# How can I convert from international units (IU) to milligrams or micrograms?

Jul 28, 2014

It varies from one substance from another.

The international unit is based on the activity or effect of biologically active substances. Here are some examples.

• Vitamin A: 1 IU is the biological equivalent of 0.3 μg of retinol or
of 0.6 μg of beta-carotene.

• Vitamin C: 1 IU corresponds to 50 μg of L-ascorbic acid

• Vitamin D: 1 IU is the biological equivalent of 0.025 μg of
cholecalciferol.

• Vitamin E: 1 IU is the biological equivalent of ²/₃ mg of
d-alpha-tocopherol or 0.9 mg of dl-alpha-tocopheryl acetate.

• Insulin: 1 IU is equivalent to 0.0347 mg of human insulin.

For other substances, you may have to consult a pharmacist.

EXAMPLE

The recommended dietary allowance (RDA) of Vitamin D is 600 IU. What mass of Vitamin D does this represent?

Solution

Mass of Vitamin D = 600 IU × $\left(0.025 \text{µg")/(1"IU}\right)$ = 15 µg