The Role of Sleep Hormones in Newborns

Ever wondered why your newborn drifts off peacefully one night but fights sleep the next? If you’re navigating the unpredictable world of infant sleep, understanding the role of sleep hormones can be a game-changer. These tiny chemical messengers are more powerful than you might think, especially melatonin, often dubbed the “sleep hormone”.

In adults, sleep hormones follow a familiar rhythm. But in newborns, this system is still very much under construction. Knowing how and when these hormones develop can help you manage expectations, optimise your baby’s sleep environment, and foster better sleep habits from day one.

In this article, we’ll explore how baby melatonin production, cortisol balance, and other newborn sleep hormones impact your infant’s sleep development. We’ll break down the science in a practical, parent-friendly way and provide expert-backed advice to help you support your little one’s sleep journey.

What Are Sleep Hormones?

Sleep hormones are naturally occurring chemicals in the body that regulate when we feel sleepy or alert. They help control circadian rhythms — the internal clock that aligns our sleep-wake patterns with the 24-hour day.

Key Sleep Hormones in Infants

• Melatonin: Signals the body to prepare for sleep
• Cortisol: Encourages wakefulness and alertness
• Adenosine: Builds up sleep pressure throughout the day
• Serotonin: A melatonin precursor and mood stabiliser

In newborns, the production and regulation of these hormones are still immature. This explains the fragmented, often unpredictable sleep patterns you see in the early weeks.

Baby Melatonin Production: What Parents Need to Know

When Does Melatonin Production Begin?

Newborns do not produce their own melatonin in significant amounts until around 8 to 12 weeks of age. Until then, they rely partly on melatonin passed through breast milk, especially in breastfed babies whose mothers produce higher levels at night.

How Melatonin Works

Melatonin is triggered by darkness and suppressed by light. In adults, levels begin to rise in the evening, peak overnight, and decline by morning. In babies, this rhythm takes time to develop.

Before 3 months:

• Sleep is spread randomly across 24 hours.
• Melatonin production is minimal or inconsistent.
• Sleep is driven mainly by feeding needs and basic biological cycles.

After 3 months:

• Melatonin follows a more regular pattern.
• Sleep starts consolidating more at night.

Want to know how this aligns with broader sleep development? Take a look at how circadian rhythms impact baby sleep for a clearer timeline.

Cortisol: The Wake-Up Hormone

Cortisol often gets a bad reputation because of its link to stress, but in healthy amounts, it’s essential, especially for babies.

What It Does

• Peaks in the early morning, helping your baby wake up.
• Declines by evening, allowing melatonin to take over.

In newborns, cortisol rhythms are just as immature as melatonin. This contributes to babies waking frequently or appearing alert at odd hours.

Disruptions to Cortisol Rhythms

• Overstimulation before bedtime can spike cortisol, delaying sleep.
• Stressful environments or prolonged crying may keep cortisol elevated.
• Sudden changes to sleep schedules can throw off natural cycles.

The Interplay Between Serotonin and Sleep

Serotonin is another key player in infant sleep development. It supports mood, digestion, and — importantly — acts as a building block for melatonin.

How to Boost Serotonin Naturally

• Exposure to daylight during awake times
• Skin-to-skin contact and cuddling
• Tummy time and gentle movement

These activities encourage the body’s natural serotonin production, laying the groundwork for healthy melatonin levels later in the day.

How Hormones Shape Infant Sleep Development

As these hormones mature, they gradually help babies develop more structured and restful sleep. But this doesn’t happen overnight.

Key Milestones

• 6–8 weeks: Slight increase in melatonin; longer stretches of sleep may emerge.
• 12 weeks: Circadian rhythms begin maturing; hormonal patterns become more predictable.
• 4–6 months: Baby may sleep 5–8 hours at night; naps follow a more regular pattern.

But just as things begin to improve, you might hit a bump — the 4-month sleep regression. This phase is a normal, if frustrating, result of maturing sleep cycles. For help navigating this tricky period, read what to expect during the 4-month sleep regression.

Support Your Baby’s Sleep Hormones Naturally

You can’t control when your baby’s hormones develop, but you can create the right conditions to support and nurture their natural rhythms.

1. Use Light Strategically

• Expose your baby to daylight during wake times, especially in the morning.
• Keep nights dark and quiet, using blackout curtains or dim lighting during feeds.

2. Establish a Consistent Bedtime Routine

Even before hormones are fully established, routines offer cues to the brain that it’s time to wind down.

Consider a sequence like:

• Warm bath
• Gentle massage
• Soft lullabies or white noise
• Feed in a darkened room

3. Respond Calmly to Night Wakings

Try to keep stimulation low. Avoid bright lights, loud voices, or active play during night-time feeds or soothing.

4. Prioritise Skin-to-Skin Contact

This boosts both serotonin and oxytocin, promoting bonding and a sense of calm, both helpful for sleep readiness.

5. Protect Nap Times

Naps contribute to hormone regulation by preventing overtiredness, which can lead to spikes in cortisol and disrupted nights.

Common Misconceptions About Sleep Hormones

Myth 1: Babies Should Sleep Through the Night from Birth

Reality: Until sleep hormones mature, frequent night wakings are biologically normal.

Myth 2: Melatonin Supplements Help Babies Sleep

Reality: Supplementing melatonin in infants is not recommended unless directed by a medical professional. Natural melatonin regulation is safer and more sustainable.

Myth 3: Keeping Baby Awake During the Day Improves Night Sleep

Reality: This often backfires, leading to overtiredness and higher cortisol levels, which interfere with night-time sleep.

Real-Life Example: Ava and Her 10-Week-Old Son

Ava noticed her son would fall asleep easily during morning walks but struggled to settle at bedtime. After learning about the role of light exposure in melatonin production, she began taking him outside every morning and dimming the lights consistently each evening.

Within two weeks, her baby began sleeping longer stretches at night and napping more predictably during the day. Her story is a testament to how simple changes can align with natural hormone development.

Setting the Hormonal Stage for Sleep Success

Understanding sleep hormones offers you a powerful lens through which to view your baby’s sleep challenges — not as failures or flaws, but as biological development in progress.

By supporting melatonin production through light, nurturing cortisol rhythms with calm routines, and encouraging serotonin with bonding and movement, you’re actively helping your baby develop healthy sleep habits.

And as your baby grows, these early investments pay off in more consistent, restorative sleep for both of you.

Building Restful Rhythms from the Inside Out

Your baby’s sleep isn’t just about routine — it’s about biology. The slow emergence of sleep hormones like melatonin and cortisol is what eventually allows for consolidated night-time rest and predictable naps.

While you can’t force your baby’s hormones to mature, you can gently guide the process. Through exposure to natural light, consistent routines, and responsive care, you’re laying the groundwork for a lifetime of better sleep.

Remember, every baby is different. Some find their rhythm early, while others take a bit longer. Trust the process — and yourself.

Have questions or your own hormone-sleep success story? Share it in the comments or pass this guide on to a fellow parent looking for answers. Let’s help more babies (and parents) get the sleep they deserve.