Anemia, defined as a decreased quantity of circulating functional red blood cells, is a major source of morbidity and mortality affecting a-third of the worldwide population. As a functional component of erythrocytes hemoglobin, iron is essential for oxygen storage and transport. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure the proper supply of iron to the bone marrow for red blood cells synthesis. However, mounting evidence suggested that another factor may exert a similar function. Inventors identified the hepatokine FGL1 as a previously undescribed suppressor of hepcidin that is highly induced in the liver in response to hypoxia during the recovery from anemia and in thalassemic mice. Inventors demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo. Deletion of Fgl1 in mice results in a blunted repression of hepcidin after bleeding. Finally, FGL1 is a BMP antagonist that directly binds BMP6 to impair the canonical BMP-SMAD signaling cascade that governs hepcidin regulation. Accordingly, the present invention relates to a FGL1 polypeptide for use in the treatment of a patient affected with an iron deficiency-related disease.