How does breast milk help develop circadian rhythm in babies?

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As any sleep-deprived new parent will testify, there’s no sleep-wake cycle or circadian rhythm in babies. Your little one will only develop circadian rhythm after the first three months of life. So how does your baby know when it’s time to wake up, eat, and sleep? 

The answer lies in breastfeeding for babies. It’s breast milk that works like an internal clock for your newborn. It helps them develop circadian rhythm over the course of the first three months of their life.

Breast milk is no ordinary meal. The nutritious components of breast milk build a newborn baby’s immunity, strength, and cognition. However, its most intriguing property is that it changes its composition throughout the day and night, personalizing the hormones and nutrients for the baby. It helps in developing circadian rhythm in babies through cortisol and melatonin – the hormones responsible for our sleep-wake cycle.

Did you know?
While cortisol is like an energy drink, melatonin is like a sleep-inducing potion.

Bottle of energy drink depicting cortisol and bottle of sleeping potion depicting melatonin

Cortisol rises in the breastmilk in the morning hours and acts like an energy drink for the baby. Melatonin rises in the breastmilk in the evening hours and acts like a sleeping potion.

Breast milk hormones

Both these hormones rise and fall in the breast milk at specific times during the day. So a large gap between when the milk is expressed and when your newborn is ingesting it, might be a bit of a problem. You might be feeding your baby breast milk pumped in the morning at night. It’s pretty much like feeding coffee to your little one!

But how does breast milk help your baby develop circadian rhythm? Do babies produce their own cortisol and melatonin? How can you help your baby develop a well-adjusted circadian rhythm through breast milk? Let’s find out.

Circadian rhythm and its working

Circadian rhythms are physical, mental, and behavioral changes that take place in our body in a 24-hour cycle, synchronized with the sun. These changes tell us the time of day. Our sleep-wake cycle is our body’s natural tendency to become alert and active with sunrise and slow down to sleep with the sun set. It is one of the most important circadian rhythms.

And despite being the most important circadian rhythm, humans are not born with it. It takes months to develop, but more on that later. First, we gotta see how our bodies function like clockwork.

Mechanism of circadian rhythm

Every cell in our body has a tiny clock of its own. This army of tiny clocks takes orders from a Master Clock that’s located in our brain. It has a fancy name – SCN or suprachiasmatic nucleus. Every process in our body is controlled by this master clock. This master clock, in turn, gets its cues of what to do from sunlight and is synchronized with the light-dark cycle.

The Suprachiasmatic Nucleus (SCN) as a masterclock inside our brain.
This is how we fall asleep – Our eyes have light and color sensitive cells called rods and cones. Rods are extremely sensitive to light and can be triggered by a single photon of light! Cones help us see the colors and sharpness of objects. As the sun sets and the rod cells in our eyes detect darkness, a signal is sent to the master clock or SCN in our brain. This master clock then signals to produce a hormone called melatonin or the sleep hormone. As this hormone is released in our body, a signal is sent to all the tiny clocks in our cells to prepare the body for sleep. Similarly, with the cues of light and dark, the master clock keeps dictating the tiny clocks in all our cells what to do. 

Did you know?
Sleep, hunger, blood pressure, alertness, and pretty much everything else in your body happens in sync with the circadian rhythm.

Is there any circadian rhythm in babies?

Newborn baby on a clock confused about sleep and wake hours
Newborn babies don’t have a well developed circadian rhythm. That’s why they don’t have a sleep-wake cycle – they don’t know which time is for sleeping and which is for waking up.

Well, sort of. While they do have a faint sense of circadian rhythm in the womb, it is a completely different environment. Inside the womb, the sense of circadian rhythm in babies comes from the mother. However, after birth, babies start developing a circadian rhythm at 11 weeks of age, around the end of the third month. 

Two of the most important factors that help in development of circadian rhythm in babies are-

  • Sunlight
  • Breast milk

Breast milk helps your baby develop hormones responsible for the sleep cycle. And exposure to sunlight helps them develop a sense of day and night. Without exposure to sunlight, the baby will not be able to understand the difference between light and dark. This understanding is necessary for production of hormones that aid the sleep-wake cycle.

