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Fatigue is one of the most common symptoms women speak to practitioners about.
But not all fatigue is the same.
In clinic, I tend to see three very common physiological patterns behind persistent tiredness:
• Iron-related fatigue
• Nervous system depletion (often magnesium-related)
• Low vitamin D fatigue
On the surface, they can feel similar.
But biologically, they are very different.
Understanding the difference can make a huge impact on how fatigue is investigated and supported.
Let’s break them down.
Iron Fatigue
The “heavy” tired
Iron-related fatigue often feels like a deep, physical exhaustion.
Women will commonly describe it as feeling like their body is simply running out of fuel.
Typical signs can include:
• Needing to sit down frequently
• Breathlessness when climbing stairs
• Cold hands and feet
• Hair shedding
• Poor exercise tolerance
• General weakness or heaviness
When investigating iron status, a few key markers are important.
Minimum labs to check include:
• Ferritin
• Transferrin saturation
• Full blood count
Ferritin is particularly important as it reflects stored iron levels.
Many women are told their results are “within range”, but that doesn’t always mean they are optimal.
For example, a ferritin level below 50 µg/L may technically fall within laboratory reference ranges, but many practitioners see fatigue symptoms emerge well before levels drop into the severely deficient range.
Magnesium Fatigue
The “wired but exhausted” tired
This type of fatigue feels very different.
Instead of heaviness, women often describe feeling exhausted but unable to switch off.
Common signs include:
• Difficulty relaxing
• Muscle tension
• Restless sleep
• Waking around 3am
• Feeling overstimulated
• Anxiety layered over fatigue
Magnesium plays an essential role in many processes involved in energy production and nervous system regulation, including:
• ATP production (the body’s cellular energy currency)
• Nervous system regulation
• Muscle relaxation
• Cortisol and stress hormone balance
Chronic stress increases magnesium utilisation.
When the nervous system is stuck in a fight-or-flight state, it becomes much harder for the body to generate steady, restorative energy.
This is why magnesium-related fatigue often presents as burnout-style exhaustion rather than physical heaviness.
Vitamin D Fatigue
The “flat” tired
Vitamin D deficiency tends to produce a different pattern again.
Rather than feeling wired or physically heavy, women often describe feeling flat, low and unmotivated.
Symptoms may include:
• Low mood
• Reduced motivation
• Getting sick frequently
• Bone or muscle aches
• Feeling tired despite adequate sleep
Despite Australia’s sunny reputation, vitamin D deficiency is still common.
This is particularly true during:
• Winter months
• Periods of reduced sun exposure
• Indoor lifestyles
• Pregnancy and breastfeeding
Testing vitamin D levels is relatively straightforward through a blood test measuring:
• 25-hydroxyvitamin D (25(OH)D)
Supplement doses should ideally be tailored to individual blood levels.
Not everyone needs high doses such as 5,000 IU, and not everyone will maintain adequate levels on lower doses like 1,000 IU.
The Problem With Guessing
When women say:
“I’m just so tired.”
They’re often given one of three responses:
• A generic multivitamin
• Advice to simply rest more
• Reassurance that their bloodwork is “fine”
But fatigue is rarely that simple.
Iron fatigue feels different to magnesium fatigue.
Magnesium fatigue feels different to vitamin D fatigue.
And sometimes, more than one factor is present at the same time.
A More Practitioner-Led Approach
Instead of guessing, a more considered approach tends to include:
-
Testing what can be tested
-
Interpreting laboratory ranges with clinical context
-
Supporting the body with appropriate nutrients where needed
-
Re-testing where appropriate to track progress
This isn’t about throwing supplements at symptoms.
It’s about understanding why fatigue is happening in the first place, and addressing the underlying physiology.
