Anemia: Symptoms, Causes, Types & How It's Treated
Anemia: When Your Blood
Can't Carry Enough Oxygen
Fatigue that sleep won't fix. Skin that looks washed out. A heart that races going up stairs. These aren't vague complaints, they're your body running low on oxygen delivery. Here's what's actually happening.
What Anemia Actually Is
Anemia isn't a disease on its own — it's a sign that something else is wrong. The definition is simple: not enough healthy red blood cells, or red blood cells that can't carry sufficient oxygen.
Red blood cells carry oxygen using a protein called haemoglobin. Iron sits at the centre of each haemoglobin molecule; without enough iron, the molecule can't be built. Without enough haemoglobin, every cell in your body gets a slightly reduced oxygen supply. That's what produces the fatigue, the breathlessness, the pale skin, the racing heart.
Anemia is essentially your body running an oxygen deficit. Every organ — your brain, your muscles, your heart — is working harder than it should for the fuel it's getting.
Clinically, anemia is defined as haemoglobin below 13.5 g/dL in men and below 12.0 g/dL in women, though some labs use slightly different cut-offs. Children's normal values vary by age.
Over 2 billion people worldwide have some form of anemia, making it one of the most common medical conditions on the planet. Iron deficiency alone affects roughly 1.2 billion people. The burden falls heaviest on women of reproductive age, pregnant women, children, and people in low-income countries — though it's genuinely common everywhere.
Symptoms: From Mild to Severe
Mild anemia often produces no symptoms at all. The body compensates remarkably well — the heart pumps a little faster, breathing deepens slightly — and people function without realising anything is wrong. This is why anemia gets caught incidentally on routine blood tests far more often than it gets caught from symptoms alone.
As haemoglobin drops, the compensation breaks down and symptoms appear.
Iron deficiency adds some distinctive features beyond standard anaemia symptoms. Pica — craving non-food items like ice, clay, or dirt — sounds bizarre but is clinically documented and often resolves completely with iron treatment. Restless legs syndrome, a crawling sensation in the legs at night, is also associated with iron deficiency specifically.
In B12 deficiency anaemia (pernicious anaemia), neurological symptoms can appear even before the blood count changes significantly: tingling or numbness in the hands and feet, difficulty walking, memory problems, and mood changes. These are caused by damage to the myelin sheath, the protective coating around nerves, and won't reverse with iron — only B12 replacement helps.
Chest pain with breathlessness and racing heart, severe dizziness or fainting, haemoglobin below 8 g/dL confirmed on a blood test, or any signs of active bleeding (dark stools, blood in urine, heavy unexplained vaginal bleeding). These presentations need same-day or emergency evaluation.
Types of Anemia
Doctors classify anemia in 2 main ways: by the size of red blood cells (which points to the cause), and by the underlying mechanism. Both systems are useful and used simultaneously.
By red cell size
Real patients often have 2 deficiencies at once — iron and B12, for instance, after bariatric surgery or in long-standing malabsorption. The microcytic and macrocytic effects cancel each other out, producing a falsely normal MCV. The clue is a wide RDW (red cell distribution width) on the CBC, showing abnormal variation in cell size. Always check ferritin, B12, and folate in unexplained normocytic anaemia.
Diagnosis: CBC, Ferritin, and What the Numbers Mean
The starting point is always a complete blood count (CBC). This gives haemoglobin, red cell count, MCV (mean cell volume), and several other parameters in a single test. But the CBC alone rarely tells you why someone is anaemic — it just confirms they are.
| Haemoglobin Level | Classification | Typical Symptoms |
|---|---|---|
| >12 g/dL (women) / >13.5 g/dL (men) | Normal | None |
| 10–12 g/dL | Mild anaemia | Fatigue, exertional breathlessness |
| 8–10 g/dL | Moderate anaemia | Fatigue at rest, pallor, palpitations |
| <8 g/dL | Severe anaemia | Chest pain, dizziness, may need transfusion |
| <7 g/dL | Critical — transfusion threshold | Most guidelines recommend transfusion at this level |
The tests that tell you why
Serum ferritin is the most important test for iron stores. Ferritin below 30 ng/mL indicates depleted stores, even if haemoglobin is still normal (this is called iron deficiency without anaemia). One caveat: ferritin is an acute-phase reactant. Inflammation, infection, or liver disease can elevate ferritin even when stores are low, masking the deficiency. In this context, a ferritin below 100 ng/mL should prompt suspicion of co-existing iron deficiency.
