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Role of free Radicals


Cataracts are one of the major causes of blindness worldwide. The disease affects up to 50% of the population over 75 years of age in the USA, with a greater incidence in developing nations. The lens has substantial supplies of antioxidant reserves, antioxidant enzymes and secondary defenses, to prevent cataract formation. Exposure to environmental stress, such as UV light, smoking and oxygen results in the production of radical species, which damage lens proteins. Superoxide and hydroxyl radicals cause damage to cell membrane lipids and proteins, which deposit on the surface of the lens causing opacities. Decreased levels of ascorbate and ß-carotene, and increased incidence of cataract formation, have been reported in smokers. This increased exposure to oxidative stress and decreased antioxidant protection is thought to contribute to the increased incidence of the disease. Many epidemiological studies have examined the association between cataract formation and nutrition. High nutritional intake of vitamin E, C and ß-carotene, associated with a decreased risk of cataract formation. Ascorbate levels in the lens are significantly higher than plasma levels and vitamin C is reportedly the most effective grade at reducing cataract incidence. One study described a 70 % lower incidence of cataract formation in individuals supplemented with vitamin C compared to those without vitamin C-supplementation.


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