Antioxidant

In medicine, antioxidants are "naturally occurring or synthetic substances that inhibit or retard the oxidation of a substance to which it is added. They counteract the harmful and damaging effects of oxidation in animal tissue".

Antioxidant supplements include beta-carotene, vitamin A (retinol), vitamin C (ascorbic acid), vitamin E (tocopherols), and selenium.

Medical uses
In spite of early, positive research, antioxidants do not seem to prevent gastrointestinal cancer.