I.U. (International Units)

An internationally acknowledged unit of measure for substances including hormones, enzymes and fat soluble vitamins A, D and E.  The comparable measurements vary for each substance and is the amount of each substance needed to produce a response.  For example: Vitamin A 1 mg = 833 IU; Vitamin D 2.5 mcg = 100 IU; Vitamin E 1 mg = 1 IU.