Abstract
In the last 30 years, the research on vitamin E metabolism has made great progress. Initially, dietary vitamin E was thought to be absorbed by passive diffusion in the small intestine, but it has become clear that transporter proteins, such as Niemann-Pick C1-like 1 and ATP- binding cassette transporter A1, are involved in at least a part of the intestinal absorption of vitamin E. The α-tocopherol transfer protein (α-TTP) has also been shown to play an important role in maintaining levels of vitamin E in the body. Among vitamin E isoforms, α- tocopherol, which has the highest affinity for α-TTP, is preferentially transported from the liver to extrahepatic tissues. The importance of α -TTP in vitamin E metabolism has influenced the Dietary Reference Intake for Japanese. In addition, carboxyethyl-hydroxychroman was identified as the major metabolite of vitamin E. This finding revealed that vitamin E is metabolized by a kind of drug metabolism reaction.
