Human plasma and tissue α-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E

Abstract

We report a comparison of natural and synthetic vitamin E in humans using deuterium labeling to permit the two forms of vitamin E to be measured independently in plasma and tissues of each subject. Differences in natural and synthetic vitamin E concentrations were measured directly under equal dosage conditions using an equimolar mixture of deuterated RRR-α-tocopheryl acetate and all-rac-α-tocopheryl acetate. Two groups of five adults took 30 mg of the mixture as a single dose and as eight consecutive daily doses, respectively. After a 1-mo interval the schedule was repeated but with a 10- fold higher dose (ie, 300 mg). In each case, the ratio of plasma d3-RRR-α- tocopherol to d6-all-rac-α-tocopherol (RRR:rac) increased from ≃ 1.5-1.8 to ≃2 after dosing ended. In an elective surgery study in which 22 patients were given 150 mg/d for up to 41 d before surgery, the RRR:rac in tissues was lower than in plasma and the percentage of deuterated α-tocopherol was lower in all tissues except gallbladder and liver. In a terminally ill patient given 30 mg/d for 361 d, plasma and tissue (x̄ ± SD) RRR-rac ratios (and % deuterated α-tocopherol) at autopsy were 2.06 (6.3%) and 1.71 ± 0.24 (5.9 ± 2.2%), respectively. In a second terminally ill patient given 300 mg/d for 615 d, the corresponding values were 2.11 (68%) and 2.01 ± 0.17 (65 ± 10%), respectively. The results indicated that natural vitamin E has roughly twice the availability of synthetic vitamin E. This 2:1 ratio is significantly higher than the currently accepted RRR:rac of 1.36:1.00. γ-Tocopherol, expressed as a fraction of total unlabeled tocopherols in 15 elective surgery patients, was 1.4.-4.6 (mean: 2.6) times greater in adipose tissue, muscle, skin, and vein than in plasma, which is a substantially larger fraction than had been recognized previously.