Vitamin Supplements May Reverse Endurance Training Benefits

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Taking certain types of vitamin supplements may make it harder to train for big endurance events such as marathons, new research from Norway suggests. Researchers at the Norwegian School of Sports Sciences say vitamin C and E supplements should be used with caution as they “may blunt the improvement of muscular endurance by disrupting cellular adaptions in exercised muscles” and affect the way muscles respond to exercise.

In the 11-week trial, 54 healthy men and women were given either 1,000mg of vitamin C plus 235mg of vitamin E or a sugar pill placebo. 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 programme.

The study found those taking the supplements experienced no difference in their performance during a 20 metre shuttle test. However, blood samples and tissue biopsies suggested there were differences developing inside the muscle. Each muscle cell contains lots of tiny mitochondria; these give the muscle cell its energy. Markers for the production of new muscle mitochondria increased only in the group not taking supplements. The researchers say future studies are needed to determine the underlying mechanisms of the results of this study.

Dr Goran Paulsen, who led the study, said: “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. 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.”

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

The findings, published in The Journal of Physiology, have led to other experts questioning the research. Speaking to the BBC, Mike Gleeson, a professor of exercise biochemistry at Loughborough University, was not convinced. He said the biggest factor in performance was how fast the heart and lungs could get oxygen to the muscle, not mitochondria, saying the lack of difference in athletic performance “makes it difficult to interpret”.
Professor Gleeson, said: “The bottom line is studies show change 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.”

In a separate four-week randomised controlled trial evaluating vitamin C and E supplementation among female athletes, supplementation had shown a benefit. Supplementation appeared to reduce markers of oxidative stress and reduced muscle damage markers associated with aerobic exercise.

Dr Emma Derbyshire from the Health Supplements Information Service, advises: “Eating as healthy a diet as possible is very important for sportspeople and athletes. However, if they have a hectic training schedule, particularly for those doing endurance training, who are not able to eat as well as they should, a multivitamin and mineral supplement provides a method of ensuring that the intakes of these essential nutrients, including vitamins C and E, follow recommended guidelines.”

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