Serum iron and total iron-binding capacity (TIBC) add useful information: in iron deficiency, serum iron is low and TIBC is high (the body desperately increases its capacity to grab any iron available). In anaemia of chronic disease, both serum iron and TIBC are low.
For B12 and folate deficiency, serum B12 and red cell folate are measured directly. A peripheral blood smear showing hypersegmented neutrophils is a classic and specific sign of megaloblastic anaemia.
Iron deficiency anaemia in adult men and post-menopausal women should always be investigated for a bleeding source, even if symptoms are mild. The most common serious cause is gastrointestinal bleeding from an ulcer, polyp, or colorectal cancer. Treating the iron without finding the source is poor clinical practice — the Merck Manual puts it plainly: "Iron therapy without pursuit of the cause is poor practice."
Iron Deficiency Anemia in Depth
Iron deficiency anemia has 3 progressive stages, and most people are somewhere in stage 2 or 3 before they know anything is wrong.
Stage 1: Iron stores (ferritin) fall below normal. Haemoglobin is still normal. You probably feel fine, but a blood test shows low ferritin. Stage 2: The bone marrow starts making red cells without enough haemoglobin. The CBC starts showing abnormalities — low MCV, high TIBC. Symptoms may begin. Stage 3: Haemoglobin drops below the normal range. Full anaemia is established. Symptoms are now clearly present.
Who's most at risk
Women with heavy periods lose significant iron every month — this is the single most common cause of iron deficiency in pre-menopausal women. Pregnant women need roughly 3 times more iron than usual: extra blood volume, the placenta, fetal development. Infants and toddlers going through rapid growth spurts have high iron requirements that breast milk alone can't meet after 4–6 months. Vegetarians and vegans get iron primarily from plant sources, where absorption is far less efficient. People with coeliac disease, Crohn's disease, or a history of gastric bypass surgery often can't absorb iron properly regardless of dietary intake.
The ferritin vs haemoglobin distinction
Iron deficiency without anaemia — normal haemoglobin, low ferritin — is nearly twice as common as iron deficiency with anaemia, and it still causes symptoms. Fatigue, poor concentration, and reduced exercise capacity have all been documented in iron deficiency even before the haemoglobin falls. This is why checking ferritin matters, not just haemoglobin.
Vitamin B12 and Folate Deficiency Anemia
B12 and folate are both required for DNA synthesis in developing red blood cells. Without them, the bone marrow produces large, immature red cells that break down faster than normal. The result is macrocytic (large-cell) anaemia.
B12 deficiency is particularly insidious because it can cause permanent neurological damage — subacute combined degeneration of the spinal cord — even before the blood count is noticeably abnormal. Tingling in the extremities, unsteady gait, and cognitive changes are the warning signs. These won't reverse with iron, and they won't reverse at all if left too long.
The most common cause of B12 deficiency in adults is pernicious anaemia — an autoimmune condition where the stomach stops producing intrinsic factor, a protein that B12 needs to be absorbed. Dietary B12 deficiency alone is relatively rare but does occur in strict vegans, since B12 exists almost exclusively in animal products.
Folate deficiency causes identical blood changes but no neurological damage. It's most commonly from poor diet, alcohol dependence, or pregnancy (folate requirements double). The practical clinical importance: if you give folate to someone who actually has B12 deficiency, you correct the blood picture but allow the neurological damage to continue progressing. Always check both before treating.
