International Unit – What is this and how to use it?

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Imagine, you have received Certificate of Analysis, where values for components are listed in IU per weight or IU per volume. Imagine, you have in your hand a supplement and on a label you see composition listed in IUs. How to interpret these values and how to deal with them? What do they mean?

What is International Unit?

International Unit (IU in English, UI in French, Spanish, IE in German) is a measurement unit that is primarily used on nutrition labelling or in pharmacology. International Unit varies from substance to substance. This variance is based on the biological activity or effect, which is caused by a certain substance. The International Unit has been implemented (by the WHO Expert Committee on Biological Standardization) for the purpose of easier comparison across substances. International units are used to quantify vitamins, hormones, some medications, vaccines, blood products, and similar biologically active substances. For example for vitamin A, one IU of Vitamin A is an equivalent to 0.3 mcg of retinol or 0.6 mcg of beta-carotene. But the other side, there is no equivalence between IU measurements of different biological agents. For instance, one IU of vitamin E cannot be equated with one IU of vitamin A in any way, including mass or efficacy.

IU conversion factors.

Let’s look into conversion factor used for different vitamins:

  • for Vitamin A, 1 IU is equivalent of 0.3 mcg of retinol, or of 0.6 mcg of beta-carotene,
  • for Vitamin C, 1 IU is equivalent of 50 mcg of L-ascorbic acid,
  • for Vitamin D, 1 IU is equivalent of 0.025 mcg of cholecalciferol or ergocalciferol,
  • for Vitamin E, 1 IU is equivalent of about 0.67 mg of d-alpha-tocopherol, or 0.9 mg of of dl-alpha-tocopherol.

IUs in practice.

International Units can be used to compare an activity of different compounds in the same biological process in our body. They can be also used to compare different food products in relation to an amount of active substance in a weight unit.

In table below are listed products rich with Vitamin A per 100g of product.

If you need any help in an interpretation of the International Units feel free to contact me.