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Health-promoting effects of exercise diminished by vitamin C, E in patients with diabetes
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Vitamins C and E nearly eliminated the health-promoting effects of physical exercise on glucose metabolism and insulin sensitivity.
In the prospective, randomized, four-week study, researchers randomly assigned 40 healthy men aged 25 to 35 to 500 mg of vitamin C twice-daily and 400 IU of vitamin E once-daily or placebo.
Twenty participants were considered to be previously untrained (<two hours of exercise per week) and 20 participants were previously trained (>six hours of exercise per week).
All participants completed physical training sessions for five consecutive days during a four-week period. Training sessions included biking or running for 20 minutes, circuit training for 45 minutes and 20-minute periods of warming up and cooling down.
Fat free mass (P=.03) and VO2 maximum (P<.001) were significantly higher among participants in the pre-trained group.
Following exercise training, participants in the control group had a more than twofold increase in oxidative stress marker TBARS (thiobarbituric acid reactive substances) and a significant increase in insulin-stimulated glucose utilization during a euglycemic hyperinsulinemic clamp. In contrast, participants in the antioxidant group did not have a significant increase in the formation of thiobarbituric acid-reactive substances following three days of exercise compared with the control group (P=.03). At the same time, these individuals also did not have an increase in glucose utilization.
“We therefore are concerned for people taking antioxidants that it could block this small oxidative stress response and may actually block the beneficial effect of exercise — which is exactly what happened,” C. Ronald Kahn, MD, president and director of the Joslin Diabetes Center in Boston, told Endocrine Today.
Ristow M. PNAS. 2009; doi:10.1073/pnas.0903485106.
The recent paper in the Proceedings of the National Academy of Sciences raises concerns about the possibility that the anti-oxidants, vitamin C and E, may prevent the health related effects of exercise in diabetics. Administering these two anti-oxidants to a group of individuals who were sedentary or who exercised showed similar reductions in the beneficial responses to exercise. If confirmed in other studies, this raises concerns about the widespread use of these antioxidants in individuals seeking the benefits of exercise.
– George A. Bray, MD
Endocrine Today Editorial Board member