Physical exercise generates free radicals. These are generally considered as harmful to the cells and thus supplementation with antioxidant vitamins is recommended. However, results from a number of laboratories, including

our own, indicate that reactive oxygen species (ROS) are signals which serve to up-regulate the expression of a number of genes. Thus ROS can exert favourable effects to the cells.

Training for six weeks increased the maximal running time from 100 minutes (in untrained rats) to approximately 300 minutes (P<=0.01). This was completely prevented by a daily supplementation with vitamin C. We tested the effect of vitamin C on the mitochondriogenic pathway in cells. PGC-1 is a recently identified coactivator of nuclear receptors. It powerfully induces mRNA for respiratory factor 1 (NRF-1) and mitochondrial transcription factor A (mTFA). The proximal promoter of the mTFA gene is highly dependent on NRF-1. mTFA protein binds to sequence elements and stimulates transcription of itochondrial DNA. We found a significant increase in the expression of PGC-1 in the group of rats trained during 3 weeks. This was completely prevented by supplementation with vitamin C. Mitochondrial content is estimated by the change in content of a typical "marker enzyme" such as citrate synthase.

In our study we found a significant increase in the expression of citrate synthase in the group of rats trained during 6 weeks. This was partially prevented by supplementation with vitamin C. The common practice of taking vitamin C supplements during training should be seriously questioned.