Iron Deficiency and Fatigue: Why Your Blood Test May Be Missing the Full Picture

Persistent fatigue, brain fog, hair loss? Low iron — even without anaemia — could be a root cause your standard blood test isn't catching. Here's what to ask for.

If you wake up tired even after a full night's sleep, feel like daily life has become heavier than it used to be, and notice things like hair falling out in the shower, a short walk leaving you more breathless than it should, or a persistent foggy feeling that follows you through the day — iron deficiency may be worth exploring. Because unlike many contributors to long-term fatigue, this one is both identifiable and treatable. I know this firsthand. For years I pushed through exhaustion while managing work, family, and the everyday demands of life — assuming it was just my lot. When an iron deficiency was eventually identified, supplementing changed things in ways I hadn't expected. My energy came back. The low-level anxiety lifted. And perhaps most meaningfully: I had something left in the evenings to actually be present with my children.

In this article:

• Gut health and iron levels are linked

• What iron deficiency actually is — and the type most often missed

• What low iron does to your body, thyroid, and mood

• What you can do, and what to ask your GP

Your gut and your iron levels are more connected than you might think

Poor gut health — whether through low-grade inflammation, changes to the microbiome, or a compromised intestinal lining — can significantly reduce how much iron your body actually absorbs, even if you are eating iron-rich foods regularly. When the gut lining is disrupted, inflammatory signalling molecules enter the bloodstream and affect other organs, contributing to a persistent fatigue that doesn't lift with rest. The gut is not just a bystander in iron deficiency. For some women, it is the reason the deficiency exists in the first place. This is an important connection that rarely comes up in standard consultations — and it is one reason why addressing gut health and nutrient status together often unlocks progress that neither approach achieves alone.

What iron deficiency actually is — and the type most often missed

Iron is central to the production of haemoglobin, the protein in red blood cells that carries oxygen to every tissue and organ in the body. It is also stored inside cells as part of a protein called ferritin, which acts as the body's iron reserve. This gives us two distinct clinical pictures: Iron deficiency anaemia (IDA): both haemoglobin and ferritin are low Non-anaemic iron deficiency (NAID): haemoglobin is normal, but ferritin — stored iron — is low Iron deficiency anaemia currently affects approximately 1.2 billion people worldwide. Non-anaemic iron deficiency is estimated to be at least twice as common — and it is the type most likely to be missed. A recent review published in the Canadian Medical Association Journal puts it plainly: "Iron deficiency without resulting anemia, or NAID, is associated with fatigue, reduced work performance, and reduced cognitive function. Iron deficiency is the most common cause of anemia despite being preventable and easily treated." [1] A routine blood count may come back entirely normal, and yet someone can be running on depleted iron reserves — with real, measurable consequences for how they feel and function every day.

Why your results might be "normal" and still be a problem

Even when anaemia is absent, low ferritin can produce symptoms indistinguishable from full iron deficiency anaemia: fatigue, brain fog, poor exercise tolerance, low mood, and hair loss. Yet ferritin is routinely left out of standard blood panels. Current clinical guidance is shifting on this. The same CMAJ review specifies: "Treatment is indicated when ferritin is below 50 µg/L in a pregnant person, below 30 µg/L in other adults, and below 20 µg/L in children." [1] Many integrative practitioners go further, suggesting a target of at least 50 µg/L for all adults — though this is something to explore with your GP in the context of your individual results. The practical implication is straightforward: if you have only ever had your haemoglobin checked, you may not have the full picture.

What low iron does to your body — beyond tiredness

Iron's role in the body extends well beyond red blood cells, which is why its deficiency can show up in such varied and seemingly unrelated ways.

Thyroid function

Iron is essential for the activity of thyroid peroxidase, an enzyme that catalyses the production of thyroid hormones. Iron deficiency has been associated with impaired thyroid hormone production and increased prevalence of thyroid autoimmunity, particularly in women of reproductive age [2]. This matters because hypothyroid symptoms and iron deficiency symptoms overlap considerably — fatigue, cold sensitivity, weight changes, brain fog — and without testing both, the picture can remain frustratingly unclear.

Mood and mental health

Iron is a cofactor for the enzymes responsible for producing serotonin, dopamine, and noradrenaline — the neurotransmitters most closely linked to mood regulation. Research suggests its role in neurotransmission is not sufficiently considered by practitioners [3], and that iron status should be routinely assessed in people presenting with depression or persistent low mood, particularly in women and in cases that have not responded well to standard treatment.

What you can do: a practical starting point

Step 1: Get the right tests

Ask your GP to test both haemoglobin and ferritin. It is also worth requesting CRP (C-reactive protein), a marker of inflammation. Ferritin is an acute-phase protein that can appear falsely elevated when inflammation is present, so CRP provides an important control for interpreting your results accurately.

Step 2: Understand your results in context

If your ferritin or haemoglobin is low, prescribed supplementation is usually necessary to bring levels up to a meaningful threshold. Dietary changes alone are unlikely to be sufficient if levels are significantly depleted — particularly in menstruating women, where ongoing iron loss makes it difficult to rebuild stores from food alone.

Step 3: Support absorption through diet

Regular intake of iron-rich foods remains a valuable foundation, for example:

• Red meat and organ meats

• Beans and lentils (black beans, chickpeas)

• Dark leafy greens (spinach, kale)

• Pumpkin seeds

Pairing these foods with a source of vitamin C — a squeeze of lemon, orange juice, some peppers, or tomatoes — increases iron absorption meaningfully. Some evidence suggests that properties of tea and coffee can reduce absorbption, so if you’re struggling to get your levels up then you may want to avoid these near the time you eat or when you take your supplements. It is also worth noting that haem iron from animal sources is considerably more bioavailable than non-haem iron from plant sources.

Iron is one piece of a larger picture

Persistent fatigue rarely has a single cause. Iron deficiency is one of the most common and most overlooked contributors — but it sits alongside thyroid function, hormonal changes, vitamin D, B12, gut health, and other factors that are worth exploring systematically. For many of the women I work with, mapping out these possible biological contributors is the first time anyone has taken a thorough look at the full picture. And what often follows is a significant shift — not just in energy, but in how they understand what has been happening in their bodies. The fatigue wasn't in their head. It wasn't a failure to manage stress well enough. There was something biological that hadn't been found yet. If that resonates with your experience, a discovery call is a good place to start. 👉 Book a free discovery call at savourcoaching.com/appointments

References

1. Leung, A. et al. (2025). Diagnosis and management of iron deficiency in females. Canadian Medical Association Journal. PMC12237530. This review outlines the clinical significance of both anaemic and non-anaemic iron deficiency, and provides updated ferritin thresholds for diagnosis and treatment.

2. Li, M. et al. (2021). Iron Deficiency, a Risk Factor of Thyroid Disorders in Reproductive-Age and Pregnant Women: A Systematic Review and Meta-Analysis. Frontiers in Endocrinology. PMC7947868. This meta-analysis demonstrates that iron deficiency significantly increases the risk of thyroid autoimmunity and impaired thyroid hormone production in women of reproductive age

3. Berthou, C. et al. (2022). Iron, neuro-bioavailability and depression. eJHaem. PMC9175715. This paper explains the mechanistic link between iron deficiency and depression through impaired neurotransmitter synthesis, and calls for iron status to be assessed as part of standard depression workups.