evaluated the change in the intima-media thickness as a measure of atherosclerotic progression and reported that progression was 92 percent greater in the lowest (less than or equal to 0.27 µmol/L [14 µg/dL]) versus the highest (more than or equal to 0.64 µmol/L [34 µg/dL]) quartile of plasma β-carotene.

Dietary carotenoids have been suggested to decrease the risk of age-related macular degeneration (AMD), the most common cause of irreversible blindness in people over age 65 in the United States, Canada, and Europe (Seddon et al., 1994; Snodderly, 1995). The macula lutea (macula) is a bright yellow spot in the center of the retina and is specialized and functions to maintain acute central vision. Of all the carotenoids circulating in the body, only two polar species, lutein and zeaxanthin, are contained in the macula (Bone et al., 1985; Handelman et al., 1988). Two groups of investigators have suggested pathways by which these two carotenoids are biochemically interchanged in the macula (Bone et al., 1993; Khachik et al., 1997a).

The potential role of carotenoids in the prevention of AMD has been comprehensively reviewed (Snodderly, 1995). Seddon et al. (1994) analyzed the association between carotenoid intake and advanced AMD in a large, multicenter, case-control study involving 356 cases and 520 control subjects with other ocular conditions. Those in the highest quintile of dietary carotenoid intake had a 43 percent lower risk for macular degeneration compared with those in the lowest (OR = 0.57; 95 percent CI = 0.35−0.92). Among the specific carotenoids, intake of lutein and zeaxanthin (grouped in the carotenoid food composition database) was most strongly associated with decreased risk. Those in the highest quintile of intake had a 60 percent lower risk compared to the lowest quintile of intake.

Some, but not all, studies using blood carotenoid concentrations also suggest protective effects against risk of AMD. The Eye Disease Case-Control Study (EDCCSG, 1993) measured serum carotenoids in 391 cases with neovascular AMD and 577 control subjects. The study reported protective effects of total carotenoids, α-carotene, β-carotene, β-cryptoxanthin, and lutein and zeaxanthin, with odds ratios ranging from 0.3 to 0.5 for the high group (more than the eightieth percentile) versus the low group (less than the twentieth percentile). Carotenoid concentrations associated with the lowest risk are shown in Table 8-4.