So, let’s say you’re walking down the aisle and you’re looking for a supplement your doctor’s recommended. You check the label and you see terms like “mcg” or “mg” – or even, sometimes, something called “IU.” Well, what are you supposed to do? Stand in the aisle and do mathematical conversions? Just what are these terms, what do they mean, and how should they affect your vitamin intake? Needless to say, when you’re taking vitamins, it’s good to know how much you’re taking and why. In this article, we’ll look at and discuss the most common vitamin dose measurements, with a particular focus on the most common of all: micrograms (mcg).
Mcg stands for microgram, which is a weight-based measurement used for vitamin supplements. One microgram is one millionth of a gram and one thousandth of a milligram. So, whenever you see that “mcg” abbreviation on a vitamin label, that’s what’s being talked about. Microgram is also sometimes abbreviated as “ug.” Don’t let this confuse you: Mcg and ug are the same.
Micrograms are used for measuring nutrients that we need very small amounts of. You may see micrograms used for measuring nutritional values for nutrients like folate and vitamin B12. In recent years, the U.S. government issues new regulations requiring labels to consistently use mcg on labels.
Micrograms, milligrams (mg), and International Units (IU) are all different units of measurement. Be sure to pay attention to your supplement labels so that you know how your vitamins are being measured.
The difference between a microgram and a milligram is simply a difference in size. They both measure weight, and milligrams are bigger. One microgram is one-thousandth of a milligram.
IU measurements aren’t about weight, but rather, they concern the biological activity of a substance in the body; IU measures the activity of vitamins, hormones, enzymes, and drugs. IU measurements are determined by a committee of researchers commissioned by the World Health Organization. To put the matter simply: Measurements like mg and mcg tell you something about the physical weight of the vitamin you’re holding; IU tells you about the biological effectiveness of the vitamin, but nothing about the weight. There’s no clear 1-to-1 conversion between IU and mcg and mg.
In May 2016, the U.S. Food and Drug Administration (FDA) announced some new regulations that required supplement labels to be updated. The regulations, which became mandatory as of 2019, released guidance on how to convert previous units of measurement for folate, niacin, vitamin A, vitamin D, and vitamin E to the new units required on updated nutritional fact labels. Some of the changes included:
In general, the new regulations led to IU measurements being converted to metric units (mcg or mg), though most supplement labels now include both IU and mcg.
A milligram measures weight – it’s one-thousandth of a gram – while an International Unit measures the biological activity of a substance. Again, these are differences in kind rather than degree. When you see mg, think weight; when you see IU, think “biological activity.”
One milligram is equal to 1,000 micrograms.
Micrograms are a weight-based measurement used consistently on supplement labels, particularly for nutrients the human body only needs very small amounts of. They stand in contrast to International Units (IUs), which are not measurements of mass or volume, but rather are measurements of biological activity. IUs are determined by researchers commissioned by the World Health Organization.