Effects of exercise on soluble transferrin receptor and other variables of the iron status

Background: Soluble transferrin receptor (sTfr) is a new marker of iron status and erythropoietic activity. It has been included in multivariable blood testing models for the detection of performance enhancing erythropoietin misuse in sport. Objective: To evaluate the effect of different types and volumes of physical activity on sTfr concentration, variables of iron status (ferritin, transferrin, iron, and protein), and haematological indices. Methods: Thirty nine subjects were divided into three groups: I, untrained (n = 12); 2, moderately trained (n = 14); 3, highly trained (n = 13, seven men, six women). Groups 1 and 2 carried out two exercise tests: an incremental running test until exhaustion (test A) and a 45 minute constant speed running test at 70% VO(2)MAX (test B). Group 3 performed three days (women) or four days (men) of prolonged aerobic cycling exercise. The above variables together with haemoglobin and packed cell volume were analysed in venous blood samples before and after exercise. Changes in blood and plasma volume were estimated. Results: sTfr levels were slightly increased in trained and untrained subjects immediately after test A. Test B and aerobic exercise had no significant effect on sTfr. Ferritin levels were increased after the laboratory tests for trained and untrained subjects and after prolonged aerobic exercise in male cyclists. Transferrin was increased significantly in trained and untrained subjects after both laboratory tests, but remained unchanged after prolonged exercise. Plasma and blood volumes were decreased after the laboratory tests but increased after aerobic exercise. No differences in the variables were observed between trained and untrained subjects with respect to response to exercise. Conclusion: The changes in sTfr and the variables of iron status can be mainly attributed to exercise induced changes in volume. Taking these limitations into account, sTfr can be recommended as a marker of iron deficiency in athletes.