Illustrative spinach leaves and pumpkin seeds, not a VITAMIZED product photograph or a statement about any supplement's ingredient sources.
Open a few magnesium product pages and the form names pile up fast: oxide, citrate, glycinate, malate, taurate, chloride. A product called a "magnesium complex" may list several source forms. For a quantity comparison, start with elemental magnesium rather than the number of forms named. This guide shows where that number sits on the panel and how the declaration works.
Elemental magnesium vs. compound weight
A magnesium-containing compound includes magnesium and other chemical components. The entire compound therefore weighs more than its magnesium content alone. The NIH Office of Dietary Supplements puts the labeling rule plainly: "The Supplement Facts panel on a dietary supplement label declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound." So the milligrams on the panel are the magnesium itself. If a front label or listing also gives a compound-weight figure, do not treat it as an elemental magnesium amount. Read the magnesium line and the serving size together.
How panels declare it
Under 21 CFR 101.36(d), a source ingredient may appear in parentheses immediately after or indented beneath the nutrient name, introduced by "as" or "from." An illustrative entry is "Magnesium (as magnesium citrate)." If several sources supply magnesium and are listed inside the panel, all of those sources belong in the parentheses in descending order by weight. The panel can show a total elemental magnesium amount without a separate quantitative line for each source form.
The source names are not required to appear inside the panel: if they are not identified there, the rule places them in the separate ingredient statement. Read both parts of the label. The magnesium % Daily Value uses a Daily Value of 420 mg for adults and children age 4 and older. That is a labeling reference value, not an individual intake recommendation.
Where the forms still matter
Elemental amount makes forms comparable on quantity; it does not make them identical. NIH ODS notes that the absorption of magnesium forms varies - in general, forms that dissolve well in liquid are more completely absorbed, and small studies found the aspartate, citrate, lactate and chloride forms more bioavailable than magnesium oxide and sulfate. That is ODS's summary of the research, and absorption is not something a label line can show you. Use the label to identify the declared elemental amount, the %DV and the named source ingredients. Do not turn an elemental-amount comparison into a performance ranking.
A quick comparison habit
Comparing two magnesium products - or a complex against a single-form product - starts with the serving size, the elemental magnesium amount and the %DV. Then find the source ingredients in the panel or separate ingredient statement. A complex and a single-form product with the same elemental total provide the same declared amount of magnesium; their source forms can still differ. A compound-weight number answers a different question from the elemental amount.
Keep reading
For another guide to distinguishing different kinds of declared amounts, read Powder Equivalency and Capsules Per Serving.
The bottom line
Compare declared elemental magnesium per serving, not the weight of the entire magnesium-containing compound. Check the serving size and source names as well. The amount is a useful basis for a quantity comparison, but it does not settle how different formulations perform.
Sources: NIH Office of Dietary Supplements - Magnesium Fact Sheet for Health Professionals; 21 CFR 101.36 - Nutrition Labeling of Dietary Supplements.
