Anemia in Athletes: How Nutrition Can Help

Paula Findaly, a Canadian triathlete, competed in the London Olympic Games at the age of 23—an experience she would never forget. Unfortunately, Paula crossed the finish line in 52nd place, her legs did not respond, her fatigue was greater than her desire to reach the podium. The Canadian triathlete came in 12 minutes and 21 seconds behind the gold medalist and one minute behind the penultimate triathlete. When she returned to her country, her doctors were stunned to see that his iron levels were so low that they hardly understood how she could get out of bed.

This true story illustrates one of the most common deficiencies in sport, iron deficiency, affecting 24 to 47% of women and 0-17% of men.

Before we begin: Why is iron important in the body?

This mineral has important functions in your physiology. It is not only responsible for the formation of hemoglobin and the transport of oxygen to the tissues, but it is also part of many proteins that need this mineral for their proper functioning. To give you an idea, iron is present in the proteins of the electron transport chain of the mitochondria, which allows energy to finally be produced in the form of ATP. In addition, mitochondrial metabolism of fats and carbohydrates requires oxygen as a final electron acceptor. In this way, if your oxygen transport capacity is lower due to iron deficiency, the production of energy via oxidation will also be lower leading to an increase in glycogen use and depletion, a decrease in the pH of muscle cells and fatigue. Now you can, at least in part, understand why Paula could barely move her legs. These are not the only functions of iron, many others accompany this mineral whose homeostasis is fundamental.

"Aerobic capacity, an important requirement in the endurance athlete, can be limited by an inadequate supply of oxygen to the muscle"

Increasing demands on athletes Why?
However, and as we said at the beginning, its deficiency is not uncommon. Different reasons such as the increased demand for iron due to the increase in the production of red blood cells in athletes, losses due to sweating, hemolysis or rupture of red blood cells typical of some sports, gastrointestinal bleeding, blood loss through urine, menstrual losses, hypoxia and also, due to the transient increase after exercise of a hormone known as hepcidin, make iron homeostasis in the athlete sometimes difficult to maintain. Figure 1

Hepcidin: a hormone that regulates iron

The state of iron is tightly controlled in the body by the homeostatic regulation of iron through the gut and cells. In 2004, a protein that regulates the absorption and availability of this mineral, hepcidin, was discovered. Its function is essential to prevent iron from being absorbed when it is not needed, thus avoiding iron overload, use of iron by microorganisms for its growth or excessive production of reactive oxygen species.

"The studies identified that a small hormone, hepcidin, is the key regulator of systemic iron metabolism."

Hepcidin exerts its main action on ferroportin channels by internalizing them. These channels are located in the area where iron leaves intestinal cells to the blood and in other cells such as macrophages, which contain iron from aged red blood cells, thus promoting its recycling. Simply put, increases in hepcidin levels result in decreased iron absorption and availability.

It is important that you now know that after exercise there is a period between 3-6 hours later where hepcidin can remain elevated, which hinders the absorption and availability of iron (Figure 2). An inflammatory protein known as IL-6 rises and signals the liver to produce this iron-regulating hormone. IL-6 rises mainly in relation to exercise duration, although exercise intensity, glycogen availability and carbohydrate intake during exercise can also influence the concentration of this inflammatory protein.

"It seems important to maintain adequate glycogen levels and adequate carbohydrate availability to attenuate the post-exercise hepcidin response"

Therefore, after exercise there is a window period that should be considered when establishing guidelines for correcting iron insufficiency with or without anemia, especially in athletes who are in the margins close to deficiency and when they perform frequent high-volume training.

The path to anemia

An interesting question to answer in this article is how our athlete came to an iron deficiency with anemia. To illustrate what an analysis in each phase would say, we leave you this table (Table 3)

How can we act in each of the phases?

In the stages of suboptimal iron and stage 1 iron depletion, a food-centric approach should be used. Current recommendations for iron intake range from 8 mg in men to 18 mg in women. We do not know if athletes really need more iron, but due to the factors that condition greater use and loss, everything points to it. A recent study showed that iron intake following these recommendations during a period of intense training was not enough, with a reduction in ferritin in the group of athletes between 25-40%.

