Conclusions that supplements of vitamins C and E may blunt the positive effects of exercise are a "gross over extrapolation of the experimental findings", says a nutrition expert.

German researchers have reported that antioxidant vitamins C and E may blunt the positive effects of exercise, with respect to insulin sensitivity. Findings were published in the Proceedings of the National Academy of Sciences.

Dr Rob Childs, nutritional biochemist with the British consultancy agency Alimentarius, told NutraIngredients.com that the study “forms part of popular trend claiming that antioxidants attenuate the adaptive responses to exercise”.

“The benefits provided by antioxidant supplementation provide key drivers for their use by exercising populations.”
Dr Rob Childs, Alimentarius

The German study used a combination of 1,000 mg per day of vitamin C and 400 IU per day of vitamin E, and investigated how insulin sensitivity was affected following 85 minutes of exercise five days per week for four weeks. Participants were both trained and untrained.

Responding to the findings, Dr Childs said: “Studies dating back to the 1980s have shown that antioxidants reduce muscle damage, while more recent investigations demonstrate that they can also improve both ventilatory and exercise performance. Such effects are of particular relevance to exercising populations.”

Commenting on the design of the study, Dr Childs said it was unclear if the subjects encountered the same absolute level of muscle fatigue during exercise in the supplement and control conditions and hence stimulus for antioxidant up-regulation. “Because of this, the reported ‘prevention of the ‘health promoting effects of antioxidants’ may be nothing more than an experimental artefact,” he said.

In addition, Dr Childs said that comments by the authors that antioxidants may block many of the beneficial effects of exercise were a “gross over extrapolation of the experimental findings on two levels”.

“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.

“The benefits provided by antioxidant supplementation on these parameters provide key drivers for their use by exercising populations,” said Dr Childs.

Adding to the debate, Dr Elizabeth Weichselbaum, nutrition scientist from the British Nutrition Foundation, said: “This study shows that just because something is good for you, it does not mean that more of it is better! Vitamins C and E are antioxidants naturally occurring in many foods, mainly fruits and vegetables (vitamin C), and vegetable oils (vitamin E).

“Antioxidants protect the cells in your body from damage and therefore help to reduce the risk of certain diseases such as cancer. But you should not consume high doses on a regular basis as this can have negative effects on the body.

“If you stick to a healthy and varied diet, you generally get enough of the nutrients you need and you don’t run the risk of consuming large amounts that may be harmful. Plus, if you eat plenty of fruits and vegetables you get a whole package of nutrients that are good for you and help you stay fit and healthy,” she said.