Continuous training in young athletes decreases hepcidin secretion and is positively correlated with serum 25(OH)D and ferritin

Background Iron deficiency is known to impair muscle function and reduce athletic performance, while vitamin D has been reported to induce iron deficiency. However, the mechanism underlying exercise-induced changes in iron metabolism and the involvement of vitamins in this mechanism are unclear. The present study examined changes in biological iron metabolism induced by continuous training and the effects of vitamin D on these changes. Methods Diet, physical characteristics, and blood test data were collected from 23 female high school students in a dance club on the last day of each of a 2-month continuous training period and a 2-week complete rest periods. Results Serum hepcidin-25 levels were significantly lower during the training period than the rest period ( p = 0.013), as were the red blood cell count, hemoglobin, and hematocrit (all p < 0.001). Serum erythropoietin was significantly higher ( p = 0.001) during the training period. Significant positive correlations were observed between 25(OH)D levels and serum iron, serum ferritin, and transferrin saturation during the training period. Multiple regression analysis with serum 25(OH)D level as the dependent variable and serum ferritin and iron levels as independent variables during the training period revealed a significant association with serum ferritin. Conclusion Continuous training may promote hemolysis and erythropoiesis, contributing to the suppression of hepcidin expression. The relationship between serum 25(OH)D and iron in vivo may be closely related to metabolic changes induced by the exercise load.