Vitamin E: alpha-Tocopherol and the Other Forms of Vitamin E

ABSTRACT

Vitamin E has been a generic term for all tocopherol and tocotrienol derivatives. The most active form of vitamin E isoforms in vivo is regarded to be alpha-tocopherol which is the only form defined as vitamin E in the US Food and Nutrition Board, causing controversy over setting dietary reference intake (DRI) of vitamin E. However, most of the countries other than the US maintain the original concept that all isoforms are accepted as vitamin E but with different biopotency. The roles of the isoforms of vitamin E other than alpha-tocopherol have received continuous attention. Among them those of gamma-tocopherol and alpha-tocotrienol have been most studied in comparison with alpha-tocopherol, since gamma-tocopherol comprises major form of vitamin E in many plant seeds and those of the both vitamin E have been implicated in unique physiological functions. This review summarizes findings that have led a better understanding of vitamin E absorption, transport, tissue storage and various functions common and specific to vitamin E isoforms focusing alpha- and gamma-tocopherol as well as tocotrienols. It is expected to help redefining vitamin E and setting its DRI for Koreans.