1.Insufficient iron in food Mainly due to long-term partial diet or dieting. 2, the growth of iron needs increase such as growth period of children and adolescents, pregnant women, lactating women need to increase the amount of iron, and the diet does not contain enough iron. 3, iron absorption is not enough Mainly seen in chronic gastritis, enteritis and other diseases affecting iron absorption, or long-term use of certain drugs that affect iron absorption, such as certain gastric drugs (H-blockers), or tea, coffee addicts, iron absorption will also be reduced. 4, iron, too much loss Mainly seen in excessive menstruation, repeated gastrointestinal bleeding (peptic ulcer, gastrointestinal tumors, hemorrhoids, hookworm infection, etc.) and repeated intravascular hemolysis, etc.