Selenium and Other Antioxidant Issues

Recently an increasing amount of attention has been given to the concept that
oxidative and reactive oxygen-initiated processes may play key roles in the
initiation and/or progression of several chronic health disorders, including
atherosclerosis, certain cancers, cataractogenesis, and rheumatoid arthritis.
Indirect support for this concept is robust and evidenced by an extensive epidemiological literature demonstrating inverse correlations of varying magnitudes between the consumption of foods rich in antioxidant composition and certain chronic diseases.


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


Based on the above idea, a number of investigators have tested the hypothesis
that selenium supplements may be benef~cial in the attenuation of exercise-
induced oxidative stress. Olinescu et al.9 and Tessier et al.10,11 have reported
that selenium supplementation can be associated with a reduction in oxidative
stress in athletes. Both groups suggested that the reduction in oxidative
stress was secondary to a supplement-induced increase in blood and muscle
GSHPx activity. Although the above studies are intriguing, it is important
to note that other investigators have not been able to document an increased
need for selenium in athletes.12


It is significant to note that the increase in GSHPx activity noted following
selenium supplementation was not observed by Rokitzki et al.,13 when they provided vitamin E and C supplementation to trained athletes. Thus, the rise in GSHPx activity reported in the selenium supplementation studies may not occur if antioxidant supplements lacking selenium are provided.


Similar to the case for selenium, several investigators have suggested that
supplementation of zinc, copper, and/or magnesium may be of benefit to the
athlete with respect to the attenuation of exercise-induced tissue
oxidative damage.14 These theories will be briefly reviewed.




References


1. Consolazio et al., 1964.


2. Singh et al., 1991.


3. Ji LL. Oxidative stress during exercise: implication of antioxidant nutrients. Free Radic Biol Med 1995; 18: 1079-86.


4. Kanter MM. Free radicals, exercise, and antioxidant supplementation. J Sport Nutr 1994;4:205-20.


5. Sen CK. Oxidants and antioxidants in exercise. J Appl Physiol 1995;79:675-86.


6. Tidus PM, Houston ME. Vitamin E status and response to exercise training. Sports Med 1995;20: 12-23.


7. Leeuwenburgh C, Fiebig R. Chandwaney R. Ji LL. Aging and exercise training in skeletal muscle: responses of glutathione and antioxidant enzyme systems. Am J Physiol 1994;267 R439-45.


8. Pereira B. Costa Rosa LF, Safi DA, Medeiros MH, Curi R. Bechara EJ. Superoxide dismutase, catalase, and glutathione peroxidase activities in muscle and Iymphoid organs of sedentary and exercise-trained rats. Physiol Behav 1994;56:1095-9.


9. Olinescu R.Talaban D, Nita S. Mihaescu G. Comparative study of the presence of oxidative stress in sportsmen in competition and aged people, as well as the preventive effect of selenium administration. Rom J Int. Med 1995;33: 47-54.


10. Tessier F. Hilda H, Favier A, Marconnet P. Muscle GSHPx activity after prolonged exercise, training and selenium supplementation. Biol. Trace Elem Res 1995;47:279-85.


11. Tessier F. Margaritis I, Richard MJ, Moynot C., Marconnet P. Selenium and training effects on the glutathione system and aerobic performance. Med Sci Sports Exerc 1995;27:390-6.


12. Clarkson PM, Haymes EM. Trace mineral requirements for athletes. Int J Sports Nutr 1994;4:140-19.


13. Rokitzki L, Logemann E, Sagredos, et. Al Lipid peroxidation and antioxidative vitamins under extreme endurance stress. Acta Physiol Scand 1994; 151: 149-58.


14. Keen CL. Effects of exercise and heat on mineral metabolism and requirements. In: Marriot BM, ed. Nutritional Needs in hot environments. Washington, DC: National Academy Press, 1993. p. 1117-35.


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Avatar Written by Carl L. Keen PhD

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