Mass balance and non‐compartmental analysis of an oral tracer dose of RRR‐α‐tocopherol in humans

Abstract

The use of a minute tracer dose combined with a long study period enable the tracer to fully equilibrate with its tracee without perturbing the body's steady state. Based on this principle, we aimed to quantify and interpret in vivo human metabolism of ingested natural-source vitamin E in twelve healthy adults. Each subject ingested 1.811 nmol, 100 nCi of [5-14CH3]-RRR-α-tocopherol, then the 14C in urine and feces were followed over a 21 d period since the ingestion. The 14C in plasma and Red Blood Cells (RBC) were followed over a consecutive 70 d period. Urine, feces, plasma and RBC were also collected at 460 d after dosing. The mass balance and the true digestibility of 14C were 79.2 % (0–4 d) and 81.6% (4–21 d), respectively. A total of 4.3 % and 23.2 % of ingested 14C were eliminated in urine and feces, respectively, over 21 d. The remaining 73 % was still in the body on the 21st d after dosing. Plasma t1/2, 0–70 d and t1/2, 0–∞ were 7.3 d and 17.8 d, respectively. RBC t1/2, 0–70 d and t1/2, 0–∞ were 13.7 d and 81.6 d, respectively. The apparent digestibility of natural-source vitamin E matched prior estimates and its true digestibility was reported for the first time. Plasma and RBC 14C half-lives were longer than prior estimates due to the long sampling duration of the study design. Grant Funding Source: National Institute of Health