The source of iron that is introduced into the athlete's diet is important. Iron that comes from foods of animal origin, normally heme iron, has a higher bioavailability than iron from mainly vegetable sources known as non-heme. This is important, especially knowing that the greatest contribution of iron in the diet comes from non-heme. In addition, attention should be paid to factors that enhance or decrease the bioavailability of non-heme iron. For example, it is well known that vitamin C promotes the absorption of non-heme iron. However, typical foods in the athlete's nutrition and recovery such as milk, given their calcium content, can interfere with the absorption of non-heme iron. In addition, other substances present in coffee, tea or cereals can also act by interfering with this absorption. We leave you this table where you can see some of the factors that favor or interfere with iron absorption.

The macronutrient composition of the diet and its effect on iron metabolism after exercise should be monitored. This can be particularly important in athletes who have higher requirements such as those who are in periods of growth, altitude or endurance athletes. In addition, those with low-iron diets such as vegan athletes or weight-category athletes should carefully plan their diet.

Finally, we can try to use nutrition to act on the production of hepcidin. Several studies have tried to see the influence of different strategies on this hormone. Post-exercise carbohydrates do not seem to significantly influence it, waiting to finish the exercise may be too late. However, low glycogen levels during intense exercise do seem to increase IL-6 and after exercise hepcidin, which suggests that starting exercise with adequate glycogen stores may be interesting to attenuate the response of this hormone to exercise. This is important to consider, especially in view of current training strategies with low carbohydrate availability, which should be introduced in light training sessions that are focused on improving molecular adaptations to exercise.

"There does not appear to be any additional benefit in iron regulation from increasing carbohydrate intake to very high levels, with moderate carbohydrate intake being sufficient to mediate the various factors that we know have an impact on iron regulation."

Recently, the impact of the ketogenic diet on iron status in athletes is being observed. Beyond the effect of this type of diet on glycogen content, it appears that these types of approaches can lead to cumulative increases in hepcidin levels (both at the start and end of exercise) which can have a negative effect on iron status, however, more studies are needed that can look at the chronic effect of carbohydrate restriction on hepcidin. However, the exclusion of some foods from these types of diets can also affect iron intake. For example, a recent study found that in athletes who followed a ketogenic diet, the iron content of their diet was 25% lower than those who had a diet rich in carbohydrates, which may have been due to the exclusion in the first case of fortified foods such as cereals and grains. Other studies have seen these same results where athletes who followed a high-carb diet consumed significantly more iron than those who opted for a high-fat, low-carb diet.

Finally, we would like to highlight the importance of energy availability in the regulation of iron. There seems to be a bidirectionality between iron status and energy availability, and iron may be involved in some of the clinical manifestations of low energy availability or low energy availability contributing to low iron status. High iron deficiency has been observed in athletes with low energy availability. In addition, hepcidin appears to be increased under conditions of low energy availability, linking the production of these hormones to another factor independent of the exercise-derived inflammatory stimulus.

Conclusions

Iron status in athletes should be constantly monitored throughout the training year. Early detection of low iron stores is important, with nutritional intervention being the main action in the early stages, followed by oral iron supplementation in the next stage and finally, in the case of iron insufficiency with anemia, the use of intravenous iron. Both oral iron supplementation and parenteral route of administration should be prescribed by the physician. Low iron levels until reaching a state of depletion of the reserves typical of anemia, leave a path of negative consequences in athletes such as compromised immune function, lethargy, weakness, decreased physical performance and even psychological alterations. Nutritional strategies should include ensuring adequate intake of foods with an adequate amount of bioavailable iron or applying strategies that increase its bioavailability and reduce interference in its absorption by some substances. It is important to avoid adopting dietary approaches that can chronically affect energy levels and compromise glycogen stores, adopting strategies that ensure adequate carbohydrate intake for exercise, and deliberately performing low-carbohydrate training approaches in light sessions in order to improve adaptations.

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AUTHOR

Fernando Mata (Col. AND-01053)

MSc Physiology; Msc. Biomedicine; Msc. Nutrition; PhD. Student
Director General of the Center for Advanced Studies in Nutrition