Understanding Iron Deficiency: The World's Most Common Nutrient Deficit

Iron sits in haemoglobin — the blood's oxygen transporter — as well as in muscle and enzymes. The body can hardly excrete it actively, but can also only absorb it to a limited degree; it is lost above all through blood. That yields the risk map: menstruating women (by far the most common case), pregnant women (sharply increased need), regular blood donors, endurance athletes (micro-losses and absorption-inhibiting inflammatory signals from hard training) and people on predominantly plant-based diets — plant iron is absorbed markedly worse than the haem iron from meat and fish. Gastrointestinal conditions and certain acid blockers can also depress absorption. A 2026 Cochrane review confirms this specifically for blood donors: regular donation raises deficiency risk, and accompanying iron monitoring or supplementation can be worthwhile. And a current guideline (SOGC 2026) underscores that iron status deserves regular attention across the entire female life cycle — menstruation, pregnancy, menopause.

The typical signs: persistent tiredness and exhaustion, paleness, breathlessness on exertion, concentration problems, increased hair loss, brittle nails, cracked mouth corners, restless legs — and in training: stagnating endurance despite consistent work. The problem: every single one of these symptoms has a dozen possible causes, from sleep deprivation via the thyroid to B12.

Hence the route through the blood panel: the central value is ferritin (storage iron), complemented by haemoglobin and, depending on the case, transferrin saturation — a deficiency can begin long before measurable anaemia and still cause symptoms. Exactly this constellation (exhausted, low ferritin, no anaemia yet) was studied in the Swiss trial of 2012: medically dosed iron measurably reduced fatigue versus placebo. Interpreting the values belongs in the practice — also because ferritin can look deceptively normal during infections and inflammation.

• The cause question is the real diagnosis: in men and postmenopausal women, iron deficiency is so atypical that guidelines demand an active search for the cause — particularly for unnoticed blood loss in the gastrointestinal tract. Covering that finding with drugstore iron loses precious time in the worst case.
• Haemochromatosis is more common than assumed: the hereditary iron-storage disease affects roughly one in 200–300 people of Northern European descent — for them, extra iron is directly organ-damaging. Without a test you do not know which side you are on.
• Side effects are real: iron preparations frequently cause gastrointestinal complaints — one more reason to have dose and form (and whether at all) set medically. Modern regimens often dose lower or every other day, because that can improve absorption. More modern medical options: a 2026 meta-analysis shows that intravenous iron can be more effective than tablets for diagnosed pregnancy anaemia — but diagnosis and choice of therapy remain a matter for the treating practice.
• Interactions: iron hampers the absorption of thyroid hormones and certain antibiotics, among others (keep a time gap!) — another argument for a supervised plan instead of solo action.

Preventing and supporting mild deficits is very much a self-service job: haem iron from meat and fish is absorbed best; whoever eats plant-based relies on legumes, whole grains, oats, pumpkin seeds, sesame — and uses two simple absorption tricks: vitamin C with the meal (peppers, an orange, a glass of juice) markedly improves plant-iron uptake, while coffee and tea taken with the meal inhibit it — an hour's gap suffices. For female athletes with high training volumes: iron status belongs in the regular check-up, like blood pressure.

And the closing perspective: if the test shows a deficiency, medically supervised treatment is gratifyingly effective — energy, resilience and training progress typically return over weeks. Which is exactly why the blood test beats the guessing game: it turns "something is off" into a solvable task.