Iron deficiency is one of the most common nutritional deficiencies globally and can manifest as fatigue, brain fog, low mood, pale skin and nails, shortness of breath on exertion, cold extremities, brittle nails, and restless legs. A less obvious but classic sign is pica - unusual cravings, particularly for ice.
Diagnosis
The only conclusive way to confirm iron deficiency is bloodwork. The key markers are:
- Serum ferritin - measures iron stores. Below ~30 µg/L is functionally deficient even if hemoglobin appears normal
- Full blood count (FBC) - measures hemoglobin levels for overt anaemia
Ferritin is the more sensitive early indicator. Hemoglobin only drops once stores are substantially depleted.
Iron Absorption
Not all dietary iron is equal. There are two forms:
| Type | Source | Absorption Rate |
|---|---|---|
| Heme iron | Animal tissue (meat, organs, shellfish) | 15-35% |
| Non-heme iron | Plants, fortified foods | 2-5% |
This means 100g of spinach with ~2.7mg of iron delivers roughly 0.05-0.14mg of usable iron, while 100g of beef steak with ~3mg delivers 0.45-1.05mg - up to 20x more in practice.
Absorption Enhancers
- Vitamin C - significantly boosts non-heme iron absorption. Pair plant iron sources with citrus, capsicum, or tomato
- Heme iron - eating meat alongside plant sources improves absorption of the non-heme iron as well
Absorption Inhibitors
- Tannins (tea, coffee) - strongly inhibit absorption. Separate from iron-rich meals by 30-60 minutes
- Oxalates (spinach, rhubarb) - bind iron and reduce availability. Spinach is often cited as iron-rich but is one of the worst delivery vehicles due to high oxalate content
- Phytates (whole grains, legumes) - moderate inhibition
- Calcium - competes for absorption at high doses
Dietary Sources Ranked by Bioavailable Iron
| Source | Iron per 100g | Bioavailability | Notes |
|---|---|---|---|
| Liver (beef/chicken) | 6-9mg | High (heme) | Richest common source |
| Shellfish (oysters, clams) | 5-8mg | High (heme) | Excellent but expensive |
| Biltong / dried beef | 5-8mg | High (heme) | Concentrated due to dehydration. Shelf-stable, snackable. Watch sodium content |
| Red meat (beef, lamb) | 2.5-3.5mg | High (heme) | Most practical regular source |
| Lentils / beans | 3-6mg | Low (non-heme) | Requires vitamin C pairing for meaningful absorption |
| Fortified cereals | 4-12mg | Low (non-heme) | Varies wildly by brand |
| Dark leafy greens | 1-3mg | Very low (non-heme) | Oxalates severely limit absorption |
Daily Requirements
| Group | RDI |
|---|---|
| Adult men | ~8mg/day |
| Pre-menopausal women | ~18mg/day |
| Pregnant women | ~27mg/day |
Repletion Timeline
Iron repletion is not instant. A single iron-rich meal does not meaningfully shift ferritin levels. Expect:
- Symptomatic improvement: days to 1-2 weeks after consistent dietary improvement
- Ferritin normalisation: weeks to months depending on severity
- Full haemoglobin recovery (if anaemic): 2-3 months of sustained intake or supplementation
Practical Strategies
- Keep shelf-stable heme iron sources available (biltong, canned sardines) to prevent gaps in intake
- Pair plant iron sources with vitamin C at the same meal
- Avoid tea and coffee within 30-60 minutes of iron-rich meals
- If supplementing, take on an empty stomach with vitamin C for best absorption (though this increases GI side effects)
- Cook in cast iron cookware - small amounts of iron leach into food, particularly with acidic dishes