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.
Reacting to the study, Alexander Schauss, PhD, from AIBMR Life Sciences, a nutraceutical products consultancy, told NutraIngredients.com that the title of the study (Antioxidants prevent health-promoting effects of physical exercise in humans) was misleading.
“The primary objective of this study was to study the effect of a 4-week intensive 5-days a week exercise program on insulin sensitivity. Yet the title of the paper leads one to believe otherwise,” he said.
“This is a small gender-biased study of 40 male subjects, 25 to 35 years of age. When I read through the study for the first time I had to wonder how could the authors have come up with such a title for their paper?” he asked.
In addition to questioning the study design, particularly with respect to assigned both trained and untrained people to an intensive exercise programme of underwent 85 minutes of exercise five days per week for four weeks, Dr Schauss also questioned the conclusions drawn from the data.
“Skeletal muscle biopsies were obtained from the right vastus lateralis muscle of study subjects. But some of the data is missing for a number of subjects, and reported as such by the authors,” said Dr Schauss.
The authors noted that biopsies for the ‘early’ time-point were only obtained from five people in the vitamin group, and four in the placebo group. “Yet the authors conclude a “strong induction of PGCl-alpha, PGCl-beta, and PPAR-gamma expression in skeletal muscle following 4 weeks of exercise training in previously untrained, antioxidant naïve individuals” and “markedly reduced exercise-related induction” in those taking antioxidants, based on these limited number of biopsies,” said Dr Schauss.
“Would it not have made more sense to appropriately increase the intensity and duration of exercise slowly and then see if the subject’s bodies didn’t accommodate handling of ROS without a significant change in induction of these markers?” he said.
The study reflects a ‘transient’ increase in ROS during ‘limited periods of physical exercise only’, noted Dr Schauss, “whereas the bulk of the literature, including that in non-primate models have not observed these concerns obtained in models of ‘continuous exposure to increased levels of ROS’”, he said.
Dr Schauss also noted that the authors presented no evidence of adverse effects by any of the individuals from vitamin C and E supplementation.
British Nutrition Foundation comment
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.
To read NutraIngredients.com coverage of the study, please click here.