Iron is a critical micronutrient that is needed in the diet since the body cannot produce iron on its own. Iron is important and required for numerous processes in the body, ranging from proper immune cell function to the formation of red blood cells. Likely a few of the most important functions of iron for endurance athletes are its role in oxygen transport via hemoglobin and myoglobin as well as its role in oxidative production of adenosine triphosphate (ATP) within the electron transport chain (3). Therefore, a compromised storage of iron could potentially disrupt the formation of red blood cells and the ability to generate ATP via oxidative metabolism, both of which could impair endurance performance capacity.
Iron deficiency is one of the most common deficiencies in the world, and so rightfully so it tends to be a micronutrient that gets a lot of attention in general. However, iron deficiency is also one of the more common micronutrient deficiencies among athletic populations, particularly endurance athletes and team-based athletes. It is estimated that ~15-35% of female athletes and ~3-11% of male athletes are deficient in iron; however, some smaller studies suggest even higher numbers than these (3). The rates of iron deficiency are much higher in athletes than they are in non-athletes as well (3).
What makes athletes more likely to experience iron deficiency? It has been proposed that any one, or all, of the factors below increase the likelihood of athletes being at greater risk of iron deficiency compared to non-athletes (3):
Hemolysis (breakdown of red blood cells) exacerbated by ground-contact forces during running
Post-exercise inflammatory responses which leads to greater post-exercise interlekin-6 (IL-6) concentration, which increases hepcidin concentration, and hepcidin is the master regulating hormone of iron, with higher hepcidin leading to reduced iron absorption from the gut
Greater potential for gastro-intestinal bleeding
Potential for iron loss through sweat
Greater breakdown and production of red blood cells due to adaptations in response to exercise
Of note, women also have a higher need for iron, and therefore a greater likelihood of becoming deficient, due to the loss of blood and iron associated with their menstrual cycle. This is of course not unique to only female athletes, however.
In regards to iron deficiency, it important to note, that like other micronutrient deficiencies, there are differing stages of iron deficiency ranging from initial less severe stages that may not exhibit any overt symptoms all the way to the most severe stage in which there are significant negative consequences and symptomatology. Iron is stored in the body as ferretin or hemosiderin, and these stores are usually what is depleted initially, with actual hemoglobin and red blood cell production affected in later stages of deficiency when iron stores get severely depleted. For iron deficiency in athletes, the following three stages of deficiency have been proposed:
Stage 1: iron deficiency (ID): iron stores in the bone marrow, liver and spleen are depleted (ferritin < 35 μg/L, Hb > 115 g/L, transferrin saturation > 16%).
Stage 2: iron-deficient non-anaemia (IDNA): erythropoiesis diminishes as the iron supply to the erythroid marrow is reduced (ferritin < 20 μg/L, Hb > 115 g/L, transferrin saturation < 16%).
Stage 3: iron-deficient anaemia (IDA): Hb production falls, resulting in anaemia (ferritin < 12 μg/L, Hb < 115 g/L, transferrin saturation < 16%).
Most people reading this might think that iron deficiency is really only a problem if anemia (low red blood cell volume and reduced hemoglobin concentration) is present. While it is true that low red blood cell volume and iron-deficiency anemia has well-documented negative consequences on athletic performance, some research also might suggest a reduction in performance from iron-deficiency non-anemia, likely due to impaired oxidative metabolism in the absence of reduced red blood cell volume (3). Therefore, catching iron deficiency at any stage is critical, not just for general health and well-being, but also for athletic performance. This is why it is usually recommended for endurance athletes to have iron status checked annually, or even biannually or quarterly if you have had evidence of impaired iron status previously (3).
What Happens if Iron Status is Compromised?
Firstly, it should be mentioned that an athlete should never guess when it comes to iron status. If an athlete wants to know what their iron status is, whether it is due to simple curiosity or because they experience some potential symptoms indicating iron deficiency (e.g., lethargy, weakness, fatigue, reduced endurance performance, etc.), they should have their iron levels tested by your primary care physician. There are also micronutrient testing options that one can get as well, and these don’t necessarily always have to be ordered through one’s primary care physician. Regardless of how the testing is done, so long as it is an accurate test, it is imperative that an athlete gets tested before manipulating iron intake as supplementing with iron when one is not deficient has no benefit. The benefits from increasing iron intake through food or supplementation typically only come when someone is deficient.
