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Don’t Take Those Vitamins!

Exercise promotes health, but vitamins C and E block this benefit.

It seems obvious that we should take supplements to prevent free-radical formation and reactive oxygen species (ROS). Exercise produces ROS by activating mitochondrial metabolism, but exercise also improves insulin sensitivity. These researchers examined how antioxidant vitamins alter the insulin-sensitizing effects of exercise in 40 healthy men (mean age, 26) who were either active (exercising >6 hours/week) or sedentary (exercising <2 hours/week).

All participants were randomized to receive placebo or vitamin E (400 IU/day) plus vitamin C (500 mg twice daily) and underwent an exercise regimen for 4 weeks (5 days/week: biking or running, 20 minutes; circuit training, 45 minutes; warm-up/cool-down, 20 minutes).

At baseline and after 4 weeks, researchers measured oxidative stress, insulin sensitivity during glucose infusion, adiponectin levels, fasting plasma insulin levels, RNA expression levels of insulin-sensitivity regulators, and expression of transcriptional coactivators linked to insulin sensitivity. On all measures, the administration of vitamins C and E blocked the beneficial insulin-sensitizing properties of exercise. On some measures, the effects of supplementation were weaker (but still significant) in the previously sedentary group than in the active group.

Comment: This elegant study shows that antioxidants prevent the glucose-regulating effects of exercise. That free radicals may be beneficial appears counterintuitive. However, we tend to forget that the body is highly adaptive; interfering with its processes might be detrimental. Apparently, exercise transiently increases ROS, which induces genes to express enzymes that ultimately increase insulin sensitivity and help to detoxify ROS.

These findings suggest that researchers who study insulin resistance, obesity, and dementia should control for the use of supplements. This study does not distinguish between the separate effects of the two vitamins and does not address any dose-effect response or the use of other popular "antioxidant" supplements. Many people take antioxidants in the belief that they are helpful or, at worst, "couldn’t hurt." Well, surprise — they do. Save your money and keep a well-balanced diet — and exercise!

— Jonathan Silver, MD

Published in Journal Watch Psychiatry June 8, 2009

Citation(s):

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.

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Reader Remarks:

Review and add to remarks on this article

• Vitamins may be harmful at 10X the RDA!
  Jean L. Gutierrez, PhD, The George Washington University, 29 Oct 2009 4:01 PM EST
  It is interesting to see that antioxidant vitamins may block certain exercise adaptations.
  
  It should be noted, however, that the... [more]
• A response from JW Associate Editor Jonathan Silver
  Jonathan Silver, MD, Clinical Professor of Psychiatry, New York University School of Medicine, 30 Oct 2009 12:30 PM EST
  Dr. Gutierrez is correct regarding the "high" dosage of Vitamins C and E used in this study. While this is... [more]
• Natural Antioxidants
  Rachel G Sagar, 29 Dec 2009 1:07 PM EST
  I have insulin resistance and I have recently been eating a lot of red fruits - berries, cherries, purple grapes... [more]
• Nutritional assessment in research
  Ruth Leyse-Wallace PhD, RD, Author, Clinician retired from practice in psychiatric dietetics, 22 Jan 2010 10:31 AM EST
  This provides an example of how lack of nutritional intake/assessment could skew results when comparing control and experimental groups that... [more]
• re: Don't take those vitamins
  Deborina Patreus, DVM; BSN, 28 Dec 2010 11:46 AM EST
  Specialty: General Practice
  I've always wondered why studies are done at 10-100X the dosages of meds/substances. Isn't this a waste of much needed... [more]

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