Have you ever looked at the label on your multivitamin or vitamin D supplement and wondered what the “µg” or “IU” means?
These two units of measurement are often used interchangeably with vitamin D, as it is not typically measured in “mg” like most other vitamins and minerals.
µg is the symbol for the metric measurement microgram, which is one thousandth of a milligram or one millionth of a gram. The letter µ is a greek letter, which means “small”, though often it “ug” or “mcg” (microgram) are used in its place due to typographical unavailability.
So, what about “IU"?
IU is an abbreviation for International Unit. 1ug is equal to 40IU. Both are measurements of active vitamin D concentration.
But, what’s the difference between IU and ug? If they both measure the same thing, why are they used interchangeably?
Well, ug or mcg is a physical unit of measurement, referring to a particular mass or volume that you can literally see and feel.
On the other hand, IU measures something less obviously tangible, such as a product's biological activity or potency.
This measurement is often used to account for different forms of a supplement. For example, there are two different forms of vitamin D, D2 and D3, which differ in regards to bioavailability and potency.
So, it wouldn’t make much sense to use a unit of measurement that accounts solely for the physical weight of the product. Instead, IU measures the potency and accounts for the different biological effects they provide.
Same goes for vitamin A and E, which also come in various forms.
In summary, ug or mcg (micrograms) is a unit of measurement used to measure the physical weight of a product. IU is a unit that measures potency and biological activity and exists to help us ensure were comparing the physical effects of supplements on a “like for like” basis!
