Increase in selenium requirements with physical activity loads in well-trained athletes is not linear.

Selenium requirements in athletes are supposed to be increased with energy expenditure (EE) to preserve selenium status and an optimal antioxidant balance. The question of whether selenium intakes are related to EE and whether plasma selenium status induces up-regulation in erythrocyte endogenous antioxidant defense and decreases plasma oxidative damage markers in athletes was addressed. 118 well-trained athletes completed 7 d food and activities records in a cross-sectional study. Blood was sampled on day 8. Among the athletes, 23% of the males and 66% of the females had selenium intakes below two-third of the French RDA. Plasma selenium concentrations in most of less trained athletes were lower than the postulated concentration to be required to maximize erythrocyte GSH-Px activity. Athletes with the highest daily EE had the highest selenium intakes, percentage of vegetal protein intakes and plasma selenium concentrations. Only 2.6% of the athletes exhibited low plasma selenium concentrations (< 0.75 micromol/l). The relation between plasma selenium and EE was polynomial (r = 0.50; P < 0.005). Erythrocyte GSH-Px activity in athletes was not linked to selenium status. Selenium requirements are increased in athletes without being linearly related to EE.

Antioxidant vitamin status in high exposure to oxidative stress in competitive athletes.

We conducted a cross-sectional study in 118 well-trained athletes to investigate 'high exposure' to sub-deficient antioxidant status, and consequently to oxidative damage, in relation to estimated daily energy expenditure (EE) and dietary antioxidant intake. Subjects completed 7 d food and activity records. Blood samples were obtained on day 8. Of the athletes 81, 60 and 43% had intakes of vitamins E, C and beta-carotene below two-thirds of the French RDA respectively, which is adjusted for EE (FRDAa). The deficit in vitamin E intake was positively correlated with EE (r 0.51, P<0.0001). All the athletes had normal plasma vitamins E and C and 14% had marginal plasma beta-carotene. Plasma thiobarbituric acid-reactive substances (TBARS) did not increase with increased EE. As evidenced by ANOVA, EE-induced vitamin C intakes increased and consequently led to increased plasma ascorbic acid concentrations. In male athletes, plasma total carotenoids were negatively correlated with plasma TBARS concentrations (r -0.31, P<0.006). The relationship between vitamin C intakes and plasma concentrations was logarithmic (r 0.59, P< 0.0001). To summarize, it is not clear whether vitamin E requirements are overestimated with reference to EE in the FRDAa. Daily requirements for vitamin C do not exceed 200 mg. Our present results could be interpreted as meaning that carotenoids play a protective role as exogenous antioxidants. Carotenoid intakes in athletes must be considered carefully.

Antioxidant supplementation preserves antioxidant response in physical training and low antioxidant intake.

The present controlled-training double-blind study (supplemented (S) group, n 7; placebo (P) group, n 10) was designed to investigate whether an antioxidant mixture (Se 150 microg, retinyl acetate mg, ascorbic acid 120 mg, alpha-tocopheryl succinate 20 mg) would allow overloaded triathletes to avoid adaptation failure in the antioxidant system [corrected]. Dietary intakes were recorded. The supplement of Se, and vitamins A and E provided 100 % of the French RDA. Four weeks of overloaded training (OT) followed 4 weeks of normal training (NT). After NT and OT, biological studies were conducted at rest and after a duathlon test (run 5 km, cycle 20 km, run 5 km). During the 4-week period of NT, blood levels of GSH levels increased in response to supplementation (P<0.05) and remained elevated during OT. Plasma glutathione peroxidase activity was significantly higher in the S group in all situations after NT and OT (P<0.01). The S group had increased erythrocyte Cu,Zn-superoxide dismutase activity in response to OT (P<0.05). Supplementation significantly reduced (P<0.05) the magnitude in duathlon-induced creatine kinase isoenzyme MB mass increase, which tended to be higher with OT (P=0.09). We conclude that the antioxidant mixture helped to preserve the antioxidant system during an OT-induced stress in subjects with initially low antioxidant intakes. Effects of supplementation during NT and/or OT are shown mostly by the alleviated muscle damage. The effects of the antioxidant mixture were observed for doses that can be provided by a diversified and well-balanced diet. The maintenance of normal nutritional status with regard to the antioxidant intake (Se, vitamins C and E) plays a key role in antioxidant adaptive effects during NT and OT.

Overloaded training increases exercise-induced oxidative stress and damage.

We hypothesized that overloaded training (OT) in triathlon would induce oxidative stress and damage on muscle and DNA. Nine male triathletes and 6 male sedentary subjects participated in this study. Before and after a 4-week OT, triathletes exercised for a duathlon. Blood ratio of reduced vs. oxidized glutathione (GSH/GSSG), plasma thiobarbituric acid reactive substances (TBARS), leukocyte DNA damage, creatine kinase (CK), and CK-MB mass in plasma, erythrocyte superoxide dismutase (SOD) activity, erythrocyte and plasma glutathione peroxidase (GSH-Px) activities, and plasma total antioxidant status (TAS) were measured before and after OT in pre- and postexercise situations. Triathletes were overloaded in response to OT. In rest conditions, OT induced plasma GSH-Px activity increase and plasma TAS decrease (both p < 0.05). In exercise conditions, OT resulted in higher exercise-induced variations of blood GSH/GSSG ratio, TBARS level (both p < 0.05), and CK-MB mass (p < 0.01) in plasma; and decreased TAS response (p < 0.05). OT could compromise the antioxidant defense mechanism with respect to exercise-induced response. The resulting increased exercise-induced oxidative stress and further cellular susceptibility to damage needs more study.

Antioxidant supplementation and tapering exercise improve exercise-induced antioxidant response.

OBJECTIVE AND METHODS: The present controlled-training, double-blind study (supplemented, n = 7; placebo, n = 9) investigated whether taper training (TT) and antioxidant supplementation, i.e., 150 micro g of selenium, 2000 IU of retinol, 120 mg of ascorbic acid and 30 IU of alpha-tocopherol, modulates antioxidant potential, redox status and oxidative damage occurrence both at rest and in response to exercise. Two weeks of TT followed four weeks of overloaded training. Dietary intakes were recorded. Before and after TT, triathletes did a duathlon consisting of 5-km run, 20-km bike and 5-km run. Biological studies were conducted at rest and after exercise. RESULTS: Whatever the nutritional status, TT induced a decrease in resting blood reduced glutathione (GSH) concentration (p < 0.001), erythrocyte superoxide dismutase (SOD) activity (p < 0.0001) and plasma total antioxidant status (TAS) (p < 0.05). Only in the supplemented group (Su) with TT, did plasma glutathione peroxidase (GSH-Px) activity decrease (p < 0.05) and CD4(+) cell concentration increase (p < 0.05). However, antioxidant supplementation increased plasma TAS increase in response to exercise and TT (p < 0.05). After exercise, TT also induced a lower decrease in blood reduced and oxidized (GSSG) glutathione (p < 0.01) in both groups, but TT had no effect on lipoperoxidation as estimated by plasma thiobarbituric reactive substances or on muscular damage occurrence estimated by plasma creatine kinase isoenzyme MB mass. CONCLUSION: During TT, antioxidant supplementation at nutritional doses reinforces antioxidant status response to exercise, with an effect on exercise-induced oxidative stress, and no effect on oxidative damage.