Numerous conditions are thought to induce increased levels of oxidative stress in humans, including excessive exposure to sunlight, heavy metals, cigarette smoke, alcohol, and air pollution. Assays measuring putative biomarkers of oxidative damage in cell cultures, experimental animals, and humans support the concept that these conditions can result in increased oxidative stress. Even lifestyle habits that are viewed as "positive," such as exercise, have been shown to be associated with an increased risk for oxidative stress and tissue damage. For many of the disease states described above, there is evidence that antioxidant supplements may provide some protection with respect to disease progression. However, to a significant extent, the antioxidant supplements in these cases may often be viewed as a means of correcting disease-induced deficiencies of select nutrients. Less clear is whether the provision of antioxidant supplements will also provide protection to healthy well-nourished subjects engaged in activities such as modest exercise. In this talk, the effect of select antioxidant supplements on exercise-induced tissue oxidative damage is reviewed. Evaluation of the putative value of selenium and other essential mineral supplements is also emphasized.

During the last decade there has been increasing interest in the idea that individuals engaged in strenuous exercise may have an increased need for several essential minerals. This concept has resulted in the widespread perception that mineral supplements may be advantageous to this population group. The concept is based on two perceptions: (1) Individuals engaged in strenuous exercise have a higher requirement for some minerals compared with sedentary individuals because of increased rates of urinary and sweat losses of select minerals and (2) the perceived inadequate intake of these minerals results in a reduced performance ofthe individual and/or an Impairment/delay in his/her ability to recover from injury.

With respect to selenium, a limited literature suggests that chronic exercise can influence selenium metabolism. In an early study, Consolazio et al. reported that sweat losses of selenium could exceed 300 ug/day in individuals who exercised rigorously.¹ However, given the fact that typical dietary selenium intake is often less than lOO ug/day, this value for sweat loss seems excessive. Sleigh reported that plasma selenium concentration decreased in men who were engaged in a 5-day rigorous training program, despite "adequate" dietary selenium intake.² Singh and her colleagues suggested that this decrease in plasma selenium is hi part due to a shift in selenium from the plasma pool to tissues which required it for antioxidant protection-a suggestion that would be consistent with the increased oxidative stress that can be associated with exercise.^3,6 Consistent with their suggestion, several investigators have reported a rise in muscle and/or blood glutathione peroxidase (GSHPx) activity following exercise training.^7,8