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Journal of Lipid Research, Vol. 44, 1591-1600, August 2003
Copyright © 2003 by American Society for Biochemistry and Molecular Biology

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

Shawna L. Lemke^*, Stephen R. Dueker^1,*, Jennifer R. Follett^*, Yumei Lin^*, Colleen Carkeet^*, Bruce A. Buchholz^*, John S. Vogel^*, and Andrew J. Clifford^*

^* Department of Nutrition, University of California, Davis, One Shields Ave, Davis, CA 95616
Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94551

¹ To whom correspondence should be addressed. e-mail: srdueker{at}ucdavis.edu

The effect of vitamin A supplements on metabolic behavior of an oral tracer dose of [¹⁴C]ß-carotene was investigated in a longitudinal test-retest design in two adults. For the test, each subject ingested 1 nmol of [¹⁴C]ß-carotene (100 nCi) in an emulsified olive oil-banana drink. Total urine and stool were collected for up to 30 days; concentration-time patterns of [¹⁴C]ß-carotene, [¹⁴C]retinyl esters, and [¹⁴C]retinol were determined for 46 days. On Day 53, the subjects were placed on a daily vitamin A supplement (10,000 IU/day), and a second dose of [¹⁴C]ß-carotene (retest) was given on Day 74. All ¹⁴C determinations were made using accelerator mass spectrometry. In both subjects, the vitamin A supplementation was associated with three main effects: 1) increased apparent absorption: test versus retest values rose from 57% to 74% (Subject 1) and from 52% to 75% (Subject 2); 2) an 10-fold reduction in urinary excretion; and 3) a lower ratio of labeled retinyl ester/ß-carotene concentrations in the absorptive phase. The molar vitamin A value of the dose for the test was 0.62 mol (Subject 1) and 0.54 mol (Subject 2) vitamin A to 1 mol ß-carotene. Respective values for the retest were 0.85 and 0.74.

These results show that while less cleavage of ß-carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.

Supplementary key words accelerator mass spectrometry • isotope • kinetic

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