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Small Intestine and Its Role in Iron Absorption

By Stephen Christensen ; Updated September 26, 2017

Iron is essential for life. Without iron, you could not capture oxygen from the atmosphere and transport it to your vital organs. You would also be unable to manufacture chromosomes, produce energy from the foods you eat or detoxify the potentially dangerous chemicals that pass through your tissues every day. Because iron is so important, your body has devised efficient mechanisms for absorbing, storing and recycling it. Despite these safeguards, iron stores can be depleted if you lose blood, do not eat enough iron or if intestinal iron absorption is impaired.

Intestinal Absorption

Although your body tenaciously clings to its iron supply, a few milligrams of iron are lost daily in sweat, urine, feces and sloughed skin cells. Menstruating women lose an additional 30 to 40 mg of iron during each monthly cycle. None of these processes is closely regulated. By contrast, intestinal iron absorption is tightly controlled, making this the principal mechanism for regulating iron uptake and, ultimately, maintaining your total body iron stores.

Different Forms

Dietary iron occurs in three forms, each with a different absorption mechanism. Heme iron -- the most efficiently absorbed form of iron -- is found in red meat and other flesh foods. Heme iron uptake is regulated by a heme carrier protein in your intestinal lining.

Non-heme ferritin iron comes from plants that contain the mineral, such as beans, lentils and other legumes. This form of dietary iron is pulled through the membranes of your intestinal cells through a process called endocytosis.

Non-heme, low molecular-weight iron -- such as that found in supplements -- is carried across the lining of your intestine by the same transporter molecule that transfers manganese, copper and several other metallic nutrients into your bloodstream.

Impaired Absorption

Although some iron absorption occurs throughout your small intestine, most takes place in your duodenum and upper jejunum, which comprise the first 18 to 24 inches of your small intestine. Any factors that damage or eliminate this portion of your gastrointestinal tract could interfere with iron absorption.

People with the inflammatory bowel condition Crohn disease or celiac disease, which is triggered by an immune reaction to proteins in certain grains, may become iron-deficient due to inflammation of the inner lining of their intestine. Gastric bypass surgery is another frequent cause of iron deficiency, partly because it diverts consumed food past the absorptive surface of the upper small intestine.


Iron deficiency is the most common nutritional disorder worldwide, according to the World Health Organization. Iron deficiency is common in developing countries where other nutritional deficiencies are prevalent, but it is a public health problem in wealthy nations, too. Once iron deficiency develops, it takes weeks to months to correct. Even though your intestine can increase iron absorption in times of need, it regulates iron uptake to avoid the toxicities that can occur if you absorb too much.

Although your body needs a certain amount of iron, excess iron can damage your liver, heart, pancreas, nervous system and joints. Ask your doctor if you need supplemental iron. In most cases, iron pills are enough to correct an iron deficiency, but injectable forms of iron are available for severe deficiency or for people whose intestines do not absorb iron.

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