Folic acid supplementation should start at least 1 month before conception and continue through the first trimester. It reduces the risk of neural tube defects (spina bifida, anencephaly) by up to 70%. This is one of the most evidence-backed interventions in antenatal care.
Treatment: Oral Iron, IV Iron, Diet, and More
Treatment depends entirely on what's causing the anaemia. Giving iron to someone with B12 deficiency does nothing. Giving B12 to someone bleeding from a bowel cancer helps the blood count briefly and masks a serious problem. Find the cause first, then treat it.
Oral iron supplementation
Ferrous sulphate is the standard first-line treatment for iron deficiency anaemia — cheap, effective, and widely available. The usual adult dose is 200 mg of ferrous sulphate (containing 65 mg of elemental iron) taken 1–3 times daily. Take it on an empty stomach, 30 minutes before food: absorption is significantly better than with food. Vitamin C taken alongside it improves absorption further.
Side effects are the main practical problem: constipation, nausea, dark stools, and a metallic taste are common and cause many people to stop taking the supplements. Switching to a lower-dose preparation, taking it every other day (which reduces GI side effects with comparable efficacy), or switching to ferrous gluconate or ferrous fumarate (better tolerated in some patients) are all reasonable adjustments.
Response: reticulocytes (new red cells) rise within 1 week. Haemoglobin improves by roughly 1 g/dL per 2 weeks. Anaemia should be corrected within 2 months. Supplements should continue for at least 3–6 months after that to replenish ferritin stores.
Intravenous (IV) iron
IV iron bypasses the gut entirely and delivers iron directly into the bloodstream. It's used when oral iron fails, can't be absorbed (coeliac disease, post-bariatric surgery), isn't tolerated, or when rapid repletion is needed (severe anaemia, third trimester of pregnancy, pre-surgical patients). Modern IV iron formulations (ferric carboxymaltose, iron sucrose) are safe when given correctly. Anaphylaxis risk is low but real — administration requires clinical supervision.
| Type | Primary Treatment | Duration |
|---|---|---|
| Iron deficiency anaemia | Oral ferrous sulphate + treat cause of blood loss | 3–6 months after Hb normalises |
| B12 deficiency (pernicious anaemia) | IM hydroxocobalamin injections | Lifelong (every 2–3 months) |
| B12 deficiency (dietary) | Oral B12 supplements or dietary change | Until stores replenished, then maintenance |
| Folate deficiency | Oral folic acid 5 mg daily | 4 months (or lifelong if ongoing risk) |
| Anaemia of chronic disease | Treat underlying condition; erythropoietin if renal | Ongoing |
| Severe anaemia (<7 g/dL) | Blood transfusion | Acute intervention |
Dietary iron sources
| Food | Iron Type | Absorption Rate |
|---|---|---|
| Red meat, liver, organ meats | Haem iron | 20–30% (best absorbed) |
| Chicken, turkey, fish | Haem iron | 15–20% |
| Lentils, chickpeas, kidney beans | Non-haem iron | 2–10% |
| Tofu, tempeh | Non-haem iron | 2–8% |
| Spinach, dark leafy greens | Non-haem iron | 1–5% (oxalates reduce absorption) |
| Iron-fortified cereals | Non-haem iron | Varies by formulation |
The practical point on plant-based iron: non-haem iron absorption drops dramatically when eaten with tea, coffee, calcium, or high-phytate foods (like whole grains). It improves significantly when eaten alongside vitamin C. A glass of orange juice with your lentil dal isn't just tasty — it genuinely increases how much iron you absorb from the meal.
Tannins in tea and coffee bind non-haem iron in the gut and reduce absorption by up to 60–70%. This is particularly relevant in South Asian populations where tea is consumed with meals daily. Shifting tea consumption to between meals rather than with them is a simple, evidence-backed change that can meaningfully improve iron absorption over time.
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