There seems to be a lot of confusion about the use of antioxidants. Some swear by it and supplement companies seem to love it. Antioxidants are everywhere: in foods, in supplements, in skincare products, shampoos etc. They are often associated with health. On the other hand, there are reports that antioxidants can impair training adaptation. Recently I was in Keystone Colorado where one of the worlds experts, Professor Scott Powers from the University of Florida at Gainesville addressed exactly this issue. Although he acknowledging that there is still a lot we don’t know, he had a wonderful way of removing confusion. Here I will try to discuss his message (and I hope that I am doing your messages justice Scott!).
First, we need to understand what antioxidants are. Oxidation is the removal of electrons (The opposite of reductions which add electrons). We often think of antioxidants as things that scavenge free radicals. Free radicals are molecules that possess an unpaired electron in their outer orbital. They are highly reactive. There are also reactive species. These are molecules that promote oxidation (i.e. Oxidants) and these can be radicals or non-radicals. Anti-oxidants are molecules that prevent oxidation. The radicals are a highly reactive chemical species capable of damaging muscle fiber components such as proteins and lipids.
Because of the highly reactive nature of free radicals, they are very difficult to measure. They react very quickly and electrons move from one molecule to the next, making it almost impossible to measure them. We therefore measure some of the biomarkers of oxidative stress top get an indication. We measure lipids, protein or DNA that has been oxidized. The assumption is that the biomarker we measure is a reflection of oxidative stress, and this is not always the case.
Physical exercise increases the cellular production of reactive oxygen species (ROS) in muscle, liver, and other organs. In contrast to common belief, there is NO evidence that the source is increased mitochondrial production. Scott was quick to point out that the simplistic reasoning of exercise requires more oxygen, more oxidation at the site where oxidation takes place (mitochondria) cannot be backed by evidence. Originally, ROS were considered detrimental and thus as a likely cause of cell damage associated with exhaustion. This view is still portrayed a lot in the popular press. In the past decade, evidence showing that ROS act as signals that are important (amongst other functions) for training adaptation. ROS may thus be seen as positive not negative!
Of course excessive oxidation needs to be prevented and the body has several mechanisms for this. There are numerous enzymes in the body with an antioxidative capacity. These enzymes are the most important defence system.
Dr Powers pointed out that dietary antioxidants, when they get to the site of oxidation can be used as an antioxidant only once. They are used up and thus we need large amounts of exogenous antioxidants for these to be effective and these antioxidants must be at the specific site where oxidation is taking place. The antioxidant enzymes in our bodies can be used over and over again and these enzymes are upregulated (increase) with training. Many studies have shown thattraining increases the expression of classical antioxidant enzymes such as superoxide dismutase and glutathione peroxidase. So the more we exercise, the more enzymes we will make and the more protected we will be, independent of antioxidant intake.
Several studies have demonstrated now that high dose antioxidants are actually removing the signal for raining adaptation and the raining adaptations are impaired. Thus, the idea that antioxidant supplementation in exercise should always be recommended is incorrect.
Although the theoretical background may be sound, there is no scientific evidence to recommend increased quantities of antioxidants to physically active people, exceeding the amount provided by healthy balanced nutrition.
1. There is no evidence that physical training requires antioxidant supplementation above the normal antioxidants from a well-balanced diet.
2. Dietary supplementation of antioxidants can play a role when food intake is restricted or where a dietary deficiency of antioxidants is clinically determined (Rare!)
3. There is NO evidence that anti-oxidants have a positive effect on recovery
4. There is little or no evidence that anti-oxidants improve performance
5. There is emerging evidence that antioxidant supplementation in high doses can reduce training adaptation.
The practical implications are pretty straight forward
There is no need for antioxidant supplementation if you have a diet with varied fruits and vegetables, this is a sensible means of obtaining a balance of exogenous antioxidants. Studies have shown no advantages of antioxidant supplementation and high doses of antioxidants can be detrimental and should be avoided.
Further reading
Gomez-Cabrera, M.C., E. Domenech, M. Romagnoli, A. Arduini, C. Borras, F.V. Pallardo, J. Sastre, and J. Vina (2008). Oral administration of vitamin C decreases muscle mitochondrial
biogenesis and hampers training-induced adaptations in endurance performance. Am. J. Clin. Nutr. 87:142-149.
König D, Wagner KH, Elmadfa I, Berg A. Exercise and oxidative stress: significance of antioxidants with reference to inflammatory, muscular, and systemic stress. Exerc Immunol Rev. 7:108-33, 2001.
Powers, S.K., and M.J. Jackson (2008). Exercise-induced oxidative stress: cellular mechanisms and impact on muscle force production. Physiol. Rev. 88:1243-1276.
Powers, S.K., L.L. Ji, A.N. Kavazis, and M.J. Jackson (2011). Reactive oxygen species: impact on skeletal muscle. Compr. Physiol. 1:941-969.