Purpose: Studies in both animals and humans show a relationship between iron depletion without anemia (IDNA) and physical performance. Compared with their sedentary counterparts, female endurance athletes are at greater risk of IDNA, and consequences relevant to endurance athletes include reduced work capacity and energetic efficiency (EF). We conducted a randomized placebo-controlled trial to investigate the effects of iron (Fe) supplementation on Fe status and performance in nonanemic female rowers during training. Methods: At the beginning of a training season, 40 rowers were randomized to receive either 100 mg/d FeSO4 (n = 21) or placebo (n = 19) using a double-blind design. Thirty-one (n = 15 Fe, 16 placebo) completed the 6-wk trial. Fe status (hemoglobin, serum ferritin, soluble transferrin receptor), body composition, and laboratory tests of physical performance (4-km time trial, VO2peak, energetic EF, and blood lactate) were assessed at baseline and after training. Results: Rowers in both groups increased their fat-free mass (P < 0.001) and VO2peak (P < 0.001) after training. Multiple regression analyses revealed improvements in Fe stores (serum ferritin) in the Fe treatment group after controlling for baseline Fe stores (P = 0.07). Rowers in the Fe group had slower lactate response during the first half of the time trial and after 5 min of recovery (P = 0.05) and showed greater improvements in energy expenditure (P = 0.01 for group-by time) and energetic EF compared with placebo (P = 0.03 for group-by time). Conclusions: Female rowers with depleted Fe stores who consumed supplemental Fe during training improved their Fe status and energetic EF during endurance exercise. These results are important for endurance athletes whose dietary patterns and physical training increase their risk of IDNA and suggest that Fe supplementation may maximize the benefits of endurance training.
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