Chris Kresser: Virtually all so-called antioxidants work as pro-oxidants, so that shouldn’t necessarily concern us. Pro-oxidants that have an antioxidant effect have that effect because of hormesis. Hormesis is a stressor that leads to a positive adaptation, and almost everything … not everything, but a lot of things that benefit us are because they have a hormetic effect. Intermittent fasting, that’s hormesis. Exercise, that’s hormesis. If you lift weights, for example, you do a bicep curl, and you do it until you reach failure, basically the body will then rebuild. You’re tearing the muscle fibers. That’s a stressor, but the body then rebuilds those fibers stronger so it can meet the challenge of that weight the next time that you lift that weight, and that’s an evolutionary survival mechanism. Let’s say you run away from a predator and you barely escape. Then if you continue to face a challenge like that, your body will increase your cardiovascular capacity so that you can escape that challenge next time, and that increases evolutionary fitness. That’s why exercise, whether you’re talking about running or lifting weights, that’s how it works, and those are all pro-oxidant, hormetic changes.
With vitamin C, so far, there’s not a safe upper limit that has been identified other than just bowel tolerance that I’m aware of. If anyone has any other studies that contradict that, let us know, but I haven’t seen any.