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Preventing and treating an iron deficiency

Iron is a mineral with a critically important role for performance (read our previous blog) yet, iron deficiency is common in athletes, especially female endurance athletes. Here we will answer the following questions: How to prevent iron deficiency? Which foods are rich in iron? How to treat iron deficiency?

The body cannot produce iron, and therefore it must be obtained from external sources eg food or supplements. In principle, the methods for prevention are the same as those for treatment. In daily practice, prevention is usually done through diet, supplements are used for prevention as well as treatment and injections are used almost exclusively for treatment.

How should we prevent or treat of an iron deficiency?

With regards to treatment of an iron deficiency, several factors should be considered when deciding upon the course of treatment, including the underlying aetiology, the severity of the deficiency and the time frame in which iron levels need to be restored (1).

Strategy 1: Dietary Adjustments

A ‘food first’ approach should be adopted in order to prevent an iron deficiency. Iron requirements are greater for athletes compared to the normal population and therefore you must ensure that you are consuming sufficient amounts of dietary iron. A nutritionist/dietitian can advise you on this by carrying out a dietary assessment. Dietary adjustments can also be used as an initial phase of treatment.

However, the biggest problem with getting iron is not iron intake but its bioavailability (how much of what we ingest will actually become available in the body). Iron’s bioavailability is generally poor, but it also depends on the source of iron. There are two forms of dietary iron which are heme and non-heme; heme iron is more readily absorbed in the gut than non-heme iron. Animal-based foods (e.g. beef, poultry, lamb, seafood, pork) contain a mixture of heme and non-heme iron, whereas plant-based foods (e.g. legumes, leafy green vegetables, cereals, dried fruits and nuts) contain almost 100% non-heme iron. The absorption of non-heme iron is ~5% compared to ~40% from heme iron (2). These numbers may vary depending on the study, but in general heme iron seems to be absorbed 8-10 times better than non-heme iron.

In Western diets, iron obtained through heme sources constitutes around two thirds of total iron stores, even though only one third of dietary iron consumption is heme iron (3). The presence of heme iron in a meal can increase the absorption of non-heme iron, and therefore it is beneficial to include both heme and non-heme containing foods into meals.

Improving iron absorption

Iron absorption can be increased by optimising the timing of iron intake around certain foods. Consuming foods that contain Vitamin C (e.g. oranges/orange juice, peppers, kiwis, strawberries) alongside iron-rich foods can enhance absorption. Whereas calcium containing foods (e.g. milk, yogurt and cheese) and caffeine (e.g. tea, coffee) can inhibit iron absorption, and therefore should not be consumed in close proximity to iron rich foods, if your aim is to optimise iron absorption (4).


It is a fable that spinach is a great source of iron. Popularised by Popeye, spinach is often seen as a great source of iron. However, it contains 2.1-2.7 mg of iron per 100 grams of raw spinach. To make the claim that something is high in iron, a food must contain at least 15% of the recommended daily intake of iron per 100g portion. For a food to be classed as "high in" iron, it needs to have double this number. So, at best, spinach can be classed as a “source of” iron but it is certainly not “high in” iron. In addition to this, the absorption of iron from spinach is poor with some studies reporting as little as 2%.

Strategy 2: Oral Iron Supplementation

Supplementation is used following dietary adjustments if iron status does not improve/ symptoms are still present (or sometimes it used alongside depending on the level of deficiency). It is usually provided in the form of tablets or liquids and should be used under the guidance of a sports physician.

There are many different forms of iron that can be used in iron preparations; usually in the ferrous form (e.g. sulphate, fumarate or gluconate), but sometimes ferric forms are used (e.g. citrate or sulfate). In a review comparing ferrous and ferric preparations, it was concluded that “slow-release ferrous sulphate preparations remain the established and standard treatment of iron deficiency, irrespective of the indication, given their good bioavailability, efficacy, and acceptable tolerability” (5). However, it is worth noting that all athletes are individual and what works well for one athlete may not for another.

All athletes are individual and an oral iron supplement that works well for one athlete may not for another

Gastrointestinal issues are common when using oral iron therapy. They can be minimised by consuming the iron supplement alongside food (e.g. a glass of orange juice to enhance iron uptake with Vitamin C) or by using tablets with an enteric coating.

A sports physician will decide on the dose and frequency of iron supplementation depending on the level of deficiency, gastrointestinal comfort and the speed at which iron repletion is required. It is important to note that greater or more frequent doses are not always favourable. For example, a study demonstrated that consuming two separate doses of iron daily (at 8AM and 5PM) resulted in reduced iron absorption compared to supplementation as a single dose, or as a single dose on alternate days (6).

Greater or more frequent doses of iron are not always favourable

Strategy 3: Intravenous (IV) Injections

In order to treat an iron deficiency, a sports physician may administer an IV iron injection if oral and dietary therapy fail to increase iron status, or if iron repletion is required in a very short time frame. In addition, it may be used if an athlete suffers from severe gastrointestinal issues from oral iron therapy, because it bypasses the gut (where iron is absorbed).

Monitoring of iron status

Once any of the strategies above have been initiated in an iron deficient athlete, iron status should be measured every 6-8 weeks (4). This allows continuation with the chosen course of treatment, or modification depending on the results. If the iron deficiency is only moderate then iron status will need to be monitored less regularly; twice per year is recommended (1).


  1. Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. Eur J Appl Physiol. 2019;119(7):1463-1478. doi:10.1007/s00421-019-04157-y

  2. Björn-Rasmussen E, Hallberg L, Isaksson B, Arvidsson B. Food iron absorption in man. Applications of the two-pool extrinsic tag method to measure heme and nonheme iron absorption from the whole diet. J Clin Invest. 1974;53(1):247-255. doi:10.1172/JCI107545

  3. Carpenter CE, Mahoney AW. Contributions of heme and nonheme iron to human nutrition. Crit Rev Food Sci Nutr. 1992;31:333–367.

  4. Clénin G, Cordes M, Huber A, et al. Iron deficiency in sports - definition, influence on performance and therapy. Swiss Med Wkly. 2015;145:w14196. Published 2015 Oct 29. doi:10.4414/smw.2015.14196

  5. Santiago P. Ferrous versus ferric oral iron formulations for the treatment of iron deficiency: a clinical overview. ScientificWorldJournal. 2012;2012:846824. doi:10.1100/2012/846824

  6. Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. The Lancet. Haematology. 2017 Nov;4(11):e524-e533. DOI: 10.1016/s2352-3026(17)30182-5.

  7. Zijp IM, Korver O, Tijburg LB. Effect of tea and other dietary factors on iron absorption. Crit Rev Food Sci Nutr. 2000;40(5):371-398. doi:10.1080/10408690091189194

  8. Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hultén L. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 1991;53(1):112-119. doi:10.1093/ajcn/53.1.112


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