De sterkte van vitamine E preparaten wordt uitgedrukt onder de vorm van eenheden. DL-alpha tocoferyl acetaat wordt gebruikt als uitgangspunt bij de vergelijkingen in vitamine E activiteit. In onderstaand fragment uit de Martindale kunt u de verklaring van de eenheden terugvinden:
“Though the potency of preparations of vitamin E is still sometimes expressed in units, the International Standard for vitamin E was discontinued in 1956. The International Unit was the activity contained in 1 mg of a standard preparation of dl-alpha-tocoferil acetate. Past editions of the USP have stated that in expressing vitamin E activity of tocopherol products, the following equivalents of 1 mg were to be used:
d-alpha tocopherol, 1.49 units
dl-alpha tocopherol, 1.1 units
d-alpha tocoferil acetate, 1.36 units
dl-alpha tocoferil acetate, 1 unit
d-alpha tocoferil acid succinate, 1.21 units
dl-alpha tocoferil acid succinate, 0.89 unit.”