Antioxidant

Antioxidants stabilise free radicals without becoming destructively reactive themselves. Some are dietary — vitamins C and E, carotenoids, polyphenols — and some the body makes, including glutathione and the enzymes superoxide dismutase and catalase, which do most of the actual work.

It matters because the endogenous enzyme system is far more significant than the dietary component, a fact that most antioxidant marketing declines to mention. Diets rich in antioxidant-containing foods do associate with better health outcomes; isolated high-dose supplements have repeatedly failed to reproduce that in trials, and some have shown harm.

In practice the sensible position is food first: colourful plants, in variety. High-dose supplements taken around training are specifically discouraged, since they can blunt the adaptive signal exercise depends on.