Gradually, with the help of breast milk and daily sunlight exposure, the number of hours that your baby sleeps during the night increases.

Components of circadian rhythm

Research states that circadian rhythm in babies has certain components that develop gradually.

Component Age at which it develops 
Rhythm of cortisol8 weeks
Melatonin and sleep efficiency9 weeks
Body temperature rhythm and rhythm of circadian genes11 weeks

Internal and external cues for developing circadian rhythm in babies

Adults have a well-developed brain that houses the master clock. This master clock in turn dictates all the tiny clocks in all our cells what and when to do. Newborn babies, on the other hand, don’t have well-developed and mature brains, and thus, a master clock either. The tiny clocks in the baby’s cells don’t have any orders to follow.

The master clock inside a baby’s brain is under construction
A baby’s master clock develops over a period of time. Factors like breast milk and sunlight help in its development. Slowly, the tiny clocks in each cell of the baby’s body develop a sense of time.

And though the sun and the environment can act as external cues to developing circadian rhythm, what about the internal cues?

That’s where breast milk comes in. 

Pillars of a baby’s circadian rhythm

The two pillars on which a baby’s circadian rhythm develops are – breast milk (nutrition) and environmental cues. The latter is an obvious factor – get your baby some sun during the day and avoid unnecessary exposure to artificial light after the dark. That will automatically help their bodies develop a sense of light and dark, and synchronize with the day-night cycle.

A mother getting her baby a daily dose of sunlight in the open.
Daily exposure to sunlight helps babies develop a sense of light and dark, which is necessary for circadian rhythm.

The former, breast milk, is complex. How? Well, it acts like an energy drink in the morning and a sleep-inducing potion at night. All on its own.

Let’s see how that happens.

The dynamic nature of breast milk composition

The breast milk composition changes not only throughout day and night, but throughout the feeding period, as per the nutritional demands of the baby. That means that the morning and evening breast milk is wildly different from each other. And unless you’re breastfeeding your baby in real time, this difference can confuse your little one’s body.

The hormones that the baby ingests depend on the timing of breastfeeding or when the milk is expressed. The morning milk is high in an energy drink-like hormone called cortisol. And the evening milk is high is a sleep-inducing hormone called melatonin. Before going into detail of these hormones, let’s first take a look at how babies develop circadian rhythm through breast milk.

Connection between breast milk and circadian rhythm

Well, like we said, babies don’t have circadian rhythms or a master clock in their brain. So how will the cells in their bodies develop their own clocks? And how will those little clocks function when there is no master clock to give orders? 

The composition of breast milk changes with day and night. So when your baby ingests it, they are also taking in the little clocks from your body. Over time, three things happen.

One, your baby ingests breast milk having hormones which act like tiny clocks for the baby’s body. 

Two, nutrition and sleep help your baby’s brain mature and develop at an unprecedented pace. This helps them develop a master clock of their own. 

Three, daily exposure to sunlight and darkness helps the baby’s body get in sync with the light-darkness cycle.

Combine all these three factors over the course of the first few months of your baby’s life, and voilà! Now your baby’s brain has its own master clock. This clock signals the tiny clocks in each cell of their body when it’s time to sleep and wake up. This sense of circadian rhythm in your baby grows with age. You’d be able to tell the difference when the number of hours that your baby sleeps during the night increases.

Now let’s get back to the hormones that are responsible for making us feel alert each morning and sleepy each night.

Morning milk vs evening milk : Cortisol and Melatonin


Often called the ‘stress hormone’, cortisol is in fact nature’s in-build alarm system in our body. It helps us stay alert during the day. In short, the morning breast milk has the components of an energy drink. It will help your baby in waking up and feeling alert and active.

Did you know?
Scientists have found that babies with higher levels of cortisol cried easily or became easily agitated when placed in unfamiliar environments or situations.

When does cortisol start getting produced in babies?

