Iron Status and Athletes
Iron is a micronutrient with many essential functions in the body that are particularly relevant to athletic performance. Perhaps one of its most vital roles pertains to its distribution of oxygen throughout the body as a component of hemoglobin and myoglobin. Iron is a constituent of mitochondrial enzymes required for oxidative phosphorylation, and thus aerobic metabolism relies upon this mineral as well. It is through these mechanisms of oxygen delivery and oxidative capacity that it can be understood how poor iron status can result in feelings of fatigue and ultimately reduce endurance capacity.
Iron deficiency is the most common nutrient deficiency worldwide. In the United States alone, 16 percent of premenopausal women face iron deficiency, and 3 to 5 percent of women have iron deficiency anemia (IDA) (Cogswell et al. 2009). IDA is defined as hemoglobin (Hgb) levels <12 g/dL in women and <13 g/dL in men. Individuals at risk for iron deficiency include menstruating women (due to menstrual blood loss), vegetarians, and individuals at stages of the lifecycle involving growth and development including childhood, adolescence, and pregnancy and lactation. Because exercise can increase iron requirements by up to 70 percent (Whiting and Barabash 2006), athletes and especially female athletes are at much greater risk of iron deficiency. In fact, female athletes are twice as likely to suffer IDA as their nonathletic counterparts. Athletes may exhibit low iron stores for a variety of reasons, including plasma volume expansion, low dietary iron intake, low iron bioavailability, and excessive iron excretion or loss (such as through red blood cell hemolysis, sweat, and hematuria) (Goodman et al. 2011).
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Indeed, athletic performance has been shown to suffer in the presence of IDA. Poor oxygen transport as seen with reduced Hgb levels impairs VO2max in athletes, in some studies by up to 50 percent in the presence of IDA. Additionally, with compromised tissue oxidative capacity, endurance performance is reduced. What is less clear is if athletes who are iron deficient in the absence of IDA experience impaired performance. Research is mixed on this topic, in part due to methodological issues as well as inconsistencies of definitions of iron deficiency; this requires further investigation.
The RDA for iron is 8 mg for ages 9 to 13 years; 11 and 15 mg for males and females of ages 14 to 18 years, respectively; and 8 and 18 mg for males and females of ages 19 to 50 years, respectively. Iron can be consumed from meats, as well as from plant sources such as legumes, leafy greens, nuts, and fortified grain products. There are two different dietary sources of iron, heme iron, and nonheme iron. While overall iron bioavailability is low, heme iron found in meat (comprising 40 percent of the iron in meat) is significantly more bioavailable than nonheme iron found in plant foods. This accounts for why vegetarians have a much greater need for iron (see following section on Vegetarian Athletes). See Table 8.5 for dietary sources of iron. Consuming nonheme iron along with Vitamin C (supplemental or food forms), or consumption of meat, poultry, and seafood at the same time can improve nonheme iron absorption. Phytates found in grains and legumes impede iron absorption, as well as calcium, tea, and coffee.
Athletes do not always consume adequate iron from dietary sources, which can be due to dietary preferences, dietary approaches such as vegetarianism, and overall inadequate EI due to restrictive eating patterns or efforts toward weight loss. Recognizing that intake may be suboptimal, athletes have higher iron losses and thus increased iron requirements, and understanding iron’s role in achieving optimal athletic performance emphasizes the importance of accurately assessing iron status and helping athletes achieve optimal iron stores. However, this is not always a straightforward process.
Iron supplementation. Routine iron supplementation irrespective of iron status is not warranted due to concerns of iron overload. Iron induces oxidative damage and production of free radicals, which can eventually result in organ and cellular damage in individuals consuming high amounts of iron. Iron overload is most common among individuals supplementing with large amounts of iron, and is more frequently seen in men versus women. Thus, individuals in good iron status should not routinely take iron supplements, especially given that for these individuals there is not a performance benefit, and the risks associated with iron overload are great. Supplementation is appropriate for certain populations, including athletes moving from sea level to training at altitude, and especially for individuals diagnosed with IDA and those with chronic low iron intake (vegetarians, athletes in weight-sensitive sports). In the case of the latter group, iron status should be assessed before initiating supplementation. While it is unclear whether individuals with iron deficiency in the absence of anemia or those experiencing iron depletion will see improvements in performance with iron supplementation, it is believed that in this population supplementation should be initiated to prevent the progression to IDA, especially in the presence of symptoms such as fatigue and poor performance (DellaValle 2013).
Iron salts are the most commonly consumed forms of supplements, with ferrous forms having better bioavailability than ferric forms. Ferrous fumarate and gluconate are available, though ferrous sulfate is the most common. Different forms of iron have varying amounts of elemental iron, which references the amount of iron available for intestinal absorption. For example, 100 mg of ferrous sulfate has 20 mg of elemental iron, though the amount of elemental iron in a supplement will be listed on the label making it easy to determine. As with food sources of nonheme iron, coconsumption of vitamin C and consuming meats, poultry, and seafood will improve iron absorption, whereas phytates, calcium, and caffeine can impede absorption. Helping athletes understand these factors and providing practical tips for improving absorption (such as eating an orange when consuming a supplement) will support improvements in iron status. Another consideration is taking a supplement already containing vitamin C that are commercially available.
The amount of iron needed depends upon the degree of deficiency, and iron repletion can take several months. A dose of 100 mg of ferrous sulfate has shown to be effective in increasing serum ferritin levels over 6 to 8 weeks, though a higher dose may be warranted with severe
IDA (Goodman et al. 2011). Side effects of iron supplementation may be experienced, including gastrointestinal distress, nausea, and constipation; if these are experienced, the dosage can be lowered. Dividing the dose up into two smaller doses a day can also improve side effects. Once iron levels reflect healthy iron stores, supplementation should cease in order to prevent toxic effects of excessive iron. However, given that individuals who were once diagnosed with iron deficiency are at greater risk for deficiency in the future, these individuals should be encouraged to focus on dietary sources of iron.
Consistent monitoring is recommended to assess iron status and avoid excessive supplementation. Those undergoing a supplementation regime should ideally get their serum ferritin levels checked every 8 to 12 weeks. Individuals at risk for iron deficiency, including those with a history of IDA, vegetarians, individuals with bleeding or menstrual disorders or both, and those with symptoms such as fatigue and poor performance should get assessed periodically.
In summary, female athletes are at greater risk for iron deficiency than their nonathletic and male counterparts, and thus should be screened routinely for iron deficiency. It is evident that performance is impaired with IDA, and while it is less clear if performance suffers with iron deficiency in the absence of anemia, iron supplementation may be warranted given symptomology. A moderate supplementation protocol should be initiated as well as educating the athlete on dietary strategies for increasing iron intake. Athletes undergoing iron supplementation should be monitored to avoid iron overload, and future screenings should continue given they are at increased risk for future deficiency.
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