The homeostasis of free radicals is vital to the evolution and life of oxygen-requiring organisms. Under normal physiological conditions, rates of the production of free radicals are virtually equal to rates of their removal. The cytotoxic effect of free radicals is deleterious to cells and mediates the pathogenesis of a wide array of diseases. Therefore, antioxidants (e.g. vitamin C, vitamin E, β-carotene, and glutathione) are essential to the survival, health, and reproduction of animals, including humans. Antioxidants may be classified as nutritionally essential (e.g. vitamin antioxidants), indirectly essential (e.g., dietary fibre), conditionally essential (e.g. flavonoids and other effective phytochemicals) or non-essential. In the body, appropriate nutrition should not only prevent diseases, but also promote free radical homeostasis. Thus, it is crucial to develop useful indicators of oxidative stress, such as the cellular ratio of /, lipid peroxidation, oxidative modification of protein and DNA damage. On the basis of the recent report that the improper therapy of iron deficiency results in free radical-mediated dysfunction of the gastrointestinal tract, it is important to verify whether the formulated requirement of nutrients meet the need of maintaining the homeostasis of free radicals. The recommended intake of vitamin E, vitamin C and other antioxidants may need to be revised so as to protect the body against oxidative stress brought about by endogenous and exogenous factors. In order to delay aging and promote health in humans of all ages, and eliminate oxidative damage in response to the treatment of certain diseases, special nutritional measures should be taken. These measures may include the control of caloric intake, reduction in the absorption of free radicals and electrophilic substances, and adequate provision of antioxidant nutrients as well as effective phytochemicals and nutraceuticals. We predict that the concept of free radical biology will continue to greatly advance life sciences, including nutrition and medicine. The 21st century holts great promise for both discoveries and applications in this rapidly emerging field of"antioxidants and health".
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