With the 2014 Winter Olympics just around the corner, hundreds of athletes are in training for one of the most important competitions of their lives. But according to new research, they should stay away from vitamin C and E supplements if they want to do well. A study has found that these supplements may hinder endurance training.
The Office of Dietary Supplements of the National Institutes of Health recommend that women should have 75 mg of vitamin C each day and men should have 95 mg, while both men and women should have 15 mg of vitamin E each day.
Vitamin E is naturally found in some foods, such as vegetable oils, nuts and green vegetables, while citrus fruits and vegetables - including potatoes and broccoli - can be a good source of vitamin C.
However, vitamin C and E supplements are available for those who want to boost their intake.
Because these supplements are so widely used, the research team, led by Dr. Gøran Paulsen of the Norwegian School of Sport Sciences, wanted to see if they interfered with cellular or physiological mechanisms during exercise.
Subjects randomized to vitamin or placebo groups
For their study, recently published in The Journal of Physiology, the researchers analyzed 54 young and healthy men and women for 11 weeks.
Participants were randomly allocated to one of two groups. The first group was required to take 1,000 mg of vitamin C and 235 mg of vitamin E each day, which the researchers say is consistent with the amount found in store-bought supplements. The second group received a placebo pill each day.
The investigators note that they did not know which groups the participants were in, and neither did the participants.
During the study period, all subjects were required to carry out an endurance training program. This consisted of three to four training sessions each week that mainly involved running.
They also underwent fitness tests, muscle biopsies, and had blood samples taken at the baseline of the study and after the study ceased.
High doses of vitamins C and E 'should be taken with caution'
Results of the study revealed that markers for the production of new muscle mitochondria - structures that supply power to the cells - only increased in the participants who received the placebo pill.
The researchers note that the supplements had no impact on the participants' maximal oxygen uptake or their results in a 20-meter shuttle test.
According to the researchers, previous studies have shown that exercising increases the production of oxygen in the muscles. This plays a part in the signaling process that causes muscle changes.
The investigators hypothesize that since vitamins C and E are antioxidants, high doses may take away some of the oxidative stress and block the development of muscular endurance.
Commenting on the findings, Dr. Paulsen says:
"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.
Future studies are needed to determine the underlying mechanisms of these results, but we assume that the vitamins interfered with cellular signaling and blunted expression of certain genes."
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