Iron supplements are frequently needed in pregnancy and in pre-menopausal women who lose blood in the menstrual cycle each month. Iron supplements sold over the counter often contain one of two types of iron, ferrous iron and ferric iron. Ferrous iron, the most frequently prescribed type of iron, is the best absorbed. Iron supplements can be given parenterally, in injections, intravenously or via pills or liquid supplements. Do not take iron supplements without discussing their use with your medical provider; too much iron can cause side effects.
Ferrous Iron
Ferrous iron supplements, which include ferrous sulfate, ferrous fumarate and ferrous gluconate are well absorbed but have more gastrointestinal side effects, such as abdominal pain, nausea, vomiting, constipation or diarrhea. Dark-colored stools occur with all different types of iron supplements. Each of the ferrous supplements contains a different type of iron and each contains a different amount of elemental iron, the amount of iron that's actually absorbed. Ferrous fumarate is best absorbed, with 33 percent absorption; 20 percent of ferrous sulfate and 12 percent of the iron in ferrous gluconate are absorbed. Because increasing the dose decreases the amount of iron absorbed, ferrous iron is often given in smaller doses several times a day, the Office of Dietary Supplements states.
Ferric Iron
Ferric iron is harder for your body to absorb than ferrous iron, because it has to be reduced to ferrous iron before it can be absorbed in the intestine. Ferric iron causes fewer gastrointestinal side effects than ferrous iron. The most commonly used ferric iron is ferric ammonium citrate. Another form of ferric iron, a polysaccharide-iron complex is odorless and tasteless and has similar absorption rates as ferrous sulfate, according to the Therapeutic Research Center. Manufacturers claim that this form of ferric iron causes fewer gastrointestinal side effects, but this claim has not been proven.
Chelated Iron
Chelated irons such as ferrous bisglycinate are conjugated forms of iron bound to amino acids, the building blocks of protein. The goal of chelating iron is to make it more similar to heme iron, the type of iron obtained from animal sources. This supposedly increases the bioavailability of the iron by preventing its conversion to insoluble ferric hydroxide after being ingested. Chelated forms of iron may cause less intestinal disturbances.
Heme-Iron Polypeptide
This form of iron is made from hemoglobin taken from red blood cells of pigs. This type of iron supplement is better absorbed than iron salts such as ferrous and ferric iron and is well tolerated. This form of iron is classified as a medical food instead of a dietary supplement, since it comes from an animal source, the Therapeutic Research Center explains.
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