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Definition: IU

IU stands for International Units and is used as a means of measurement for vitamins, hormones, some drugs, vaccines, and blood products. IU measures these substances based on measured biological activity or effect, agreed upon as an international standard.

What this means is that IU is dependent on the potency of the substance, and each substance would have a different IU to milligram conversion. For example, 1000 IU of Vitamin C would have a different weight than 1000 IU of Vitamin A.

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