Iron Deficiency Anemia in Athletes
Iron Deficiency (ID) is a spectrum of disease common in athletes, especially among females and those that participate in endurance sports. There are two forms of ID: iron deficiency non anemia (IDNA), defined by decreased iron stores, and iron deficiency anemia (IDA), which is defined by a drop in iron stores and hemoglobin. Generally speaking, this is due to iron losses exceeding iron intake and absorption. Early on in the disease, athletes will have ID with normal hemoglobin levels, while in later or more severe phases of the disease they will develop IDA.
A 23 year old female track athlete at a division 1 university presents with increasing fatigue and decreasing performance over the last few months of training. She is a vegan but has met with a dietician who told her she was consuming enough calories. There have been no changes in her training program. She has no history of stress fractures and has a normal body habitus. Her point of care glucose is normal. Which of the following is the most likely diagnosis?
A) Iron Deficiency Anemia
B) Overtraining Syndrome
C) Diabetes Mellitus
D) Relative Energy Deficiency in Sport
Iron Deficiency Anemia
Iron deficiency is fairly common among athletes, ranging from 15-35% among females and 3-11% among males (Sim 2019). IDA is far less common, seen in 0-2% of all athletes but has been reported as high as 15% among female athletes (Garza 1997). It is important to consider other causes of fatigue, malaise and decreased exercise performance. Examples would include relative energy deficiency in sport, female athlete triad, hypothyroidism, diabetes, overtraining syndrome, sleep dysfunction and depression among many others.
Image 1. The consequences of iron deficiency (adopted from http://dgscctf.com/)
Iron is not synthesized by the human body and must be replenished by dietary intake. Dietary iron is difficult to replenish even in the non-athlete. Heme iron, which comes from animal-based foods has a bioavailability of 15-35% while non-heme iron from plant-based sources has a bioavailability of 2-20%. This puts vegetarians at increased risk of ID (Björn-Rasmussen 1974). The recommended daily intake is 8 mg/day in males and 18 mg/day in pre-menopausal adult women.
Image 2: Example of iron supplement
Treatment is primarily aimed at iron supplementation and is generally an oral route. Indications for treatment are any degree of anemia and ferritin below normal cutoffs. Ferrous sulfate is most commonly given at 100 mg per day which is shown to increase athletes’ iron stores 30-50% over 6-8 weeks (Fogelholm 1992). The biggest side effect is gastrointestinal distress which makes compliance challenging (Tolkien 2015). The best available evidence says that to avoid this GI toxicity, athletes should take 100 mg every other day and will still have a similar increase in iron stores with less total iron ingested (McCormick 2020). To maximize absorption, athletes should consume their supplement in the morning, 30 minutes prior to exercise to help potentiate absorption (McCormick 2019). There are other oral formulations which are less commonly used but may be promising for future management.
Answer A is the correct answer. This vignette is most consistent with iron deficiency anemia. The fatigue and decreased performance could be attributable to any of the answers. A normal blood glucose excludes diabetes. Overtraining syndrome and relative energy deficiency in sport are unlikely given the correct calorie intake, no changes in her training, no other stress related injuries and a normal body habitus. Her symptoms, sport of choice, gender and choice of veganism put her at high risk of iron deficiency. Because of the decrease in performance and fatigue she is likely anemic at this point. The patient needs serum hemoglobin and ferritin levels checked and perhaps a further workup if the diagnostic picture is unclear.
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