Weights and measures
Part of Wolfie’s Nutrition Guide : An occasional series
Milli-whats?
I realise that my post the other day about vitamin C may have confused some people, because of the use of “mg”. As not everyone is familiar with the system of weights and measures that is used in relation to nutritional supplements, I thought I’d give you a brief guide.
Most vitamins, minerals and other nutrients are measured in milligrams or micrograms. These are indicated as “mg” for milligrams and “mcg” or “?g” for micrograms. (”?g” is the correct form, but you will see “mcg” in some places - particularly websites where the character set may not be 100% accurate).
In the same way that a gram (g) is a 1,000th part of a kilogram (kg), so a milligram is 1,000th of a gram and microgram is 1,000th of a milligram. So:
1 gram (1g) = 1,000 milligrams (1,000mg)
1 milligram (1mg) = 1,000 micrograms (1,000?g)
0.1 milligram (0.1mg) = 100 micrograms (100?g)
What are these IU things?
There are three special nutrients, though, that are also measured in International Units (iu). These are vitamins A, D and E. International Units are a system that was introduced to offer a standard for the potency of each of these three nutrients. They are all available in many different forms, all with different potencies, so by introducing International Units it was hoped to standardise things and make things clearer for the consumer.
Unfortunately, this didn’t really work because a different standard was adopted in some parts of the world. In the UK, however, this is how International Units are defined:
3.3iu vitamin A = 1?g retinol (pre-formed vitamin A) or 6?g beta carotene
40iu vitamin D = 1?g vitamin D
1iu d-alpha tocopherol equivalent (?-TE) = 0.67mg vitamin E
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