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Nutrient Metabolism
Research Communication

The Relative Vitamin A Value of 9-cis ß-Carotene Is Less and That of 13-cis ß-Carotene May Be Greater than the Accepted 50% That of All-trans ß-Carotene in Gerbils¹

Denise M. Deming^*, David H. Baker^*, and John W. Erdman, Jr.^*,**2

^* Division of Nutritional Sciences, Department of Animal Sciences and ^** Department of Food Science and Human Nutrition, University of Illinois, Urbana, IL 61801

²To whom correspondence should be addressed. E-mail: jwerdman{at}uiuc.edu.

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

KEY WORDS: • vitamin A • all-trans ß-carotene • 9-cis ß-carotene • 13-cis ß-carotene • bioavailability • gerbils