What is iron deficiency and how do you know if you have it?

Iron deficiency is the most common nutritional deficiency in the world. In the UK, approximately 1 in 3 women are affected at any one time. Yet it is frequently missed, dismissed, or inadequately treated.

Understanding what iron deficiency is, how to identify it, and what can be done about it is the first step toward feeling significantly better.

What does iron actually do?

Iron is essential for producing haemoglobin — the protein in red blood cells that carries oxygen from your lungs to every cell in your body. Without sufficient iron, haemoglobin levels fall. Your cells receive less oxygen. And you feel the consequences in almost every aspect of how you function.

Iron also plays a critical role in energy metabolism, immune function, and brain health. It is involved in the production of dopamine and serotonin, which is why iron deficiency frequently affects mood, concentration, and sleep.

What is the difference between iron deficiency and iron deficiency anaemia?

These are not the same thing, and the distinction matters.

Iron deficiency means your iron stores are low — measured by a blood test looking at serum ferritin. You can have iron deficiency and feel significantly unwell, even if your haemoglobin is still within the normal range.

Iron deficiency anaemia means iron stores are low enough that haemoglobin has also fallen below normal. This is a more advanced stage of the same process.

Many women are told their blood tests are normal because haemoglobin is checked and found to be borderline normal — but ferritin is not checked, or is low and dismissed. Symptoms in this situation are real and deserve investigation and treatment.

What are the symptoms?

Iron deficiency presents differently in different people. Some have many symptoms severely; others have one or two but find them significantly impair their daily life. The most common include:

• Persistent fatigue that does not improve with rest — often described as bone-deep exhaustion
• Breathlessness on exertion that feels disproportionate to the activity
• Poor concentration, brain fog, difficulty remembering things
• Hair loss — more than usual coming out in the shower or brush
• Pale skin, pale gums, or pale inner eyelids
• Heart palpitations — a racing or fluttering heartbeat
• Brittle nails, or nails with ridges
• Restless legs syndrome — an urge to move the legs, particularly at night
• Headaches, dizziness, or feeling faint

Why are women more affected?

Menstruation is the primary reason. Every period involves blood loss, and blood loss means iron loss. For women with heavy periods, this loss consistently exceeds what can be replaced through diet. Over months and years, iron stores become progressively more depleted.

Pregnancy significantly increases iron demands, as the body must produce additional blood to support the growing baby. Childbirth involves further blood loss. The postpartum period is one of the highest-risk times for significant iron deficiency.

Dietary factors also play a role. Red meat is the richest source of highly bioavailable iron. Women who are vegetarian or vegan rely on plant-based iron, which is absorbed less efficiently than iron from animal sources.

 

What can be done about it?

Treatment depends on the severity of the deficiency and the underlying cause. For mild deficiency, dietary changes and oral iron supplements may be sufficient. For more significant deficiency — or when tablets are not tolerated or not working — intravenous iron is the appropriate next step.

IV iron delivers a full therapeutic dose directly into the bloodstream in a single session, bypassing the gut and its absorption limitations entirely. Most patients notice meaningful improvement within two to four weeks of treatment.

If you have been told your iron levels are fine but you continue to feel unwell, it is worth seeking a second opinion. Iron deficiency is real, it is common, and it is treatable.