Circadian rhythm, melatonin, & your baby

Did you know that there are certain functions that work together internally in your baby’s body to help them sleep? Chances are you’ve heard of a few of them but there are three main ones that play a significant role in the quality of your baby’s sleep.

Let’s break down a few of them…

Circadian rhythms

Circadian rhythms are biological processes that occur in a 24-hour cycle. They are part of our body’s internal clock and they drive our sleep patterns, which is why many of us feel sleepy at the same times every day, for example around mid-afternoon and again in the evening. Circadian rhythm is primarily driven by light and darkness, which is why we tend to get sleepy in dark environments.

However, newborns are not born with a functioning circadian rhythm. They mix up their days and nights, which leaves parents exhausted as they tend to their newborn several times throughout the night. (See here for our newborn sleep tips)

This is why it's so important to expose babies to light first thing in the morning and during each awake period, and also why it's important to keep naps and nighttime DARK with blackout shades. This helps them learn to distinguish day from night as they adjust to life outside the womb. Their circadian rhythm will finally kick in around 3 or 4 months.

This is why we shouldn't place unrealistic expectations on newborns to follow a schedule or to start sleeping through the night within a few weeks.

Melatonin

It takes about 6 weeks until newborns can start doing longer stretches at night, but regular sleep schedules are not common until about 6 months. Newborns just don't have the biological components in place to have predictable sleeping patterns. For example, melatonin isn't produced naturally in babies until about 3 months. While you can work on healthy habits in the newborn stage, don’t stress about a schedule yet because your baby is still adjusting to life outside the womb and so is their body!

Melatonin, otherwise known as our sleepy hormone, is a natural hormone that is released in your brain in the evening when darkness occurs, causing a sudden increase in tiredness. It then remains for about 12 hours until it subsides in the morning. Basically, it regulates our sleep wake cycle.

Melatonin is very sensitive to light, and, in some causes, won't be produced at all until you're in a darker environment. Bright lights, like those from screens, can suppress melatonin, which is why exposure to electronics is not advised during the hour or two before bed (See How screen time is affecting your child’s sleep). Having screentime before bed can hinder your body’s ability to know that it’s tired, and you may miss your appropriate sleep window. The supplement melatonin is often used to help those who have trouble falling asleep (or those who fight through their natural melatonin and stay awake too late at night!), but it's important for us to mention that melatonin supplements are not recommended for babies and young children, unless first discussed with a pediatrician. In order for us to naturally help melatonin do its job, we need to make sure we are putting our babies to sleep within their natural sleep windows, as well as eliminating light close to bedtime.

Cortisol

Another hormone that plays in a role in the quality of sleep is cortisol. This is a stimulating hormone that is mainly related to stress. It drives the body's fight-or-flight response, but also regulates blood pressure, balances blood sugar, regulates energy levels, and helps to

control the sleep-wake cycle. Cortisol helps to keep your baby awake during the day while gradually allowing other hormones to take over as the day goes on and the body prepares for rest.

But cortisol can also get in the way of sleep, especially when your baby is exposed to stressful situations or even bright lights. This is also a reason that we don’t encourage prolonged periods of crying in the evening, as it can work against us when we are trying to get our babies to fall asleep! If cortisol levels are raised from being in a stressful environment or from long spurts of hard crying (see our article on The truth about the cry-it-out method to get an idea of how much is too much), then sleep can definitely be affected.

Adrenaline

The hormone adrenaline can also interfere with sleep, which means that too much exercise or excitement in the evening can definitely affect the body's ability to fall asleep. This is why it's scientifically recommended to have a calming bedtime routine, both for children and adults, so that our bodies are able to relax, unwind, and de-stress (See here and here for our bedtime routine tips).

For more information on the science of sleep, check out:

What you need to know about your baby’s sleep cycles and their quality of sleep

How much sleep does your child need?

The alarming danger of sleep deprivation & how to fix it

Here’s why consistent bedtimes are more important than you think