Humberto Nicastro, PhD, Laboratory of Applied Nutrition and Metabolism, School of Physical Education and Sports, University of São Paulo, Brazil.
“Oxidative stress occurs when there is an imbalance in the human body homeostasis, i.e., the production of pro-oxidant molecules becomes excessive and the cellular antioxidant mechanisms cannot neutralize these radicals. Excessive production of free radicals can be triggered by several endogenous and exogenous factors. Among them, exhaustive physical exercise can be considered a strong exogenous trigger. Regular exercise induces several adaptations in cardiovascular, skeletal muscle and respiratory systems, providing positive results for the prevention and treatment of metabolic diseases. However, despite the undeniable health benefits, exercise may increase mitochondrial formation of reactive oxygen species which may cause cellular damage. When produced in excess, free radicals may cause cellular oxidation, damage in the DNA structure, aging and a variety of diseases, impair skeletal muscle function and pain and thereby affect exercise performance. In an attempt to minimize the effects of oxidative stress during physical activity, many athletes and sports professionals are supplementing with antioxidant vitamins.
To evaluate the effect of antioxidant vitamin supplementation on oxidative stress in adults submitted to endurance exercise and in trained adults, the results of 12 studies published in the last years were analyzed. In general, it was observed that there are controversial results about supplementation with antioxidants, such as vitamin C, vitamin A, vitamin E, beta-carotene and combinations, during high-intensity exercise. According to two studies evaluated (1, 2), the placebo group presented significantly better physical perfor- mance, fatigue resistance and antioxidant protection when compared to the supplemented groups. The scientists suggested that exercise alone could increase the oxidative capacity of skeletal muscle and poten- tiate the action of endogenous antioxidants, which is sufficient to counteract the negative effects of oxidative stress induced by the mechanical stimuli. In addition, regular intakes of high antioxidant doses may impair exercise performance. In contrast, two other studies evaluating the effects of vitamin and mineral supple- mentation on muscle activity of athletes observed that dietary supplementation provided a slight advantage over the placebo group in maximum voluntary muscle contraction after high-intensity exercise (3, 4). Thus, the researchers considered the antioxidant supplementation as an external aid that can enhance perfor- mance. Regarding the other studies, no differences were found between the groups. It was observed that several studies did not perform dietary control of the subjects (1) or performed an inadequate control (3) to assess the possible interference of diet on the outcome. The dietary control is quite important since some vitamins and minerals may compete in terms of absorption in the gastrointestinal tract. Thus, the absence or inadequate dietary control can be considered a bias of the published studies. Dietary control was only perfor- med in one study through food records (5). However, the authors did not identify differences in physiological parameters between participants with normal diet and those using a supplement.
The differences between the results in all the studies described can also mainly be attributed to the different methodologies, conveyed vitamin dosage, study length, sample size, differences in gender, age, and sub- jects characteristics (athletes and non-athletes). These differences make it difficult to draw conclusions about the advantages and disadvantages of antioxidant vitamins supplementation to ensure better results in exer- cise. An alternative in attenuating exercise-induced oxidative stress could be a balanced diet based on foods with the recommended amounts of antioxidants in order to improve exercise performance.”
Based on: Draeger C. L. et al. Controversies of antioxidant vitamins supplementation in exercise: ergogenic or ergolytic effects in humans? J Int Soc Sports Nutr. 2014; 11(1):4.
1. Ristow M. et al. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci U S A. 2009; 106:8665–8670.
2. Gomez-Cabrera M. C. et al. Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance. Am J Clin Nutr. 2008; 87:142–149.
3. Gauche E. et al. Vitamin and mineral supplementation and neuromuscular recovery after a running race. Med Sci Sports Exerc. 2006; 38:2110–2117.
4. DLouis J. et al. Vitamin and mineral supplementation effect on muscular activity and cycling efficiency in master athletes. Appl Physiol Nutr Metab. 2010; 35:251–260.
5. Bloomer R. J. et al. Prior exercise and antioxidant supplementation: effect on oxidative stress and muscle injury. J Int Soc Sports Nutr. 2007; 4:9.