Vitamin E: Not only a single stereoisomer

Area of Science:

• Biochemistry
• Human Physiology
• Nutritional Science

Background:

• The definition of vitamin E is debated, with some arguing only RRR-α-tocopherol possesses physiological activity.
• Ataxia with Vitamin E Deficiency (AVED) is a condition linked to vitamin E deficiency, historically treated with RRR-α-tocopherol.

Purpose of the Study:

• To investigate the physiological definition of vitamin E.
• To evaluate the efficacy and safety of different vitamin E forms beyond RRR-α-tocopherol.

Main Methods:

• Review of existing literature on vitamin E biological activities and mechanisms.
• Analysis of the binding affinity of α-tocopherol transfer protein (α-TTP) to various stereoisomers.
• Examination of clinical data regarding the treatment of AVED with different vitamin E forms.

Main Results:

• Physiological vitamin E activity is confirmed to be limited to specific α-tocopherol forms.
• All 2R-stereoisomers of α-tocopherol, not just RRR-α-tocopherol, bind effectively to α-TTP.
• 2R-forms are retained in human plasma and tissues, unlike rapidly excreted 2S-stereoisomers.
• AVED has been successfully treated with vitamin E forms other than RRR-α-tocopherol.
• No safety concerns are associated with the broader definition of vitamin E.

Conclusions:

• The physiological definition of vitamin E should include all 2R-stereoisomers of α-tocopherol, not exclusively RRR-α-tocopherol.
• The broader definition of vitamin E has gained scientific and regulatory acceptance.
• Current evidence supports the safety and efficacy of this inclusive definition for treating vitamin E deficiency.