Iron Supplementation Maintains Ventilatory Threshold And Improves Energetic Efficiency In Iron-deficient Nonanemic Athletes

PURPOSE to determine the effect of iron supplementation on iron status and endurance capacity in iron deficient nonanemic, trained males and females. METHODS Twenty iron deficient (serum ferritin, sFer < 16 μg/l; serum transferrin receptor, sTfR > 8.0 mg/l; or sTfR/log sFer index > 4.5), nonanemic (hemoglobin, Hb > 12 g/dl) males and females (18- 41 y) received 30mg elemental iron or placebo daily for 6 weeks in a randomized, double blind trial. Each subject performed two exercise tests on a cycle ergometer pre- and postsupplementation: 1. Maximal oxygen consumption (VO2max); 2.60-minute submaximal test at 60% of VO2max. Data were analyzed using 2x2 ANOVAs with repeated measures on time (pre- and post-supplementation) and Pearson correlations. RESULTS Three-day dietary records and daily training logs showed no differences in iron intake or physical activity between groups before or after supplementation. Iron supplementation significantly increased sFer (p = 0.003) and tended to decrease the sTfR/ log sFer index (p = 0.072) compared to placebo, while other indicators of iron status remained unchanged for both groups. Iron supplementation prevented the decline in absolute and relative ventilatory threshold (VT) observed in the placebo group from pre- to post-supplementation. Average workload maintained during the submaximal test (91.4±11.0 to 97.7±12.1 watts) increased significantly in the iron group without a concurrent increase in average HR or energy expenditure, resulting in an increase in efficiency (energy expended/work performed, kcal/watt). In the placebo group, average workload did not change, but HR increased significantly (146±4 to 153±5 bpm) after six weeks of treatment. Changes in serum ferritin over the six-week intervention were negatively correlated with changes in average respiratory exchange ratio (RER) during the submaximal test. CONCLUSIONS Iron supplementation significantly improves iron status and endurance capacity in trained males and females. These results suggest that even marginal repletion of iron stores in iron deficient individuals benefits aerobic function.