Tocopherols, tocotrienols and tocomonoenols: Many similar molecules but only one vitamin E

Abstract

The aim of this article is to correct a very general error in scientific articles, in textbooks and in the Internet that has become an accepted fact. In this literature, the term "vitamin E″ is used for several similar molecules (both tocopherols and tocotrienols) that have never been shown to have vitamin property, i.e. a protective effect against the human deficiency disease. In fact, the name "vitamin E″ should only be used to define molecules that prevent the human deficiency disease "Ataxia with Vitamin E Deficiency" (AVED). Only one such molecule is known, α-tocopherol. This error may confuse consumers as well as medical doctors, who prescribe vitamin E without realizing that the current use of the name includes molecules of unknown, if not unwanted functions.

Graphical abstract

Fig. 1

The differences in the α, β, γ and δ forms are in the number and position of the methyl groups on the chromanol ring. Only the β- and γ- forms of tocopherols or tocotrienols can be called isomers, having the same formula but a different arrangement of atoms in the molecule. The difference between the tocopherols and the tocotrienols is in the presence of three double bonds in the side chain of the latter.

Fig. 2

Matsumoto et al. [4] discovered α-tocomonoenol in palm oil, (A) and Yamamoto et al. [5] isolated an isomeric and chemically distinct α-tocomonoenol from the lipophilic fraction of salmon eggs having an unusual methylene unsaturation at the isoprenoid-chain terminus (B).

Fig. 3

l-ascorbic acid and d-ascorbic acid. The circles indicate the only difference of the two molecules of a hydrogen atom in opposite stereo position. l-ascorbic acid prevents scurvy but d-ascorbic acid does not.

Fig. 4

Rickets is a skeletal disease caused by lack of vitamin D. Vitamin D is also structurally specific: 1,25-dihydroxycholecalciferol prevents the development of rickets but 25-hydroxycholecalciferol, just lacking one OH group (circled in the active molecule), is inactive. Consequently, only 1,25-dihydroxycholecalciferol is called Vitamin D

Fig. 5

The recycling of vitamin E. The radical scavenging property of tocopherols [3] has been assumed to be at the basis of disease prevention, but this assumption was never proven. An additional claim of vitamin function for β-, γ-, and δ-tocopherol was based on their protection against fetus resorption in rats [6], but was incorrectly extended to the prevention of the human disease (AVED), the human neurological disease [7]. Based on a wrong assumption and an illogical extension of the animal effects to human disease, all tocopherols (wrongly defined frequently as “vitamin E isomers”) and tocotrienols, have been therefore called vitamin E.