Scientists from the Norwegian School of Sport Sciences report that vitamin C and E supplements can interfere with cellular signaling and handicap the development of muscular endurance. Their report, published in The Journal of Physiology, hints that the blunting effect may be caused by a reduction of oxidative stress.
“Our results show that vitamin C and E supplements blunted the endurance training-induced increase of mitochondrial proteins, which are needed to improve muscular endurance,” said study leader Goran Paulsen. “As vitamin C and E supplements are widely used, understanding if they interfere with cellular and physiological adaptations to exercise is of interest to people exercising for health purposes as well as to athletes.”
In the 11-week trial, 54 young, healthy men and women were randomly allocated to receive either 1000mg vitamin C and 235mg vitamin E (consistent with amounts found in common supplements), or a placebo. Neither the subjects nor the investigators knew which participant received the vitamins or placebos.
The participants then completed an endurance training program (primarily running) of three to four sessions per week. Fitness tests, blood samples, and muscle biopsies were taken before and after the intervention.
Paulsen said that while the supplements did not affect maximal oxygen uptake or the results of a 20 meter shuttle test, the results showed that markers for the production of new muscle mitochondria – the power supply for cells – increased only in the group that did not take supplements.
“Our results indicate that high dosages of vitamin C and E – as commonly found in supplements – should be used with caution, especially if you are undertaking endurance training,” warned Paulsen.
Previous studies have shown that exercising increases muscle oxidant production, which is a part of the signaling process that leads to muscle adaption. Paulsen thinks it is possible that high doses of vitamins C and E act as antioxidants and take away some of this oxidative stress, hence blocking muscular endurance development.
“Future studies are needed to determine the underlying mechanisms of these results, but we assume that the vitamins interfered with cellular signaling and blunted expression of certain genes,” concluded Paulsen.
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