Exercise has many health benefits, and one of the ways it achieves this is by the oxidative stress it places on the body. Now new research has found that athletes who take high doses of antioxidant supplements can impair the training adaptations from the beneficial stress which exercise causes.
For active people, regular training is as important part of maintaining and increasing fitness. About the only real downside to regular exercise is the transient toll it takes on the body after a hard training session. The pain and soreness after training needs sufficient time to recover from before another hard session can be performed.
A very plausible theory pushed for many years is that the post-exercise oxidative stress in the body is the primary cause of the muscle damage and fatigue experienced. If you could reduce this oxidative stress, then it would allow quicker recovery, and then more time spent training. What this theory ignores though is that oxidative damage is a natural part of how the body adapts to stressful exercise, allowing the body to repair and grow stronger to allow higher levels of performance in the future.
A small scale study has previously found that trained and untrained individuals who dose up on antioxidant supplements impair important exercise training adaptations such as improved insulin sensitivity and production of oxidative stress defence proteins. Now researchers have extended this study by looking at the effect of antioxidants in trained female runners, and published their findings in the European Journal of Sports Science.
Twenty-three well trained female runners took part in three separate 3-week training blocks where they took either 1 gram of vitamin C, blackcurrant juice, or a placebo drink for each of the training blocks. Each of the dietary interventions involved drinking a similar volume of fruit drink of a total of half a litre per day split over the morning and evening.
The training performance of each runner was carefully measured at the beginning and end of each 3-week treatment period. The runners stuck to a set training schedule which allowed a more accurate assessment of any changes in performance over the training period.
The runners enjoyed favourable training performance improvements through the study, but there was evidence that those taking the vitamin C had less of an improvement of around 1% compared to those taking the placebo. When blood markers of oxidative stress were measured, some of these were found to actually be higher in those taking the vitamin C. One theory to explain the higher oxidative stress is that when high doses of antioxidants are taken, they can actually turn into pro-oxidants, doing more harm than good.
Just looking at the faster runners in the group, there was some indication that blackcurrant juice could have a small benefit in performance which wasn’t seen in the placebo or vitamin C groups. Antioxidant levels in natural juices are much lower than high dose supplements, plus also contain a whole range of other nutrients.
What it all means
This was a small scale study, with overall mixed results. The study though still supports current recommendations that athletes should avoid high dose antioxidant supplements for lack of any clear training benefit, and some evidence of a negative impact on performance.