Iron Deficiency & Iron Deficiency Anaemia — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Iron is an essential mineral required for haemoglobin synthesis (the oxygen-carrying protein in red blood cells), myoglobin (oxygen storage in muscle), cytochrome enzymes (mitochondrial energy production), and numerous enzymatic functions in DNA synthesis and immune cell function. Iron deficiency (ID) exists on a spectrum before anaemia develops: Stage 1 — iron depletion (reduced stored iron — low ferritin below 12-30 mcg/L — but normal haemoglobin and serum iron); Stage 2 — iron-deficient erythropoiesis (insufficient iron for normal red blood cell production — low transferrin saturation below 16%, elevated TIBC, but haemoglobin still near normal); Stage 3 — iron deficiency anaemia (IDA — frank anaemia with microcytic hypochromic red blood cells, haemoglobin below 130 g/L in men and below 120 g/L in women). Iron deficiency is the most common nutritional deficiency globally, affecting over 2 billion people, with iron deficiency anaemia affecting approximately 1.2 billion. It is the leading cause of anaemia worldwide, responsible for approximately 50% of all anaemia cases. Women of reproductive age, pregnant women, infants, and children in low-income countries carry the highest burden.

Iron deficiency results from one or more of three mechanisms: inadequate intake, increased demand, or blood loss. Inadequate dietary intake: vegetarian and vegan diets (plant-based non-haem iron has 2-5% bioavailability versus 15-35% for haem iron from meat); restrictive eating disorders; poor diet with ultra-processed foods low in iron; exclusive breastfeeding beyond 6 months without complementary iron-rich foods. Blood loss (most common cause in adults): menstrual blood loss, particularly heavy periods (menorrhagia — blood loss above 80 mL per cycle causes negative iron balance and is the most common cause of IDA in premenopausal women); gastrointestinal bleeding — peptic ulcer (H. pylori, NSAIDs), colorectal cancer (iron deficiency in a man or postmenopausal woman = colorectal cancer until proven otherwise), oesophageal varices, angiodysplasia, coeliac disease, haemorrhoids (less commonly significant). Malabsorption: coeliac disease (villous atrophy in the duodenum and proximal jejunum — primary site of iron absorption — critically impairs iron uptake); Helicobacter pylori infection; inflammatory bowel disease; post-bariatric surgery (gastric bypass reduces gastric acid and bypasses proximal small bowel); atrophic gastritis. Increased demand: pregnancy (requires approximately 1000 mg additional iron for maternal erythropoiesis, foetal transfer, and delivery losses); rapid growth in infancy and adolescence.

Many patients with mild iron deficiency are asymptomatic — detected only on routine blood testing. Symptoms of anaemia (reduced oxygen delivery to tissues): fatigue and exhaustion (the most common presenting complaint — may precede frank anaemia in iron depletion); pallor (pale skin, conjunctivae, palmar creases, and mucous membranes); breathlessness on exertion; palpitations and tachycardia; dizziness and lightheadedness; reduced exercise tolerance and cognitive impairment; headaches; and cold intolerance. Specific symptoms of iron deficiency (may occur even before anaemia): pica (craving non-food items — ice [pagophagia], dirt [geophagia], chalk, clay); restless leg syndrome (uncomfortable urge to move legs especially at night — responds to iron treatment); koilonychia (spoon-shaped nails — concave nail plates); angular cheilitis (cracking at corners of mouth); glossitis (smooth, sore tongue); and hair loss. In children: impaired neurocognitive development, reduced school performance, and growth retardation are critical consequences of iron deficiency even in the absence of frank anaemia.

Full blood count (FBC): iron deficiency anaemia produces microcytic (low MCV — below 80 fL), hypochromic (low MCHC) red blood cells with low haemoglobin and elevated red cell distribution width (RDW). Serum ferritin: the single best test for iron stores — below 30 mcg/L diagnostic of iron depletion (note: ferritin is an acute-phase protein that rises with inflammation — a ferritin of 30-100 mcg/L may still represent iron deficiency in the presence of chronic inflammatory disease). Serum iron: decreased; total iron binding capacity (TIBC): increased; transferrin saturation: below 16% in established iron deficiency. Reticulocyte haemoglobin content (CHr or RetHe): highly sensitive early marker of functional iron deficiency. Investigation of the underlying cause is essential. In premenopausal women with heavy periods: gynaecological assessment. In all men and postmenopausal women with IDA: upper and lower GI endoscopy (OGD and colonoscopy) to exclude upper GI pathology and colorectal cancer — this is mandatory. Coeliac antibodies (IgA anti-tissue transglutaminase, total IgA). H. pylori testing (urea breath test, stool antigen). Small bowel imaging if upper and lower endoscopy are normal.

