Vitamin C, E Negatively Affect Endurance Training

New research from Norway suggests that vitamin C and E reduce the body's ability to train for endurance events such as marathons.

According to researchers at the Norwegian School of Sport Sciences, vitamin C and E interfere with muscle development during endurance training.

Vitamin supplements are commonly available. Recently, there have been a number of studies showing that these supplements might be a waste of money. The current study doesn't exactly dismiss the usefulness of these pills but shows that people training for high endurance-activities should watch the levels of vitamin supplements that they are consuming.

"Our results show that vitamin C and E supplements blunted the endurance training-induced increase of mitochondrial proteins, which are needed to improve muscular endurance," Dr Gøran Paulsen, from Norwegian School of Sport Sciences, lead author of the study.

The study was based on data from 54 men and women taking part in a double blind randomized controlled trial. All participants were randomly given either 1000mg vitamin C and 235mg vitamin E or a placebo.

Participants were then put on an endurance training program. Blood samples, fitness tests and biopsies were taken before and after the use of vitamins/ placebo, according to news release.

Study results showed that there was no difference between beep tests, which involves running faster between two points set 20 meters apart, BBC reported. However, researchers found differences in muscle development between the participants; with fewer mitochondria being formed in the group that took vitamin supplements.

Also, the four participants that showed the greatest improvement in endurance training belonged to the placebo group, Livescience reported.

According to Office of Dietary Supplements, the upper safe limit for Vitamin C in adults is 2,000 mg while the upper safe limit for vitamin E is 1,000 mg (1,500 IU).

"Our results indicate that high dosages of vitamin C and E - as commonly found in supplements - should be used with caution, especially if you are undertaking endurance training," Paulsen said.

Paulsen added that more research is required to understand the mechanism that prevents muscle development in the presence of vitamins. Some researchers say the vitamins might be interfering with certain genes.

Mike Gleeson, a professor of exercise biochemistry at Loughborough University told BBC that he is not convinced by the results of the Norway study.

"The bottom line is studies show changes in the ability to adapt to exercise could be impaired by high-dose vitamins, but until there are studies showing them affecting athletic performance people shouldn't be worried," he said, according to BBC. 

The study is published in the Journal of Physiology.