Babies: When do they develop a circadian rhythm?

The circadian rhythm is your body’s internal clock. It refers to the changes we experience closely aligned to a 24-hour cycle and can be biological or behavioral in nature. The activation of these processes are predominantly light dependent with the most well known being the sleep/wake cycle - set for sleep when it’s dark and awake when it’s light.

Regardless of your age, the circadian rhythm operates in the same way - whether you are a baby, toddler, teenager, adult or senior. The basic process is as follows - light enters the eye, the amount of light is detected by the photoreceptors in the retina, this information is relayed to the suprachiasmatic nucleus, the body’s master clock. We have millions, if not billions of internal clocks, but it’s this central clock that keeps the whole process in sync - sending signals to different parts of the body and brain, activating and deactivating a cascade of functions that operate in a balanced fashion. This highly coordinated process is collectively called the circadian rhythm. 

If you’d like more information, check out these articles

What is the circadian rhythm

How to reset your circadian rhythm

Key components of the circadian rhythm include melatonin (hormone that signals sleepiness), cortisol (hormone that signals alertness and wakefulness), body temperature, movement, blood pressure, and digestion. All these components evolve and change as we age, which leads to alterations in the timing of the circadian rhythm. 

Let’s start at the beginning, as a newborn.

When do you develop a circadian rhythm? 

Soon after a baby is born, the question on every parent’s mind is - when will my baby sleep through the night? And another question quickly follows - when will I get to sleep again?

Babies aren’t born with a pre-programmed circadian rhythm, due to the total lack of light exposure while in the womb. At birth, they come packaged with a very weak sleep/wake cycle that is closely related to the mothers. Eventually they develop their own rhythms, in sync with their external environment, but it takes time and patience. And when it comes to establishing their circadian rhythm, light exposure is the most critical factor you have complete control over.

What is happening during this newborn stage?

Newborns typically sleep for an average of 70% of the day (16 or 17 hours), at scattered times throughout the day, and in most cases, for no more than a 4 hour stretch at a single time. 

As the weeks progress and development continues, various components of the circadian rhythm fall into place. 

Around 8 weeks: Production of cortisol begins. It’s at this time babies start to develop a greater awareness of their surroundings, and exhibit more alertness.

Around 9 weeks: Next melatonin production and secretion starts, helping increase the length of the time a baby is able to stay asleep. 

Around 11 weeks: Another key component of sleep, rhythm of the body temperature, starts to develop a consistency. The result is a drop in temperature typically occurring at night, assisting with a longer sleep pattern.

Between 12-16 weeks: The diurnal sleep pattern (active during the day, asleep at night) becomes more consistent and frequent.

At around 16 weeks (4-months): Sleep time has decreased from 16-17 hours to 14-15 hours per day. So too is the length of time a baby stays asleep, gradually increasing, with 4+ hour stretches happening more regularly.

Of course, this is a generalization with some babies following exactly this pattern, others occasionally, and then there is always those that never seem to develop a rhythm at all…

What can you do to help the circadian rhythm fall into place as quickly as possible?

As mentioned earlier, you are in control of their external environment, which means the amount of light they are exposed to. 


The circadian rhythm is linked directly to light exposure. Whether a baby or an adult, it makes sense to consider the amount of light in the environment and how to time it accordingly. Instituting healthy light habits during the early stages of development is critical and this should include exposure to early morning light, for the optimal production of melatonin, release of cortisol as well as eliminating artificial blue light at night, for the adequate secretion of melatonin. Hopefully babies aren’t staring at screens at night, but the main source of blue light at night is from LED light bulbs that are in most homes today. In exactly the same way an adult's brain is tricked into thinking it’s still day-time when the lights are switched on, a baby feels this same effect. Arguably even more so, given how weak the melatonin signals are during the newborn stage.

What should you do? 

Ideally you shouldn’t expose a baby (or yourself for that matter…) to bright lights once the sun has set. An easy solution is to replace the lightbulbs for night-time use with red tinted light bulbs. 

Read this article for more information about the difference between blue and red light, but the quick summary is - red light has a calming effect in direct contrast to blue light, which increases energy and alertness. 


Babies thrive on routines, even though they may seem to fight it...

Going to bed at the same time, breastfeeding or eating at the same time, bathing at the same time. Playing when it’s day-time, being calm when it’s night-time. All these activities help establish a pattern, bringing comfort and peace to a baby. And this routine should be directly related to Tip #1 - following the light pattern of day and night, engaging in energetic activities when the sun is up, calming and restful activities after the sun goes down. 

What is happening to their circadian rhythm after the 6-month mark?

From around 6-months onwards, many of the foundations of sleep are in effect and now is the time to practice them, getting a consistent rhythm happening. The production and secretion of cortisol and melatonin has been activated, now it is being further refined. Body temperature fluctuations between day and night are becoming more consistent, allowing for sleep to be consolidated into less frequent, longer periods. As a consistent eating schedule emerges, with more being consumed during daylight hours, a baby’s body learns to digest food at specific times, outside of the sleep windows. 

In conclusion…

Babies may seem to follow the beat of their own drum, but that’s not really the case. Parents and carers are in control of their external environment, which has a direct impact on how their body functions. 

Our body’s circadian rhythm only knows one pathway, it’s up to us to decide if we want to follow it or not. And whilst the body is a complicated system, with each of us an individual, day is day and night is night, and there are consequences if we try to trick it into thinking otherwise... 

It may seem like every day is different, and sometimes it will be, but each and every day a small piece of the pattern is being put into place, which makes sense to align it closely to nature, rather than an artificial one.

Maybe you have a teenager instead...they have a different circadian rhythm too. Read all about why they are likely to want to stay up late. 

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