Athletes supplementing with vitamin C and E could be harming their endurance ability, a study by Norwegian researchers suggests.
Research by the Norwegian School of Sport Sciences published in The Journal of Physiology said that vitamin C and E supplements diminished the improvement of muscular endurance.
‘Use with caution’
"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,” said lead author Gøran Paulsen.
"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."
The trial: 54 participants
The researchers conducted a double-blind, randomized, controlled trial involving 54 young men and women.
The study group were randomly allocated either 1000 mg vitamin C and 235 mg vitamin E daily or a placebo for 11 weeks.
The participants were given an endurance training program during the supplementation consisting of three to four sessions a week, mostly involving running. Fitness tests, blood samples and muscle biopsies were taken before and after the intervention.
“Daily vitamin C and E supplementation attenuated increases in markers of mitochondrial biogenesis following endurance training. However, no clear interactions were detected for improvements in VO2max and running performance,” found the study.
“Consequently, vitamin C and E supplementation hampered cellular adaptions in the exercised muscles, and although this was not translated to the performance tests applied in this study, we advocate caution when considering antioxidant supplementation combined with endurance exercise,” it concluded.
‘Nail in the coffin’ for supra-physiological doses
Robert Verkerk, executive and science director at the Alliance for Natural Health International (ANH-Intl) told NutraIngredients that the study largely confirmed what was already known.
"Endurance athletes produce high levels of free radicals that need to be effectively scavenged if long-term damage to DNA and cells is to be avoided. But this study represents another nail in the coffin for those hoping that supra-physiological doses of vitamins C and E might be all that’s needed to counter this oxidative stress and allow improved endurance performance. “
“Researchers are still hooked at looking at isolated vitamins as the key antioxidants when our evolutionary history and diets show that plant-derived phytochemicals and internally-generated antioxidants like glutathione are likely to be more important."
The UK’s National Health Service (NHS) says that taking less than 540mg vitamin E and 1000mg vitamin C supplements per day is unlikely to cause any harm.
Previous research published in Nutrition suggested that vitamin C supplements were beneficial for exercise. A four-week study with 20 adults found that a daily supplement of 500 mg of vitamin C was associated with an average 11 fewer heart beats during exercise, compared to three fewer beats in the control group.
The present study was partly funded by Norwegian firms Smartfish, VitaeLab and the Norwegian Olympic Federation.
Journal of Physiology (2014), Published online before print February 3, 2014
‘Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind randomized control trial’
Authors: Paulsen G et al.