Vitamin E: a reexamination

Area of Science:

• Biochemistry
• Nutritional Science
• Pharmacology

Background:

• Vitamin E encompasses eight natural forms (tocopherols and tocotrienols) and synthetic epimers.
• Understanding the differential biological activities of these forms is crucial for nutritional and therapeutic applications.
• Current Recommended Dietary Allowances (RDAs) for vitamin E may require re-evaluation based on updated research.

Purpose of the Study:

• To critically assess and compare the biological activities of natural vitamin E isomers versus synthetic vitamin E epimers.
• To investigate the impact of administration frequency and co-administration with alpha-tocopherol on the biological value of non-alpha-tocopherol compounds.
• To analyze existing data to support potential adjustments to the current RDA for vitamin E.

Main Methods:

• Comparative analysis of existing literature and biological data on various vitamin E forms.
• Evaluation of pharmacokinetic factors, specifically biological turnover rates, influencing vitamin E efficacy.
• Interpretation of recent findings on vitamin E's effect on blood clotting time.

Main Results:

• Reported differences in biological activity are largely attributable to variations in biological turnover rates.
• Administration timing and co-feeding with alpha-tocopherol significantly affect the observed biological value of vitamin E compounds.
• Evidence suggests alpha-tocopherol oxidation to tocopherylquinone may inhibit vitamin K, prolonging blood clotting time.

Conclusions:

• The relative biological activities of vitamin E forms are significantly influenced by their metabolic fate and administration protocols.
• The current RDA for vitamin E may need revision based on a comprehensive understanding of differential activities and turnover rates.
• Vitamin E's role in blood coagulation, potentially via tocopherylquinone formation, warrants further investigation.