Figure 9.251 Only the yellow bars count toward the 2001 DRI requirement
Another level of complexity is added by the introduction of international units (IU). IUs are a unit that are used to describe the bioactivity of different compounds, including 4 vitamins: A, D, E, and C. It would be less confusing if these units were not used. However, most supplements use IUs. IUs are not as common on food items.
For vitamin E, IUs are specific for alpha-tocopherol and adjusted for the molecular weight of the different forms (alpha-tocopherol acetate etc.). The conversion factors for converting IU to mg of alpha-tocopherol are:
0.67 for RRR-alpha-tocopherol (and its esters)
0.45 for all-rac-alpha-tocopherol (and its esters)
Here are some example calculations showing how to use these conversion factors:
Example 1. For a supplement containing 100 IU of RRR-alpha tocopherol:
100 IU X 0.67 = 67 mg alpha-tocopherol
Example 2. For a supplement containing 100 IU of all-rac-alpha tocopherol:
100 IU X 0.45 = 45 mg alpha-tocopherol
References & Links
1. Wagner KH, Kamal-Eldin A, Elmadfa I. (2004) Gamma-tocopherol–an underestimated vitamin? Ann Nutr Metab 48(3): 169-188.
2. DRI (2000) Dietary reference intakes for vitamin C, vitamin E, selenium, and carotenoids.