What are Antioxidants?
The terms antioxidants and free radicals are being used more and more by nutritionists and other health professionals. Antioxidants are compounds that are thought to be good for you and free radicals are harmful. In general, antioxidants neutralize free radicals that are generated in the body and prevent damage to cell proteins, lipids and carbohydrates. Antioxidants can be water-soluble or lipid-soluble, thus some exist within the lipid or within the water portion of cells.
Cellular antioxidant defense mechanisms can be classified into primary and secondary systems. The primary defenses include familiar nutrients such as vitamins (vitamin E and vitamin C), carotenoids (b -carotene, lycopene), thiols (glutathione, lipoic acid), ubiquinols, flavonoids and polyphenols (from herbs, teas, grape skins) and so on and a variety of enzyme systems (catalase, superoxide dismutase, glutathione peroxidase). Primary defense mechanisms are thought to interact directly with harmful free radicals. The secondary defenses include enzymes that breakdown proteins and lipids and DNA repair mechanisms. Secondary defenses are primarily involved in repair of already damaged proteins and lipids.
Why Do We Need Antioxidants?
Harmful free radicals are generated in the body during normal metabolism and upon exposure to environmental insults such as infectious agents, pollution, UV light and radiation and so on. When harmful free radicals are not neutralized by the body's primary and secondary defense mechanisms, an excess of harmful radicals exists. Thus, if the generation of harmful radicals has exceeded the body's or cell's capacity to effectively neutralize these radicals, then these harmful radicals will damage vital proteins, lipids and DNA. Therefore, we need antioxidants to ensure that our defense mechanisms for neutralizing harmful radicals will not be exceeded. Numerous epidemiological studies have demonstrated an association between higher intakes or higher blood concentrations of certain antioxidants and a lower incidence of certain degenerative diseases. Clinical studies have also shown that supplemental levels of antioxidant vitamins (vitamin E, vitamin C and b -carotene) reduce an individual's risk for certain cancers and cardiovascular disease. Moreover, a protective relationship has been shown between cancer risk and fruit and vegetable consumption (the major source of antioxidant nutrients).
Antioxidants and Health Maintenance
Awareness of the potential benefits of antioxidant nutrients in health maintenance is growing. Evidence is now available that indicates that harmful free radicals play a role in most major health problems such as cancer, cardiovascular disease and degenerative diseases associated with aging. The function of antioxidant nutrients in the body is quite varied. Antioxidants effect cell differentiation and proliferation, block nitrosamine formation, stimulate the immune response, help maintain the integrity of cell membranes and matrixes, and aid in the maintenance of normal DNA repair. It is currently believed that antioxidants do not act alone, but rather carry out their protective effects by using various combinations of antioxidant defense mechanisms. For example, when vitamin E neutralizes a harmful radical, vitamin E is recycled back to its original form by interacting with vitamin C. Vitamin C is recycled by interacting with another antioxidant such as glutathione. Recycling is just one mechanism the body uses to maintain and adequate supply of antioxidants. Our knowledge of the effect of this recycling and other interplay mechanisms within the antioxidant defense systems is far from complete. However, evidence gathered to date suggest that these antioxidant nutrients must be constantly replenished through the diet and/or by dietary supplementation.
Joy E. Swanson, Ph.D.,
Division of Nutritional Sciences,
Cornell University © 1998-99 Cornell University
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