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How Much Actual Magnesium is in a Dose of a Magnesium Compound?
Question: Help! How do I know how much magnesium I am actually getting from my supplement? The label says it contains 500 mg of magnesium "as magnesium citrate" -- but how much of that is magnesium and how much is citrate?
Answer: This is a good question, since magnesium can make up less than half the weight of compounds which include it, such as magnesium citrate, magnesium chloride, and magnesium glycinate.
The amount of actual magnesium (sometimes listed as "elemental magnesium) you are getting from your supplement should be indicated on the label, but that's not always the case, so it's important to notice how the information is stated. For example, if your supplement label states: "Magnesium (as magnesium citrate)....500 mg" it should contain 500 mg of actual magnesium. However, if the label says "Magnesium citrate 500 mg," this means the entire compound is 500 mg — of which only a small percentage is magnesium (in fact, it's only 16.2%). Also, remember that even when a supplement appears to be properly labeled, the only way to know for sure whether it contains what it claims is if it has been tested by an independent group like ConsumerLab.com. Not all products contain what they claim.
For more about how to read magnesium supplement labels, including an example of a misleading label from a product reviewed by ConsumerLab.com, see the Magnesium Supplements Review >> (The Review includes the results of our latest product tests and information about what magnesium does, proper dosage, side effects, and how the forms of magnesium differ.)
Note that this labeling rule applies to other essential minerals, such as calcium, iron and zinc. See the "ConsumerTips" section of our Reviews of supplements made from each for more about the different forms and what to look for on labels.