We often hear about melatonin as the sleep-inducing hormone, don’t we? Our bodies naturally release it in sync with our circadian rhythm, making our sleep schedules fairly predictable. But here’s a fun fact: newborn babies don’t yet have a circadian rhythm and can’t produce melatonin in predictable patterns. Thankfully, breast milk steps in to help. It contains melatonin and its precursor, serotonin, which serve as a baby’s main supply until their own production ramps up.

Night time breast milk, in particular, has higher concentrations of melatonin compared to daytime milk, especially when parents’ circadian rhythms are supported by environmental factors such as dim lighting.

Beyond helping regulate sleep rhythms, melatonin in breast milk offers anti-inflammatory, antioxidant, and immune-boosting properties. It enhances phagocyte (a type of white blood cell that eats harmful bacteria and dead cells) function and supports lymphocyte survival in infant colostrum, playing a crucial role in neonatal growth and development. Impressive!

Since melatonin levels naturally rise at night, you might wonder if night-expressed milk should only be fed to babies during night time hours. The simple answer is no – any milk you express is beneficial, and when dealing with top-ups, focusing on a rigid schedule adds unnecessary stress. Still, for families feeding exclusively expressed milk, marking the time milk is expressed may be an option worth considering. While there isn’t sufficient research to confirm if this approach is beneficial, it’s certainly a personal choice.

If keeping track of milk timing fits well into your routine and reduces any stress, go for it! But if it’s complicating things, feel free to use milk whenever it’s needed.

By 2-3 months, your little one will start producing their own melatonin, though it takes several more months for their pattern to resemble that of an adult. As babies grow and development their own bodies will become more in tune with environmental factors such as light/dark cycles and chrononutrition (timing of meals). But even after those early months, breast milk continues to play a role in supporting your baby’s sleep-wake cycles!

Fun facts:

Research has shown that melatonin levels are even higher in preterm milk than in full-term milk, aligning with the increased maternal melatonin secretion after week 32 of pregnancy.

One study showed that melatonin levels in defrosted expressed milk remain stable from 4-24 hours. Defrosted milk should be used within 24 hours regardless.

Milk that has been pasteurised is likely to have lower levels of melatonin due to the heat treatment process.

Further Reading/resources:

Journal article – Melatonin in Human Breast Milk

Kathryn Stagg – Melatonin

IABLE – Melatonin in Breastmilk