Antioxidants Take a Hit: Vitamins C and E May Work Against Your Attempts to Stave Off or Deal With Type 2 Diabetes

A German and American research team found that exercisers who take vitamins C and E for their antioxidant effects may experience decreased insulin sensitivity, thus negating one of the major benefits of exercise.

May 26, 2009

If you have type 2 diabetes, you know that regular sustained exercise is one of the best and easiest ways to manage the disease. At the same time, proper nutrition-eating low glycemic foods, avoiding carbohydrates, and taking supplements, such as vitamins and omega-3 fatty acids-is the other key to non-medicinal control of blood sugar levels.

But what happens if some of the vitamins you've been told over the years are essential components to your diabetes management turn out to work against the beneficial effects of exercise?

A joint German and American research team has found that exercisers who take vitamins C and E for their antioxidant effects may actually experience decreased insulin sensitivity, thus negating one of the major benefits of exercise. Additionally, the vitamins, intended to combat damage from reactive oxygen molecules that are liberated by the body's metabolization of glucose during exercise, may actually inhibit the body's own built-in antioxidant ability.

Antioxidants have long been touted as a way to slow the aging process and prevent the cumulative damage brought on by reactive oxygen compounds. But it turns out that while exercise creates these free-ranging oxygen molecules, it also "turns on" the body's own natural defenses against them. In other words, the vitamins, although consumed with good intent, work against the body rather than for it. By destroying the reactive oxygen before the body can get to it, the vitamins short-circuit a natural process that is one of the chief benefits of exercise.

The researchers were led by Dr. Michael Ristow, a nutritionist at the University of Jena in Germany, who also worked with a team from the Joslin Diabetes Center in Boston. They tested their suspicion that vitamins C and E might be working against exercisers by dividing 40 young men into four groups and tracking them over four weeks of identical exercise programs:

  • One group, whose members were already in athletic training programs, took 1,000 mg of vitamin C and 400 IUs of vitamin E daily over the four weeks.
  • A second group, whose members had not previously been in athletic training programs, also took 1,000 mg of vitamin C and 400 IUs of vitamin E per day over the four weeks.
  • A third group, whose members were already in athletic training programs, took no vitamins over the four weeks.
  • A fourth group, whose members had not previously been in athletic training programs, also took no vitamins over the four weeks.

At the end of the study, the young men who had taken vitamins experienced no improvement in insulin resistance and almost no activation of their bodies' natural antioxidant defenses.  

The researchers said their findings carry enough weight for them to strongly suggest that people who exercise regularly should not take antioxidant vitamins. However, they cautioned against extending their conclusions about vitamins C and E to fruits and vegetables, which are high in antioxidants. Those foods, they said, contain other substances that probably counter or alter the strength of their antioxidant properties.

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Categories: Blood Sugar, Diabetes, Diabetes, Exercise, Food, Insulin, Type 2 Issues

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Posted by Anonymous on 5 June 2009

Who sponsered this study? There should be a rule that all posted study conclusions include the name of the sponsers. Often, drug companies are behind these studies and use very loose controls with skewed results.

Posted by ijamall on 5 June 2009

This should come as no surprise. It has been known in the peer-reviewed literature for almost a decade that Vitamin acts as an antioxidant in cells grown in culture (in vitro) but as a pro-oxidant in animals and humans due to its ability to generate free radicals in the presence of iron. Vitamin E being fat soluble, acts as an antioxidant only in those situations where the free radicals attack cell membranes. In the context of diabetes, Exenatide (Byetta) and sodium selenite would be more potent antioxidants than Vitamin C or E could be, based on an understanding of the biochemical lesion associated with type 2 diabetes.

Ijaz S. Jamall, Ph.D., DABT

Posted by Anonymous on 5 June 2009

These type of Trials are not conclusive.After having innumeable references/ trials which prove that anti oxidants do prevent non-infectious diseases like Diabetes or help them to manage Diabetes better by neutralizing Free Radical's damage. Since diabetic have restrictions in eating foods they do miss important nutrients which function as antioxidants. Both exercises and Foods are complementary to each other.
Perhaps high doses of antioxidants may not be necessary but Diabetic do not them at least to meet RDAs of these Vitamins.

Posted by seashore on 6 June 2009

What were the blood sugar levels of the subjects in the tests? What were the A1c levels and the peak post-meal blood glucose levels? The diabetics should be kept on low-carb diets that keep A1c below 6% and keep peak post-meal blood glucose below 140 mg/dL (7.6 mmol/dL, as I remember). When these critical limits are achieved, the tests of vitamins are meaningful.

Posted by Dick on 7 June 2009

Once again, studies that have used fragmented vitamins (many man-made)have not demonstrated positive heleth benefits. However, the vast majority of studies that have used real whole foods such as fruits and vegetables have demonstrated beneficial health results. There are thousands of phytonutirnets in fruits and vegetables and they work together in synergy with the body. We don't need mega doses of vitamins, but we do need a little of everything that Mother Nature has to offer.

Posted by Anonymous on 10 June 2009

4 weeks may not be enough time to throughly evaluate effect. Changes in insulin resistance don't happen overnight and don't resolve that quickly either. We generally allow 4-6 weeks, minimum, to see if TZD's are having a positive effect.

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