The causes of iron deficiency anemia primarily refer to the disruption of the normal dynamic balance between iron absorption and excretion, leading to the consumption of stored iron as well as an increased need for iron and insufficient iron intake, especially in cases of chronic blood loss, resulting in a long-term negative iron balance. The causes of iron deficiency can be divided into two main aspects: insufficient iron intake and excessive iron loss. In the first aspect, decreased iron intake includes dietary insufficiency, meaning inadequate food intake, and reduced absorption, which includes decreased absorption due to lack of stomach acid and reduced absorption following gastric surgery. Excessive iron loss includes the following eight aspects: 1) gastrointestinal bleeding, which includes bleeding caused by tumors, gastrointestinal ulcers, gastritis, as well as bleeding due to parasites and hookworm infections. It also includes bleeding caused by hemorrhoids in men and arteriovenous malformations; 2) excessive menstrual bleeding; 3) frequent blood donations; 4) multiple pregnancies in women; 5) chronic intravascular hemolysis causing hemoglobinuria; 6) hereditary hemorrhagic telangiectasia; 7) primary pulmonary hemosiderosis; and 8) coagulation disorders or the use of anticoagulants leading to iron deficiency. These eight categories all result from excessive loss of iron, causing iron deficiency which leads to iron deficiency anemia.