Iron is a trace element in the human body and is the most abundant trace element in the body. Most of the iron entering the body is transported to the bone marrow, where it is involved in the synthesis of hemoglobin, which is a 2-valent iron ion involved in the transport of oxygen. A small proportion of iron is involved in the synthesis of ferritin and ferric heme, which are stored in the liver, spleen, bone marrow and small intestine mucosa. Ferritin and iron-containing heme are forms of iron reserves that are released as soon as the body needs them and participate in hemoglobin synthesis, such as mobilization of iron reserves when hemoglobin decreases sharply during massive blood loss. When the body is iron deficient, hemoglobin synthesis decreases and the size of red blood cells in the blood becomes smaller, which can lead to microcytic hypochromic anemia.