Relative bioavailability of RRR- and all-rac-α-tocopheryl acetate in humans: studies using deuterated compounds

Vitamin E in nutritional supplements in its most common form is α-tocopheryl acetate. Available stereoisomeric forms are RRR- (1 stereoisomer) and all-rac- (8 stereoisomers). We evaluated the relative bioavailability of RRR- and all-rac-α-tocopheryl acetate using the deuterium-labeled isotopes [5-CD3] 2R, 4′R and 8′R-α-tocopheryl acetate (d3), and [5,7-(CD3)2]-all-rac-α-tocopheryl acetate (d6). Six adults (three males, three females), aged 25–59 y, received 150 mg each of d3 and d6 for 11 consecutive days. Blood samples were collected on days −1, 0, 1–11, 13, 14, 20, 25, 30, 60, 74, 88, 102, 122, and 137. Plasma and red blood cell tocopherol were evaluated by using HPLC and gas chromatography/mass spectrometry to distinguish between d3 and d6 tocopherols. Cholesterol, triglycerides, and LDL and HDL cholesterol were measured. Relative bioavailability of d3 when compared with d6 was 2.0 ± 0.06 when area under the plasma time concentration curve (AUC d3/d6) by trapezoidal rule (P < 0.05) was used. Correcting for lipid yielded the same finding. Unlabeled tocopherol (d0) decreased (P < 0.05) with vitamin E administration. It was concluded that the ratio of bioavailability of RRR-/all-rac-α-tocopheryl acetate is significantly greater than the currently accepted ratio of 1.36.