Cortisol production starts in babies from about 6 weeks of age. This production also follows a rhythm, peaking in early morning and dropping down in evening. This pattern becomes stable across the first year of your baby’s life. However, full maturity in this pattern isn’t reached until preschool years.

When does cortisol production peak in breast milk?

Cortisol is highest in the morning milk around 6 am. It gradually decreases during the day, finally reaching its lowest point at midnight. The level of Cortisol is three times higher in the morning milk, at around 7 am, than the evening milk.

U-shaped diagram showing difference in cortisol and melatonin levels during day and night.
Cortisol levels peak at 6 am in the breast milk and keep on gradually decreasing throughout the day, becoming negligible at midnight. Melatonin levels start increasing with the night and peak at 3 am.
Things that increase cortisolThings that decrease cortisol
– Physical stress
– Emotional stress
– Injury
– Caffeine
– Meditation
– Regular exercise
– Healthy diet
– Doing things you enjoy


Also called the sleep hormone, melatonin is mainly responsible for our sleep-wake cycle. 

As our eyes sense the darkness that sets in with the nighttime, the master clock in our brain signals our body to secrete melatonin. This is the reason why your body starts to automatically go into the shut-down mode at night. You start feeling drowsy and less alert. Melatonin is nature’s in-build sleeping pills in our bodies.

Did you know?
Melatonin is a prerequisite to falling asleep.

When does melatonin start getting produced in babies?

Melatonin secretion doesn’t start in newborn babies up until the third and fourth months after birth. For the first three to four months of life, babies depend on the melatonin in breast milk for sleep regulation.

Did you know?
Two processes coincide at the age of 3 months:
– Beginning of melatonin development
– Beginning of development of a circadian rhythm. 

When does melatonin production peak in breast milk?

Melatonin peaks in breast milk at 3 am. Research has pointed out that this timing of spike in melatonin corresponds to the 3 am – 7 am deep sleep in newborns. This happens during the first few weeks of their life.

Like clockwork, melatonin levels in breast milk start decreasing after 3 am as the morning hours kick in. At 10 am till noon, melatonin levels are at the lowest, being nearly undetectable at noon. They start rising again before the nighttime sleep and peak again in the early morning hours.

In her book, Why Your Sleep Matters, Sarah Oakwell digs deeper into the correlation between circadian rhythm and breast milk. She writes that circadian rhythm affects night-time breast milk through something called ‘neuropeptides’. 

Neuropeptides are small, protein-like molecules that are released by neurons in the brain. They act as chemical signals in our body and brain. Some of these chemical signals are related to sleep. And the neuropeptides that specifically affect sleep are:

  • 5’UMP
  • 5’AMP 
  • 5’GMP

Interestingly, the levels of these three neuropeptides rises at night. And in turn, their levels also rise in the night-time breast milk. The conclusion is simple – Night-time breast milk induces sleep and regulates circadian rhythm.

Clocks showing the time at which the 5’AMP, 5’UMP, and 5’GMP neuropeptides rise in the breast milk.
Levels in breastmilk
5’AMP Works to induce sleep in the first place5’AMP levels are higher in post-8pm breast milk. The levels are particularly high in the hours up to midnight.
5’UMPHelps to increase the number of both REM and nREM episodes of sleep5’UMP levels are significantly higher in breastmilk in the middle of the night.
5’GMPHelps to regulate circadian rhythms5’GMP levels fluctuate in breast milk over a twenty-four hour period. 

Melatonin and breastfeeding: How to increase melatonin in breast milk?

Since melatonin is responsible for developing a healthy sleep-wake cycle, new moms often wonder if they can increase melatonin levels in their breast milk. Well, you can! Since your newborn is not producing their own melatonin, it’s more important that their body gets an adequate amount of melatonin through breast milk. 

