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Body regularly generates free radicals and oxidative stress in normal physiological and pathological conditions. Radicals and reactive species play essential roles in cellular functions, whereas the unregulated reactions by those reactive species potentially cause tissue damage and diseases. Antioxidants can be small molecules such as vitamin C, E, lipoic acid, beta-carotene and non-vitamin including glutathione and bilirubin, and also be many antioxidant enzymes for instance; superoxide dismutase, catalase and thioredoxin reductase. Antioxidant system plays critical role in eliminating harmful free radicals and modulating cellular oxidation and reduction (redox) state, where redox status acts as if a switch to turn on and off various redox-sensitive function of enzymes and proteins. Moreover, antioxidant system also functions to restore or reactivate oxidatively modified molecules. The vitamins and enzymes coordinately work as networks for recycling important molecules and enhancing efficiency and to enable the system to perform in both aqueous and lipid environments.