Iron Improves Muscle Strength

Women with iron deficiency but without anemia are able to perform leg exercises with less fatigue after receiving iron supplements, according to a new study in the American Journal of Clinical Nutrition (2003;77:441–8).

Iron deficiency is a major health problem throughout the world. The prevalence of iron-deficiency anemia in women in the United States between 18 and 44 years of age is 3 to 5%. Iron deficiency without anemia is more common, affecting 11 to 13% of U.S. women in the same age range. Iron is a component of hemoglobin, which carries oxygen in red blood cells to all parts of the body. It is also present in other cells outside of the blood, where it plays a role in energy production and muscle function.

When iron deficiency is severe, it can lead to anemia, which impairs the ability of blood to carry oxygen to the tissues. Less severe forms of iron deficiency do not result in anemia, but still may compromise a person's endurance and potentially cause fatigue. Studies have demonstrated that muscles tire more quickly in iron-deficient laboratory animals and that restoration of normal iron levels normalizes muscle contraction stamina. Human studies, however, have had conflicting results.

In the current study, 20 women with iron deficiency without anemia were asked to perform knee extension exercises in order to measure the rate at which muscle fatigue would develop. The women were then assigned to receive either 10 mg of elemental iron twice daily or placebo for six weeks. Following the supplementation period, the same exercises were performed and the time until muscle fatigue was again measured. The women who received the iron supplements had a significant increase in muscle endurance, but the women who received placebo showed no improvement. Specifically, after six weeks of iron supplementation, the women had 10 to 15% less muscle fatigue after the fourth minute of leg exercises, and leg muscle strength after completion of the exercises was increased by 26.5%.

The results of this study suggest that iron supplementation might improve endurance and help overcome muscle fatigue in women with iron deficiency, even in the absence of anemia. Tests for evaluating iron status, such as serum ferritin, are inexpensive and widely available. Iron supplements are inexpensive although they can cause gastrointestinal side effects in some cases and iron does interact with some medications. In addition, preliminary studies suggest that taking iron when it is not needed might increase the risk of cardiovascular disease and possibly diabetes. Furthermore, a small proportion of the population carries a gene that predisposes them to excessive accumulation of iron; in these individuals iron supplementation can cause severe liver damage. For these reasons, people should not take iron supplements without the supervision of a healthcare practitioner knowledgeable about nutrition.

Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, Vermont, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.

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