Vitamin D also affects the haemopoietic system; its receptors (VDRs), in fact, are present in bone marrow, including stromal and accessory cells [6] and vitamin D deficiency represents an additional cofactor of anemia, beyond erythropoietin (EPO) and iron deficiency or inflammation [7, 8]; significant relationships, moreover, exist between plasma levels of 25-hydroxyvitamin D and hemoglobin (Hb) concentrations in health [9] and disease [8, 10]. The gene discussed is EPO; the disease is anemia.