[The biological activity of vitamin E]

Area of Science:

• Biochemistry
• Nutritional Science
• Pharmacology

Background:

• Tocopherols (vitamin E) exhibit varying biological potencies.
• The United States Pharmacopoeia (USP) previously used International Units (IU) to denote differences in alpha-tocopherol biopotency.
• The USP XXII-NFXVII (1990) revision removed IU, impacting the standardization of vitamin E forms.

Purpose of the Study:

• To summarize the relative biopotency of different tocopherol and tocotrienol forms.
• To highlight the need for updated metabolic and bio-discrimination studies.
• To identify areas for further research into tocopherol biological activity.

Main Methods:

• Compilation of existing data on the relative biopotency of tocopherol and tocotrienol homologues.
• Review of pharmacopoeia standards concerning vitamin E units.
• Identification of knowledge gaps in tocopherol metabolism and discrimination.

Main Results:

• Tables summarizing the relative biopotency of alpha-, beta-, gamma-, and delta-tocopherol, and tocotrienols are presented.
• The removal of USP International Units signifies a shift in how alpha-tocopherol stereoisomers are quantified.
• Differences in biopotency between d-alpha-tocopherol and dl-(2-ambo)-alpha-tocopherol are noted but lack current standardized units.

Conclusions:

• Further metabolic and bio-discrimination studies are essential to accurately determine the relative biopotency of d-(RRR)- and dl-(all-rac)-alpha-tocopherol.
• The synergistic effects of alpha-tocopherol stereoisomers and biotransformation pathways warrant additional investigation.
• Clarifying the biological activity of various tocopherol forms is crucial for nutritional and pharmaceutical applications.