Iron for Sports & Fitness

Also known as: Ferrous Sulfate

What is it?

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.

Why do athletes use it?*

Some athletes say that iron

helps boost energy levels.

What do the advocates say?*

Athletes are not at risk of developing iron deficiency or anemia any more than others; however, metabolically, athletes utilize more minerals, including iron, than non-athletes do.

Women have a greater risk of developing iron deficiency than men. Premenopausal women, in particular, are at risk of becoming iron-deficient because of the blood loss that occurs every month during menstruation.

Doctors often screen for iron deficiency by testing for anemia. However, individuals who have a mild deficiency of iron may not be anemic, since blood counts do not typically drop until iron stores in the body are almost completely depleted. If you suspect you are deficient in iron, ask your doctor to perform a more specific blood test, known as a “ferritin” test, rather than the routine “CBC” or “total iron” tests.

Prior to taking supplemental iron, people should be tested by a doctor to make sure such supplementation is appropriate. Although supplemental iron may help those who are deficient, too much iron may cause adverse side effects, including stomach and intestinal cramps, nausea, and constipation.

How much is usually taken by athletes?

Iron is important for an athlete because it is a component of hemoglobin, which transports oxygen to muscle cells. Some athletes, especially women, do not get enough iron in their diet. In addition, for reasons that are unclear, endurance athletes, such as marathon runners, frequently have low body-iron levels.¹ ² ³ However, anemia in athletes is often not due to iron deficiency and may be a normal adaptation to the stress of exercise.⁴ Supplementing with iron is usually unwise unless a deficiency has been diagnosed. People who experience undue fatigue (an early warning sign of iron deficiency) should have their iron status evaluated by a doctor. Athletes who are found to be iron deficient by a physician are typically given 100 mg per day until blood tests indicate they are no longer deficient. Supplementing iron-deficient athletes with 100 to 200 mg per day of iron increased aerobic exercise performance in some,⁵ ⁶ ⁷ though not all,⁸ ⁹ double-blind studies. A recent double-blind trial found that iron-deficient women who took 20 mg per day of iron for six weeks were able to perform knee strength exercises for a longer time without muscle fatigue compared with those taking a placebo.¹⁰

Are there any side effects or interactions?

Iron (ferrous sulfate) is the leading cause of accidental poisonings in children.¹¹ ¹² ¹³ 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.¹⁴ Deaths in children have occurred from ingesting as little as 200 mg to as much as 5.85 grams of iron.¹⁵ 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,¹⁶ cancer,¹⁷ increased risk of infection,¹⁸ systemic lupus erythematosus (SLE),¹⁹ exacerbation of rheumatoid arthritis,²⁰ and Huntington’s disease.²¹ The greatest concern has surrounded the possibility that excess storage of iron in the body increases the risk of heart disease.²² ²³ ²⁴ Two analyses of published studies came to different conclusions about whether iron could increase heart disease risk.²⁵ ²⁶ One trial has suggested that such a link may exist, but only in some people (possibly smokers or those with elevated cholesterol levels).²⁷ 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.²⁸

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. ²⁹

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.³⁰ 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.³¹

Many foods, beverages, and supplements have been shown to affect the absorption of iron.³²

Foods, beverages and supplements that interfere with iron absorption include

Green tea (Camellia sinensis).³³ ³⁴ ³⁵ ³⁶ 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.³⁷
Coffee (Coffea arabica, C. robusta).³⁸ ³⁹ ⁴⁰
Red wine, particularly the polyphenol component (also found in tea).⁴¹ ⁴² 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.⁴³ ⁴⁴ ⁴⁵
Whole wheat bran, independent of its phytate content, has been shown to inhibit iron absorption.⁴⁶
Calcium from food and supplements interferes with heme-iron absorption.⁴⁷ ⁴⁸
Soy protein.⁴⁹ ⁵⁰
Eggs.⁵¹ ⁵²

Foods and supplements that increase iron absorption include

Meat, poultry, and fish.⁵³ ⁵⁴ ⁵⁵ ⁵⁶ ⁵⁷

Although vitamin C increases iron absorption,⁵⁸ ⁵⁹ ⁶⁰ ⁶¹ the effect is relatively minor.⁶²

Taking vitamin A with iron helps treat iron deficiency, since vitamin A improves the absorption and/or utilization of iron.⁶³ ⁶⁴

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.⁶⁵ Some soy sauces may also enhance iron absorption.⁶⁶

Alcohol, but not red wine, has been reported to increase the absorption of ferric, but not ferrous, iron.⁶⁷ ⁶⁸

Iron has been reported to potentially interfere with manganese absorption. In one trial, women with high iron status had relatively poor absorption of manganese.⁶⁹ 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.⁷⁰ These interactions suggest that taking multiminerals that include manganese may protect against manganese deficiencies that might otherwise be triggered by taking isolated iron supplements.

Are there any drug interactions?
Certain medicines may interact with iron. Refer to drug interactions for a list of those medicines.

Resources

See a list of books, periodicals, and other resources for this and related topics.

*Athletes and fitness advocates may claim benefits for iron based on their personal or professional experience. These are individual opinions and testimonials that may or may not be supported by controlled clinical studies or published scientific articles on iron. For more complete and detailed information, including references and safety information, see Iron as a nutritional supplement.

References
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications.

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