Do you exercise?
Read on for a study that found a deleterious effect of vitamin C supplementation:
Oral Administration Of Vitamin C Decreases Muscle Mitochondrial Biogenesis And Hampers Training-Induced Adaptations In Endurance Performance, American Journal of Clinical Nutrition, January 2008
Researchers gave vitamin C to humans and rats.
- The humans were 14 sedentary men, randomized into 2 groups: one group received 1 gram vitamin C daily. All men exercised on a stationary bicycle for 8 weeks.
- The rats were 36 Wistar males, randomized into 6 groups: 18 were divided into 3 groups (untrained, trained, trained w/vit C) and trained for 3 weeks. The other 18 were trained for 6 weeks. Rats given vitamin C received a dose about 4 times that used in humans.
1. Vitamin C reduced endurance.
"Training increased the maximal running time in rats [by 186.7%]. However, this increase was prevented by daily supplementation with vitamin C. In the supplemented animals, the running time increased only 26.5%."2. Vitamin C reduced the number of mitochondria (energy-producing factories) bodies make in response to exercise/stress.
The graph below shows the change in level of transcription factors needed for mitochondrial production. Look at the vitamin C group - almost equal to levels in untrained rats.
The number of mitochondria is linked to endurance and fatigue. (See No. 1 above.)
"Endurance capacity [time to fatigue] is dependent mainly on the mitochondrial content of skeletal muscle."
3. Vitamin C also reduced the amount of endogenous (made by our body) antioxidants.
(Two antioxidant enzymes, superoxide dismutase and glutathione peroxidase (GP), were found in lower levels in those taking vitamin C. Recall that acrylamide in browned/aged foods is metabolized by GP - a good thing. In fact, GP is widely used in cells to prevent damage from oxidation.)
The graph below shows the change in levels of these two antioxidants. Again, the vitamin C group was almost equal to levels in untrained rats.
Exercise generates oxidized compounds. It was thought that by consuming more antioxidants, e.g. vitamin C, we could protect our cells against these oxidized compounds (known as reactive oxygen species: ROS).
We're finding that ROS aren't altogether bad. The body uses them as signals. Previous posts discussed this, e.g. the case of too much selenium reducing ROS leading to insulin resistance and weight gain.
In this case, ROS signals the body to make more mitochondria, and more in-house antioxidants. It probably does other things, but this study measured just those variables.
Final quote from the study:
"Thus, the common practice of taking vitamin C supplements during training (for both health-related and performance-related physical fitness) should be seriously questioned."