RELATIVE BIOAVAILABILITY OF RRR-ALPHA-TOCOPHERYL AND ALL-RAC-ALPHA-TOCOPHERYL ACETATE IN HUMANS - STUDIES USING DEUTERATED COMPOUNDS

Vitamin E in nutritional supplements in its most common form is alpha- tocopheryl acetate. Available stereoisomeric forms are RRR- (1 stereoi somer) and all-rac- (8 stereoisomers). We evaluated the relative bioav ailability of RRR- and all-rac-alpha-tocopheryl acetate using the deut erium-labeled isotopes [5 CD3] 2R, 4'R and 8'R-alpha-tocopheryl acetat e (d3), and [5,7-(CD3)(2)]/-all-rac-alpha-tocopheryl acetate (d6). Six adults (three males, three females), aged 25-59 y, received 150 mg ea ch 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 an d gas chromatography/mass spectrometry to distinguish between d3 and d 6 tocopherols. Cholesterol, triglycerides, and LDL and HDL cholesterol were measured. Relative bioavailability of d3 when compared with d6 w as 2.0 +/- 0.06 when area under the plasma time concentration curve (A UC d3/ d6) by trapezoidal rule (P < 0.05) was used. Correcting for lip id yielded the same finding. Unlabeled tocopherol (d0) decreased (P < 0.05) with vitamin E administration. It was concluded that the ratio o f bioavailability of RRR-/all-rac-alpha-tocopheryl acetate is signific antly greater than the currently accepted ratio of 1.36.