A previous study showed that supplementing vitamins C and E interfered with strength-training gains. The same research group showed that the vitamins also hampered adaptations to endurance training. The study, which was led by Gøran Paulsen from the Norwegian School of Sports Scientists, concluded that high doses of vitamins C and E (1,000 milligrams per day for C and 235 milligrams per day for E) interfered with training-induced changes in mitochondrial proteins. The mitochondria are the powerhouses of the cells and the centers for energy metabolism. The vitamins did not interfere with maximal oxygen consumption or running performance.
Vitamins C and E are powerful antioxidants that reduce free radicals— highly reactive chemicals produced naturally during metabolism. Excessive levels have been linked to cell damage, suppression of the immune system and premature death. However, these chemicals also promote adaptation to exercise stress. Some oxidative stress is good, while excessive oxidative stress is harmful. (Journal of Physiology, 592: 1887-1901, 2014)