Iron Deficiency in UK Women: Symptoms, Testing and Supplementing Safely

Iron Deficiency in UK Women: Symptoms, Testing, and Choosing the Right Supplement

Iron deficiency is the most common nutritional deficiency globally, and in the UK, premenopausal women are disproportionately affected. Surveys suggest that up to 25% of UK women of reproductive age have low iron stores, with many more in a state of functional iron deficiency that affects energy and cognitive performance without yet causing clinical anaemia. Understanding the stages of depletion, the importance of ferritin testing, and the significant differences between iron supplement forms can make a substantial difference to both treatment outcomes and tolerability.

Why Women Are at Higher Risk

The primary driver of iron deficiency in premenopausal women is menstrual blood loss. Each millilitre of blood contains approximately 0.5mg of iron; the average menstrual period involves blood loss of 30–80ml, representing a regular iron loss of 15–40mg per cycle. Women with heavy menstrual bleeding (HMB) — defined clinically as loss exceeding 80ml per cycle — may lose 40–200mg per period, dramatically outpacing typical dietary intake.

The UK Reference Nutrient Intake (RNI) for iron in premenopausal women is 14.8mg per day — substantially higher than the 8.7mg RNI for men and postmenopausal women, reflecting this additional loss. Average UK dietary iron intake in women is consistently below this level, making even modest menstrual losses a route to progressive depletion.

Pregnancy imposes further demand: iron requirements rise sharply in the second and third trimesters, and postpartum depletion is common.

Understanding the Stages of Iron Depletion

Iron deficiency progresses through stages, and the stage at which it is identified significantly affects interpretation and management:

Stage 1 – Iron store depletion: Serum ferritin falls (often below 20–30 mcg/L, though optimal levels for symptom resolution may be considerably higher). Haemoglobin remains normal. Many women in this stage experience fatigue, brain fog, and reduced exercise tolerance, but a standard full blood count will appear entirely normal.

Stage 2 – Iron-deficient erythropoiesis: Iron stores are exhausted. Red blood cell production becomes iron-limited. Transferrin saturation falls, and haematocrit begins to drop. Ferritin is very low; haemoglobin is still borderline.

Stage 3 – Iron deficiency anaemia: Haemoglobin falls below 12g/dL in women. Red cells become microcytic (small) and hypochromic (pale). This is the stage conventionally diagnosed via full blood count alone.

The Case for Ferritin Testing

The most important practical point for any woman with persistent fatigue is this: a normal full blood count does not rule out iron deficiency. Haemoglobin is the last marker to fall. Ferritin — a measure of stored iron — is depleted long before anaemia develops, and many women experience debilitating symptoms at ferritin levels well above the clinical "low" threshold.

Research, including work by Verdon and colleagues (BMJ, 2003), showed that iron supplementation improved fatigue scores in women with ferritin below 50 mcg/L but normal haemoglobin. Requesting a serum ferritin alongside a full blood count gives a much more complete picture. Many clinicians now consider ferritin below 30 mcg/L (and some below 50 mcg/L) functionally suboptimal for symptom-free function, even when haemoglobin is normal.

Symptoms of Iron Deficiency

Common symptoms of iron depletion (even before frank anaemia) include:

- Persistent fatigue and reduced stamina - Difficulty concentrating, poor memory, and brain fog - Breathlessness on exertion - Restless legs syndrome (particularly at night) - Cold intolerance - Hair shedding (telogen effluvium) - Brittle nails and spoon-shaped nails (koilonychia) in more advanced deficiency - Pallor of the inner eyelid and nail beds - Palpitations

Iron Supplement Forms: Tolerability and Efficacy

Iron supplements vary significantly in tolerability and absorption. The standard pharmaceutical form, ferrous sulphate (200mg tablets containing approximately 65mg elemental iron), is effective but associated with high rates of gastrointestinal side effects: nausea, constipation, stomach cramps, and dark stools. These side effects frequently cause people to stop supplementation before repletion is achieved.

Iron bisglycinate (also called iron glycinate chelate or ferrous bisglycinate) is a chelated form in which iron is bound to two glycine molecules. Clinical studies suggest comparable or better absorption than ferrous sulphate with substantially reduced GI side effects. A 2014 Brazilian comparative trial found iron bisglycinate achieved similar haemoglobin and ferritin recovery to ferrous sulphate with significantly fewer GI complaints and higher completion rates.

For individuals who cannot tolerate standard iron supplements, iron bisglycinate at 18–36mg elemental iron daily is a well-tolerated alternative. Liquid iron formulations also tend to be gentler.

Enhancing Absorption: Vitamin C

Non-haem iron (the form in plant foods and supplements) is absorbed in its ferrous (Fe2+) state. Gastric acid helps maintain this reduced form, but taking vitamin C (ascorbic acid) alongside iron supplements further enhances absorption by reducing Fe3+ to Fe2+ and forming a soluble chelate that resists precipitation by dietary inhibitors. Taking iron supplements with a small glass of orange juice — or a 200mg Vitamin C tablet — can meaningfully increase absorbed iron.

Conversely, tannins in tea and coffee, calcium in dairy, and phytates in wholegrains all inhibit iron absorption. Iron supplements should be taken two hours apart from tea, coffee, and calcium-rich foods.

Practical Guidance on Dosing

Therapeutic repletion typically requires 100–200mg of elemental iron daily in divided doses, in the form of ferrous sulphate or equivalent. For maintenance or mild deficiency, lower doses (25–50mg elemental iron) may be appropriate — and evidence suggests that every-other-day dosing achieves comparable repletion with fewer side effects, as it avoids hepcidin upregulation that occurs with daily dosing.

Bottom Line

Iron deficiency is common, often missed by haemoglobin-only testing, and highly symptomatic before anaemia develops. UK premenopausal women should request ferritin alongside any full blood count for fatigue assessment, aiming for a ferritin of at least 50 mcg/L for symptom resolution. For supplementation, iron bisglycinate at 18–36mg elemental iron is a well-tolerated first choice; taking it with vitamin C and away from tea and dairy optimises absorption. Severe or persistent deficiency warrants GP review to exclude underlying blood loss.