ABSTRACT
I. INTRODUCTION Vitamin E was discovered by Evans in 1936 at the University of California at Berkeley (1), after Evans and Bishop had already described vitamin E deficiency in 1922 (2). Vitamin E was characterized as α-tocopherol (3). In the following years, other isoforms were isolated and characterized (4). Apart from other tocopherols, which are discussed in detail in Chapter 5, four tocotrienols were also discovered. When these forms of vitamin E were compared with α-tocopherol for their biopotency in a rat assay, which is based on the prevention of fetal resorption, none of them reached the biopotency of α-tocopherol. While d-α-tocotrienol still achieves 50% of the efficacy of RRR-α-tocopherol, which corresponds to 0.75 IU/mg (as compared with 1.49 IU/mg for RRR-α-tocopherol), the activity of d-β-tocotrienol is only 5% (0.08 IU/mg). The activities of γ - and δ-tocotrienol in the rat assay are unknown (5). This low biological activity of tocotrienols after oral supplementation has limited their practical use, although their antioxidant properties may be superior to tocopherols in certain applications.
