Researchers in Germany reporting in an online edition of the Proceedings of the National Academy of Sciences (PNAS) this week found that antioxidant supplements prevented some blood glucose benefits of exercise.1As the article states, and as we've posted previously:
"Physical exercise has been shown to be effective in preventing type 2 diabetes in high risk individuals and may be even more effective than the most widely used anti-diabetic drug, metformin."How does the presence of antioxidants curtail this?
During exercise our muscles produce free radicals, or reactive oxygen species (ROS). These free radicals can be beneficial - they act as signals to produce more mitochondria (energy-producing factories inside cells), and to produce more endogenous (made by our body) antioxidants. Supplemented antioxidants, such as vitamins C and E, can prevent this signaling:
"Taken together, physical exercise induces numerous molecular regulators of insulin sensitivity and antioxidant defense, most of which are almost completely inhibited by antioxidant pretreatment in healthy young men."In this study, 40 healthy men underwent physical training, 5 days a week for 4 weeks. Half of the men received 1000 mg vitamin C and 400 IU vitamin E daily along with the taining. Researchers found:
"Exercise increased parameters of insulin sensitivity only in the absence of antioxidants in both previously untrained and pretrained individuals."Another recent study produced similar findings. In the January 2008 issue of the American Journal of Clinical Nutrition, healthy men were given 1000 mg of vitamin C or placebo, then exercised for 8 weeks. Men who took vitamin C experienced reduced endurance, reduced mitochondria production, and reduced levels of endogenous antioxidants, compared to those who didn't supplement.2
2 Oral Administration Of Vitamin C Decreases Muscle Mitochondrial Biogenesis And Hampers Training-Induced Adaptations In Endurance Performance, AJCN, January 2008.
