text: Functional or actual iron deficiency can result from a variety of causes. These causes can be grouped into several categories:
  * Increased demand for iron, which the diet cannot accommodate.
  * Increased loss of iron (usually through loss of blood).
  * Nutritional deficiency. This can result due to a lack of dietary iron or consumption of foods that inhibit iron absorption. Absorption inhibition has been observed caused by phytates in bran, calcium from supplements or dairy products, and tannins from tea, although in all three of these studies the effect was small and the authors of the studies cited regarding bran and tea note that the effect will probably only have a noticeable impact when most iron is obtained from vegetable sources.
  * Acid-reducing medications: Acid-reducing medications reduce the absorption of dietary iron. These medications are commonly used for gastritis, reflux disease, and ulcers. Proton pump inhibitors (PPIs), H2 antihistamines, and antacids will reduce iron metabolism.
  * Damage to the intestinal lining. Examples of causes of this kind of damage include surgery involving the duodenum or diseases like Crohns or celiac sprue which severely reduce the surface area available for absorption. Helicobacter pylori' infections also reduce the availability of iron.
  * Inflammation leading to hepcidin-induced restriction on iron release from enterocytes (see above).
  * Is also a common occurrence in pregnant women, and in growing adolescents due to poor diets.
  * Acute blood loss or acute liver cirrhosis creates a lack of transferrin therefore causing iron to be secreted from the body.