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

To determine the effect of iron supplementation on iron status and endurance capacity. Randomized, double-blind iron supplementation. University of Missouri-Columbia and surrounding community. 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>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. A 30 mg measure of elemental iron as ferrous sulfate or placebo daily for 6 weeks. 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). Iron supplementation significantly improves iron status and endurance capacity in iron-deficient, nonanemic trained male and female subjects. Missouri University Alumni Association, by the Elizabeth Hegarty Foundation and by the Department of Nutritional Sciences.