Have you ever wondered how the amounts of substances in supplements are determined? What do the abbreviations for the measurements of the substances mean? The answer is quite simple actually…
Every substance used in a supplement has a certain recommendation for intake by the average person over a certain time period to ensure they remain in good health. Measurements for these recommendations may be expressed as IU (international units), GDU (gelatin digestion units) and USP (United States Pharmacopeia) units among others. 
International units are measurement units used to measure the amounts of certain substances that elicit biological activity and these units are determined based on the specific substance that is measured. International units are agreed upon internationally for various substances that are used in product formulations worldwide. The effect and biological activity of a substance is taken into consideration in order to simplify the comparison of different substances. Vitamins, for instance, are quantified through international units. 
The conversion explanation
Milligrams are a unit of measurement of the metric system that is often used to measure supplements like vitamins. The following conversion table explains how grams (g) are converted into milligrams (mg) and milligrams into micrograms (mcg):
1 g = 1000 mg
1 mg = 1000 mcg
Milligrams and micrograms can furthermore be converted into IU (International Units) that are calculated for each specific substance in every specific active form. Here are some examples of the conversion:
It is clear to see that each active substance has a different biological effect and should be quantified accordingly into IU. 
Gelatin digesting units
Enzymatic activity can be used to determine the correct measurements of enzymes that are used in supplements. One way of quantifying enzyme activity is by using the measurement of the speed at which the enzyme degrades gelatin. The digestion action of Bromelain (a certain enzyme), for example, is expressed in gelatin digesting units (GDU’s) and 1g of Bromelain equals around 1200 GDU. This number may vary depending on the procedure used for the isolation, separation and also the purification of the final product. 
United States Pharmacopeia units
“The United States Pharmacopeia Convention” is a scientific organization who has made it their responsibility to set standards for supplements and other products like food ingredient and medicines to ensure the quality, strength and purity of such products and to make sure that they can be clearly identified. USP units are an indication of the measurement of dosage recommendations of certain supplements etc. For the greatest part, these units are similar to International Units, although some differences should be considered. 
From now on you will know what all those different measurements mean and just imagine how smart you will seem when you chat to a friend about it!
ts mean and just imagine how smart you will seem when you chat to a friend about it!
- Recommended Dietary Allowances. 9th ed. Washington DC: National academy of sciences; 1980. p. 1.
- Dietarysupplementdatabase [homepage on the Internet]. DSID. [updated 2015 March 20]. Available from: http://dietarysupplementdatabase.usda.nih.gov/ingredient_calculator/help.php#q2.
- SS Gautam, SK Mishra, V Dash, AK Goyal, G Rath. Comparative study of extraction, purification and estimation of bromelain from stem and fruit of pineapple plant. Thai J Pharm Sci. 2010; vol. 34: 67-76.
- The United States Pharmacopeial Convention [homepage on the Internet]. USP [updated 2015]. Available from: http://www.usp.org.