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Here is the abstract:
ORIGINAL RESEARCH COMMUNICATION
Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance1,2,3
Mari-Carmen Gomez-Cabrera, Elena Domenech, Marco Romagnoli, Alessandro Arduini, Consuelo Borras, Federico V Pallardo, Juan Sastre and Jose Viña
1 From the Department of Physiology, Faculty of Medicine, University of Valencia, Valencia, Spain (M-CG-C, ED, AA, FVP, JS, and JV); the Catholic University of Valencia, Valencia, Spain (CB); and the Polytechnic University of Valencia, Valencia, Spain (MR)
Background: Exercise practitioners often take vitamin C supplements because intense muscular contractile activity can result in oxidative stress, as indicated by altered muscle and blood glutathione concentrations and increases in protein, DNA, and lipid peroxidation. There is, however, considerable debate regarding the beneficial health effects of vitamin C supplementation.
Objective: This study was designed to study the effect of vitamin C on training efficiency in rats and in humans.
Design: The human study was double-blind and randomized. Fourteen men (27–36 y old) were trained for 8 wk. Five of the men were supplemented daily with an oral dose of 1 g vitamin C. In the animal study, 24 male Wistar rats were exercised under 2 different protocols for 3 and 6 wk. Twelve of the rats were treated with a daily dose of vitamin C (0.24 mg/cm2 body surface area).
Results: The administration of vitamin C significantly (P = 0.014) hampered endurance capacity. The adverse effects of vitamin C may result from its capacity to reduce the exercise-induced expression of key transcription factors involved in mitochondrial biogenesis. These factors are peroxisome proliferator–activated receptor co-activator 1, nuclear respiratory factor 1, and mitochondrial transcription factor A. Vitamin C also prevented the exercise-induced expression of cytochrome C (a marker of mitochondrial content) and of the antioxidant enzymes superoxide dismutase and glutathione peroxidase.
Conclusion: Vitamin C supplementation decreases training efficiency because it prevents some cellular adaptations to exercise.
Key Words: Free radicals • VO2max • antioxidant enzymes • antioxidant supplements • exercise • exhaustion • vitamins • gene expression • hormesis • reactive oxygen species
And here is the news release
Thursday, January 17, 2008
NEW YORK (Reuters Health) - Taking vitamin C can blunt the body's response to endurance training, a new study in humans and rats shows.
Based on the findings, "the common practice of taking vitamin C supplements during training (for both health-related and performance-related physical fitness) should be seriously questioned," principal investigator Dr. Jose Vina of the University of Valencia in Spain and colleagues conclude.
Exercisers take the antioxidant based on the assumption that it protects their muscles from the oxidative stress that results from physical exertion, Vina's group reports in the American Journal of Clinical Nutrition. However, the researchers point out, oxidative stress during exercise may actually help the body to build endurance by forcing muscles to adapt.
To investigate, Vina and his team had 14 sedentary men undergo 8 weeks of training, during which 5 of them took 1 gram of vitamin C daily. They also put 24 rats through 3- and 6-week exercise training protocols, and gave half of the animals vitamin C daily.
The men who didn't take vitamin C showed a 22-percent increase in their body's ability to take up and use oxygen during exercise, compared with just a 10.8-percent increase for the men given vitamin C. Similar results were seen for the rats.
When the animals were forced to run to the point of exhaustion after 6 weeks of endurance training, those that weren't dosed with vitamin C were able to run nearly twice as far as they had before training, while those given the vitamin only increased their distance by 25 percent. Tests on the muscle tissue of the animals found that rats that weren't given vitamin C had added more mitochondria, the "engines" within cells that convert nutrients into energy.
The findings suggest that the release of free radicals during exercise helps muscles to adapt by changing gene expression, Vina and his team note, while antioxidants such as vitamin C may interfere with this process. In fact, they add, exercise itself could act as an antioxidant by boosting the body's expression of antioxidant enzymes.
"Taking into account that a high fitness level is associated with a lower risk of premature death from any cause, the effect of vitamin C administration on endurance capacity has important implications for nutritionists, physicians, and exercise trainers and practitioners," they conclude.
SOURCE: American Journal of Clinical Nutrition, January 2008.