Can giving baby your expressed breast milk be 'mistimed' because of melatonin levels?

Does melatonin in your breast milk send your baby to sleep?

The diurnal fluctuation of melatonin in your breast milk is mostly controlled by your body clock. Your breast milk's natural melatonin levels don't make your breastmilk-fed baby sleep, and don't control your baby's body clock! When it comes to sleep, the melatonin produced naturally by your body and contained in your breast milk is a follower, not a leader. Amounts of melatonin in your milk track or follow your body clock settings. Your body clock itself is controlled by the sun and our planet's cycles of light and dark.

Melatonin diffuses from the blood serum into a woman's saliva and also into her breast milk. The same circadian pattern in plasma melatonin is found in both saliva and breast milk. Melatonin plasma levels start to rise at about nine o'clock at nights, peaking around two or three o'clock in the morning, and are undetectable during the day. Milk has about 35% of the melatonin concentration that is found in blood serum.

As a result, some breastfeeding advocates have claimed that melatonin in a mother's milk entrains the baby's body clock in the first two or three months, before pineal synthesis and secretion of melatonin become detectable. This is not true.

Good alignment of a baby's body clock with his parents' body clock can occur in both formula and breastfed babies well before 12 weeks of age regardless of melatonin levels, if parents know how to promote healthy settings of baby's sleep regulators, in the way we discuss in The Possums Sleep Program.

The environmental circadian cues of light and dark are by far the most powerful controllers of the ciradian rhythm, or body clock. This is why melatonin in your breast milk doesn't bring on sleep or make your baby sleep better.

There are many causes of sleep problems and excessive night waking, but low melatonin in your breast milk or expressed breast milk is not one of them.

Does 'mistimed' breast milk cause baby to have sleep problems?

The belief that sleep problems can arise from giving your baby expressed breast milk which was removed from your breasts at a time of day different to the time you feed it to your baby (referred to as 'mistimed breast milk') isn't true, and can in fact make life (and sleep) much harder than it needs to be for your family. Here's why.

• Melatonin levels follow disrupted sleep. The timing of, and the amounts of melatonin in, your milk don't cause disrupted sleep. The usual cause of disrupted sleep and excessive night waking is disrupted body clock settings (which will then result in disrupted melatonin levels). There are many things to consider which actually seriously impact on your baby's sleep, but these might be missed if a family feels they have to focus on matching expressed breast milk feeds.

• You're already working incredibly hard pumping your milk for your baby. It's certainly ok to label the milk if you wish, and to try to give milk from a certain time of the day to your baby at around that same time when you use it. Some families find this easy to do. But there's no reason to believe doing so will improve your baby's sleep or your nights. For some, this might significantly worsen work loads.

• Feeling that you have to get the timing of expressed breast milk (EBM) feeds right can worsen worry and stress for you, your family, and your baby's carers, and might even make you feel you have to give up on trying to give her EBM altogether, because it's too hard to get right.

• You might feel that the amount of breast milk you can use from a donor or milk bank becomes limited by the timing of milk removal.

No expressed breast milk is mistimed. If you or someone else is feeding your EBM to your baby (whether by a bottle or supplemental nursing system or cup), even if at a different time from when you collected it, your EBM is perfectly timed for your baby. What a wonderful gift you are giving your little one!

What does the research tell us about melatonin and mistimed breast milk?

In a 2022 study by Booker et al, commonly cited on the topic of infant sleep and mistimed breast milk, 329 women completed an online survey. Their babies were on average 24 weeks of age (six months) at time of participating, so many were already taking solids. Feeding type in the past four weeks was established, and The Brief Infant Sleep Questionnaire-Revised delivered, which self-reports duration of sleep, night-time awakenings and whether the infant has had a sleep problem over the past two weeks. Unfortunately, self-report of these infant sleep indicators has been shown elsewhere to be quite unreliable. The authors found that infants who consumed mistimed EBM took 12.5 minutes longer to get to sleep at night.

This study doesn't prove that carers can improve their baby's sleep if they align the time of pumping with the time the baby is fed that EBM. This is because

• Research more generally shows that naturally produced melatonin is not responsible for bringing on sleep

• Research more generally shows that large supplemental doses of melatonin are not reliably associated with improved sleep outcomes, and particularly not over time

• So many other factors impact powerfully upon baby sleep, which weren't considered in this study.

A subsequent study by Booker et al 2024 investigating the effects of shift work on melatonin levels in women's milk confirmed that melatonin levels track maternal circadian rhythm disruption.

It does seem to me that claims that 'mistimed' breastfeeding is likely to have consequences for the wellbeing of babies and their families is yet another example of the One Study Fallacy.

The most important way your breast milk melatonin supports your baby's health occurs in his gut

Neuroendocrine cells in the lining of the adult gut secrete melatonin. The concentration of melatonin in the gastrointestinal tract of adults is 10-100 times that of plasma, and 400 times more than that of the pineal gland.

The infant gut is immature in the first months of life. From an evolutionary perspective, the infant gut is dependent upon the mother's immune system for optimal function. The melatonin found in a woman's breast milk is just another extension (amongst a myriad of known examples) of her own physiological and neurohormonal systems, which protect her baby's immature gut and immune system while it is developing. The melatonin in your breast milk acts on the many melatonin receptors in the baby's gut to regulate

• Gut contractility and motility

• Immunity

• Anti-inflammatory effects

• Antioxidant effects.

This is, in my view, the most important way in which melatonin in your breast milk supports your baby's wellbeing. It doesn't matter what the levels are at any moment in time - what matters is the way melatonin washes through the gut over and over, day and night.

Recommended resources

Will dim lights in the evening increase melatonin and make sleep easier for your baby?

Will dim lights in the evening increase melatonin and make sleep easier for your toddler?

Melatonin and human sleep

Melatonin: production in babies (term + preterm) and supplementation

Melatonin research doesn't support the belief that dimming the lights helps with infant sleep

Selected references

Akanalci C, Bilici S. Biological clock and circadian rhythm of breast milk composition. Chronobiology International. 2024;41(8):1226-1236.

Bonmati-Carrion M-A, Rol M-A. Melatonin as a mediator of the gut microbiota-host interaction: implications for health and disease. Antioxidants. 2024;13(34):https://doi.org/10.3390/antiox13010034.

Booker LA, Spong J, Deacon-Crouch M, Skinner TC. Preliminary exploration into the impact of mistimed expressed breast milk feeding on infant sleep outcomes, compared to other feeding patterns. Breastfeeding Medicine. 2022;17(10):853-858.

Booker LA, Wilson D, Spong J. Maternal circadian disruption from shift work and the impact on the concentration of melatonin in breast milk. Breastfeeding Medicine. 2024;19(1):33-39.

Egeli TU, Tufekci KU, Ural C. A new perspective on the pathogenesis of infantile colic: is infatile colic a biorhythm disorder? Journal of Pediatric Gastroenterology and Nutrition. 2023;77(2):171-177.

Eidelman AI. Chrononutrition and the consequences of mistimed breastfeeding. Breastfeeding Medicine. 2022;17(10):777-778.

Oliveira F, Dieckman K, Mota D, Zenner AJ, Schleusner M, Cecilio J, et al. Melatonin in human milk: a scoping review. Biological Research for Nursing. 2025;27(1):142-167.