Effect of antioxidant supplementation on insulin sensitivity in response to endurance exercise training

Abstract

production of reactive oxygen and nitrogen species (RONS) is associated with some of the beneficial adaptations to regular physical exercise, it is not established whether RONS play a role in the improved insulin-stimulated glucose uptake in skeletal muscle obtained by endurance training. To assess the effect of antioxidant supplementation during endurance training on insulin-stimulated glucose uptake, 21 young healthy (age 29 Ϯ 1 y, BMI 25 Ϯ 3 kg/m 2 ) men were randomly assigned to either an antioxidant [AO; 500 mg vitamin C and 400 IU vitamin E (␣-tocopherol) daily] or a placebo (PL) group that both underwent a supervised intense endurance-training program 5 times/wk for 12 wk. A 3-h euglycemic-hyperinsulinemic clamp, a maximal oxygen consumption (V O2max) and maximal power output (Pmax) test, and body composition measurements (fat mass, fat-free mass) were performed before and after the training. Muscle biopsies were obtained for determination of the concentration and activity of proteins regulating glucose metabolism. Although plasma levels of vitamin C (P Ͻ 0.05) and ␣-tocopherol (P Ͻ 0.05) increased markedly in the AO group, insulin-stimulated glucose uptake increased similarly in both the AO (17.2%, P Ͻ 0.05) and the PL (18.9%, P Ͻ 0.05) group in response to training. V O2max and Pmax also increased similarly in both groups (time effect, P Ͻ 0.0001 for both) as well as protein content of GLUT4, hexokinase II, and total Akt (time effect, P Յ 0.05 for all). Our results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.

Normal adaptations to exercise despite protection against oxidative stress

“…We conclude on the basis of our findings in this study and the results of the studies by Yfanti and colleagues (36,37) that, contrary to the reports by Gomez-Cabrera et al (6) and Ristow et al (23), antioxidant vitamin supplementation does not have an inhibitory effect on the adaptive responses of skeletal muscle to exercise. We also conclude that antioxidant vitamin supplementation does not lower the mitochondrial content of muscle in sedentary animals.…”

“…This is not due to a species difference, because there is extensive evidence that the skeletal muscle adaptations to exercise are similar in humans and rats (2,3,7,8,25,26,29). Furthermore, studies by Yfanti and colleagues (36,37) on the effects of supplementation with large doses of vitamins E and C have shown that antioxidant supplementation does not affect the adaptive responses of V O 2 max , muscle citrate synthase, hydroxyacyl-CoA dehydrogenase activities, or insulin action in young healthy individuals.…”

Redox Control of Skeletal Muscle Regeneration

“…Some groups have reported that antioxidant supplementation has a negative effect on training-induced adaptations and health (73,121,201,202,252,281). On the contrary, other groups reported no alterations of traininginduced performance improvements (225,357,358). These conflicting results have to be considered in the light of training status, type of exercise, and qualitative and quantitative supplementation.…”

Impact of current treatments on liver disease, glucose metabolism and cardiovascular risk in non-alcoholic fatty liver disease (NAFLD): a systematic review and meta-analysis of randomised trials

“…Although these data have not been recently confirmed [112,113], the impact of antioxidants on muscle insulin sensitivity in insulin-resistant individuals is unclear. An increased all-cause mortality has been associated with long-term administration of doses of vitamin E typically used in these trials [114]. Finally, antioxidant effectiveness in diabetic NAFLD patients, characterised by prominent systemic oxidative stress and severe liver histology, is unknown, as only 9% of enrolled patients were diabetic.…”