We present here current data on the distribution and metabolism of vitamin E analogs in vivo. There are eight different naturally occurring forms of vitamin E : four tocopherols (α-,β, γ- and δ-toc) and four tocotrienols (α-,β-,γ and δ-toc). With regard to the bioavailability of vitamin E, it has been established that the affinity of various vitamin E analogs for α–tocopherol transfer protein (α-TTP), which may determine their plasma levels, is a major determinant if their biological activity however, a novel function of toc-3 has been noted as a result of its unique distribution in the skin and the adipose tissue. In addition, following the discovery that the final metabolites of Toc and Toc-3 are in the form of carboxyethyl hydroxychroman, it is now possible to examine the intermediary metabolites of vitamin E analogs. The metabolites of vitamin E is known to be involved in the actions of drug metabolic enzymes (CYP3A, CYP4F2). However, the relationship between α –TTP and the metabolic enzymes that are responsible for the regulation of vitamin E metabolism has yet to be clarified. Future research will focus on the elucidation of the vitamin E metabolic regulation system.
