Antioxidant Supplements Blunt Exercise-Induced Improvement of Insulin Sensitivity
Regardless of their previous exercise patterns, young men did not benefit from vitamin E or C supplementation.
Regular exercise increases insulin sensitivity and decreases risk for type 2 diabetes. One mechanism is known: Exercise stimulates glucose-transporter molecules to proliferate and move to the cell membrane, where they ferry glucose into the cell. Exercise also increases the formation of mitochondria, which give cells more energy but also create more harmful reactive oxygen species (ROS).
An international team randomized 39 young men (19 nonconditioned and 20 with prior physical conditioning) to exercise either with or without having ingested daily antioxidant supplements (1000-mg vitamin C and 400-IU vitamin E). In the groups that did not receive antioxidants, mean insulin sensitivity was higher after exercise among both nonconditioned and conditioned men; exercise raised production of ROS but also activated natural antioxidant systems. However, in both antioxidant groups, researchers noted no improvement in insulin sensitivity, and natural antioxidant systems were blunted.
Comment: Surprisingly, use of antioxidant supplements blunts the beneficial effects of regular exercise on insulin sensitivity, even though diets that are rich in fruits and vegetables (and, thus, contain high concentrations of antioxidants) lower risk for developing type 2 diabetes. Overall, little evidence of benefit from regular use of vitamin C or E supplements exists, and this study offers one reason to discourage their use and to encourage diets that are rich in fruits and vegetables.
Published in Journal Watch General Medicine June 4, 2009
Citation:
Ristow M et al. Antioxidants prevent health-promoting effects of physical exercise in humans. Proc Natl Acad Sci U S A 2009 May 26; 106:8665. [Free full-text online] [Medline® Abstract]
Copyright © 2009. Massachusetts Medical Society. All rights reserved.
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