International Units (IU)

International Units are a measurement system for the biological activity of vitamins A, D and E (and formerly some of the other vitamins too). Many products, particularly those in the higher dosage range, are still sold in International Units because consumers are accustomed to this system. However scientists no longer use International Units, and prefer to measure vitamins by weight.

1 IU vitamin A = 0.3 micrograms

1 IU vitamin D = 0.025 micrograms

1 IU vitamin E = 0.7 milligrams if the vitamin is in the usual supplement form of d-alpha tocopherol. Other forms of vitamin E have different equivalences.

Intrinsic factor

A protein secreted by the stomach which forms a complex with vitamin B12 in the diet, thus enabling this vitamin to be absorbed. A lack of intrinsic factor can lead to pernicious anaemia (severe vitamin B12 deficiency).

Inulin (see Probiotics)