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August 19, 2020 3 min read

It’s very much the responsible thing to take the time to actually read the labels of the vitamin supplements you’re comparing in a high-street health store, or for that matter, to scrutinise the specifications you might see listed for such products online.

However, it can be an altogether different task to actually properly understand what you read on the label of a given product, especially when it comes to measurements and dosing.

What on Earth do the likes of ‘MG’, ‘MCG’ and ‘µg’ mean? And what does it mean when you see ‘IU’ being used instead? Is there any difference between ‘NRV’ and ‘RDA’?

You get the idea – it’s all a bit bewildering. So, here are the basics of what you need to know.

Introducing MG... or is it MCG?

This can be an especially confusing one, not least given that – and let’s make this clear right away – ‘MG’ is not the same as ‘MCG’.

The first acronym stands for milligrams, and the second for micrograms. This is crucial because, with a microgram literally being one thousandth of a milligram, you won’t want to get the two confused, and therefore go 1,000 times over or under your intended dose of the given vitamin.

Micrograms are the preferred unit of measurement in most of Europe, so you’ll probably see them referenced a lot when poring over vitamin supplement labels. However, they won’t necessarily be described as ‘micrograms’ or even ‘MCG’.

That’s because you might also see ‘µg’ or ‘ug’ (the latter because of the µ’s unavailability on a traditional keyboard). The ‘µ’, by the way, comes from the Greeks and means ‘small’, while the ‘g’, of course, is short for ‘gram’. So that’s an easy way to remember it – it’s just a small gram, or microgram!

OK, so where does IU come in?

Now, you may have noticed that with certain vitamins, the label doesn’t use ‘MG’ or ‘MCG’ to indicate the amount, but instead something known as ‘IU’.

This acronym stands for ‘International Unit’. But unlike MG or MCG, it is not a physical unit of measurement, referring to a particular mass or volume that you might literally see or feel.

Instead, IU measures something less obviously tangible: a particular product’s biological activity or potency. This system was devised due to some vitamins coming in multiple forms, each of which has a different potency or level of biological activity.

Vitamin D, for example, comes in two forms in supplements: D2 (also known as ergocalciferol) and D3 (cholecalciferol). It might not therefore make much sense to use a physical weight measurement, such as MG or MCG, for a vitamin D supplement, given that the same quantity of D2 and D3 would produce different biological effects.

And vitamin D isn’t the only vitamin that exists in multiple forms with different levels of potency; the same applies to vitamin A, which you can get in the form of retinol or beta-carotene, and vitamin E, which is supplied in both d-alpha-tocopherol and dl-alpha-tocopherol forms in supplements.    

The existence of the IU measurement therefore helps us to ensure that when we’re comparing vitamin supplements, we’re genuinely comparing ‘like with like’ as far as their actual effect on the body is concerned.

Finally... that NRV versus RDA question

We thought we’d throw in an explanation of this one, as they’re another two very relevant acronyms to any conversation about vitamin supplements and appropriate intake.

RDA stands for ‘Recommended Daily Allowance’, and is the term that many of us used to look for on labels, and are still most familiar with. It was effectively replaced with NRV – or ‘Nutrient Reference Value’ – when a new European regulation came into effect in December 2014.

The actual values of RDA and NRV, though, are exactly the same – where ‘100% RDA’ may have once appeared on a given label, you’ll now simply see ‘100% NRV’ instead.

There you have it – armed with the above information, you’ll hopefully be much more confident in the future when running the rule over the labels of all kinds of vitamin supplements and health products. These are certainly details that are well worth knowing when you are seeking to make the right decisions for the health of you and your family.  

Other sources:

https://www.justvitamins.co.uk/blog/rda-or-nrv/

https://vitaminddrops.co.uk/uk_en/blog/research-guidelines/mcg-ug-vitamin-d-label

https://vitaminddrops.co.uk/uk_en/blog/research/what-does-iu-mean