a SI conversion factor used for total caroteniods, α- and β-carotene, and lycopene = 0.01863 µg/dL to µmol/L; for β-cryptoxanthin = 0.01809; and for lutein and zeaxanthin = 0.01758.
SOURCE: EDCCSG (1993).
Mares-Perlman et al. (1994) examined the association between serum carotenoid concentrations and age-related maculopathy in 167 case-control pairs and reported no association for any of the carotenoids, except lycopene, with persons in the lowest quintile of lycopene having a doubling in risk of maculopathy (cutpoint not stated). West et al. (1994) examined the relationship between plasma β-carotene concentration and AMD in 226 subjects and found the risk was lowest for the highest quartile of plasma β-carotene (more than 0.88 µmol/L [47 µg/dL] ) (OR high quartile versus low = 0.62). Plasma lutein and zeaxanthin were not measured in this study.
Hammond and Fuld (1992) developed an optical system that, in situ, measures the intensity of the unique yellow color of the macula and presumably estimates the levels of lutein and zeaxanthin. This measure is known as Macular Pigment Optical Density (MPOD). Dietary intake of carotenoids, fat, and iron, as well as plasma concentrations of lutein and zeaxanthin, were positively related with MPOD in men, but only plasma concentrations of lutein and zeaxanthin were associated with MPOD values for women (Hammond et al., 1996). In the same studies, men had significantly higher MPOD readings than women despite similar plasma carotenoid concentrations and similar dietary intake, except for fat. These investigators also demonstrated that the MPOD of most subjects could be substantially increased by the addition of relatively small amounts of foods to the diet that are high in lutein (1/2 cup