Why such a question, will you say … Because it is at the heart of a nutritional debate. When we talk about the term oxidative stress, we often think of its deleterious effects. The idea of resorting to antioxidant supplementation, as an athlete subjected to intense metabolic activity, therefore appears logically. Yes, but.
Nature is still well done
Oxidative stress – or oxidative stress – is a physiological process essential to life. When you breathe deeply, the inspired air will oxygenate each of your cells to reach the mitochondria, your energy plants. Particularly abundant in muscle, they will make the energy you need from sugars (glucose), fats (fatty acids) and oxygen through a series of particularly complex chain reactions. However, a small part of the oxygen consumed, about 2% (1), will form particularly unstable molecules, free radicals. These are chemical species with an unpaired electron, said to be single, giving them a very unstable character with respect to surrounding molecules. It’s a bit like the hot potato game:
Fortunately, nature is still well planned, it does nothing to chance. If this mechanism exists, it is indeed useful. And indeed, oxidative stress is a vital mechanism for life. The cells of the immune system will for example use it to destroy the pathogenic molecules, as well as the inflammatory mechanisms and the detoxification of toxic molecules by the liver depend on the existence of this oxidative stress. So all is well … As long as this oxidative stress remains controlled by the cells of the body.
It’s all about balance
Si ce stress oxydant se propage de manière incontrôlée, il va alors s’attaquer aux différentes composantes cellulaires : aux glucides (mécanisme dit de glycation), aux lipides (lipopéroxydation) et aux protéines, accélérant ainsi leur vieillissement et leur perte de fonctionnalité. Même le cœur de notre information génétique n’est pas épargné, le stress oxydant pouvant aller jusqu’à casser les brins de la double hélice d’ADN, représentant d’ailleurs un mécanisme initiateur de la formation de cellules malignes, donc de la cancérisation. De plus un excès de radicaux libres peut altérer l’efficacité des défenses immunitaires à l’exercice (2). Pour éviter que la cellule « prenne feu », celle-ci dispose heureusement de pompiers et peut faire appel si besoin à des brigades extérieures. La défense antioxydante endogène correspond aux pompiers internes et la défense exogène aux brigades extérieures. Nos pompiers internes sont regroupés en deux principales brigades, les complexes enzymatiques plus connus sous les termes de Glutathion Peroxydase (GPx) et de Super Oxyde Dismutase (SOD), présents dans les mitochondries et le cytosol, nécessitant des statuts optimaux en Sélénium pour les premières ; en Zinc, Cuivre et Manganèse pour les secondes. Les brigades extérieures sont les vitamines et les végétaux apportés par l’alimentation au quotidien : béta-carotène ou provitamine A, vitamines C et E, polyphénols, flavonoïdes, acides phénoliques, etc. Ainsi, si vous disposez d’un statut nutritionnel optimal, vous permettez à vos cellules de contrôler ce stress oxydant et ainsi de favoriser votre adaptation cellulaire à l’effort.
The very principle of performance optimization is based on the adaptation of cells to the effort. The repetition of this one generates a local and punctual inflammation essential to the setting up of the mechanisms of cell repair. Indeed, during endurance sports, especially in the eccentric phase, alterations of the cellular structure can appear both for mechanical causes (breaks in elements of the cellular architecture) and because of the oxidative stress increased by the consumption of ‘oxygen. This increased production can however, under resting conditions, be considered as physiologically beneficial: free radicals stimulate the production of cytokines, leading to a cascade of inflammatory reactions. Immune cells are then recruited to the site of inflammation to produce free radicals that will “cleanse” and repair tissue damage (3). However, it is easy to understand that excessive or uncontrolled production of free radicals can then “pack the system” because of an increased secretion of mediators of inflammation causing an alteration of cellular structures (readmy article on the control of inflammation ). Moreover, the increased exposure of the regular athlete to oxidative stress is at the origin of a better efficiency and a better inducibility of the enzymes of protection against the oxidative stress in particular according to the VO2max (1), except at the intestinal level (4), but that’s another story.
In synthesis, sports practice induces an increased consumption of oxygen at the origin of an increased oxidative stress, necessary for the improvement of the performances via the cellular adaptation to the effort. To prevent this oxidative stress becoming major and uncontrolled, then synonymous with mismatch to the effort or overtraining or deterioration of health, the proper functioning of antioxidant protective enzymes and optimal status of antioxidants are indispensable elements. We then understand the potential challenge of using antioxidant supplementation to allow cells to better protect themselves. But one can also wonder about the possible deleterious effects of this supplementation vis-à-vis the mechanisms of cellular adaptation to the effort. Once again, everything is a question of balance.
Should we supplement with antioxidants?
Just go to a line of dietary products and dietary supplements to understand the craze for antioxidant supplementation, this seductive term so blithely used by the brands of products. According to a study published in 2007, up to 85% of athletes would have recourse to nutritional self-supplementation (5). However, the scientific literature indicates that antioxidant supplementation may in some cases have deleterious effects on training adaptations, both in endurance and strength adaptations (6, 7). For example, a moderate production of free radicals is necessary to increase the number of mitochondria, but vitamin C or E supplementation may be detrimental to these adaptations (9-11). Michael Reid’s team in Texas has demonstrated an optimization of the contractile function of muscles via free radicals (8). IIt then becomes necessary to distinguish the potential effects of an antioxidant intake on the acute muscle production of free radicals, which appear to be deleterious to the adaptation process, in contrast to a favorable effect in case of insufficient antioxidant protection. in the face of increased and generalized oxidative stress, at the origin of accelerated cellular aging . It has been shown that chronic and increased production of free radicals also adversely affects muscle adaptations induced by contractile activity in aging (12). Otherwise,in high-level athletes or performing a large training volume, a chronic state of oxidative stress could be the cause of a lower recovery between each training session, due to a lower capacity of the muscle cell to return to normal homeostasis (13). In this case, supporting antioxidant defenses with moderate supplementation with antioxidants may be warranted.
Thus, the question of the interest of an antioxidant supplementation in the athlete seems to make sense, not according to the timing of the taking and especially during the recovery, but according to the general antioxidant status of the athlete . An optimal status in antioxidant micronutrients (Zinc, Selenium, Copper, Manganese, vitamins A, C, E, polyphenols and other plant extracts, glutathione, Coenzyme Q10) represents one of the nutritional pillars of the athlete, through the consumption of rich foods in these nutrients. The use of supplementation, in case of increased and chronic oxidative stress, increased exposure to factors favoring the production of free radicals (pollution, tobacco, UV, etc.) or identified deficits, will then find all its legitimacy. Especially in athletes under heavy training load or lacking sufficient recovery phases to allow the cell to regain basal homeostasis. Conversely, wanting to “extinguish” the radical background noise essential to the processes of cellular adaptation to stress, particularly during the recovery phase, does not only seem to be not beneficial, but turns out to be quite the opposite. deleterious mechanisms.