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Vitamin Supplements Block Beneficial Effect of Exercise on Diabetes Risk

Research Examines Adverse Effects of Antioxidants

Type 2 diabetes is a highly prevalent disease that promotes multiple conditions, including stroke, heart attacks, kidney failure and blindness. Physical exercise is known to prevent type 2 diabetes, and a related condition named insulin resistance.

On the other hand, exercise also induces formation of free radicals, a form of very active oxygen, producing oxidative stress, which, if it persists for long periods of time, is commonly thought to be harmful. Accordingly, athletes, as well as non-athletes, consume antioxidant supplements to ameliorate the presumably harmful side-effects of oxidative stress. Moreover, a significant percentage of the general population uses antioxidant supplements on a daily basis in hopes to prevent other kinds of oxidative tissue damage and thereby improve health and longevity. The most commonly used anti-oxidants are vitamins C and E.

A study published today in the "Proceedings of the National Academy of Sciences" (PNAS) suggests that vitamin C and E supplements may actually be harmful, at least in regards to diabetes risk and glucose metabolism. According to this study, the health-promoting effects of exercise require the formation of oxidative stress during sports and if this is blocked, some of these effects do not occur. In the particular study, the intake of antioxidants during a four-week exercise training class abolished the effects of exercise to improve insulin sensitivity and glucose metabolism which would help prevent diabetes, while those individuals not taking the antioxidants had major benefits in terms of metabolism from exercise.

Dr. Michael Ristow, lead-author of the study which was published by a team of researchers from Leipzig and Jena Universities (both Germany) and Harvard Medical School, points out: "Exercise causes repeated boosts of free radicals, which - according to our results - induce a health-promoting adaptive response in humans. Subsequently, our body activates molecular defense systems against stress, and metabolizes carbohydrates more efficiently, both of which prevents diabetes, and possibly other diseases. Blocking these boosts of free radicals by antioxidants accordingly blocks the health promoting effects of exercise." He further says that "short-term doses of free radicals may act like a vaccine, helping the body to defend itself from chronic stressors more efficiently by inducing a long-term adaptive response".

Dr. C. Ronald Kahn, a collaborating author from the Joslin Diabetes Center and Harvard Medical School, noted: "This is a very important study for the millions of people at risk for type 2 diabetes. Exercise is a proven way to improve insulin action and reduce diabetes risk, but clearly this beneficial effect can be largely blocked by taking these very commonly used vitamin supplements. We need larger studies to fully assess this effect, but in the meantime, individuals at risk for diabetes and maybe even some with type 2 diabetes itself, need to think carefully about the use of these vitamin supplements, especially if they exercise regularly to improve there health."

Original Publication:
Ristow, M., Zarse, K., Oberbach, A., Klöting, N., Birringer, M., Kiehntopf, M., Stumvoll, M., Kahn, C. R., Blüher, M.: Antioxidants Prevent Health-Promoting Effects of Physical Exercise in Humans. Proceedings of the National Academy of Sciences of the United States of America (PNAS), early edition:
Prof. Dr. Michael Ristow, M.D., Dept. for Human Nutrition, Institute for Nutrition, University of Jena, Germany; tel. +49-3641-949630, e-mail:; additional material at:


Prof. Dr. C. Ronald Kahn, M.D., Joslin Diabetes Center, Harvard Medical School, Boston, MA, USA; tel. +1-617-732-2635, e-mail:

Manuela Heberer | idw
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