Minerals play an important role in the physiology of the body. Generally they act as co-enzymes for many bio-chemical processes and many are linked to the actions of organic vitamins which are responsible for many different aspects of life. Calcium is the most abundant mineral in the body, constituting approximately 40% of the total mineral content. Calcium is critical for nerve impulse transmission. You cannot be alive without adequate calcium present so the body stores calcium in bones, which it later robs if the diet begins to lack sufficient calcium. By contrast, iron is a micro-mineral.
Iron is present in the body in relatively small amounts (35-50 mg per kilogram of body weight). Iron plays a crucial role in oxygen transportation by the bloodstream in the cardiovascular system. Iron has a unique chemical attraction to oxygen as evidenced by rusting iron that we commonly see in the environment. In the cardiovascular system, iron is required for the formation of both hemoglobin and myoglobin, which are two necessary proteins of the body. Hemoglobin, located in the red blood cells, binds with oxygen in the lungs and then transports to the body tissues via the blood. Myoglobin, found in muscle cells, combines with oxygen as the gas diffuses from the capillaries into the muscle cells and stores it until the mitochondria needs it for aerobic respiration.
Iron deficiency is prevalent throughout the world. By some estimates, as much as 25% of the world’s population is iron deficient. The major problem associated with this condition is iron-deficiency anemia, in which hemoglobin levels are reduced, decreasing the blood’s oxygen-carrying capacity. In the general population this causes fatigue, headaches, lethargy, and other symptoms. In endurance runners this causes a reduction in training capacity and limits performance. It also makes recovery between intervals and regeneration between sessions incomplete.
Numerous studies suggest that 22% to 25% of female distance runners and 10% of male distance runners between the ages of 15 and 22 in the United States are iron deficient as reflected in their hemoglobin count. Iron-deficient anemia is confirmed when the hemoglobin concentration is below 12 g per 100 ml of blood. Other studies indicate that hemoglobin concentration is not the only marker of anemia or necessarily the best. Serum ferritin levels provide a good marker of the body’s iron stores. For the general population, a serum ferritin concentration of 13-200 is considered normal. When values are below 20-30, this indicates low body iron stores and becomes quite problematic for the endurance athlete. For various reasons, it is quite difficult to have a distance or middle-distance runner with a concentration of more than 40. Thus, it becomes an on-going struggle of eating the right foods in the right combinations in order for the body absorb and use as much heme iron as possible.
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Endurance athletes tend to have lower hemoglobin concentrations because expansion of the blood plasma volume is one of the earliest body adaptations to regular aerobic exercise. Some distance runners lose iron through intermittent bleeding from the gastrointestinal tract and consequently develop iron-deficiency anemia. A small amount of iron is lost through sweat, but for every 50 liters of sweat produced only 1 gr of iron is measured. Footstrike hemolysis (impacting) can contribute to anemia in distance runners. The impact of feet striking the ground can destroy normal red blood cells in the bloodstream.
When footstrike hemolysis occurs, destroyed red blood cells release hemoglobin that is subsequently bound by plasma haptoglobin (another iron binding protein in the blood) to the liver, where iron is salvaged. The plasma content of haptoglobin, however, can be depleted if sufficient numbers of red blood cells are destroyed. In fact, haptoglobin can drop to nearly zero in the blood.
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Independent studies done in the late 1990’s indicated that more shock absorbent running shoes can reduce footstrike hemolysis in runners. Other studies indicated footstrike hemolysis can limit the training induced increases in red blood cell mass that enables the middle-distance to reach peak performance.
When iron supplements are give to distance runners that have low serum ferritin levels, performance measures, particularly aerobic capacity (VO2 max), typically improve. However, supplementation of iron in those distance runners who are not deficient appears to have no benefit. In fact, iron supplements can be a health risk because excess iron is toxic for the liver and ferritin levels of more than 200 are associated with an increase for coronary heart disease.
If iron problems are suspected in your athlete send them to a clinic for blood testing and ask them to bring you a copy of the clinic report. This will give you the information you need as the coach. However, for all of your athletes, a constant reminder of eating nutritional food containing iron is necessary. This should include four servings per week of red meat. All endurance athletes need to be aware of the need for iron.
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