What Does "iu" Mean In Vitamins?

The international unit, often abbreviated as IU, is a measure of the activity, or effect, of a group of essential organic compounds known as vitamins, and it is used to calculate intakes, potency and doses. You can categorize vitamins into two distinct families: water-soluble and fat-soluble. International units typically are used to measure activity of the fat-soluble vitamins.

History

Before it was possible to purify and isolate vitamins, international units were commonly used as a standardized method of measuring vitamin activity. These days, you will usually only see vitamins A, D and E measured in international units. These vitamins are found in different forms in nature, and it is more convenient to express their activity than to describe their mass.

Definition

The international unit is used to measure biological activity and you have to be careful not to confuse international units with the International System of Units. That is the contemporary version of the metric system, and includes units of mass such as micrograms or milligrams. You can convert international units to SI units, but remember that international units are an arbitrary measurement, and that the conversion factor is different for each vitamin.

Vitamin A

Your diet provides compounds called retinol and carotenoids, both of which have vitamin A activity. The different compounds have different levels of vitamin A activity with retinol having a higher activity than carotenoids. Beta carotene has a higher activity than the other carotenoids. One international unit of vitamin A is equivalent to 0.3 micrograms (mcg) of retinol, 0.6 mcg of beta carotene and 1.2 mcg of other carotenoids.

Vitamin D

Two main forms of vitamin D exist. The type that you get from your diet and is formed in your skin through sunlight is called cholecalciferol. The other type is a synthetic form of vitamin D that you find in enriched or fortified foods, and is called ergocalciferol. Your body metabolizes both types of vitamin D in the same way, and both forms have the same biological activity. One international unit of vitamin D is equivalent to 0.025 mcg of cholecalciferol or ergoclaciferol.

Vitamin E

Vitamin E describes two families of compounds, tocotrienols and tocopherols. The different groups have different vitamin E activity. The most potent form of vitamin E is alpha tocopherol. Vitamin E is usually measured in terms of milligrams of alpha tocopherol equivalents. You can also measure vitamin E in international units, where one international unit is equal to 0.67 mg of alpha tocopherol equivalents.