Vitamin C supplements decrease effectiveness of training

Vitamin C is an antioxidant sometimes taken in high doses in the belief that it helps prevent oxidative stress in muscles caused by intensive training.

Researchers in Spain, however, have found the opposite effect.

As well as an animal study, they had 24 men aged between 27-36 years undertake an 8-week physical training regime. Five of the men received a 1g (1000mg) vitamin C supplement each day, while the others did not. From both the animal and human studies, they found those who were supplemented with vitamin C had poorer results from their training. From the analysis of their data, the researchers had two key conclusions. Firstly, exercise itself is an antioxidant, in that training increases the cellular amount of two antioxidant enzymes related to longevity. Secondly, they concluded that supplementing with vitamin C actually reduces training efficiency.

Source: American Journal of Clinical Nutrition, January 2008