Zinc

Zinc helps form a large number of enzymes, many of which function in energy metabolism and in wound healing. Inadequate dietary intake of zinc causes a variety of health problems, including stunted growth, slow wound healing, and failure of the immune system.⁹⁶ Zinc also plays an important role in the removal of carbon dioxide from cells and is part of an important antioxidant enzyme called superoxide dismutase. Excessive intake can lead to anemia, vomiting, and immune system failure.

Meat, liver, eggs, and seafood are good sources of zinc. The adult RDA for zinc is 12 to 15 milligrams per day.

Zinc levels at the lower end of the normal range, or lower, have been observed in male and female endurance runners. Athletes with lower serum zinc values had lower training mileage, probably from not being able to train as hard, than those who had higher values.^97-99 Therefore, there appear to be training deficits in the small number of athletes who have poor zinc status. The effect of zinc supplementation on performance has not been extensively studied, and the level of supplementation in these studies has been extremely high (around 135 milligrams per day). Also, the athletes tested were not assessed for zinc status before the initiation of the research protocol. Nevertheless, this intake level did lead to an improvement in both muscular strength and endurance.¹⁰⁰ A recent study of elite athletes found an important positive relationship between normal zinc status and the athletes'ability to respond to the antioxidant mechanisms associated with intense exercise.¹⁰¹ Perhaps the greatest potential problem associated with inadequate zinc is in athletes who have inadequate diets and who also use sweat loss as a means of achieving desirable weight. Athletes, usually gymnasts and wrestlers, with inadequate diets and heavy sweat losses are reported to have impaired growth and zinc deficiency.¹⁰²

Athletes should be cautioned that chronically high zinc intakes have never been tested over time and may well have negative side effects. Toxicity and malabsorption of other nutrients are both likely and possible with high supplemental intake. ^103-105