Having anemia, a type of iron deficiency, can make you feel weak and fatigued all the time. Your doctor may want you to take an iron supplement to treat or prevent a deficiency, And some types of iron are easier for your body to absorb, or bioavailable, than others. Check with your healthcare provider before you begin taking iron supplements, to avoid having any adverse effects.
Why You Need Iron
Iron is a component of several proteins throughout your body. It is essential for carrying oxygen to almost all cells, tissues and organs so they can function properly. About two-thirds of iron in your body attaches to hemoglobin, the protein that transports most oxygen. Any remaining iron is found in myoglobin, another type of protein. Myoglobin helps transport oxygen to muscles and plays a role in several biochemical reactions.
Heme vs. Nonheme Iron
Heme and nonheme are two types of iron that have varying degrees of bioavailability in your body. You get heme iron from animal foods such as beef, dark poultry meat, tuna and oysters. It is the form of iron that is easier for your body to absorb and store, but most of the iron in your diet comes from nonheme sources, since nonheme foods are common foods you consume regularly. Foods rich in nonheme iron include beans, lentils, tofu and spinach, as well as fortified breakfast cereals and dietary supplements. Your body absorbs about 15 to 35 percent of the heme iron you ingest, versus only 2 to 20 percent of nonheme iron, explains the Office of Dietary Supplements.
Iron Supplements
Nonheme iron, the type in dietary supplements, comes in either ferrous or ferric forms. Ferrous salts are more bioavailable and absorbed in higher amounts than ferric iron. Your iron supplement has a certain amount of elemental iron that is available for absorption; the nutrition panel should list the amount of elemental iron it contains. For example, ferrous fumerate provides the highest amount of elemental iron, 33 percent, making it the most bioavailable type of iron supplement. Ferrous sulfate is a close second place, providing 22 percent elemental iron, reports the Linus Pauling Institute. Other forms of ferrous iron supplements have less than 20 percent elemental iron available for absorption. Since ferric iron is poorly absorbed and has limited bioavailability, it is not commonly used in iron supplements.
Dosage and Toxicity
Adult women need more iron each day than men; 18 mg versus 8 mg for men. If you are pregnant, this amount jumps up to 27 mg to support increasing blood volume in your body. You are unlikely to overdose from iron by consuming too many iron-rich foods, but you can overdose by ingesting a large dosage of iron supplements. The tolerable upper limit, or UL, for iron is 45 mg daily, meaning swallowing any more than this amount may lead to toxic levels in your body. Early warning signs of iron poisoning include nausea, black tar-like stools, fatigue, rapid pulse and low blood pressure. Severe iron toxicity can cause your organs to fail and may be fatal at very high doses. Avoid toxicity by taking iron supplements under the direct supervision of your health care provider.
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