Structures of tocopherols/tocotrienols and the proposed metabolic pathways. The structures are illustrated with γ-tocopherol and γ-tocotrienol, which are both dimethylated at the 7- and 8- positions. The chromanol ring is trimethylated at 5-, 7-, and 8-positions in α-tocopherol, dimethylated at 5- and 8-positions in β-tocopherol, and methylated at 8-position in δ-tocopherol. The arrows (from right to left) indicate the sequential side chain degradation and the resulting metabolites.