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by Melvin H Williams
Department of Exercise Science, Old Dominion University
Originally Published by the Journal of the International Society of Sports Nutrition 2005
Minerals are essential for a wide variety of metabolic and physiologic processes in the human body. Some of the physiologic roles of minerals important to athletes are their involvement in: muscle contraction, normal hearth rhythm, nerve impulse conduction, oxygen transport, oxidative phosphorylation, enzyme activation, immune functions, antioxidant activity, bone health, and acid-base balance of the blood. The two major classes of minerals are the macrominerals and the trace elements. The scope of this article will focus on the ergogenic theory and the efficacy of such mineral supplementation.
Introduction
This is the second in a series of six articles to discuss the major classes of dietary supplements (vitamins; minerals; amino acids; herbs or botanicals; metabolites, constituents/extracts, or combinations). The major focus is on efficacy of such dietary supplements to enhance exercise or sport performance.
Minerals: Ergogenic Theory
Minerals represent a class of inorganic substances found naturally in a variety of foods. The human body needs about twenty different minerals in order to function properly. The two major classes of minerals are the macrominerals and the trace elements. In the United States, Recommended Dietary Allowances (RDAs) and Adequate Intakes (AIs) have been developed for 3 macrominerals and 9 trace elements.
Minerals are essential for a wide variety of metabolic and physiologic processes in the human body. Speich and others recently reviewed the physiological roles of minerals important to athletes, noting that minerals are involved in muscle contraction, normal hearth rhythm, nerve impulse conduction, oxygen transport, oxidative phosphorylation, enzyme activation, immune functions, antioxidant activity, bone health, and acid-base balance of the blood [1]. Because many of these processes are accelerated during exercise, an adequate amount of minerals is necessary for optimal functioning. Athletes should obtain an adequate amount of all minerals in their diet, for a mineral deficiency may impair optimal health, and health impairment may adversely affect sport performance. Maughan and others note that iron and calcium are the two micronutrients most likely to be low in the diet, particularly in young athletes [2]. In support of this viewpoint, Ziegler and others recently noted that dietary intake of both iron and calcium was inadequate in female figure skaters during the competitive season [3]. Although all minerals may play a role in a variety of metabolic and physiologic processes, this presentation will focus on those minerals that have received research attention or consideration relative to effects on physical performance or health of the athlete.
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Mineral Supplements: Efficacy
Calcium
About 99 percent of the calcium in the body is stored in the skeletal system, while the remaining one percent is present in other cells, such as muscle cells. Although this muscle cell calcium is involved in a variety of physiologic processes associated with energy metabolism and muscle contraction, calcium supplementation is not considered to possess ergogenic potential because, if necessary, the muscle cells may draw on the vast reserves stored in the bone tissue. However, as noted above, young women involved in weight-control sports, such as figure skating and distance running, may have inadequate dietary intake of calcium. Additionally, exercise may increase calcium losses. For example, Dressendorfer [4]and others examined the effects of 10-week intense endurance training, including volume, interval and tapering phases, on serum and urinary minerals levels. They found that urinary calcium increased and serum calcium decreased below the clinical norm following the high-intensity interval phase, but these changes were reversed following the tapering phase. Thus, it appears that calcium excretion may be increased with high-intensity training.
Inadequate calcium intake and increased calcium losses may predispose one to osteoporosis. This may be especially so in women who develop the female athlete triad (disordered eating, amenorrhea, osteoporosis). For example, Gremion and others [5]recently noted that long-distance runners with oligo-amenorrhea had greater decreases in bone mineral density in the spine than in the femur, even though they had similar energy, calcium and protein intakes compared to eumenorrheic runners. The National Institutes of Health consensus panel on osteoporosis indicated that supplementation with calcium, along with vitamin D, may be necessary in persons not achieving the recommended dietary intake such as these female athletes [6]. Additionally, athletes with amenorrhea should consult with their physician regarding the need for drug or hormonal therapy to help prevent osteoporosis.
Phosphates
Phosphates are incorporated into many compounds in the body that are involved in energy metabolism, such as ATP as an energy substrate, thiamin pyrophosphate as a vitamin cofactor, sodium phosphate as a buffer, and 2,3-diphosphoglycerate (2,3-DPG) for RBC function. All of these roles could provide ergogenic potential, but the most researched theory involves the effect of phosphate salt supplementation on 2,3-DPG. Increased levels of 2,3-DPG could facilitate release of oxygen from hemoglobin in the red blood cell and possibly enhance aerobic endurance exercise performance. Previous studies have generally, but not universally, shown that phosphate salt supplementation increases serum 2-3-DPG levels. Most recently, Bremner and others found that a 7-day phosphate loading protocol would increase erythrocyte phosphate pools and 2,3-DPG [7].
About a dozen studies have been conducted with phosphate salt supplementation and their effects on physical performance, and the results are clearly equivocal. However, no study has reported decreases in performance, and four studies from independent laboratories have shown remarkable similarities relative to increased levels of VO2max following phosphate supplementation and improved performance on bicycle ergometer exercise tests such as a simulated 40-kilometer cycle time trial [8-11]. Although these results are impressive, Tremblay and others [12] indicated that a number of confounding variables in previous research have been identified and more controlled research has been recommended. Research conducted during the past 10 years has also been equivocal, but some favorable effects have been shown. For example, Goss and others recently reported that although phosphate supplementation did not affect physiological responses during exercise at about 70–80 percent VO2max, the rating of perceived exertion (RPE) was lower suggesting a beneficial psychological effect [13].
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