gastritis, risk factors for gastric cancer, are low compared to those of apparently healthy individuals and are increased by eradication of the H. pylori infection or by vitamin C supplementation (Rokkas et al., 1995; Waring et al., 1996). However, H. pylori infection and accompanying inflammation do not alter vitamin C levels or antioxidant potential in the gastroduodenal mucosa (Phull et al., 1999). Despite the epidemiological associations and the evidence that gastric juice vitamin C is protective against nitrosation and oxidant damage, the two vitamin C supplementation studies conducted to date have not shown a subsequent decrease in gastric cancer incidence (Blot et al., 1993; O'Toole and Lombard, 1996).
Although many of the above studies suggest a protective effect of vitamin C against specific cancers by site, the data are not consistent or specific enough to estimate a vitamin C requirement based on cancer.
Ocular tissue concentrates vitamin C, which might suggest, teleologically, that the tissue needs this vitamin (Rose et al., 1998). It is reasonable to expect, therefore, that oxidative damage to ocular tissue is an important source of degenerative eye disease and that supplementation by vitamin C would be an effective means of lessening the risk of diseases such as cataract.
In a case-control comparison of 77 subjects with cataract and 35 control subjects with clear lenses, vitamin C intakes of greater than 490 mg/day were associated with a 75 percent decreased risk of cataracts compared with intakes of less than 125 mg/day (Jacques and Chylack, 1991). Similarly, vitamin C intakes greater than 300 mg/day were associated with a 70 percent reduced risk of cataracts (Robertson et al., 1989). In a second case-control comparison with 1,380 cataract patients and 435 control subjects, similar results were found: although intake numbers were not reported, above-median vitamin C intake was associated with a 20 percent decrease in the risks of cataracts (Leske et al., 1991). In contrast, an analysis of data derived from the Baltimore Longitudinal Study on Aging found no increased association between 260 mg/day of vitamin C and risk of cataracts compared to 115 mg/day (Vitale et al., 1993).
In an 8-year prospective study, Hankinson et al. (1992) evaluated the experience of more than 50,000 nurses in the Nurses Health Study. Dietary vitamin C intakes were not associated with a decreased risk of cataract, but cataract risk was 45 percent lower among the nurses who consumed vitamin C supplements for 10 or