I.U. (International Unit)

An internationally recognized standard unit of measure for some hormones and enzymes and fat soluble vitamins A, D and E. The measure of an IU is the amount of each substance required to produce a response. The conversions for fat soluble vitamins are as follows:
Beta Carotene (Vitamin A) — 1mg = 833 IU; Vitamin D — 2.5 mcg = 100 IU; Vitamin E — 1mg = 1 IU.