Iron, zinc and magnesium nutrition and athletic performance.

During the last decade there has been considerable interest in the idea that dietary trace elements supplementation can result in an improvement in athletic performance. The current paper discusses this idea as it relates to 3 elements: iron, zinc and magnesium. Emphasis has been placed on examining the implicit assumptions underlying the idea that mineral supplements help the athlete. These assumptions include the beliefs that the athlete has a higher than normal requirement for minerals; that the athlete consumes a diet inadequate in these minerals; and that a marginal deficiency of these elements has a direct effect on athletic performance. Evidence is presented that both iron deficiency and magnesium deficiency can result in a significant reduction in exercise performance; however, the biochemical lesions underlying the reductions in exercise performance have not been identified. There is evidence that dietary magnesium intake may be suboptimal in some individuals, thus dietary supplementation of this element may be useful in some population groups. Excessive magnesium supplementation is not thought to be a serious health problem. Similar to magnesium dietary iron supplements can improve athletic performance in individuals severely deficient in this element. However, few studies have documented a need for iron supplements in healthy athletes. If iron supplements are used, it is important that the level of supplementation is not excessive, as excess iron in the diet can result in an induced zinc deficiency. In marked contrast to iron and magnesium, there is little evidence for the idea that zinc deficiency influences exercise performance in humans. Despite this fact, zinc supplements have been widely advocated for the athlete, as it is known that intense exercise can result in changes in zinc metabolism. If zinc supplements are used, it is important that they are not excessive, as excess zinc in the diet can result in a secondary copper deficiency.