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The amazing way that breast milk helps develop circadian rhythm in babies

By Cradlewise Staff

As any sleep-deprived new parent will testify, there’s no sleep-wake cycle in babies. Your little one will only develop a 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 breast milk, which works like an internal clock for your newborn.

Breast milk is no ordinary meal. The nutritional 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 develop a circadian rhythm in babies through cortisol and melatonin—the hormones responsible for our sleep-wake cycle.

Did you know?
Cortisol rises in breast milk in the morning hours and acts like an energy drink for the baby. Melatonin increases in breast milk in the evening hours and acts as a sleeping potion.

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


Hormones in breast milk 

Cortisol and melatonin rise and fall in the breast milk at specific times during the day. A large gap between when you express breast milk and when your baby ingests 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 Cortisol and Melatonin? 

Circadian rhythm

Circadian rhythms are physical, mental, and behavioral changes in our body in a 24-hour cycle, synchronized with the sun. Our sleep-wake cycle is our body’s natural tendency to become alert and active with sunrise and slow down to sleep with the sunset. It is one of the essential circadian rhythms.

And despite being the most critical circadian rhythm, humans are not born with it. 

Mechanism of circadian rhythm

Every cell in our body has a tiny clock of its own. This army of little clocks takes orders from a Master Clock located in our brain—the SCN or suprachiasmatic nucleus. This master clock is synchronized with the light-dark cycle, controls every process in our body, and gets its cues from sunlight.

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

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

Do babies have a circadian rhythm?

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 babies have a vague sense of circadian rhythm in the womb, it is an entirely 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 critical factors that help in the 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 sunlight, the baby will not understand the difference between light and dark. This understanding is necessary for producing 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.

Helping your baby develop a circadian rhythm

Adults have a well-developed brain that houses the master clock. On the other hand, newborn babies 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 some time. Factors like breast milk and sunlight help in its development. Slowly, the tiny clocks in each cell of the baby’s body create 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. 

The two pillars on which a baby’s circadian rhythm develops are — breast milk (nutrition) and environmental cues. The latter is a prominent 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, necessary for circadian rhythm.

The former, breast milk, is complex.

Breast milk changes composition with day and night.

Breast milk composition changes not only throughout day and night but throughout the feeding period, as per your baby’s nutritional demands. 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 your baby ingests depend on the timing of breastfeeding. The morning milk is high in an energy drink-like hormone called cortisol. And the evening milk is high in a sleep-inducing hormone called melatonin.

How breast milk helps your baby sleep and wake up on time

Breast milk’s composition changes throughout the 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 with hormones that act like tiny clocks for the baby’s body. 

Two, nutrition and sleep help your baby’s brain mature and develops at an unprecedented pace, helping 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 first few months of your baby’s life, and voilà! Now your baby’s brain has its 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.

Morning and night breast milk

Cortisol

Often called the ‘stress hormone,’ Cortisol is, in fact, nature’s in-build alarm system in our body. It will help your baby is waking up and feel alert and active.

Cortisol production in babies

Cortisol production starts in babies from about six weeks of age.

This production also follows a rhythm, peaking in the early morning and dropping down in the evening. This pattern becomes stable across the first year of your baby’s life. 

When does cortisol peak in breast milk

Cortisol is highest in the morning milk around six 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 seven am, than the evening milk.

U-shaped diagram showing difference in cortisol and melatonin levels during day and night.
Things that increase CortisolThings that decrease Cortisol
Physical stress
Emotional stress
Injury
Caffeine
Meditation
Regular exercise
Healthy diet
Doing things you enjoy

Melatonin

Also called the sleep hormone, Melatonin is mainly responsible for our sleep-wake cycle. It’s a prerequisite to falling asleep.

When do babies produce Melatonin?

It doesn’t start in newborn babies 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.

When is Melatonin highest in breast milk?

Melatonin peaks in breast milk at three am. Research has pointed out that this timing of spike in this hormone corresponds to the three am to seven 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 three am as the morning hours kick in. 

Increasing melatonin in breast milk

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

Here are a few things you can do:

  • Reduce artificial light exposure: Light interferes with your body’s natural mechanism to make melatonin. So before your baby’s last feed of the day, limit your exposure to artificial light, including the blue light from cell phones, laptops, tablets, and television, along with other bright lights.
  • If necessary, use red LED lights: Your baby should sleep in complete darkness. But if you have to use a nightlight, use red-based light. They are the least disruptive to this sleep hormone.
  • Avoid caffeine before bedtime: Avoid ingesting caffeine a few hours before bedtime or breastfeeding. It can halt your body’s natural process of making melatonin and can also seep into your breast milk.
  • Stick to a bedtime routine: This will help your body regularize the production of making this sleep-inducing hormone.

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

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-colored lights.

Quick tips: Timing breast milk

Difference in cortisol and melatonin levels in morning milk evening milk.

For most of human history, babies ingested breast milk in real-time. But with breast pumps and refrigeration, breastfeeding for babies has changed drastically. 

Babies need 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. 
  • Refrigeration: According to CDC, 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. If you’re freezing the milk, it’s best to use use it within six months. However, as per CDC guidelines, the frozen breast is also acceptable for up to 12 months. 
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.

The bottom line

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

Sources:

  1. Development of circadian rhythm in babies. NCBI. 2018. PERSPECTIVE: The Long-Term Effects of Light Exposure on Establishment of Newborn Circadian Rhythm.
  2. Melatonin production in babies. WebMD. 2017. “Better Sleep for Baby –- and You.
  3. Refrigerating and freezing breast milk. CDC. 2021. “Proper Storage and Preparation of Breast Milk.

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