Learn More About Iron

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What is iron?

Iron is an essential mineral. It is part of hemoglobin, the oxygen-carrying component of the blood. Iron-deficient people tire easily in part because their bodies are starved for oxygen. Iron is also part of myoglobin, which helps muscle cells store oxygen. Without enough iron, adenosine triphosphate (ATP; the fuel the body runs on) cannot be properly synthesized. As a result, some iron-deficient people become fatigued even when their hemoglobin levels are normal (i.e., when they are not anemic).

Where is it found?

The most absorbable form of iron, called “heme” iron, is found in oysters, meat and poultry, and fish. Non-heme iron is also found in these foods, as well as in dried fruit, molasses, leafy green vegetables, wine, and iron supplements. Acidic foods (such as tomato sauce) cooked in an iron pan can also be a source of dietary iron.

Who is likely to be deficient?

Vegetarians eat less iron than non-vegetarians, and the iron they eat is somewhat less absorbable. As a result, vegetarians are more likely to have reduced iron stores. 1 However, iron deficiency is not usually caused by a lack of iron in the diet alone. An underlying cause, such as iron loss in menstrual blood, often exists.

Pregnant women, marathon runners, people who take aspirin, and those who have parasitic infections, hemorrhoids, ulcers, ulcerative colitis, Crohn’s disease, gastrointestinal cancers, or other conditions that cause blood loss or malabsorption are likely to become deficient.

Infants living in inner city areas may be at increased risk of iron-deficiency anemia 2 and suffer more often from developmental delays as a result. 3 4 Supplementation of infant formula with iron up to 18 months of age in inner city infants has been shown to prevent iron-deficiency anemia and to reduce the decline in mental development seen in such infants in some, 5 but not all, 6 studies. Breath-holding spells are a common problem affecting about 27% of healthy children.7 These spells have been associated with iron-deficiency anemia,8 and several studies have reported improvement of breath-holding spells with iron supplementation.9 10 11 12

People who fit into one of these groups, even pregnant women, shouldn’t automatically take iron supplements. Fatigue, the first symptom of iron deficiency, can be caused by many other things. A doctor should assess the need for iron supplements, since taking iron when it isn’t needed does no good and may do some harm.

Which forms of supplemental iron are best?

All iron supplements are not the same. Ferrous iron (e.g. ferrous sulfate) is much better absorbed than ferric iron (e.g. ferric citrate).13 14 The most common form of iron supplement is ferrous sulfate, but it is known to produce intestinal side effects (such as constipation, nausea, and bloating) in many users.15

Some forms of ferrous sulfate are enteric-coated to delay tablet dissolving and prevent some side effects,16 but enteric-coated iron may not absorb as well as iron from standard supplements.17 18 19 Other forms of iron supplements, such as ferrous fumarate,20 21 ferrous gluconate,22 heme iron concentrate,23 24 25 26 and iron glycine amino acid chelate27 28 are readily absorbed and less likely to cause intestinal side effects.

How much is usually taken??

If a doctor diagnoses iron deficiency, iron supplementation is essential. To treat iron deficiency, a common recommended amount for an adult is 100 mg per day; that amount is usually reduced after the deficiency is corrected. When iron deficiency is diagnosed, the doctor must also determine the cause. Usually it’s not serious (such as normal menstrual blood loss or blood donation). Occasionally, however, iron deficiency signals ulcers or even colon cancer.

Some premenopausal women become marginally iron deficient unless they supplement with iron. However, the 18 mg of iron present in many multivitamin-mineral supplements is often adequate to prevent deficiency. A doctor should be consulted to determine the amount of iron that is needed.

Are there any side effects of iron?

Iron (ferrous sulfate) is the leading cause of accidental poisonings in children.29 30 31 The incidence of iron poisonings in young children increased dramatically in 1986. Many of these children obtained the iron from a child-resistant container opened by themselves or another child, or left open or improperly closed by an adult.32 Deaths in children have occurred from ingesting as little as 200 mg to as much as 5.85 grams of iron.34 3 Keep iron-containing supplements out of a child’s reach.

