A recent study demonstrates that taking vitamin C and E supplements reduces muscle cell adaptations to aerobic exercise in humans following an 11 week exercise training program.
Vitamins have been under scrutiny as of late. Several studies released over the last decade questioning whether vitamins actually prolong one’s life expectancy unleashed a media frenzy on the subject. We will not wade into that debate here, choosing instead to focus on the effect of vitamins on athletic performance. A recent study published in the Journal of Physiology suggests that taking Vitamin C and E supplements reduce endurance capacity (Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomized, controlled trial, 2014. Paulsen G, et al.). The study, available for free online, highlights the negative effects of vitamin C and vitamin E on cellular adaptations to endurance training.
A number of studies have previously demonstrated that vitamins reduce endurance capacity in animal models. One study looked at the adaptations of rats to exercise training with and without vitamin C supplementation. Following the exercise training, the rats that were taking a placebo increased their time to exhaustion whereas the rats taking vitamin C showed no increase in their time to exhaustion. Muscle biopsies showed that mitochondria biogenesis was significantly reduced in the rats taking vitamin C relative to the control rats taking a placebo.
In the aforementioned study, Paulsen and colleagues looked at the effects of taking antioxidants vitamin C and vitamin E on the training adaptations to 11 weeks of endurance training. The study had 54 male and female recreational athletes complete the study. The subjects were divided into two groups: one group took a placebo, while the other group took 1000 mg of vitamin C and vitamin E per a day. A VO2 MAX test and a shuttle run was used to test aerobic fitness before and after the 11 week training program. No changes in VO2 MAX or shuttle run performance were detected between groups.
Although no changes were observed in aerobic fitness, muscle biopsies taken from the athletes showed significant differences between the experimental groups. The athletes taking vitamin C and vitamin E had a blunted training-response increase in the mitochondrial protein COX4 (see the figure above). This suggests that there was reduced mitochondria biogenesis in the vitamin supplemented group. That is, athletes taking vitamin C and vitamin E produced less mitochondria over the course of the training program. Mitochondria are the cellular powerhouses during aerobic exercise. PGC-1alpha and MAPK1 are two important cytosolic proteins that regulate a number of aerobic training responses. The mRNA levels of these two cytosolic signal proteins were decreased in the vitamin supplemented group. It should be noted that muscle biopsies were taken two days after the end of the training program to ensure that only long term effects were measured.
Vitamin C and vitamin E are antioxidants. The authors suggest that they may interfere with normal oxidation signaling that occurs when the body is under oxidative stress during endurance exercise. Furthermore, more work needs to be done to assess whether antioxidants’ effects on cellular aerobics impacts human endurance. The group taking vitamin C and vitamin E had a reduced percentage increase in endurance from baseline, but it was only 3-4% lower than the placebo group. A far larger sample size would be needed to show statistical significance. In the meantime, if you are planning on competing anytime soon, it would not hurt to lay off the antioxidants.