Anemia: Effects on Performance
Anemia decreases physical performance and is linked to decreased maximum oxygen consumption, lower endurance, increased fatigue, decreased physical work capacity, and increased lactic acidosis (a byproduct of anaerobic metabolism). Experts are not certain that iron deficiency in the absence of anemia (nonanemic iron deficiency) decreases performance, although it probably represents a preanemic state.
Studies of the effects of iron supplementation on the performance of nonanemic iron deficient athletes have produced conflicting results. Some studies of women runners after iron supplementation have indicated improvements in measures of endurance, such as treadmill times, run times, and lower blood lactate levels during submaximal exercise (exercise that is intense but does not take the participant to the point of exhaustion and inability to continue). In many cases iron supplementation also led to improvements in hemoglobin levels, suggesting that the beneficial effects were because of correction of a mild anemia. Such studies demonstrate the important point that distinguishing mild anemia from nonanemic iron deficiency is clinically difficult and that although a hemoglobin value may technically fall within the normal range, it may nevertheless represent mild anemia that will respond to iron supplementation. Other studies, however, have failed to show that iron supplementation benefits the performance of nonanemic iron deficient athletes. Such studies suggest that when hemoglobin levels are not improved, iron supplementation does not improve performance, despite an increase in levels of ferritin.