GDF-15 is thought to be a candidate that suppresses hepcidin-25 production during increased erythropoiesis and iron deficiency19,20, whereas elevation of GDF-15 in subjects with iron deficiency is controversial in clinical studies21,22, and the clinical study with subjects at altitude failed to demonstrate significant associations among GDF-15, hepcidin-25, and the endogenous EPO concentration23. This evidence concerns the gene HAMP and nutritional disorder.