ABSTRACT
Vitamin E is the term that describes eight lipophilic, naturally occurring compounds including four tocopherols and four tocotrienols (Figure 6.1). 1 Tocopherols have a saturated phytyl tail, whereas tocotrienols have an unsaturated tail. Within each class, four forms exist as α-, β-, γ-, and δ- that differ based on the number and position of methyl groups present on the chromanol head. When the chromanol head is fully methylated and the phytyl tail is saturated, this vitamer is identified as α-tocopherol. The most abundant forms of vitamin E found biologically and in the diet are α- and γ-tocopherol. 2 Structurally, they are similar and differ only in that γ-tocopherol has an unsubstituted position on the chromanol head (Figure 6.1). Thus, due to the dietary and biological abundance of these vitamin E forms, a considerable body of knowledge has accumulated since their discovery. This 106chapter will therefore focus on these vitamin E forms, although greater emphasis will be placed on α-tocopherol because this is the only form of vitamin E that is essential for humans.