Hemochromatosis, hemosiderosis, polycythemia, and iron-loading anemias (such as thalassemia and sickle cell anemia) are conditions involving excessive storage of iron. Supplementing iron can be quite dangerous for people with these diseases. Supplemental amounts required to overcome iron deficiency can cause constipation. Sometimes switching the form of iron (see “Which forms of supplemental iron are best?” above), getting more exercise, or treating the constipation with fiber and fluids is helpful, though fiber can reduce iron absorption (see below). Sometimes the amount of iron must be reduced if constipation occurs.

Some researchers have linked excess iron levels to diabetes,34 cancer,35 increased risk of infection,36 systemic lupus erythematosus (SLE),37 exacerbation of rheumatoid arthritis,38 and Huntington’s disease.39 The greatest concern has surrounded the possibility that excess storage of iron in the body increases the risk of heart disease.40 41 42 Two analyses of published studies came to different conclusions about whether iron could increase heart disease risk.43 44 One trial has suggested that such a link may exist, but only in some people (possibly smokers or those with elevated cholesterol levels).45 The link between excess iron and any of the diseases mentioned earlier in this paragraph has not been definitively proven. Nonetheless, too much iron causes free radical damage, which can, in theory, promote or exacerbate most of these diseases. People who are not iron deficient should generally not take iron supplements.

Patients on kidney dialysis who are given injections of iron frequently experience “oxidative stress”. This is because iron is a pro-oxidant, meaning that it interacts with oxygen molecules in ways that can damage tissues. These adverse effects of iron therapy may be counteracted by supplementation with vitamin E.46 Supplementation with iron, or iron and zinc, has been found to improve vitamin A status among children at high risk for deficiency of the three nutrients. 47 People with hepatitis C who have failed to respond to interferon therapy have been found to have higher amounts of iron within the liver. Moreover, reduction of iron levels by drawing blood has been shown to decrease liver injury caused by hepatitis C.48 Therefore, people with hepatitis C should avoid iron supplements. In some people, particularly those with diabetes, insulin resistance syndrome, or liver disease, a genetic susceptibility to iron overload has been reported.49

Are there any food interactions with iron?

Many foods, beverages, and supplements have been shown to affect the absorption of iron.50 Foods, beverages and supplements that interfere with iron absorption include:
Green tea (Camellia sinensis).51 52 53 54 This effect may be desirable for people with iron overload diseases, such as hemochromatosis. The inhibitory effect of green tea on iron absorption was 26% in one study.55
Coffee (Coffea arabica, C. robusta).56 57 58
Red wine, particularly the polyphenol component (also found in tea).59 60 Since wine is also a dietary source of iron, it is not clear whether drinking red wine would lead to a deficiency of iron.
Phytate (phytic acid), found in unleavened wheat products such as matzoh, pita, and some rye crackers; in wheat germ, oats, nuts, cacao powder, vanilla extract, beans, and many other foods, and in IP-6 supplements.61 62 63
Whole wheat bran, independent of its phytate content, has been shown to inhibit iron absorption.64
Calcium from food and supplements interferes with heme-iron absorption.65 66
Soy protein.67 68
Eggs.69 70

Foods and supplements that increase iron absorption include
• Meat, poultry, and fish.71 72 73 74 75

Although vitamin C increases iron absorption,76 77 78 79 the effect is relatively minor.80 Taking vitamin A with iron helps treat iron deficiency, since vitamin A improves the absorption and/or utilization of iron.81 82 Although soy protein has been shown to decrease iron absorption (see above), certain soy-containing foods (e.g. tofu, miso, tempeh) have significantly improved iron absorption.83 Some soy sauces may also enhance iron absorption.84 Alcohol, but not red wine, has been reported to increase the absorption of ferric, but not ferrous, iron.85 86 Iron has been reported to potentially interfere with manganese absorption. In one trial, women with high iron status had relatively poor absorption of manganese.87 In another trial studying manganese/iron interactions in women, increased intake of “non-heme iron”—the kind of iron found in most supplements—decreased manganese status.88 These interactions suggest that taking multiminerals that include manganese may protect against manganese deficiencies that might otherwise be triggered by taking isolated iron supplements.


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