Iron is a mineral found in red blood cells and cells within muscles that helps to carry oxygen to cells. People with low iron levels often have very little energy and are prone to infection, and iron supplements are given as treatment. Upset stomach is one of the most common side effects of iron supplementation, according to the National Anemia Action Council.
Absorption
Iron supplements can be given by mouth or injected. The oral form causes gastrointestinal symptoms such as abdominal discomfort, nausea, vomiting, constipation or diarrhea. Iron is absorbed from the upper part of the intestine, which is more acidic. Iron absorbs best on an empty stomach, but taking iron this way might cause more intestinal symptoms than taking it with food.
Types
Iron supplements contain either ferric or ferrous iron, with ferrous iron being the best absorbed and the type of iron found in most supplements. Ferrous iron comes in several forms: ferrous fumarate, ferrous gluconate and ferrous sulfate. Each contains different amounts of elemental iron, with ferrous fumarate containing 108 mg, the most per 325 mg tablet. Ferrous sulfate is the most commonly used and least expensive form, according to "Guidelines for Adolescent Nutrition Services," published in 2005 by the University of Minnesota. Ferrous sulfate contains 65 mg per 325 mg tablet and ferrous gluconate contains 35 mg. Because ferrous gluconate tablets contain the least elemental iron, they might cause fewer problems with stomach discomfort. Producers of a form of ferric acid containing a polysaccharide-iron complex claim it reduces side effects, but this is unproven, MedlinePlus reports.
Prevention
Starting with a half-dose and gradually increasing to a full dose of iron might help decrease stomach distress. Coated iron tablets and extended-release tablets might cause fewer side effects, but also might be less well-absorbed. Iron doses are often given in divided doses several times a day because the percentage of iron absorption decreases when large amounts are taken at one time. Taking your daily iron in divided doses or taking iron at bedtime also might decrease gastrointestinal symptoms. Skipping days between iron treatments might help increase absorption and decrease GI symptoms, but talk with your medical practitioner about how to do this.
Considerations
If you can't tolerate taking iron on an empty stomach, taking it with food or liquids might improve your tolerance. Dairy products, cereals, phosphorus-containing soft drinks, tea and coffee can all interfere with iron absorption; do not take these with iron supplements. If you're completely unable to tolerate the GI side effects of oral iron, iron injections, which don't cause stomach problems, might be a better choice for you. Talk with your medical practitioner about your options.
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