Antioxidants reduce the harmful effects of oxidation in some chemical reactions in the body. Oxidation causes free radicals to form, and these are associated with several diseases, including heart disease and some forms of cancer. Some vitamins, including vitamins C and E have antioxidant properties, as do some phytochemicals and some minerals. Fruits and vegetables are rich in antioxidants. See Key Nutrients in Fruits & Veggies.