Vitamins!

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

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Vitamins C and E could reverse exercise benefits, experts claim

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

Some vitamins can block this beneficial effect of exercise, the new findings published in the journal Proceedings of the National Academy of Sciences suggest.

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.

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 (ROS) 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 from the University of Jena in Germany found that the vitamins weakened the body's own exercise-induced free radical defence system, which relies on the production of natural antioxidants.

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