IU

Definition / meaning of IU

A unit used to measure the activity of many vitamins, hormones, enzymes, and drugs. An IU is the amount of a substance that has a certain biological effect. For each substance there is an international agreement on the biological effect that is expected for 1 IU. Also called International Unit.

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Source(s):

The Web site of the National Cancer Institute (http://www.cancer.gov/)

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