The Truth About Cortisol and 5 Common Causes of Tiredness for Mums

Motherhood is often described as beautiful chaos—filled with love, laughter, and late nights. But what happens when the exhaustion doesn’t lift, even when your baby starts sleeping through the night? If you’ve found yourself wondering, “Why am I still tired?”—you’re not alone, and you’re not crazy.

In this enlightening conversation on the Thriving Parenting podcast, we sat down with Sarah Chelle, a naturopath who helps tired, snappy, and overwhelmed women rediscover their spark. Together, we explore the truth about cortisol, its misunderstood role in postpartum life, and the five most common—but often overlooked—causes of tiredness in mums.

The Cortisol Confusion: It’s Not the Villain You Think

Cortisol has earned a bad reputation as the “stress hormone,” but Sarah redefines it as your "oomph hormone." It’s the reason you get out of bed, the energy behind your brainpower, and your body’s natural defense during times of stress.

So why does it feel like cortisol is the enemy?

In high-stress situations—like surviving on broken sleep while parenting—your body produces more cortisol and adrenaline to keep you alert. It’s a biological survival mechanism. But once the threat (in this case, sleep deprivation) passes, your cortisol doesn’t bounce back—it crashes. This is what Sarah and many mums describe as a “cortisol hangover.”

“You’re not just tired—you’re running on fumes because your energy hormone is tapped out,” Sarah explains.

Why You’re More Tired After the Baby Sleeps

It’s a confusing reality: your baby finally sleeps, and suddenly you feel more exhausted than ever.

Here’s why:

• Your body has been operating in high-alert mode, fuelled by elevated cortisol.

• When the threat subsides, your cortisol drops—often below healthy levels.

• You crash into a state of depletion, both physically and mentally.

To make things worse, your sleep itself might not be restorative. During periods of high stress, mums experience more REM sleep (great for emotional regulation) and less non-REM sleep (critical for energy production). So even if you’re sleeping, you’re not recharging.

5 Common but Overlooked Causes of Postpartum Fatigue

Feeling tired as a mum is often dismissed as “normal,” but Sarah urges us to look deeper. Here are five key causes she sees in her clinic:

1. Cortisol Dysregulation (Low Cortisol)

If you’re waking up groggy, needing frequent naps, craving sugar and salt, and feeling easily overwhelmed—your cortisol may be too low. This leaves you without the stamina to handle even everyday parenting tasks.

2. Iron Deficiency

Often missed after pregnancy, iron deficiency can lead to shortness of breath, heart palpitations, and a constant sense of physical fatigue—especially if you had blood loss during birth or are breastfeeding.

3. Protein/Calorie Deficiency

In the blur of motherhood, eating becomes an afterthought. Skipping meals or relying on toast and snacks can lead to protein and calorie deficits, which directly impact your energy, muscle strength, and milk supply.

4. Postpartum Thyroiditis

Post-birth, your immune system rebounds and can mistakenly attack your thyroid—especially if you’re genetically predisposed. This condition is highly underdiagnosed, yet it causes deep fatigue, cold sensitivity, mood dips, and mental fog.

5. Sleep Deprivation

This is the most obvious cause, but it’s compounded by the other four. If your sleep is poor and any of the above imbalances are present, you’re dealing with a layered form of exhaustion that sleep alone can’t fix.

“Being a mum and being tired don’t have to go hand in hand,” Sarah reassures. “It’s not selfish to seek answers—it’s essential.”

So What Can You Do? Start with a Blood Test

Sarah strongly recommends routine bloodwork at 3 months postpartum—even if your baby isn’t sleeping perfectly yet. A simple test can check iron levels, thyroid function, and cortisol, giving you insight into what’s really going on inside.

What to look for:

• Morning cortisol above 275 nmol/L

• Full thyroid panel (not just TSH—look for Hashimoto’s antibodies)

• Iron studies, including ferritin

• Protein intake and general nutrition review

The First Steps to Recharging (Without Overwhelm)

Sarah shares some gentle, mum-friendly ways to start restoring energy:

• Prioritise sleep — including naps, even short ones.

• Cool, dark sleep environment — 16–19°C is ideal for both mum and baby.

• Cut caffeine after midday — it can suppress the non-REM sleep your body desperately needs.

• Supplement smartly — with vitamin C (2g/day, split dose) and magnesium (at least 300mg/day).

• Gentle movement — walking or yoga until your body has enough cortisol to tolerate more vigorous activity.

And most importantly: tune in. If you feel worse after a workout, it’s a sign your body isn’t ready yet.

Energy Isn’t a Luxury—It’s a Birthright

Postpartum fatigue isn’t just part of the job. And if you’ve been told to “suck it up” or “this is just motherhood,” Sarah’s message is clear: you deserve better.

With the right support, knowledge, and gentle steps, you can stop surviving and start thriving—with real, sustainable energy and the emotional bandwidth to enjoy parenting again.

“Life gets lighter. You respond instead of react. You feel like you again.”