Iron, a trace mineral, is a major component of hemoglobin, whose role is to transport oxygen from the lungs to the muscles via the blood. Some research has shown that aerobic exercise creates an added demand for iron. Failure to meet this added demand through dietary intake and proper absorption of such whole food sources as whole grains, leafy greens, dried fruit, red meat, fish, and poultry can compromise blood iron stores and lead to iron-deficiency anemia (IDA). An anemic athlete may experience muscle burning, shortness of breath during exercise, nausea, frequent infections, and respiratory illnesses and have a pale, washed-out appearance. Without enough iron in the blood, the body becomes starved for oxygen; ATP cannot be properly synthesized, leading to pronounced feelings of fatigue and limiting work capacity. IDA occurs in three stages, with stage 3 having the most detrimental effect on athletic performance. Most athletes with iron depletion have a stage 1 deficiency, also known as Non-anemia iron deficiency, which is diagnosed when ferritin, the storage form of iron falls below normal. If stage 1 iron deficiency is left undetected for several months, an athlete may develop stage 2 deficiency when red blood cells and consequent oxygen transfer decrease, negatively affecting exercise capacity. The final stage of iron deficiency, stage 3, is detected by insufficient hemoglobin and a low concentration of red blood cells; stage 3 leads to feelings of intense fatigue, compromised physical ability, and decreased athletic performance.

Sports anemia is a term applied to endurance athletes who have lower than normal hemoglobin levels but normal levels of other iron status indicators. This situation is a response to the increase in blood volume that accompanies training; therefore, it is not a true anemia, nor should it be treated like one. By restoring hemoglobin and the blood iron levels of iron-deficient and anemic athletes, oxygen delivery to working muscles and ATP energy production increase, thereby allowing the athlete to better meet the metabolic demands of aerobic activity. While scientific evidence has shown a significant drop-off in endurance with iron deficiency, in part due to an adverse effect on aerobic capacity, there remains controversy about when (i.e., at what stage of deficiency) iron supplementation becomes beneficial from a performance standpoint. According to the most recent research in this regard, there appears to be no performance benefit associated with iron supplementation without iron deficiency or with non-anemia (stage 1) iron deficiency, particularly in those athletes with ferritin levels above 30 mcg/L. The RDA for iron in adults is 18 mg/day; athletes at risk for iron deficiency, including female athletes whose menstrual blood loss often affects iron or those athletes with ferritin levels under 30 mcg/L, may increase to 20-30 mg/day from whole food or supplementation doses. Properly diagnosed cases of IDA, especially stage 2 and stage 3, should be treated with therapeutic doses of supplemental iron, preferably in the ferrous sulfate or ferrous bisglycinate form due to enhanced absorption rates and in slow release form to reduce constipation. Taking 500 mg of vitamin C or drinking a glass of orange juice may help enhance absorption of the iron. Typical correction of anemic conditions take approximately 8 weeks. Dietary iron supplementation is not recommended for athletes with normal blood iron levels.