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General Health - Vitamin-exercise study questioned

By Holly Taylor BSc (Hons) DipCNM MBANT

The BBC recently ran a report on some German research that suggested vitamins C and E might blunt the positive effects of exercise, but the results of this study may not be as clear cut as they seem. 

It is well established that exercise promotes health and can reduce the risk of developing chronic diseases, such as heart problems and type II diabetes. However, exercise also increases the body’s production of harmful free radicals. It is thought that antioxidant vitamins may be able to help counter damage to the body’s tissues by mopping up these excess free radicals. 

However, Dr Michael Ristow and his team state their research shows free radicals formed in exercise have a positive effect on the body, by increasing its sensitivity to insulin - something that is lost in type II diabetes. An effect they claim is blocked by taking antioxidants. 

The study was a small, double-blind, placebo-controlled study of 40 healthy young men put on an exercise programme of 85 minutes, five days a week, for four weeks. Half the group got antioxidants in the form of 500mg vitamin C twice daily and 400iu d-alpha-tocopherol (one isomer of vitamin E) once daily; the other 20 got identical dummy pills. The outcome of the study was that markers of insulin sensitivity were increased significantly in the group that did not take the antioxidant but not in the group who took the antioxidant. From this the authors concluded, as the title indicates, that “antioxidants prevent health-promoting effects of physical exercise in humans”.

However, to make sweeping generalisations based on such a small, narrow study is hardly scientific. The title suggests that all antioxidants, not just vitamins C and E, have such an effect but this is simply not the case. 

To quote Dr. Rob Childs, nutritional biochemist for the Cervelo Pro Cycling Test Team, who was interviewed by the online publication NutraIngredients: “Firstly, the study only investigated the effects of two free radical scavengers in a highly complex system involving hundreds of antioxidant compounds. This makes it inappropriate to extrapolate the study findings to other antioxidants. Secondly, the potential advantages provided by antioxidant supplementation for attenuating muscle soreness and structural damage, while enhancing muscle recovery and performance, were not assessed.” 

It addition, the results of the study were supposed to be based on muscle biopsies, but the authors’ report states that some of the data was missing for a number of the study subjects. For example, the biopsies that were supposed to be taken from each subject at the beginning of the exercise period were actually only taken from five people in the vitamin group, and four in the dummy pill group. Yet the authors still considered their results valid! 

As well as possibly being flawed, the results are contradictory to literally hundreds of other larger studies, which show that long term exposure to excess free radicals can actually decrease insulin sensitivity, while antioxidants help to protect against diseases characterised by poor insulin sensitivity, such as diabetes.

By their own admission, the authors suggested their results are a departure from what has been found in previous studies. They also note that the oxidative stress induced by exercise occurred in short bursts, as opposed to chronic oxidative stress that is more commonly experienced. 

Overall, it seems that the study was poorly designed, inadequately sized and too short to be of any significance. It paid little regard to the synergistic effects of antioxidants and focused on a narrow group of subjects and a very specific outcome. It would be madness to consider this data as noteworthy in the face of years of solid research suggesting the opposite. 

Article References

Original Study: Ristow M, Zarse K, Oberbach A, et al. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci USA 2009 May 11 [Epub ahead of print]

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