The meaning of the term “anti-oxidant”
Both inside and outside the cell, anti-oxidant activity is largely mediated through enzymes specific to that function. Anti-oxidation is a tightly controlled process in the cell and the idea that swamping it with small-molecule enzyme-independent anti-oxidants from the diet would be beneficial seems far-fetched.
Higher primates have unusually high levels of anti-oxidant activity compared to other mammals. Concurrent with the loss of the ability to synthesize ascorbic acid they have lost the ability to degrade uric acid. Uric acid is thus present in high levels in human serum where it acts as a highly-effective anti-oxidant. Indeed humans could be considered saturated in anti-oxidant potential compare to say mice and dietary supplementation beyond overt deficiency levels likely has little affect on health outcomes and explains why promising mouse studies on anti-oxidants invariably fail when performed on humans.The point of this discussion is to argue that measures to prevent ROS damage in the first place, most popularly currently by anti-oxidant supplementation, are not likely to be effective whereas measures to enhance clean-up of the damage afterwards such as provided by autophagy are more promising. In fact many of the substances touted as anti-oxidants more likely produce their benefits by enhancing autophagy; resveratrol, for instance. One issue that clouds all the studies is that ROS provokes a general response in the cell including anti-oxidant production and autophagy. In fact a lot of substances described as anti-oxidants are really just ROS mimics that provoke this response or even pro-oxidants that generate some ROS themselves that then provokes it (exercise for example). In the same way as a vaccine provokes an immune response, some level of ROS stress may needed to provoke the cell to a proper level of anti-oxidant activity and extinguishing it with exotic antioxidants could be counter-productive.