Benefits of exercise undone by vitamins

Published on Monday 11 May 2009 18:56

ANTIOXIDANT vitamins can undo some of the most important health benefits of exercise, research has shown.

Taking vitamins C and E after a workout appears to prevent physical exercise improving the body's energy regulation, a study found.

Exercise is known to increase sensitivity to the hormone insulin, which governs the way cells use sugar as an energy source. Type 2 diabetes occurs when the body becomes resistant and less sensitive to insulin.

Some vitamins can block this beneficial effect of exercise, the new findings suggest.

Ironically, it is the supplements' health-boosting properties that appear to be to blame.

Vitamins such as C and E neutralise destructive "free radical" molecules called reactive oxygen species that can damage cells and DNA, and speed up ageing. These molecules are a by-product of metabolism and generated in larger numbers during vigorous exercise.

But the new research suggests that as well as causing damage, oxygen free radicals also spur the body into becoming more sensitive to insulin. By mopping up the molecules, antioxidant vitamins cancel out this beneficial effect.

In addition, scientists found that the vitamins weakened the body's own exercise-induced free radical defence system, which relies on the production of natural antioxidants.

Dr Michael Ristow, from the University of Jena in Germany, and colleagues published their findings in the journal Proceedings of the National Academy of Sciences.

He wrote: "We find that antioxidant supplements prevent the induction of molecular regulators of insulin sensitivity and endogenous antioxidant defence by physical exercise."

The findings add to the growing evidence that vitamins have complex effects on the body, which can do harm as well as good.