Antioxidant nutrients and nonnutrients Protection against Radical Damage

Apart from avoidance of exposure to ionizing radiation, there is little that can be done to prevent the formation of radicals, as they are the result of normal metabolic processes and responses to infection. There are, however, a number of mechanisms to minimize the damage done by radical action. As the important radicals are oxygen radicals, and the damage done is oxidative damage, the protective compounds are known collectively as antioxidants.

Antioxidants such as vitamin E (sections 7.4.3.3 and 11.4), carotene (section 7.4.3.4) and ubiquinone (section 3.3.1.2) owe their antioxidant action to the fact that they can form stable radicals, in which an unpaired electron can be delocalized in the molecule. Such stable radicals persist long enough to undergo reaction to yield non-radical products. However, because they are stable, they are also capable of penetrating further into cells or lipoproteins, and hence causing damage to DNA in the nucleus or lipids in the core of the lipoprotein. Therefore, as well as being protective antioxidants, these compounds are also capable of acting as potentially damaging pro-oxidants, especially at high concentrations. This may explain the disappointing results of trials of P-carotene against lung cancer (section 7.2.6).

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