structural:expansion, structural:summarization
α-Tocopherol

1 IU of tocopherol is defined as ⅔ milligrams of RRR -α-tocopherol (formerly named d-α-tocopherol or sometimes ddd-α-tocopherol). 1 IU is also defined as 1 milligram of an equal mix of the eight stereoisomers, which is a racemic mixture called all-rac -α-tocopheryl acetate. This mix of stereoisomers is often called dl-α-tocopheryl acetate, even though it is more precisely dl,dl,dl-α-tocopheryl acetate). However, 1 IU of this racemic mixture is not now considered equivalent to 1 IU of natural (RRR) α-tocopherol, and the Institute of Medicine and the USDA now convert IU's of the racemic mixture to milligrams of equivalent RRR using 1 IU racemic mixture = 0.45 "milligrams α-tocopherol".