Vitamin C, E supplements may blunt endurance training

An alarming study suggests that high doses of vitamin C and E supplements may blunt the improvement of muscular endurance by disrupting cellular adaptions in exercised muscles.

"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," alerted Goran Paulsen from the Norwegian School of Sport Sciences in Oslo.

As vitamin C and E supplements are widely used, understanding if they interfere with cellular and physiological adaptations to exercise is of interest to people exercising for health purposes as well as to athletes.

"Our research found that vitamin C and E supplements blunted the endurance training-induced increase of mitochondrial proteins, which are needed to improve muscular endurance," added Paulsen.

In the 11-week trial, 54 young, healthy men and women were randomly allocated to receive either 1,000 mg vitamin C and 235 mg vitamin E daily or a placebo (a pill containing no active ingredients).

Neither the participants nor the investigators knew which participant received the vitamins or placebos.

The participants completed an endurance training programme, consisting of three to four sessions per week, of primarily running.

Fitness tests, blood samples and muscle biopsies were taken before and after the intervention.

The results showed that markers for the production of new muscle mitochondria - the power supply for cells - increased only in the group without supplements.

A significant trend has been identified but the molecular processes requires further research, said Paulsen.

Exercising increases muscle oxidant production which participates in the signalling processes leading to muscle adaption.

It is possible that high doses of vitamins C and E act as antioxidants and take away some of this oxidative stress, hence blocking muscular endurance development, contended the new study published in The Journal of Physiology.

Taking less than 540 mg vitamin E and 1,000 mg vitamin C supplements per day is unlikely to cause any harm, advises the National Health Service (NHS).