Muscles gain less endurance with the same amount of training when supplemented with vitamin C, so athletes may be better off with both less efforts and less vitamins. This tip, based upon new research done in Spain, seems to be badly needed given all the marketing claims I have found, googling for vitamin supplements and training.
Two things are for sure. Training increases the so-called oxidative stress by formation of free radicals. Vitamin C, on the other hand, acts against oxidative stress. Therefore, it has been recommended for all those who perform heavy workouts.
But there is a serious drawback in this strategy because vitamin C supplements hamper the endurance training effect of exercise. In a double-blind randomized study, fourteen young men have been trained for eight weeks in Valencia, Spain. Five of the men have received a vitamin C supplement, the others only a placebo. With the same amount of training, the supplemented men gained less endurance than those taking placebo. In addition, a similar experiment has been undertaken with rats where the muscles could be analyzed after the training. It came out that vitamin C hampers the generation of mitochondria in the muscle cells. Mitochondria are the "power plants" of the cells, and the number of mitochondria in a muscle cell is a measure for its endurance capacity.
Conclusion 1: Vitamin C may help to reduce oxidative stress caused by training, but for gaining the same training effect as before, a more intensive training may be needed, causing more stress. In the light of this study, it seems to be better to leave the vitamins pills aside and take training a bit easier if done for better health.
Conclusion 2: If want to win a competition and use vitamin C against catching a flu in these days, you must face the fact that you'll need more training and a longer recovery than without the vitamin supplement.
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