Here are a few things you can do:

  • Reduce artificial light exposure – Remember that light interferes with melatonin production. So before your baby’s final feed of the day, limit your exposure to artificial light. This includes the blue light from cell phones, laptops, tablets, and television, along with other bright lights. 
  • Use red LED lights, if necessary – It’s much preferred that your baby sleeps in complete darkness. But if you have to use a nightlight, use red-based light. They are deemed as least disruptive to melatonin production.
  • No caffeine before bedtime – There’s no positive relation between breast milk and caffeine. So avoid ingesting caffeine a few hours before bedtime or breastfeeding. It can halt your natural melatonin production, and can also seep into your breast milk.
  • Stick to a bed-time routine – This will help your body regularize melatonin production.
A baby sleeping peacefully with the red night light on.
Unlike blue light, red light doesn’t interfere with the human body’s natural melatonin production. So if you have to use a night light at all, use red-based ones.

If you are wondering about taking melatonin supplements, talk to your doctor first.

Alcohol and breast milk

Alcohol and breast milk are not a good combination for your baby’s health in general.

The ideal scenario would be to abstain from drinking while you’re nursing. It’s the safest option to prevent any alcohol-related problems for your baby. 

However, researchers claim that moderate alcohol consumption of one drink per day is safe if you’re breastfeeding your little one.

Let’s say you’re just drinking one drink per day. You should still wait for at least 2 hours before you breastfeed your baby or express your breast milk.

Exposure to above moderate levels of alcohol through breast milk can be harmful to babies. It is known to impair a baby’s development and growth. It also negatively impacts baby’s sleep. A study also found that babies slept for 25% less time after ingesting breast milk with small amounts of alcohol.

But if you’re taking high levels of alcohol, you might also experience shortened breastfeeding duration as the milk production decreases over time.

Why is it important for the baby to ingest breast milk produced in real time?

Ingesting mistimed milk can hinder the natural development of your baby’s circadian rhythm. This can lead to a Pandora box of short-term and long-term problems like- 

  • Fussy sleep schedule – A disrupted circadian rhythm equals a disturbed sleep cycle. The brains of newborns develop mostly in the first three months of life. And guess when this development takes place? In REM sleep. So if your baby is not sleeping properly, a fussy sleep schedule is one of the short-term problems that you will face.
  • Lack of brain development – If the baby doesn’t develop a proper circadian rhythm, it can hinder proper brain development. It can have a negative effect on the baby’s physical and mental health in the long term.
  • Myriad health issues – According to research, lack of sleep early in life is related to many health issues later in life. These include an increased risk of depression, anxiety, cardiovascular diseases, asthma, obesity, etc.

You can significantly cut down the risk of all these issues by ensuring that your baby is ingesting timed milk.

Timing breast milk : Quick Tips 

Difference in cortisol and melatonin levels in morning milk evening milk.
Breast milk pumped in the morning is high in cortisol, the hormone that helps a baby feel energetic. The milk pumped in the evening is high in melatonin, the hormone that helps a baby feel sleepy.

For most of human history, babies ingested breast milk in real time. But with breast pumps and refrigeration, breastfeeding for babies has changed drastically. More and more infants have been drinking mistimed milk. It’s essential for babies to take timed breast milk to develop a well-adjusted circadian rhythm. You can follow these steps to make sure that your baby is ingesting timed breast milk-

  • Label the bottles – If you are using stored, pumped breast milk, mark the bottles as AM for morning milk and PM for evening milk. 
  • Feed AM milk only in the morning – Feed the AM milk to your baby in the morning (as it’s high in cortisol). 
  • Feed PM milk only in the evening – Feed the PM milk to your baby at night, as it has high melatonin levels. 
  • Refrigeration – You can store freshly expressed milk in your refrigerator for up to four days. However, it’s best to use the milk within three days.
A baby drinking bottled night-time milk high in melatonin.
Drinking melatonin-rich breast milk at night helps babies sleep better and develop their circadian rhythm.

For your little one’s physical and cognitive development, it is imperative that they develop a well-adjusted circadian rhythm. When real-time breastfeeding for babies is difficult, it’s important to ensure that they ingest timed breast milk. This can be instrumental for their sleep-wake cycle and healthy bodies.

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Disclaimer: The information on our site is only meant as general information. It is NOT medical advice for any specific person or condition. If you have any medical questions and concerns, please contact your healthcare provider.

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