anemia iron deficiency

Iron Deficiency and Anemia in Endurance Athletes

As an endurance athlete you likely know someone who struggles with anemia. Although it only affects about 5% of the general population, anemia is more common amongst athletes. By some estimates, more than 50% of female athletes and up to 30% of male athletes may be anemic. Here’s why endurance athletes are more likely to anemic, the different stages of anemia, and how anemia impacts performance.

What is Anemia

What is anemia and why are athletes more likely to struggle with it? Although not all anemias are related to iron, iron deficiency anemia is the most common form. It’s also the one most often seen in athletic populations. By its simplest definition, anemia means having low or inadequate hemoglobin. This is an issue because we rely on the hemoglobin in red blood cells to carry oxygen to our tissues.

What’s iron’s role in all this? Well, we need iron to make hemoglobin. So, although other things can cause some anemias, iron deficiency over time will always cause anemia. Iron is also critical for energy production in mitochondria (this is where you all yell… “the powerhouse of the cell”). As a result, iron deficiency can lead to fatigue, shortness of breath, impaired recovery, and diminished athletic performance.

Stages of Iron Deficiency

Three distinct stages of iron deficiency are associated with anemia: iron deficiency, iron deficient nonanemia, and iron deficient anemia.

Iron deficiency is the first and least severe stage. It is marked by a drop in serum ferritin (a marker of your iron stores) to below 35 ng/mL while other iron markers, like hemoglobin, remain normal.

The second stage, iron deficient nonanemia, is marked by a continued drop in ferritin (below 20 ng/mL). The drop is accompanied by a corresponding drop in serum iron, decreased transferrin saturation, and increased total iron binding capacity.

Up to this point, hemoglobin levels remain normal or are minorly affected. However, the final stage of iron deficiency, iron deficient anemia, includes a drop in hemoglobin itself. This, as a result, greatly impacts your body’s ability to transport oxygen.

How exercise can contribute to iron deficiency

There are many reasons why athletes are more likely to be iron deficient than the general population, one of which – hepcidin response – we discuss in a previous article on nutrient timing to optimize iron absorption. Hepcidin is a hormone designed to protect you by regulating iron homeostasis. On way is by preventing you from absorbing too much iron.

Exercise creates inflammation, specifically an inflammatory cytokine called interleukin-6 (IL-6). IL-6 is one of the main regulators of exercise-released hepcidin. An increase in IL-6 increases hepcidin levels, which decreases iron absorption. Hepcidin increases and naturally peaks 3-6 hours after hard and/or long exercise. In other words, the normal inflammation from exercise impairs your body’s ability to absorb iron.

Why athletes are more likely to be iron deficient

Other factors that make athletes more vulnerable to iron deficiency include:

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  • Menstruation: athletes who menstruate have greater risk for iron loss due to blood loss.
  • Increased iron demands: tissue remodeling from normal exercise requires more iron.
  • Reduced iron intake: athletes are greater risk for relative energy deficiency in sports (RED-S) and low energy availability (LEA). Both increase risks of not meeting daily iron requirements through dietary intake.
  • Other reasons for poor iron absorption: outside of the inflammatory hepcidin response, the redistribution of blood flow away from the GI tract and other small intestine (absorption) conditions like celiac disease result in poor iron absorption.
  • Exercise related iron loss: we lose iron when we sweat and through micro GI bleeds from intense exercise (like ultramarathons). Another ultrarunning favorite is hematuria, or losing blood in your urine. And finally, foot strike hemolysis from breaking red blood cells due to impact.

After all that, it may make sense that athletes are at higher risk for iron deficiency, and therefore anemia. But, how does this directly impact performance?

Iron Deficiency Anemia and Athletic Performance

Iron deficiency directly causes a reduction in aerobic power. The greater the deficiency, the greater the reduction. Any stage of iron deficiency inhibits oxygen transport to some degree.  However, the reduction in hemoglobin seen in stage three of iron deficiency has a profound consequence on how oxygen is transported to muscle tissue during exercise.

As a result, the ‘cost’ of exercise is higher in an iron deficient state. This makes you less efficient (altering lactate threshold and depleting muscle glycogen rapidly) at any given intensity. Being iron deficient also negatively impacts your body’s ability to adapt to new stimuli. These impacts hinder recovery from general training stimuli and impair adaptation to stimuli like altitude exposure.

Prevention and Recovery from Iron Deficiency Anemia

So, what can you do to avoid iron deficiency anemia or recover from it?

  • Watch for signs and symptoms of iron deficiency. Although unexplained fatigue is not always iron deficiency or anemia, it can be. Additionally, look out for unexplained tiredness, lethargy, paleness and shortness of breath. Detecting reduced iron stores early is important for limiting potential performance decline.
  • Complete routine bloodwork. Check with your primary care provider and consider completing bloodwork annually (okay for most males) or biannually to quarterly (okay for most menstruating athletes) to check iron status. Just make sure to ask for serum ferritin, as it’s not a standard test.
  • Proactively approach iron deficiency. If your iron levels are low, work on consuming iron rich foods. Also consider taking a supplement, but work with a physician beforehand because it is not safe to blindly take iron supplements. If you continue struggling to resolve your iron deficiency, consider working with a hematologist to help make a long-term plan.

By Corrine Malcolm,
CTS Ultrarunning Coach, co-author “Training Essentials for Ultrarunning, 3rd Ed.”, and Ultrarunning Host for the Trainright Podcast.


  1. Kuwabara, A. M., Tenforde, A. S., Finnoff, J. T., & Fredericson, M. (2022). Iron deficiency in athletes: A narrative review.PM&R14(5), 620–642.
  2. Sim, M., Garvican-Lewis, L. A., Cox, G. R., Govus, A., McKay, A. K., Stellingwerff, T., & Peeling, P. (2019). Iron Considerations for the athlete: A narrative review.European Journal of Applied Physiology119(7), 1463–1478.
  3. Tarnowski, C. (2020, October 31).Are my iron levels affecting my performance?  Retrieved June 6, 2022, from


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