The relative vitamin A value of 9-cis β-carotene is less and that of 13-cis β-carotene may be greater than the accepted 50% that of all-trans β-carotene in gerbils

The effectiveness of β-carotene (βC) as a vitamin A (VA) precursor may be influenced by the proportions of cis isomers of βC consumed in the diet. Although the metabolic fates of cis isomers of βC are poorly understood, their retinol equivalency has been assigned a value 50% that of all-trans (at) βC. A dose-response design was used to estimate the relative VA value (VAV) of atβC, 9-cis (9c) βC and 13-cis (13c) βC in gerbils using total liver retinol as a measure of VAV. Ten groups of gerbils received a daily dose of oil with or without βC isomer by gavage for 7 d. Nine groups (n = 5) were divided equally among the three βC dosing treatments with each isomer provided at 141, 275 and 418 nmol/d. Total liver VA (171-259 nmol) in gerbils administered atβC was higher than total liver βC (25-53 nmol). Stores of VA and βC in livers from gerbils administered atβC were higher than stores of VA and βC in livers from those given 9cβC or 13cβC. The relative VAV of cis βC isomers was estimated by comparing slopes of dose-response lines of all three βC isomers using atβC as a reference. Total liver VA and βC increased linearly (P < 0.05) with increasing βC intake in gerbils gavaged with all three βC isomer oils. The relative VAV of 9cβC was less (38%) and 13cβC was more (62%) than the assigned value of 50% that of atβC. Thus, the proportions of cis isomers of βC contained in a food could negatively affect the vitamin A value of the diet.