The circadian rhythm of breastmilk

And the physiology of tending to our babies at night feeds.

Human milk is rich in non-nutritive compounds including hormones and metabolites that signal complex circadian cues and maternal messages to our babes. This signalling starts in the womb when our infants are exposed to our physiological, metabolic and behavioural rhythms. After birth, the composition of our milk changes over the course of the 24hr cycle according to the circadian rhythm of the mother.

These circadian cues are physiologically important and biologically protective – especially for preterm babes and those in NICU. Immune cells, iron, fat molecules, and hormones all follow distinct circadian variations that may be important for optimal growth and development and help infants consolidate their sleep/wake cycles. Tending to our infants overnight and night feeds can ensure they download these cues and messages from mum.

Your breastmilk is talking to your baby.

MORNINGS:

Cortisol, and its inactive precursor, cortisone, follow a diurnal rhythm (day-based, the opposite of nocturnal) based on maternal hypothalamus-pituitary-adrenal (HPA) axis activity. These hormones are secreted by the adrenals and peak in the morning at around 7am. Cortisol is referred to as our stress hormone. And it most certainly is. But it also plays a vital role in regulating homeostasis by waking us up and preparing us to respond to physical and emotional stimuli of the day.

AFTERNOONS:

The concentration of tryptophan and other precursors to melatonin are higher in the afternoon suggesting a role in driving sleep pressure. Melatonin is a hormone produced in our pineal gland (aka our third eye) that helps regulate sleep and inform our circadian rhythm.

NIGHTS:

Melatonin in breast milk surges at night, peaking around 3am and dwindling during the day. This ebb and flow may signal the time of day to infants and inform the development of their own circadian rhythm.

Newborns produce very little melatonin – perhaps to reduce deep sleeping in order to maintain hydration and encourage milk flow. Serum levels of melatonin increase progressively up to 3 months old. As there is no melatonin in formula, breastmilk may improve nocturnal sleep patterns.

Had an early baby or NICU bub?

Milk produced for preterm babies has a higher concentration of melatonin. This extra sleep-fuel benefits premature infants in their first few weeks when they are especially vulnerable.

Get support

Nutrition also plays a huge role in our milk quality and quantity. If you’d like personalised support for breastfeeding, postpartum recovery, or navigating early motherhood, I’d love to help you in clinic. You can book an appointment today and feel truly supported in your journey.

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References

Arslanoglu, Bertino, Nicocia, & Moro. (2012). WAPM Working Group on Nutrition: potential chronobiotic role of human milk in sleep regulation. Journal of perinatal medicine, 40(1), 1-8. https://doi.org/10.1515/jpm.2011.134

Caba-Flores, M. (2022). Breast Milk and the Importance of Chrononutrition. Frontiers in Nutrition. https://doi.org/https://doi.org/10.3389/fnut.2022.867507

Chung, Kim, & Son. (2011, May). Circadian rhythm of adrenal glucocorticoid: Its regulation and clinical implications. Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 1812(5), 581-591. https://doi.org/10.1016/j.bbadis.2011.02.003

Engler, Hadash, Shehadeh, & Pillar. (2012). Breastfeeding may improve nocturnal sleep and reduce infantile colic: Potential role of breast milk melatonin. European Journey of Pediatrics , 171, 729–732. Https://doi.org/10.1007/s00431-011-1659-3

Gooley; Chamberlain; Smith; Khalsa; Rajaratnam; Reen, Van; Zeitzer; Czeisler; Lockley. (2011, March). Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans. Journal of Clinical Endocrinology and Metabolism, 96(3), E463–E472. https://doi.org/10.1210/jc.2010-2098

Italianer, M. F., Naninck, E., Roelants, J. A., van der Horst, G., Reiss, I., Goudoever, J., Vermeulen, M. J. (2020). Circadian Variation in Human Milk Composition, a Systematic Review. Nutrients, 12(8), 2328. https://doi.org/https://doi.org/10.3390/nu12082328

Qin; Shi; Zhuang; Liu; Tang; Bu; Sun; & Bei. (2019). Variations in melatonin levels in preterm and term human breast milk during the first month after delivery. Scientific Reports, 9(article 17984). https://doi.org/10.1038/s41598-019-54530-2

Van der Voorn; de Waard; van Goudoever; Rotteveel; Heijboer; & Finken. (2016, Nov). Breast-Milk Cortisol and Cortisone Concentrations Follow the Diurnal Rhythm of Maternal Hypothalamus-Pituitary-Adrenal Axis Activity. The Journal of Nutrition, 146(11), 2174-2179. https://doi.org/10.3945/jn.116.236349