Although free radicals have reactive chemical properties, the characteristics of free radical homeostasis have been maintained during the evolution of oxygen-requiring organisms. These characteristics are implicated in performing diverse physiological functions and none of deleterious effects resulting from neat balance of production and scavenging of free radicals, as well as the repair of radical-induced damage of bio-macromolecules under physiological conditions. Nutrients and their metabolites along with "essential" antioxidants play crucial roles in maintaining free radical homeostasis. Glutathione homeostasis interrelates synergistically with free radical homeostasis. Free radical homeostasis should be maintained well in healthy humans at different ages and under various living conditions in order that oxidative stress and its induced oxidative damage will be prevented or ameliorated before aging.
