Relative bioavailabilities of natural and synthetic vitamin E formulations containing mixed tocopherols in human subjects.

There are several reports in the literature on the relative bioavailabilities of RRR (natural) vs. all-rac (synthetic) forms of vitamin E in humans and animal models but none on the bioavailability of alpha-tocopherol in mixed vitamin E formulations. In the present study we examined the bioavailability of alpha-tocopherol in a typical commercially available product containing mixed tocopherols. We also tested a formulation containing all-rac-alpha-tocopherol with mixed tocopherols for purposes of comparison along with straight RRR- and all-rac-alpha-tocopheryl acetate as reference products. Normal male subjects were given one of the four formulations of vitamin E (800 IU per day in softgel capsule form for 10 days): 1. All-rac-alpha-tocopheryl acetate, 2. RRR-alpha-tocopheryl acetate, 3. RRR-alpha-tocopherol with mixed tocopherols, and 4. all-rac-alpha-tocopherol with mixed tocopherols. Both serum alpha- and gamma-tocopherols were determined by HPLC at baseline, and at days 2, 4, 7 and 10. The values for alpha- at baseline and 10 days were 0.80, 0.80, 0.80 & 0.79 mg/dl and 1.67, 1.72, 1.76 & 1.62 mg/dl. The values for gamma- were 0.28, 0.29, 0.30 & 0.29 mg/dl and 0.11, 0.08, 0.10 & 0.10 mg/dl. Thus the data show that a) the bioavailability of RRR- and all-rac-alpha-tocopherols is not affected by other tocopherols, and b) both RRR- and all-rac-alpha-tocopherol (free or esterified) significantly suppress the serum gamma tocopherol to the same extent. Furthermore, since there was no difference in the serum values of alpha-tocopherol between RRR- and all-rac-vitamin E given the same dose as IUs, the data also support the currently accepted ratio of 1.36 for the biopotency of RRR- vs. all-rac-alpha-tocopheryl acetate.