Exercise may increase reactive oxygen species production, which might impair cell integrity and contractile function of muscle cells. However, little is known about the effect of regular exercise on the antioxidant status of adolescents. Purpose: This study aimed to evaluate the impact of exercise on the antioxidant status and protein modifications in adolescent athletes. Methods: In 90 athletes and 18 controls (16 ± 2 yr), exercise-related energy expenditure was calculated on the basis of a 7-d activity protocol. Antioxidant intake and plasma concentrations of a-tocopherol, carotenoids, and uric acid were analyzed. Plasma antioxidant activity was determined by Trolox equivalent (TE) antioxidant capacity and electron spin resonance spectrometry. Protein modifications were assessed with structural changes of transthyretin using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Data were analyzed by two-way ANOVA and post hoc by the Tukey-Kramer test (a = 0.05). Results: Antioxidant intake correlated with energy intake and was within the recommended daily allowance for vitamins C and E and ß-carotene. Plasma levels of neither nutritional antioxidants nor uric acid differed between the groups. TE antioxidant capacity was higher in athletes (men = 1.47 ± 0.2 mmol TE per liter, women = 1.45 ± 0.2 mmol TE per liter) compared with controls (men = 1.17 ± 0.04 mmol TE per liter, women = 1.14 ± 0.04 mmol TE per liter) and increased with exercise-related energy expenditure (P = 0.007). Transthyretin cysteinylation rate differed between the groups, with the highest rate of protein modifications in moderately active subjects (P = 0.007). Conclusions: Results suggest that if the nutritional choice of athletes is well balanced, enough antioxidants are provided to meet recommended amounts. Moreover, regular exercise increases blood antioxidant capacity in young athletes, whereas chronic exercise was not shown to promote protein modifications. Thus, in young athletes who are sufficiently supplied with antioxidants, beneficial effects of exercise on antioxidant status rather than on oxidative stress may be anticipated.
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