Different Forms of Vitamin E and Their Biopotencies

There are several distinct forms of vitamin E in dietary supplements vying for consumers' attention. While tocotrienols, the form of vitamin E that features an unsaturated side chain, is becoming more popular, tocopherols (mainly alpha-tocopherol) still remain the most widely used and researched form. Tocopherol supplements usually feature either alpha-tocopherol, alpha-tocopheryl acetate or alpha-tocopheryl succinate, the latter two thought to confer enhanced stability.

Alpha-tocopherol can be derived from natural sources or can be synthetically produced. Natural­source alpha-tocopherol is a single stereoisomer and is designated by the prefix "d-" or "RRR," while the synthetic form is a combination of eight stereoisomers and is identified by the prefix "dl-" or "all-rac."

Natural­source d-alpha-tocopherol has been shown to have a higher biopotency than the dl-rac form. The currently accepted ratio is 1.36:1 (d:dl). A recent proposal has been made to the National Academy of Sciences to change this biopotency factor to 2:1 based on the results of more recent research studies. Yet, some researchers challenge this proposition believing it is based on erroneous conclusions extrapolated from these studies.¹

References

1. Hoppe PP, Krennrich G. Bioavailability and potency of natural-source and all-racemic a-tocopherol in the human: a dispute. Euro J of Nutr 2000;39:183-93.