Iron
Iron is a component of haemoglobin (which carries oxygen), myoglobin, cytochromes, and numerous enzymes. Iron deficiency anaemia affects roughly 25% of the world's population and is the most common nutrient deficiency globally.
Daily requirements
- Adult men and post-menopausal women: 8 mg/day.
- Menstruating women: 18 mg/day.
- Pregnancy: 27 mg/day.
- Vegetarians / vegans: 1.8× the standard RDA due to lower bioavailability of non-heme iron.
- Tolerable Upper Intake Level: 45 mg/day (adults) from supplements — above this, GI toxicity is common.
Heme vs non-heme
- Heme iron — from animal muscle (beef, lamb, chicken, fish). Absorbed 15–35% regardless of other dietary factors.
- Non-heme iron — from plants and fortified foods. Absorbed 2–20% depending on cofactors. Vitamin C in the same meal roughly doubles absorption; tannins in coffee/tea and calcium reduce it.
Deficiency and anaemia
Symptoms of iron deficiency (with or without anaemia): fatigue, exercise intolerance, pallor, brittle nails, restless legs syndrome, pica (ice craving), headaches, hair loss, cold intolerance. Anaemia (low haemoglobin) is a late sign — depleted iron stores (low ferritin) occur first.
Diagnosis: serum ferritin is the single best test. < 30 ng/mL is generally considered deficient (some experts push the cut-off to < 50 in symptomatic patients). Confirm with iron, TIBC, and transferrin saturation if uncertain. Investigate cause of iron loss in men and post-menopausal women — colorectal or upper GI blood loss must be ruled out.
Supplementation
| Form | Elemental Fe |
|---|---|
| Ferrous sulphate 325 mg | 65 mg |
| Ferrous gluconate | 36 mg/324 mg |
| Ferrous bisglycinate | 28 mg per 200 mg pill |
| IV iron (iron sucrose, ferric carboxymaltose) | 1,000 mg per dose |
Contemporary evidence supports alternate-day dosing for repletion — 65 mg every other day absorbs as much iron per week as 65 mg daily, with far less GI upset and less hepcidin blockade of subsequent absorption (Stoffel 2017).
Food sources
- Beef liver (3 oz): 5.2 mg heme
- Oysters (3 oz): 8 mg
- Beef, sirloin (3 oz): 2.5 mg heme
- Chicken thigh (3 oz): 1.1 mg heme
- Fortified breakfast cereal: 4–18 mg non-heme
- Lentils (½ cup): 3.3 mg non-heme
- Spinach (½ cup cooked): 3.2 mg non-heme
Iron overload — the opposite risk
Haemochromatosis (hereditary iron overload) affects ~1 in 200 people of Northern European descent. Screening with transferrin saturation and ferritin is appropriate in adults with unexplained fatigue, joint pain, liver enzyme elevation, or diabetes. Untreated haemochromatosis causes cirrhosis, cardiomyopathy, and diabetes. Never take a routine iron supplement without a documented indication.