J. Lipid Res.
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A more recent version of this article appeared on August 1, 2003

Papers In Press, published online ahead of print June 1, 2003
J. Lipid Res., doi:10.1194/jlr.M300116-JLR200
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Submitted on March 14, 2003
Revised on May 8, 2003
Accepted on May 20, 2003

Absorption and retinol equivalence of beta -carotene in humans is influenced by dietary vitamin A intake

Shawna L. Lemke, Stephen R. Dueker, Jennifer R. Follett, Yumei Lin, Colleen Carkeet, Bruce A. Buchholz, John S. Vogel, and Andrew J. Vogel

Department of Nutrition, University of California at Davis, Davis, CA 95616

Corresponding Author: srdueker{at}ucdavis.edu

The effect of vitamin A supplements on metabolic behavior of an oral tracer dose of [14C]beta -carotene was investigated in a longitudinal test-retest design with two healthy adults. For the test period, each subject ingested 1 nmol [14C]beta -carotene (100 nCi) in an emulsified olive oil-banana drink. Complete fecal and urine collections were made for 14 d and 30 d, respectively; concentration-time patterns of [14C]beta -carotene, [14C]retinyl esters, and [14C]retinol were determined for 46 d. On day 53 after the first dose, the subjects were placed on a daily vitamin A supplement (retinyl palmitate, 10,000 IU/d). A second dose of [14C]beta -carotene (retest) was given on the 74th day after the test dose and blood, urine, and stools were again collected. 14C determinations were made using Accelerator Mass Spectrometry. In both subjects, the vitamin A supplementation was associated with increased apparent absorption: test vs. retest values were raised from 57% to 74% absorption, and from 52% to 75% absorption for subjects 1 and 2, respectively. In addition, supplementation led to an ~10-fold reduction in urinary excretion of the absorbed dose in the first 48 h post dose. Circulating total beta -carotene, but not total retinol concentrations, were higher in response to supplementation. Integrated ratios of labeled retinyl ester/beta -carotene concentrations in the early absorption phase were lower after supplementation suggesting decreased intestinal cleavage. Assuming central cleavage of beta -carotene and adjusting for absorption, the molar vitamin A value of the dose for the test was 0.62 and 0.54 mol vitamin A to 1 mol beta -carotene for subjects 1 and 2. Respective values for the retest were 0.85 and 0.74 mol vitamin A to 1 mol beta -carotene. In conclusion, these results show that while less bioconversion of beta -carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.


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