A study published by Dr. Goran Paulsen in The Journal of physiology - explains that Vitamin–C and vitamin-E supplements can affect sports men and women.
A 11 weeks clinical trial was conducted on 54 young and healthy volunteers of both sexes and it was a randomized single blind placebo controlled study. These volunteers were randomly assigned in to one of the 2 groups. One group was given either vitamin-C or vitamin-E and the other group was given placebo.

Once the patient completed the endurance exercise which consistence of 3-4 sessions per week. Fitness test, blood test and muscle biopsy were taken before and after the administration of test substance. The study concluded that, there were no increase in markers for the production of new muscle mitochondria (power house of the cell) and also did not increase the maximal oxygen uptake. But study has showed improvement in the placebo group.

Dr. Paulsen says, the result indicates that high dose of vitamin-c and vitamin-E as commonly found in supplement may cause harm and one should be cautious in using it. He assumes that the probable mechanism may be the vitamins may interfere with the cellular signaling proteins or the gene expressing those protein which helps in the cellular physiological adaptation to exercise. He added that more research is required to establish this.