Oral iron supplementation is the first-line treatment for iron deficiency anaemia in most patients. Ferrous sulfate 200 mg (65 mg elemental iron) two to three times daily is the most widely used and cost-effective preparation. Other oral forms: ferrous fumarate (65 mg elemental iron per 200 mg tablet) and ferrous gluconate (lower elemental iron content — better tolerated but less efficient). Taking iron with vitamin C (ascorbic acid 250 mg) significantly increases absorption by maintaining iron in the ferrous (Fe2+) state. Avoid taking iron with tea, coffee, dairy, antacids, or calcium — all reduce absorption. Common GI side effects (nausea, constipation, dark stools) affect 30-40% of patients: take with food (reduces absorption by approximately 40% but greatly improves tolerability); start with a lower dose and titrate up; or try alternate-day dosing (emerging evidence this may be as effective due to hepcidin regulation). Haemoglobin rises approximately 10-20 g/L per month. Continue supplementation for 3-6 months after haemoglobin normalises to replenish stores (ferritin should rise above 50-100 mcg/L). Intravenous iron (ferric carboxymaltose — Ferinject; iron isomaltoside — Monofer): used for malabsorption (coeliac disease, IBD, post-bariatric), intolerance to oral iron, rapid replacement needed (severe anaemia pre-surgery, peripartum IDA), or severe inflammatory bowel disease. IV iron can replenish full stores in a single infusion. Treating the underlying cause: coeliac disease — gluten-free diet; H. pylori eradication (improves iron absorption significantly); menorrhagia — hormonal treatment (levonorgestrel IUS significantly reduces menstrual blood loss); GI pathology — appropriate endoscopic or surgical treatment.

Untreated or prolonged iron deficiency causes increasingly severe anaemia that impairs tissue oxygenation across all organ systems. Severe iron deficiency anaemia (haemoglobin below 70 g/L) causes high-output cardiac failure as the heart compensates for poor oxygen delivery by increasing cardiac output — prolonged exposure leads to left ventricular hypertrophy and cardiomegaly. Pica — compulsive craving and consumption of non-food substances including ice (pagophagia, the most common pica in IDA), soil, chalk, clay, paper, or starch — is a recognised but poorly understood complication of iron deficiency, more common in pregnancy and children; it resolves with iron replacement. Restless legs syndrome (RLS) — an irresistible urge to move the legs at rest, particularly at night — has a documented causal relationship with iron deficiency affecting dopaminergic neurotransmission in the substantia nigra and responds well to iron supplementation. In children, iron deficiency impairs neurocognitive development — causing deficits in attention, memory, and language acquisition — with evidence suggesting that some cognitive effects may persist even after iron repletion if deficiency occurred during critical early developmental windows. Brittle nails (koilonychia — spoon-shaped nails) and angular cheilitis (cracks at the corners of the mouth) are well-recognised but reversible cutaneous manifestations of chronic iron deficiency.

Dietary strategies: include haem iron-rich foods regularly (red meat, especially liver, beef, and lamb; poultry; shellfish — oysters and clams are exceptionally rich). For vegetarians and vegans: lentils, chickpeas, kidney beans, tofu, tempeh, fortified cereals, pumpkin seeds, and dark leafy greens. Always combine plant-based iron with vitamin C (a glass of orange juice with an iron-rich meal) to maximise non-haem iron bioavailability. Fortification: many countries fortify flour, cereals, and infant formula with iron — a critical public health intervention. Infant supplementation: exclusive breastfeeding infants need complementary iron-rich foods from 6 months; formula-fed infants receive iron-fortified formula. WHO recommends universal iron supplementation for pregnant women (60 mg elemental iron daily) in high-prevalence regions. Screening: pregnant women, women with heavy periods, and infants aged 6-12 months in at-risk populations should have periodic FBC and ferritin checks. Avoid excessive tea consumption with meals — polyphenols bind iron and reduce absorption.

See a doctor promptly for: persistent unexplained fatigue, pallor, breathlessness, or palpitations — request a blood test to check haemoglobin and ferritin; iron deficiency identified in a man or postmenopausal woman — urgent gastrointestinal investigation is required to exclude bleeding from cancer or peptic ulcer; new iron deficiency during pregnancy — maternal depletion can cause severe anaemia affecting the mother's ability to tolerate haemorrhage at delivery; and restless leg syndrome, pica (cravings for ice or dirt), or spooning of nails. Do not self-treat with iron supplements without medical diagnosis — iron overload (haemochromatosis) can cause serious organ damage, and self-prescribing may delay investigation of a serious underlying cause such as GI cancer. Seek emergency care for: severe breathlessness, chest pain, or rapid heart rate with known severe anaemia; or vomiting blood or black tarry stools suggesting active gastrointestinal bleeding.