Effect of fatiguing bicycle exercise on thyroid hormone and testosterone levels in sedentary males supplemented with oral zinc

Objective: The aim of this study was to determine how exercise affects thyroid hormones and testosterone levels in sedentary men receiving oral zinc for 4 weeks. Methods: The study included 10 volunteers (mean age, 19.47±1.7 years) who did not exercise. All subjects received supplements of oral zinc sulfate (3mg/kg/day) for 4 weeks and their normal diets. The thyroid hormone and testosterone levels of all subjects were determined at rest and after bicycle exercise before and after zinc supplementation. Results: TT3, TT4, FT3, and total and free testosterone levels decreased after exercise compared to resting levels before supplementation (p<0.01). Both the resting and fatigue hormone values were higher after 4 weeks of supplementation than the resting and fatigue values before supplementation (p<0.05). Conclusion: The results indicate that exercise decreases thyroid hormones and testosterone in sedentary men; however, zinc supplementation prevents this decrease. Administration of a physiologic dose of zinc can be beneficial to performance. © 2007 Neuroendocrinology Letters.