The primary cause is loss of blood through menstruation. This type of anemia also commonly occurs during pregnancy. The body's iron stores can be depleted either through insufficient intakes or excessive loss. In America, dietary insufficiency is a very rare condition, thanks to the combination of our meat-rich diet and the iron fortification of our food staples. The one notable exception to this is the case with milk-fed infants and their mothers.
Bovine milk has almost no iron.
Fortunately most infant formulas are now fortified with iron. Still, nutritional cases of IDA do occur. As mentioned above, the more important cause of iron depletion is chronic blood loss. In females, this is usually due to menstruation. Other underlying causes of blood loss include chronically bleeding lesions of the gastrointestinal tract, reflux esophagitis, peptic ulcers, or gastric or colorectal adenocarcinomas.