Iron from plant foods is not as readily absorbed as iron from animal sources.
The element iron is essential for most living organisms' survival. Hundreds of proteins in the human body, including many enzymes needed for cellular metabolism, could not function without iron. The only way you can obtain iron is to absorb it from the foods you eat, so any process that interferes with intestinal iron absorption could lead to health problems. Most notably, iron deficiency is believed to be the most common cause of anemia worldwide.
Iron is present in two forms in food. Heme iron, which is derived from meat and other animal sources, is more easily absorbed than non-heme iron, which is found in plant-based foods. Studies show that in Western cultures, heme iron accounts for about 2/3 of the iron stores in the average person's body, while it comprises only 1/3 of the iron that is consumed. Furthermore, many substances found in plant-based foods that are not present in animal foods -- such as phytates -- bind iron in your intestine and prevent its absorption. These factors may account for the higher prevalence of iron-deficiency anemia among vegetarians.
The hydrochloric acid in your stomach plays an important role in iron absorption, particularly of non-heme iron. Gastric acid helps liberate iron from your food and converts it to a chemical state that is more readily absorbed. Any condition that diminishes gastric acid secretion or reduces exposure of ingested food to stomach acid can limit intestinal iron absorption. Pernicious anemia, acid-blocking drugs and gastric bypass surgery all reduce intestinal iron absorption by this mechanism.
Your small intestine provides about 250 square yards of absorptive surface area, so its capacity for transferring vitamins, minerals and other nutrients into your bloodstream is quite remarkable. Certain diseases that affect broad areas of your intestinal lining may compromise iron absorption. People with inflammatory bowel diseases -- including Crohn disease and ulcerative colitis -- are frequently iron-deficient. Although iron deficiency among people with inflammatory bowel disease is partially due to blood loss from the intestinal lining, iron absorption is also limited by inflammation of the lining of the upper small intestine, where most iron is absorbed. Similarly, celiac disease -- an intestinal disorder triggered by an immune reaction to gluten -- can interfere with iron absorption in the small intestine. A December 2007 review in "American Family Physician" reported that 10 to 15 percent of people with celiac disease develop iron-deficiency anemia.
Impaired intestinal iron absorption can contribute to iron deficiency. Because intestinal iron absorption can be affected by many factors, you will need to discuss with your doctor whether your iron deficiency is due to an underlying medical disorder, such as celiac disease.
If you are taking an iron supplement to address iron deficiency, you can improve intestinal iron absorption by taking your supplement with vitamin C. Your doctor will prescribe the iron and vitamin C doses that are appropriate for you.