Main content area

Dual isotope test for assessing β-carotene cleavage to vitamin A in humans

Hickenbottom, Sabrina J., Lemke, Shawna L., Dueker, Stephen R., Lin, Yumei, Follett, Jennifer R., Carkeet, Colleen, Buchholz, Bruce A., Vogel, John S., Clifford, Andrew J.
European journal of nutrition 2002 v.41 no.4 pp. 141-147
beta-carotene, bioactive properties, excretion, gas chromatography, high performance liquid chromatography, humans, isotopes, mass spectrometry, oral administration, retinyl acetate, urine, vitamin A
Background: The ability of β-carotene to deliver bioactive retinoids to tissues is highly variable. A clearer understanding of the environmental and genetic factors that modulate the vitamin A potential of β-carotene is needed. Aim of study: Assess the vitamin A value of orally administered β-carotene relative to a co-administered reference dose of preformed vitamin A. Methods: Equimolar doses (30 μmol) of hexadeuterated D₆β-carotene and D₆ retinyl acetate were orally co-administered in an emulsified formulation to a male subject. The plasma concentration time courses of D₆ retinol (derived from D₆ retinyl acetate) and bioderived D₃ retinol (from D₆β-carotene) were determined for 554 h postdosing using gas chromatography/mass spectrometry. Intact D₆β-carotene plasma concentrations were determined by high-pressure liquid chromatography. The ratio of the two forms of vitamin A, D₆ retinol/D₃ retinol, at any single time point is postulated to reflect the quantity of vitamin A derived from β-carotene relative to preformed vitamin A. Additionally, a minute amount of ¹⁴C β-carotene (50 nCi; 0.27 μg) was included in the oral dose and cumulative 24-h stool and urine samples were collected for two weeks to follow absorption and excretion of the b-carotene. The ¹⁴C nuclide was detected using accelerator mass spectrometry (AMS). Results During the absorption/distribution phase (3–11 h) the D₆/D₃ ratio of the two retinols was not stable and ranged between a value of 3 and 16. Between 11 and 98 h postdosing the ratio was relatively stable with a mean value of 8.5 (95 % CI: 7.5, 8.7). These data suggest that in this subject and under these conditions, 8.5 moles of β-carotene would provide a vitamin A quantity equivalent to 1 mole of preformed vitamin A. On a mass basis, 15.9 μg of β-carotene was equivalent to 1 μg of retinol. The total administered β-carotene was found to be 55 % absorbed by AMS analysis of cumulative stool. Conclusion: The co-administration of D₆β-carotene and D₆ retinyl acetate provides a technique for assessing individual ability to process β-carotene to vitamin A. The results indicate that a single time point taken between 11–98 h after dose administration may provide a reliable value for the relative ratio of the two forms of vitamin A. However, results from more subjects are needed to assess the general utility of this method.