Antioxidants - do more harm than good?

This one is really going to sound heretical.

While we are often told to eat lots of veggies, red tea, green tea and chocolate to benefit from their antioxidants. In the past I've pointed to a couple of studies (here and here) that raised some questions about the supposed benefits of antioxidants in the diet.

This week I've spotted two new studies that indicate that taking supplementary antioxidants - including the popular Vitamin C - can actually interfere with your body's own antioxidant processes - especially in the context of exercise. Maybe chalk up another one for the high fat, low carb boys?

Here are the abstracts:

Oral administration of vitamin C decreases muscle mitochondrial biogenesis and hampers training-induced adaptations in endurance performance
Background: Exercise practitioners often take vitamin C supplements because intense muscular contractile activity can result in oxidative stress, as indicated by altered muscle and blood glutathione concentrations and increases in protein, DNA, and lipid peroxidation. There is, however, considerable debate regarding the beneficial health effects of vitamin C supplementation.

Objective: This study was designed to study the effect of vitamin C on training efficiency in rats and in humans.

Design: The human study was double-blind and randomized. Fourteen men (27–36 y old) were trained for 8 wk. Five of the men were supplemented daily with an oral dose of 1 g vitamin C. In the animal study, 24 male Wistar rats were exercised under 2 different protocols for 3 and 6 wk. Twelve of the rats were treated with a daily dose of vitamin C (0.24 mg/cm2 body surface area).

Results: The administration of vitamin C significantly (P = 0.014) hampered endurance capacity. The adverse effects of vitamin C may result from its capacity to reduce the exercise-induced expression of key transcription factors involved in mitochondrial biogenesis. These factors are peroxisome proliferator–activated receptor co-activator 1, nuclear respiratory factor 1, and mitochondrial transcription factor A. Vitamin C also prevented the exercise-induced expression of cytochrome C (a marker of mitochondrial content) and of the antioxidant enzymes superoxide dismutase and glutathione peroxidase.

Conclusion: Vitamin C supplementation decreases training efficiency because it prevents some cellular adaptations to exercise.



Moderate exercise is an antioxidant: Upregulation of antioxidant genes by training.

Exercise causes oxidative stress only when exhaustive. Strenuous exercise causes oxidation of glutathione, release of cytosolic enzymes, and other signs of cell damage. However, there is increasing evidence that reactive oxygen species (ROS) not only are toxic but also play an important role in cell signaling and in the regulation of gene expression.

Xanthine oxidase is involved in the generation of superoxide associated with exhaustive exercise. Allopurinol (an inhibitor of this enzyme) prevents muscle damage after exhaustive exercise, but also modifies cell signaling pathways associated with both moderate and exhaustive exercise in rats and humans.

In gastrocnemius muscle from rats, exercise caused an activation of MAP kinases. This in turn activated the NF-kappaB pathway and consequently the expression of important enzymes associated with defense against ROS (superoxide dismutase) and adaptation to exercise (eNOS and iNOS). All these changes were abolished when ROS production was prevented by allopurinol.

Thus ROS act as signals in exercise because decreasing their formation prevents activation of important signaling pathways that cause useful adaptations in cells. Because these signals result in an upregulation of powerful antioxidant enzymes, exercise itself can be considered an antioxidant. We have found that interfering with free radical metabolism with antioxidants may hamper useful adaptations to training.


So don't take that Vitamin C - exercise itself is an antioxidant and taking antioxidants prevents useful benefits to training! I told you it was heresy!

I have said before that:

It is also worth pointing out that Vilhjalmur Stefansson lived for years on the traditional Eskimo diet of fat and meat....no veggies.......and was, like the Eskimos he was living with, exceptionally healthy. Gary Taubes in his new and excellent book Good Calories, Bad Calories suggests that scurvy and other vitamin deficiency diseases are actually only found when people are eating diets low in meat, eggs and dairy. It seems to be the high levels of carbs that prompt the need for all the vitamins in the veggies.....