Iron deficiency
Nearly 2 billion people live with a shortage of iron — the most common micronutrient deficiency on Earth. Here's why your body needs iron, how a deficiency builds silently across three stages, which symptoms and tests actually matter, and who is most at risk. To gauge your own status, take the iron deficiency assessment.
Why the body needs iron
An adult body holds just 3–4 grams of iron — less than an ordinary nail. Yet that trace amount decides whether you can think, move, and fend off infection. Iron does four fundamental jobs:
The three stages of iron deficiency
Deficiency builds gradually. Most people never notice the first two stages — until iron-deficiency anemia finally announces itself with unmistakable symptoms.
Reserves drain away and ferritin drops below 30 ng/mL, while hemoglobin still reads normal. Symptoms are minimal — maybe some mild fatigue. This is the easiest stage to catch and correct. A hidden iron deficiency test gauges your risk from symptoms, and the assessment calculator helps you read your labs.
Stores are exhausted and hemoglobin production falters. Red blood cells shrink (microcytosis) and pale. Fatigue mounts, concentration slips, and exercise starts to feel harder.
Anemia: hemoglobin below normal (♀ <12, ♂ <13 g/dL). The symptoms are pronounced — breathlessness, marked weakness, pallor, palpitations. This stage needs treatment under medical supervision.
Symptoms you shouldn't ignore
The signs of deficiency are easy to write off as ordinary tiredness. But when several linger longer than 2–3 weeks, it's worth getting tested or taking a symptom-based test.
Five key blood tests
Together these markers paint a full picture of iron metabolism. The best starting panel is ferritin plus a complete blood count (which delivers hemoglobin and MCV).
The storage protein that holds your iron reserves. The best early marker — it falls long before hemoglobin does.
The main protein in red blood cells. It only drops at a late stage — once reserves are long gone.
The size of your red cells. In deficiency they shrink (microcytosis) and pale. Included in the CBC.
The share of transferrin loaded with iron. Below 16% is a confident sign of deficiency.
How much iron transferrin can bind. In deficiency it rises — the body makes more transferrin to catch every atom of iron.
Who's at risk
Some people are especially vulnerable — through greater losses, reduced absorption, or higher demand.
Monthly menstrual losses run 15–45 mg of iron. Heavy bleeding drives the risk up sharply.
Requirements climb from 18 to 27 mg a day. Deficiency in the first trimester raises the risk of preterm birth.
Plant-based (non-heme) iron is absorbed 3–5 times less efficiently. Keep an eye on ferritin.
Losses through sweat, foot-strike hemolysis while running, and micro-bleeding in the gut. Marathoners lose iron faster.
Celiac disease, Crohn's disease, and ulcerative colitis impair absorption. Antacids cut iron uptake by 40–70%.
A single donation (450 mL) removes 200–240 mg of iron. Frequent donations without correction lead to deficiency.
