Antioxidants are substances that protect the cells and lipoproteins against the harmful effects of free radicals. They are substances that prevent the oxidation of other molecules and compounds. There are two broad categories of antioxidants: enzymatic and non-enzymatic.
Non-enzymatic antioxidants are substances like Coenzyme Q10, vitamin C, vitamin E, glutathione, and various carotenoids. Prominent enzymatic antioxidants include catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase.