A Minute Dose of 14C-β-Carotene Is Absorbed and Converted to Retinoids in Humans

Our objective was to quantify the absorption and conversion to retinoids of a 1.01-nmol, 3.7-kBq oral dose of C-14-beta-carotene in 8 healthy adults. The approach was to quantify, using AMS, the elimination of C-14 in feces for up to 16 d after dosing and in urine for up to 30 d after dosing. The levels of total C-14 in undiluted serial plasma samples were measured for up to 166 d after dosing. Also, the levels of C-14 in the retinyl ester (RE), retinol (ROH), and beta-carotene fractions that were isolated from undiluted plasma using HPLC were measured. The apparent digestibility of the C-14 was 53 +/- 13% (mean +/- SD), based on the mass balance data, and was generally consistent with the area under the curve for zero to infinite period of C-14 that was eliminated in the feces collections made up to 7.5 d after dosing. Metabolic fecal elimination, calculated as the slope per day (% C-14-dose/collection from d 7.5 to the final day), was only 0.05 +/- 0.02%. The portion of the C-14 dose eliminated via urine was variable (6.5 +/- 5.2%). Participants [except participant 6 (P6)] had a distinct plasma peak of C-14 at 0.25 d post-dose, preceded by a shoulder at similar to 0.1 d, and followed by a broad C-14 peak that became indistinguishable from baseline at similar to 40 d. Plasma C-14-RE accounted for most of the absorbed C-14 early after dosing and P1 had the longest delay in the first appearance of C-14-RE in plasma. The data suggest that plasma RE should be considered in estimating the ROH activity equivalent of ingested beta-carotene. J. Nutr. 139. 1480-1486, 2009.