For good measure

Q: I am a long time reader who is confused by something. Some supplements are recommended in milligrams and some in IU. How do they differ and are they convertible? Thanks for your help.

JVW: IU stands for “international unit.” An IU is the amount of a particular substance required to produce a certain biological effect.

But unlike milligrams and other units of measure, the IU measurement is based on the potency of the nutrient, so 1 IU of vitamin E is not the same as 1 IU of vitamin A. And since each substance’s IU value is different, it’s impossible to have a single equation that will convert IUs into another measurement, such as milligrams.

All substances measured in international units are officially defined by the International Conference for Unification of Formulae.

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