Combined supplementation with vitamins C and E before and during endurance training seems to have no effect on insulin-stimulated glucose uptake in skeletal muscle, according to a new Danish study.
To assess the effect of antioxidant supplementation during endurance training on insulin -stimulated glucose uptake, 21 healthy men (18-40 years of age) were randomly assigned to either an antioxidant (500 mg vitamin C and 400 IU vitamin E per day) or a placebo group which both underwent a supervised intense bicycle endurance training program, 5 times per week for 12 weeks (1). The results showed that neither plasma insulin concentrations nor insulin-stimulated glucose uptake, which increased by approximately 15% after the 12-week training period, differed between the groups. The researchers commented that the results indicate that administration of antioxidants during strenuous endurance training has no effect on the training-induced increase in insulin sensitivity in healthy individuals.
Regular physical exercise is known to promote numerous health benefits, protecting against all-cause mortality and playing a critical role in the treatment of a number of chronic diseases, such as type 2 diabetes. Similarly, endurance exercise training has been shown to improve insulin resistance in patients with type 2 diabetes and to enhance both insulin-stimulated and non- insulin mediated glucose uptake in skeletal muscle. On the other hand, endurance exercise is also associated with the increased generation of reactive oxygen and nitrogen species (RONS) by the mitochondria as by-products of oxidative metabolism. This oxidative stress could potentially be counterbalanced by administering antioxidant supplements. One hypothesis that has recently emerged is that antioxidant supplementation during endurance training may attenuate some of the beneficial effects of endurance exercise (2). The new findings do not support this hypothesis.