Any substance that reduces oxidative damage (damage due to oxygen) such as that caused by free radicals. Free radicals are highly reactive chemicals that attack molecules by capturing electrons and thus modifying chemical structures. Well-known antioxidants include a number of enzymes and other substances such as vitamin C, vitamin E and beta carotene (which is converted to vitamin A) that are capable of counteracting the damaging effects of oxidation. Antioxidants are also commonly added to food products like vegetable oils and prepared foods to prevent or delay their deterioration from the action of air. Antioxidants may possibly reduce the risks of cancer and age-related macular degeneration (AMD). Antioxidants clearly slow the progression of AMD.
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An agent that inhibits oxidation; any of numerous chemical substances, including certain natural body products and nutrients, that can neutralize the oxidant effect of free radicals and other substances.Free radicals, formed in the course of normal cellular respiration and metabolism, and more abundantly under the influence of certain environmental chemicals and sunlight, have been implicated in the causation of various types of tissue damage, particularly those involved in atherosclerosis, the aging process, and the development of cancer. A free radical is any atom or molecule that has 1 or more unpaired electrons and is therefore highly reactive, seeking to acquire electrons from other substances. Free radicals are normally scavenged from tissues by the a. enzymes superoxide dismutase and glutathione peroxidase. Ubidecarenone (coenzyme Q10) is also thought to act as an a. in mitochondrial respiration reactions. In addition, a number of nutrient substances, vitamins, and minerals have been shown to contribute to a. functions, generally by serving as co-factors or co-enzymes. These include selenium, β-carotene, and vitamins C and E. It has been postulated that an imbalance between the production of free radicals and natural a. processes may be a major causative factor in aging and in many chronic and degenerative disorders, and some have speculated that a. nutrients may have a role in disease prevention. Oxidation of LDL cholesterol does indeed seem to be responsible for foam cell formation in the genesis of atherosclerotic plaques. In addition, free radicals have been shown to damage DNA in ways that can culminate in malignant change. But oxidation also occurs in many beneficial processes, including chemotaxis of cells with immunological functions, phagocytosis, clotting mechanisms, and apoptosis. Moreover, antioxidants do not exert their effects in only one way, but can act during initiation or propagation of reactions at a variety of intracellular and extracellular sites, and in some circumstances can be pro-oxidant. Claims that vitamins and other nutrients, when taken in massive doses, can prevent heart attack or cancer or retard aging are not based on scientific evidence. Although a high intake of a. nutrients from food sources appears to offer some health advantages, there is at present no unequivocal evidence that any a. nutrient, when taken in excess of normal dietary amounts, has value in the prevention or treatment of cardiovascular disease, cancer, or any other abnormal process except such as may be associated with frank nutritional or vitamin deficiency. In fact, although naturally occurring a. nutrients are vital dietary components, they can cause adverse effects when large amounts are taken for prolonged periods. A controlled trial of β-carotene and retinol not only failed to show any benefit but was aborted when statistics showed large increases in the risk of death from lung cancer and cardiovascular disease.

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an·ti·ox·i·dant .ant-ē-'äk-səd-ənt, .an-.tī- n any of various substances (as beta-carotene, vitamin C, and alpha-tocopherol) that inhibit oxidation or reactions promoted by oxygen and peroxides and that include many held to protect the living body from the deleterious effects of free radicals
antioxidant adj

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a substance capable of neutralizing oxygen free radicals, the highly active and damaging atoms and chemical groups produced by various disease processes and by poisons, radiation, smoking, and other agencies. The body contains its own natural antioxidants but there is growing medical interest in the possibility of controlling cell and tissue damage by means of supplementary anti-oxidants. Those most commonly used are vitamin C (ascorbic acid), vitamin E (tocopherols), and beta carotene. Evidence is accumulating that these substances can reduce the incidence of a number of serious diseases.

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an·ti·ox·i·dant (an″te-okґsĭ-dənt) 1. preventing or delaying oxidation. 2. a substance that prevents or delays oxidation, such as any of numerous synthetic or natural substances added to something to prevent or delay its deterioration by action of oxygen in the air. Rubber, paints, vegetable oils, and prepared foods commonly contain antioxidants.

Medical dictionary. 2011.

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