. "2 Vitamin C, Vitamin E, Selenium, and •-Carotene and Other Carotenoids: Overview, Antioxidant Definition, and Relationship to Chronic Disease." Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, DC: The National Academies Press, 2000.
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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
1998), others are much more supportive of a protective role for vitamin E in coronary heart disease (Pryor, 2000).
There have been a number of observational epidemiological studies of the risk of developing cataracts in humans. Many of these studies indicate that the risk of cataracts may be inversely proportional to the serum level of antioxidants (Knekt et al., 1992; Taylor et al., 1995) or may be reduced by supplement use (Jacques et al., 1997). These studies, however, have been considered to be inconclusive (Christen et al., 1996a; Leske et al., 1998). In the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study, 5 to 8 years of daily supplementation with either 50 mg of vitamin E or 20 mg of β-carotene or both resulted in no difference in the prevalence of cataracts in the men in this study (Teikari et al., 1997).
Age-Related Macular Degeneration
This irreversible disease, which is the major form of blindness in the elderly in the United States, Canada, and Europe, has been related to antioxidants found in the diet. This is because the pigment in the macular region of the normal retina consists of the two xanthophyll carotenoids, lutein and zeaxanthin (Bone et al., 1988; Handelman et al., 1988). This observation, coupled with the epidemiological observations of an inverse relationship between the risk of age-related macular degeneration (AMD) and the ingestion of fruits and vegetables (Goldberg et al., 1988), led a number of groups to propose that the basis of this chronic disease was a nutritional deficiency of green, leafy vegetables and yellow and orange fruits and vegetables that were rich in lutein and zeaxanthin (EDCCSG, 1992; Seddon et al., 1994; Snodderly, 1995). Another association was the observation that smokers, who have lower plasma levels of carotenoids, also have a lower macular pigment (lutein and zeaxanthin) density (Hammond et al., 1996) and an increased risk of developing AMD (Christen et al., 1996b). However, all of these reports are associative in nature and do not demonstrate a causal relationship between deficiencies of lutein and zeaxanthin and development of AMD.