Iron Deficiency and Exercise Fatigue
Women with iron deficiency may have poor endurance during exercise and may benefit from iron supplementation, even if the iron deficiency is not severe enough to cause anemia, according to a new study in American Journal of Clinical Nutrition (2004;79:437–43).
Although it occurs less frequently in the United States, iron deficiency is the most common nutritional deficiency in the world, affecting 20 to 50% of the world’s population. The most common cause of iron deficiency is inadequate intake of iron, but malabsorption and loss of iron from bleeding are significant factors in some cases. Premenopausal women are at risk of becoming iron-deficient because of the blood loss that occurs every month during menstruation.
In the study, 41 iron-depleted, nonanemic women between the ages of 18 and 33 were assigned to receive 100 mg per day of ferrous sulfate (containing 16 mg of elemental iron) or placebo for six weeks. All women participated in an exercise regimen that included training on a stationary bicycle five days a week for four weeks, starting with a 4-minute warm-up, followed by 25 minutes of cycling to achieve a predetermined target heart rate. The amount of exercise increased with each subsequent week of the study. Participants biked 5 km, in three back-to-back trials (in other words, a total of 15 km) and their times were recorded initially and after four weeks of exercise training. Other markers of endurance, such as heart rate during exercise, oxygen consumption, and work rate were measured at the same intervals.
The women receiving the iron supplements took significantly less time to complete the 5-km trials, compared with women who did not receive iron. The greatest effects of iron supplementation were observed in the women who were the most iron depleted. The work rate and oxygen consumption of the iron-supplemented group also improved, suggesting that their bodies worked more efficiently after taking iron. No significant difference in side effects was observed between the two groups.
The new study confirms findings from previous studies that show iron deficiency can lead to poor athletic performance and fatigue, even in women who do not have anemia. However, women should be tested by a doctor to make sure that taking iron 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. In addition, a small proportion of the population has a genetic disorder (hemochromatosis) that causes them to accumulate iron. In those individuals, taking extra iron could cause serious problems, including diabetes and liver disease. A simple blood test is available to determine whether a person has hemochromatosis.
Most physicians recommend taking supplemental iron until the deficiency is corrected, and then only taking it as needed thereafter. Iron absorption may be increased by taking it with 100 mg or more of vitamin C. Iron supplements should not be taken at the same time as coffee, tea, soy, or calcium supplements (and possibly milk), since these substances interfere with iron absorption. Good food sources of iron include red meat, dark greens (spinach, kale, chard, etc.), molasses, beans, Brewer’s yeast, and eggs. It is important for anyone with iron deficiency to see a physician to determine the cause.
Darin Ingels, ND, MT (ASCP), received his bachelor’s degree from Purdue University and his Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. Dr. Ingels is the author of The Natural Pharmacist: Lowering Cholesterol (Prima, 1999) and Natural Treatments for High Cholesterol (Prima, 2000). He currently is in private practice at New England Family Health Associates located in Southport, CT, where he specializes in environmental medicine and allergies. Dr. Ingels is a regular contributor to Healthnotes and Healthnotes Newswire.
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