Serum ferritin, the iron storage protein, is the most sensitive indicator of iron status. Levels below 30 micrograms per litre indicate depleted iron stores even when haemoglobin remains normal, a condition called iron depletion or iron deficiency without anaemia. This condition is estimated to affect approximately 20 to 25 percent of premenopausal women and a significant minority of male endurance athletes. Its symptoms are identical to iron-deficiency anaemia but are missed when only haemoglobin is tested.
Effects on Energy and Exercise
Iron is required for haemoglobin in red blood cells that transports oxygen to tissues, for myoglobin in muscle that stores and transfers oxygen within muscle cells, and for cytochromes in the mitochondrial electron transport chain that produce cellular energy. Depletion of any of these iron compartments reduces oxygen delivery and mitochondrial function. Research in women with iron depletion without anaemia found that iron supplementation significantly improved exercise capacity, reduced perceived exertion, and reduced cognitive fatigue during exercise.
Optimising Dietary Iron Intake
- Haem iron from red meat is absorbed at 15 to 35 percent efficiency, significantly more than non-haem iron from plant foods at 2 to 20 percent
- Eat vitamin C-rich foods alongside plant iron sources: a glass of orange juice with lentil dal increases non-haem iron absorption by 3 to 6 times
- Avoid tea and coffee with iron-rich meals: tannins in tea inhibit non-haem iron absorption by up to 60 percent
- If iron depletion is suspected, test ferritin specifically rather than relying on a full blood count which may show normal haemoglobin