Do Antioxidants Cancel Out the Benefits of Exercise?

The notion that antioxidants like Vitamin C or E are somehow healthy because they neutralise or prevent the formation of free oxygen radicals is widespread and manufacturers of antioxidant supplements definitely enjoy a thriving business based on this idea.

However, recent clinical trial have consitently failed to show any major beneficial health effects of antioxidant supplements and in fact, a recent large randomized trial showed that regular ingestion of Vitamin E supplements may actually increase your risk for heart failure.

Of course, the entire idea of taking antioxidants is based on the belief that increased formation of free oxygen radicals is detrimental to health and leads to tissue damage and premature aging. But this may not be entirely true.

As is now increasingly recognised, free oxygen radicals actually play an important role in a wide range of normal physiological processes and are often key signals in the initiation of numerous biological responses. Thus, inhibition of these natural signals by antioxidants, may very well interfere with normal functioning of the organism.

This concept is perhaps best illustrated in a recent study by Michael Ristow and colleagues from the University of Jena, Germany, published earlier this year in the Proceedings of the National Academy of Science USA, which demonstrates that the intake of antioxidant supplements effectively blocks the beneficial effects of exercise on insulin sensitivity.

The study evaluated the effects of a combination of vitamin C (1000 mg/day) and vitamin E (400 IU/day) on insulin sensitivity as measured by glucose infusion rates (GIR) during a hyperinsulinemic, euglycemic clamp in previously untrained (n = 19) and pretrained (n = 20) healthy young men.

Glucose clamps and muscle biopsies for gene expression were performed before and after a 4 week intervention of physical exercise.

Whereas exercise (as expected) clearly increased parameters of insulin sensitivity in the absence of antioxidants in both previously untrained and pretrained individuals, this positive effect was completely blocked by taking the antioxidants.

Similarly, only in the absence of antioxidants was exercise associated with increased expression of oxygen-sensitive transcriptional regulators of insulin sensitivity and oxidative defense capacity.

These findings are consistent with the concept that exercise-induced oxidative stress is a key factor in the positive effect of exercise on insulin resistance and oxidative defense capacity.

These findings have important implications for anyone exercising in the hope that this will improve their insulin sensitivity (as in diabetes prevention or treatment) – if you are also on antioxidants, you may as well stop exercising, because taking these supplements will essentially cancel out any beneficial effect of exercise on your risk for diabetes.

On a more general note – I for one, will be quite cautious about believing the health benefits of any products claiming “anti-oxidant” properties unless these benefits are clearly demonstrated in properly conducted intervention trial in humans.

Edmonton, Alberta