Vitamin E biopotency: Comparison of various ‘natural-derived’ and chemically synthesized α-tocopherols

The difference in bioactivity between d- and dl- forms of α-tocopherol is reflected in the currently established United States Pharmacopoeia Standards for vitamin E activity. Current evidence strongly supports the concept that the presently accepted values assigned to the d- and dl- forms of α-tocopherol and corresponding acetate esters are valid for application to farm animals. Consequently, there is no known advantage to supplementing animal feeds with d- forms of vitamin E (α-tocopherol) so long as what is supplemented is provided in International Units and not in milligrams.