Several epidemiological studies have identified an association between vitamin C and cataract incidence (Ferrigno et al 2005, Jacques & Chylack Jr 1991, Jacques et al 1988, Valero et al 2002); however, studies investigating whether supplementation is protective have produced mixed results (Chasan-Taber et al 1999, Chylack Jr et al 2002, Hammond & Johnson 2002, Jacques et al 1997, 2001, Kuzniarz et al 2001, Seddon et al 1994, Taylor et al 2002).
Results from the Harvard Nurses' Health Study, Physician's Health Study, the Beaver Dam Eye Study and the Australian Blue Mountains study suggests that if protective effects are to be seen, it is most likely if vitamin C is taken long-term (5-10 years or more) and/or used as part of a multivitamin combination (Kuzniarz et al 2001, Mares-Perlman et al 2000, Seddon et al 1994, Taylor et al 2002).
It is suspected that vitamin C protects the lens of the eye from oxygen-related damage over time by both direct free radical scavenging activity and indirect activity. This is achieved primarily by protecting endogenous alpha-tocopherol (the major Iipid-soluble antioxidant of retinal membranes) against oxidation induced by UV radiation and by regenerating it (Stoyanovsky et al 1995).
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