So, let’s say an athlete gets their iron status tested and they do indeed have a deficiency. How is this normally handled? Typically, the first approach is to increase iron in the diet (fortified cereals, fish, meat, poultry, green leafy vegetables, etc.) (3). A change in diet to promote increased iron intake may also be done in conjunction with consuming foods that also increase the absorbability of iron, such as vitamin C or consuming heme iron foods (meat, fish, poultry) as opposed to non-heme sources (vegetables, beans/legumes, etc.). The second approach is to supplement with an oral supplement (3). Oral supplements can be elemental iron sources such as ferrous sulfate, or they could be chelated iron sources such as ferrous bisglycenate. It is important to mention here that chelated forms of iron may be advantageous to elemental iron when it comes to supplementation as chelated forms of iron can typically be taken in lower doses due to enhanced absorbability (1,2). Chelated forms of iron are also typically better tolerated compared to elemental iron, which is commonly associated with gastrointestinal upset and nausea (1,2). Finally, the third approach is to administer iron via an intramuscular shot or intravenous drip (3). However, this approach is usually only reserved for cases of severe iron-deficiency anemia in which rapid increases in iron stores are desired (3).
When an athlete does have a compromised iron status, including milder deficiencies such as iron deficiency or iron deficiency without anemia, research has shown that endurance performance can possibly be improved when supplementing with iron (3). With the most severe cases of iron deficiency anemia, performance is likely severely compromised, and so supplementing with iron will almost surely improve performance as iron stores and hemoglobin status is improved (3).
To conclude, iron is an important and critical micronutrient for general health, but also for athletes, particularly endurance athletes. Iron deficiency is much more common among athletes than non-athletes due to various factors, and correction of iron deficiency is likely to have benefits on overall performance, particularly among those with severe iron deficiency anemia. Iron status can be improved through increasing oral iron intake (diet, supplementation) or via intramuscular shots or intravenous fluid. However, testing for iron deficiency should be done to confirm an actual iron deficiency before attempting to increase iron intake. It is, of course, good practice to regularly consume foods with iron with or without testing as iron is required in our diets, but supplementing with iron via oral supplementation or intramuscular shots or intravenous fluids should not be done if iron deficiency is not present due to the increased health risk of too much iron and the lack of performance benefit by athletes increasing iron intake without the presence of iron deficiency. If you are looking to learn more about iron and its considerations specifically for athletes, I highly recommend reading reference #3 in the reference list below as it is a 2019 review on the topic.
On a side note, if you are looking for an iron supplement to help correct an identified deficiency, I personally love the Athlete’s Iron from MOXiLIFE as it is a highly absorbable and gut-friendly chelated form of iron. As an added benefit, it also contains some gut-friendly prebiotics.
1. Ashmead. H.D., Guaiandro. S.F.M., and Same. J.J. 1997. Increases In hemoglobin and ferritin resulting from consumption of food containing ferrous amino acid chelate (ferrochel) versus ferrous sulfate. In Trace Elements in Man and Animals - 9: Proceedings of the Ninth International Symposium on Trace Elements in Man and Animals. Edited by P.W.F. Fischer. M.R. L’Abbe. K.A. Cockell, and R.S. Gibson. NRC Research Press. Ottowa. Canada. Pp. 284-285.
2. Ferrari P, Nicolini A, Manca ML, Rossi G, Anselmi L, Conte M, Carpi A, Bonino F. Treatment of mild non-chemotherapy-induced iron deficiency anemia in cancer patients: comparison between oral ferrous bisglycinate chelate and ferrous sulfate. Biomedicine & Pharmacotherapy. 2012 Sep 1;66(6):414-8.
3. Sim M, Garvican-Lewis LA, Cox GR, Govus A, McKay AK, Stellingwerff T, Peeling P. Iron considerations for the athlete: a narrative review. European journal of applied physiology. 2019 Jul;119(7):1463-78.
Happy training and racing!
-Ryan Eckert, MS, CSCS
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