ABSTRACT
Depending on their concentrations, free radicals and oxidants play a dual role as both toxic and beneficial compounds to the body. They are generated either from normal cellular processes in the organism or from various external sources such as pollution, cigarette smoke, alimentation, medication, stress, and so on. At low or moderate levels, they exert beneficial effects on cellular responses and immune function. At high concentrations, they generate oxidative stress, a deleterious process that can damage cell structures and lead to the development of chronic and degenerative illness. The human body has several mechanisms to counteract oxidative stress by producing antioxidants, which are either naturally produced in the body, or externally supplied through foods. Endogenous antioxidants include antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, and non-enzymatic compounds like lipoid acid, glutathione, L-ariginine, and coenzyme Q10. External essential antioxidants come from animal and plant foods such as vitamins: E, C, A, and trace minerals (selenium, zinc, iron, copper, and manganese). Other non-essential exogenous antioxidants include flavonoids, other phenolic compounds, and terpenoids. However, antioxidants in excess become pro-oxidants which are also harmful to the body. A delicate balance between free radicals and antioxidants in the body is necessary for maintaining a good health.
