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

The effect of vitamin A, supplements on metabolic behavior of an oral tracer dose of [C-14]beta-carotene was investigated in a longitudinal test-retest design in two adults. For the test, each subject ingested 1 nmol of [C-14]beta-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 [C-14]beta-carotene, [C-14]retinyl esters, and [C-14]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 [C-14]beta-carotene (retest) was given on Day 74. All C-14 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 similar to10-fold reduction in urinary excretion; and 3) a lower ratio of labeled retinyl ester/beta-carotene concentrations in the absorptive phase. The molar vitamin A value of the dose for the test was 0.62 mot (Subject 1) and 0.54 mot (Subject 2) vitamin A to 1 mot beta-carotene. Respective values for the retest were 0.85 and 0.74. jlr These results show that while less cleavage of beta-carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.