic coffee estates, developing a unique taste and travel experience. She lives with her husband and three boys Lorenzo, Alfie and Salvador who are responsible for the beautiful journey that inspired her to pursue The Sabi.
DISCLAIMER
The SABI blog and articles are not meant to instruct or advise on medical or health conditions, but to inform. The information and opinions presented here do not substitute professional medical advice or consultations with healthcare professionals for your unique situation.
References
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Neville MC, et al. Lactogenesis: the transition from pregnancy to lactation. J Nutr. 2001.
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Illnerová H, et al. Melatonin in human milk. J Clin Endocrinol Metab. 1993.
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Cubero J, et al. Chrononutrition: melatonin in night-time milk. Neuro Endocrinol Lett. 2005.
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Hahn-Holbrook J, et al. Daytime cortisol in breastmilk and infant behaviour. Psychoneuroendocrinology. 2019.
