Iron supplementation maintains ventilatory threshold and improves energetic efficiency in iron-deficient nonanemic athletes

Objective: To determine the effect of iron supplementation on iron status and endurance capacity. Design: Randomized, double-blind iron supplementation. Setting: University of Missouri-Columbia and surrounding community. Subjects: Twenty iron-deficient (serum ferritin, sFer < 16 mu g/l; serum transferrin receptor, sTfR > 8.0 mg/l; or sTfR/log sFer index > 4.5), nonanemic (hemoglobin, Hb > 120 g/l, women; > 130 g/l, men) men and women (18-41 years) were recruited via fliers and newspaper advertisements; 20 of 31 eligible subjects participated. Interventions: A 30mg measure of elemental iron as ferrous sulfate or placebo daily for 6 weeks. Results: Dietary iron intake and physical activity did not differ between groups before or after supplementation. Iron supplementation significantly increased sFer compared to placebo (P = 0.01), but did not affect Hb or hematocrit. Iron supplementation prevented the decline in ventilatory threshold (VT) observed in the placebo group from pre- to post-supplementation (P = 0.01); this effect was greater in individuals with lower sFer before intervention (P < 0.05). Changes in sFer from pre- to post-treatment were positively correlated with changes in VT (P = 0.03), independent of supplementation. The iron group significantly increased gross energetic efficiency during the submaximal test (P = 0.04). Changes in sFer were negatively correlated with changes in average respiratory exchange ratio during the submaximal test (P < 0.05). Conclusions: Iron supplementation significantly improves iron status and endurance capacity in iron-deficient, nonanemic trained male and female subjects. Sponsorship: Missouri University Alumni Association, by the Elizabeth Hegarty Foundation and by the Department of Nutritional Sciences.