The Link Between Iron Deficiency and Underfueling
Minerals are important in an athlete’s diet, and iron is no exception. Iron is an essential component of hemoglobin, the protein in red blood cells that carries oxygen to working muscles. Iron also builds proteins essential for immunity and DNA synthesis. The recommended daily intake of iron is 8 mg/day for male athletes and 18 mg/day for female athletes. Because of the interaction between iron and several hormones, nutrition for an iron deficiency can be more complex than just taking a supplement and adding more high-iron foods.
Iron Deficiency in Athletes
Athletes can struggle with iron deficiency for many reasons: inadequate iron intake, foot-strike hemolysis (destruction of red blood cells through running), blood loss through the GI tract, menstrual irregularities, inadequate iron absorption, and/or iron sweat losses. Iron deficiency can cause overall fatigue, increased heart rate, dizziness/light-headedness, or weakness. Athletes deficient in iron may see performance declines, especially during endurance exercise. Because iron is important for the immune system, iron-deficient athletes may see more frequent illness, leading to missed training. Certain athletes are at a higher risk for iron deficiency, including female athletes, endurance athletes, plant-based athletes, athletes with GI conditions, and athletes in an energy deficiency.
Underfueling in Athletes
Regarding energy deficiency, an athlete is operating in an energy deficiency when they are expending more energy than they are consuming. A prolonged energy deficiency can lead to a condition called Relative Energy Deficiency in Sport (RED-S), a comprehensive syndrome that refers to the health and performance consequences of underfueling.
As seen in the image above, one of the components of RED-S is “hematological” or “relating to the blood.” Someone with hematological signs of RED-S may see abnormalities in their blood chemistry, including iron deficiency. Iron deficiency and underfueling are often related.
Hepcidin, Inflammation, Underfueling, and Iron
Hepcidin is a hormone that regulates iron levels in the body. Hepcidin increases as iron concentrations increase. Higher hepcidin levels lower iron absorption, while lower hepcidin levels increase iron absorption. Hepcidin naturally peaks in the afternoon. Studies have shown that hepcidin levels are also elevated 3 and 6 hours post-exercise, concurrent with increases in exercise-induced inflammation. Lastly, underfueling can cause increased inflammation, leading to higher hepcidin levels.
Ferritin is a storage protein for iron. An optimal ferritin level for athletes is above 40 µg/L. While some studies have shown that athletes with a true iron deficiency do not experience the rise in hepcidin levels post-exercise, athletes with “sub-optimal” iron stores (measured by serum ferritin levels below 40 µg/L) may still experience this rise in hepcidin. This may impede their ability to increase their iron stores to a level optimal for training.
Low Carbohydrate Availability and Iron Deficiency
Restricting carbohydrates from the diet can lead to low carbohydrate availability, which also may affect iron levels. Firstly, many foods high in carbohydrates, such as whole grains, fortified cereals, beans, and molasses, are also high in iron. A low-carbohydrate diet leaves fewer opportunities to consume these high-iron foods. Additionally, lower carbohydrate diets tend to be overall energy-deficient. In one study, subjects were placed into two groups: one consuming an energy-deficient diet and one consuming an energy deficient diet that was also low in carbohydrates. Though both groups saw a rise in hepcidin levels, the energy and carbohydrate deficient group saw much higher increases. The effects of underfueling and restricting carbohydrates may compound, greatly increasing hepcidin levels, therefore limiting iron absorption.
Strategies to Achieve Optimal Iron Levels in Athletes
To conclude, the effects of overall underfueling, restricting carbohydrates, and exercise contribute to increased inflammation, raising hepcidin levels and inhibiting iron absorption. Athletes who do not eat enough energy and carbohydrates to fuel their body are at higher risk for iron deficiency. To promote optimal iron levels, athletes should consume a diet adequate in calories, carbohydrates, and high-iron foods, such as beef, whole grains, beans, and spinach.
Iron-deficient athletes may consider supplementation. The supplementation dosage is dependent on the degree of iron deficiency severity. Regarding supplementation timing, consider the effects of hepcidin. Alternate-day supplementation may be just as effective as daily supplementation due to the rise in hepcidin from the high-iron dose. Additionally, avoiding supplementation in the afternoon or 3-6 hours post exercise can help athletes take advantage of lower hepcidin levels.
Iron levels in athletes are dependent on more than intake of high-iron foods. It is important to thoroughly evaluate an athlete’s dietary habits to ensure optimal levels.
References
Peeling, P., Sim, M., & McKay, A. (2023). Contemporary approaches to the identification of and treatment of iron deficiency in athletes. https://www.gssiweb.org/en/sports-science-exchange/Article/contemporary-approaches-to-the-identification-and-treatment-of-iron-deficiency-in-athletes
Kong, W., Gao, G., & Chang, Y. (2014). Hepcidin and sports anemia. Cell Biosci, 4, 19.
Hayashi, N., Ishibashi, A., Iwata, A., Yatsutani, H., Badenhorst, C., & Goto, K. (2022). Influence of an energy deficit and low carbohydrate acute dietary manipulation on iron regulation in young females. Physiol Rep, 10(13), e15351.