Iron is classified as an essential mineral. It helps the body produce enzymes and proteins necessary for chemical reactions and cellular functions. Hemoglobin, the protein found in red blood cells, contains approximately two-thirds of the iron in your body. Lack of sufficient iron leads to to iron-deficiency anemia, a medical condition that results in fatigue, dizziness and shortness of breath. To treat iron-deficiency anemia doctors may recommend that you take one of several types of iron vitamins, which are more commonly called iron supplements.
Ferrous Fumarate
Ferrous fumarate contains the highest amount of elemental iron -- the amount of iron available for absorption -- of any iron supplement. The National Institutes of Health Office of Dietary Supplements reports that ferrous fumarate contains 33 percent elemental iron. Many factors affect iron absorption, so the body may not absorb all of the available iron. Medications, food ingredients and other supplements can affect iron absorption. The University of California San Diego Health Library recommends taking ferrous fumarate on an empty stomach, one hour before or two hours after eating.
Ferrous Sulfate
Ferrous sulfate is the least expensive and most widely used iron supplement, according to the National Anemia Action Council. Just as with ferrous fumarate, doctors recommend taking ferrous sulfate either one hour before or two hours after eating to avoid food interactions. However, taking this supplement on an empty stomach can cause stomach upset, so it can also be taken with a meal. If you take the iron supplement with food, avoid eating foods that contain substances known to inhibit iron absorption. Tannins, found in coffee or tea; oxalic acid in spinach or rhubarb; and isoflavones found in soy foods can all interfere with iron absorption. Ferrous sulfate contains 20 percent elemental iron, less than ferrous fumarate, but more than ferrous gluconate.
Ferrous Gluconate
Ferrous gluconate contains the least amount of elemental iron of any of the ferrous iron supplements, providing only 12 percent iron available for absorption. For maximum iron absorption, take it on an empty stomach unless it causes stomach upset. This supplement contains such a low level of elemental iron that it's helpful to take it with a source of vitamin C, such as citrus fruits, to enhance absorption. Jackson/Siegelbaum Gastroenterology reports that ferrous gluconate causes fewer gastrointestinal side effects, such as constipation, than ferrous sulfate.
Ferric Supplements
Although there are supplements containing ferric iron on the market, most doctors prefer that you take one of the other ferrous iron supplements listed, because the body more readily absorbs the iron in that form. Ferrous iron and ferric iron describe different oxidation states of iron, meaning ferric iron differs from ferrous iron in the number of negatively charged electrons it carries.
References
- National Institutes of Health Office of Dietary Supplements: Iron
- MayoClinic.com: Iron Supplements
- University of California San Diego Health Library: Ferrous Fumarate
- MedLinePlus: Ferrous Sulfate
- Jackson/Siegelbaum Gastroenterology: Ferrous Gluconate
- National Anemia Action Council: A Physician's Guide to Iron Supplements
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