Iron supplementation improves endurance after training in iron-depleted, nonanemic women

Our objective was to investigate the effects of iron depletion on adaptatio n to aerobic exercise, assessed by time to complete a 15-km cycle ergometer test. Forty-two iron-depleted (serum ferritin <16 mu g/l), nonanemic (Hb > 12 g/dl) women (18-33 yr old) received 100 mg of ferrous sulfate (S) or pla cebo (P) per day for 6 wk in a randomized, double-blind trial. Subjects tra ined for 30 min/day, 5 days/wk at 75-85% of maximum heart rate for the fina l 4 wk of the study. There were no group differences in baseline iron statu s or in 15-km time. Iron supplementation increased serum ferritin and decre ased transferrin receptors in the S compared with the P group. The S and P groups decreased 15-km time and respiratory exchange ratio and increased wo rk rate during the 15-km time trial after training. The decrease in 15-km t ime was greater in the S than in the P group (P = 0.04) and could be partia lly attributed to increases in serum ferritin and Hb. These results indicat e that iron deficiency without anemia impairs favorable adaptation to aerob ic exercise.