Background: Iron deficiency without overt anemia is a known problem in athletic and physically active women. The exact prevalence in this population in unclear but appears to range from 25-58%. The reasons for this phenomenon are multifactorial and include iron losses, decreased iron absorption and lack of iron consumption in the diet. Iron plays many roles in the human body that can affect exercise performance. Irons main function is to carry and store oxygen throughout the body as a component of hemoglobin and myoglobin. Iron is also a component of cytochromes, in coenzymes in the Krebs cycle and part of the electron transport chain all of which are necessary for endurance activity. The purpose of this review is to evaluate the effects of iron repletion on endurance performance in female athletes who are iron deficient but not anemic.
Methods: An extensive literature search of the following databases, MEDLINE-PubMed, MEDLINE-Ovid, Web of Science, and CINAHL for the terms “sports,” “dietary supplements,” and “iron” was performed. Results were further limited to articles in the English language and studies performed on human subjects. Further inclusion criteria included active females greater than 17 years of age, premenopausal, iron deficient, oral iron supplementation and studies where exercise performance was evaluated. Exclusion criteria included anemic subjects, parenteral iron supplementation and treatment less than four weeks. All included studies were double blinded and placebo controlled without crossover. The quality of the relevant studies was evaluated using the GRADE criteria .
Results: Two studies met the inclusion criteria and were reviewed. Both studies showed that iron replacement therapy increases iron stores but neither found an improvement in endurance capacity.
Conclusion: Although iron deficiency is a common problem in female athletes and active women, current studies do not show that there is a performance benefit with iron supplementation in women who are not anemic. However, this question is far from answered. Studies employing a more homogenous group of athletes performing a prescribed training program for a period longer than eight weeks are necessary to fully understand the impact of iron supplementation on athletes.
Keywords: iron, sports, dietary supplementation
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