Iron: An Essential Nutrient in Athletes

Iron:  An Essential Nutrient in Athletes

Carolyn Mercer, B.Sc., N.D.

18 May 2021

Iron: An Essential Nutrient in Athletes

Having an iron deficiency, or in severe cases, anemia, can be detrimental to athletic performance and overall health. It limits the body's capacity to carry and deliver oxygen, thus stunting potential maximal oxygen uptake (VO2 max) or work capacity. Poor iron status is also associated with higher blood lactate concentrations during exercise.

Iron is a trace mineral that is also highly significant to endurance athletes. Iron is critical to optimal athletic performance because of its role in energy metabolism, oxygen transport, and acid-base balance.

A lot hinges on the ability of the body to transport oxygen. A deficiency can impair the oxygen transport especially in athletes. A significant percentage of endurance runners can experience a small amount of gastrointestinal bleeding during longer runs. There is also a condition called "foot-strike hemolysis" where a small number of red blood cells burst in the feet due to the constant pounding of feet on the ground. Some hemoglobin and iron might be lost in the urine due to this. Women might also be at increased risk of iron deficiency due to their monthly menstrual cycles.

When we are involved in endurance exercise lactic acid can cause a burning sensation in your muscles. During endurance exercise, over a period of time, oxygen levels decrease so the body moves into a process called anaerobic respiration or fermentation in order to generate energy. This causes the muscle soreness during exercise. Obviously if we are anemic and have a lack of oxygen in our system, this can aggravate the production of acid in the muscles (see Figure 1).

In one study, they examined the effects of iron on exercise-induced lactate production in females. The body produces lactic acid when a lack of oxygen is present in the muscles in order to still derive energy for the muscles. Female athletes were asked to bike to a point of exhaustion. In those that were previously iron deficient and then supplemented with iron, the results showed a significant reduction in lactate levels after maximal exercise in those with sufficient amounts of iron as compared to the iron deficient group.

When we do have enough oxygen in our system, our system alternatively uses a process called the Krebs cycle or oxidative phosphorylation to generate energy. Energy is generated in the mitochondria of the cell via the electron transport chain. Iron is also critical to the electron transport chain in Complex I, III, and IV and therefore affects the generation of energy or ATP (see Figure 1).

Other reasons why athletes have less iron that the average person may also be due to:

  • less recuperative time between excessive exercise
  • less blood flow to the GI tract and organs as it is shunted to large muscle groups during exercise resulting in malabsorption of iron in the gut
  • muscle damage and oxidative stress through micro-rupture of muscle fibres
  • increased iron loss in sweat or urine
  • higher hepcidin levels from the body's inflammatory response that inhibits iron absorption.


With all the various types of iron available it can be difficult to choose one to use. Generally iron salts are prescribed if someone is anemic, which includes ferrous sulfate, ferrous gluconate (Fe 2+) and the ferric form (Fe3+) of iron. Usually the ferrous form is absorbed more effectively at a rate of 10-15%. Some of the side effects however can include constipation, diarrhea, heartburn, nausea, and epigastric pain. Ascorbic acid has also been shown to improve absorption.

There is however a newer alternative to the salt-based supplement which is called Carbonyl Iron. It is a metallic iron (Fe) with high (> 98%) iron content. It is not a salt. It absorbs at 69%, compared to only 10 to 15% with most other forms of iron such as the ferrous sulfate, ferrous fumarate, or ferrous gluconate forms. In addition to the high iron content, a key physical property of Carbonyl Iron is that it has increased bioavailability as compared to other iron forms.12, 13 One study showed that dosing Carbonyl Iron after a 12-week period, that anemia was corrected in 29 of the 32 subjects and serum ferritin was improved with tolerable side effects.

So, if you do suffer from iron deficiency consider looking at taking a Carbonyl form because of improved absorption rates and more tolerable side effects.


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  2. Walther, Jenna. Iron: An Essential Mineral for Athletic Performance, NASM, (accessed April 20, 2021.
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  4. Iron and Athletic Performance Blog. (accessed April 21, 2021).
  5. English, Ava. 2020. How to reduce lactic acid build up in your muscles during exercise – and why it happens. Insider health, October 16. (accessed April 25, 2021).
  6. Shoene, R.B. 1983. “Iron repletion decreases maximal lactate concentrations in females with minimal iron-deficiency anemia,” The Journal of Laboratory and Clinical Medicine, 102, 2, (August), (accessed April 23, 2021).
  7. Lumen Biology for Majors I, “Electron Transport Chain.” Module 6: Metabolic Pathways. (accessed April 25, 2021).
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  9. Willer, Chris. Iron deficiency: How it Impacts your athletic performance and what you can do about it. Triathalon Magazine Canada. (accessed April 20, 2021).
  10. Roeker, L. et al. 2005. “Iron-regulatory protein hepcidin is increased in female athletes after a marathon,” European Journal of Applied Physiology, 95 (5-6) (December) Iron-regulatory protein hepcidin is increased in female athletes after a marathon - PubMed ( (accessed April 25, 2021).
  11. Fei, Cindy. 2015. Iron deficiency Anemia: A Guide to Oral Iron Supplements. Clinical Correlations, Iron Deficiency Anemia: A Guide to Oral Iron Supplements – Clinical Correlations (accessed April 21, 2021).
  12. Pure Lab Vitamins. Carbonyl Iron. Carbonyl Iron - Helps to Prevent Iron Deficiency - Helps to form red blood cells ( (accessed April 23, 2021).
  13. Science and Nature, July 2019: Difference between Carbonyl Iron and Ferrous Sulfate. Difference Between Carbonyl Iron and Ferrous Sulfate | Compare the Difference Between Similar Terms (accessed April 23, 2021).
  14. Gordeuk V.R. et al. 1986. “Carbonyl iron therapy for iron deficiency anemia,” Blood, 67(3) (March) Carbonyl iron therapy for iron deficiency anemia - PubMed ( (accessed April 25, 2021).

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