Figure 1: Natural R,R,R-tocopherols and R,R,R-tocotrienols. The isoforms differ in the number of methyl groups on the chromanol head group. The α-tocopherol isoform is the most abundant in tissues. The γ-tocopherol isoform is abundant in the diet but, in tissues, γ-tocopherol is 10 fold less abundant than α-tocopherol because of preferential transfer of α-tocopherol in the liver by α-TTP. The other forms of tocopherols and tocotrienols are less abundant in the diet and in tissues than α-tocopherol and γ-tocopherol.