Alpha-tocopherol

Alpha-tocopherol, or α-tocopherol, is a fat-soluble compound and the form of vitamin E used to define human vitamin E requirements. Vitamin E is a broader family that includes four tocopherols and four tocotrienols, so alpha-tocopherol and vitamin E are not strictly synonymous. Tocopherols have a chromanol ring attached to a saturated side chain, and the predominant naturally occurring stereoisomer of alpha-tocopherol is RRR-alpha-tocopherol .^1,2

Alpha-tocopherol functions primarily as a lipid-soluble, chain-breaking antioxidant. It can react with peroxyl radicals generated during lipid oxidation, interrupting reactions that would otherwise propagate through susceptible lipids such as polyunsaturated fatty acids. This activity is particularly relevant within cell membranes and circulating lipoproteins .²

After intestinal absorption, alpha-tocopherol travels in lipid-containing particles and is delivered to the liver. The liver preferentially retains and returns alpha-tocopherol to the circulation through the action of alpha-tocopherol transfer protein (α-TTP). Other naturally occurring vitamin E forms, such as gamma-tocopherol, are also absorbed but are retained less effectively and are more readily metabolized and eliminated. This selective handling helps explain the preferential retention of alpha-tocopherol in human blood and tissues .^1,2

The term alpha-tocopherol can also refer to forms with different three-dimensional arrangements of their atoms. Naturally occurring RRR-alpha-tocopherol differs from synthetic all-rac-alpha-tocopherol, which is a mixture of eight stereoisomers. These forms are chemically related but are not handled identically by the human body .^1,2