Key Takeaways
✓ A mineral supplement label can show two numbers: the weight of the whole compound (for example, 2,500 mg of magnesium glycinate) and the weight of the mineral itself (275 mg of magnesium). US rules require the Supplement Facts panel to state the mineral, not the compound.
✓ The mineral is a fraction of the compound's weight: about 60 percent for magnesium oxide, 16 percent for magnesium citrate, 14 percent for magnesium glycinate and 8 percent for magnesium L-threonate, from the molecular weights.
✓ The %DV column is calculated from the elemental amount against the FDA Daily Value: 420 mg for magnesium, 11 mg for zinc, 1,300 mg for calcium.
✓ Trial doses, RDAs and upper limits are all expressed as elemental amounts, so that is the number to compare against a label.
Mineral labels are the most misread numbers in the supplement aisle. A bottle that says 2,500 mg on the front may deliver 275 mg of magnesium per serving, and both figures are honest. The difference is between the compound (magnesium bound to something that makes it stable and absorbable) and the element (the magnesium itself). This page explains the rule that governs the label, the arithmetic behind the fractions, and how to convert any label into the elemental figure that trials, dietary allowances and upper limits all use.
What the label is required to show
US regulations are specific. The amounts on a Supplement Facts panel must be the weight of the dietary ingredient itself rather than the weight of its source, with the regulation's own example being the weight of calcium rather than that of calcium carbonate (21 CFR 101.36). The source compound may be shown in parentheses after the ingredient, preceded by the word "as" or "from", as in "Calcium (as calcium carbonate)" (21 CFR 101.36). FDA's labeling guide answers the question directly: if the calcium carbonate in your product supplies calcium, you must list the weight of calcium, not the weight of the calcium carbonate (FDA Dietary Supplement Labeling Guide). The NIH Office of Dietary Supplements says the same of magnesium: the panel declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound (NIH ODS).
So the elemental figure is always on the panel. The compound weight is optional and often appears on the front of the pack because it is the bigger number.
"As" versus "from" on a label
Both words introduce the source compound, and the regulation allows either (21 CFR 101.36). "Magnesium (as magnesium glycinate) 275 mg" and "Magnesium (from 2,500 mg magnesium glycinate) 275 mg" mean the same thing: 275 mg of magnesium, supplied by magnesium glycinate. When a label states the compound weight too, you can check the arithmetic. When it does not, the elemental figure still stands on its own. A label that lists only a compound weight with no elemental figure for a mineral that has a Daily Value is not following the format the regulation describes.
The arithmetic: elemental fraction from molecular weight
The fraction of a compound that is the mineral is the atomic weight of the mineral atoms divided by the molecular weight of the compound. The molecular weights below are from PubChem; each row links to the compound record so the figure can be checked. The fractions are for the pure, anhydrous compound. Commercial raw materials can contain water of hydration or be sold as complexes rather than pure salts, so the ratio on a real label can be lower than the textbook figure; the label's declared elemental amount is the number that governs.
| Compound | Formula | Molecular weight | Mineral atoms (atomic weight) | Elemental fraction | Mineral per 1,000 mg of compound | Source |
|---|---|---|---|---|---|---|
| Magnesium glycinate (bisglycinate) | C4H8MgN2O4 | 172.42 | 1 × 24.305 = 24.305 | 14.1 percent | 141 mg | PubChem CID 84645 |
| Magnesium citrate (trimagnesium dicitrate, anhydrous) | C12H10Mg3O14 | 451.12 | 3 × 24.305 = 72.915 | 16.2 percent | 162 mg | PubChem CID 6099959 |
| Magnesium oxide | MgO | 40.305 | 1 × 24.305 = 24.305 | 60.3 percent | 603 mg | PubChem CID 14792 |
| Magnesium L-threonate | C8H14MgO10 | 294.5 | 1 × 24.305 = 24.305 | 8.3 percent | 83 mg | PubChem CID 45489777 |
| Zinc picolinate | C12H8N2O4Zn | 309.6 | 1 × 65.4 = 65.4 | 21.1 percent | 211 mg | PubChem CID 9904746 |
| Zinc gluconate | C12H22O14Zn | 455.7 | 1 × 65.4 = 65.4 | 14.4 percent | 144 mg | PubChem CID 443445 |
| Calcium citrate (tricalcium dicitrate, anhydrous) | C12H10Ca3O14 | 498.4 | 3 × 40.08 = 120.24 | 24.1 percent | 241 mg | PubChem CID 13136 |
| Calcium carbonate | CCaO3 | 100.09 | 1 × 40.08 = 40.08 | 40.0 percent | 400 mg | PubChem CID 10112 |
Worked examples
| Example | What the label shows | Conversion |
|---|---|---|
| Veluna Magnesium Glycinate (label) | Magnesium (from 2,500 mg magnesium glycinate) 275 mg per 3 capsules, 65% DV | 275 ÷ 420 = 65% DV. 275 ÷ 2,500 = 11 percent of the compound weight, below the 14.1 percent theoretical figure for pure anhydrous magnesium glycinate, which is why the declared elemental figure, not the arithmetic, is what to rely on. |
| Magnesium oxide, 500 mg elemental | The dose in the 8-week magnesium trial most often cited for sleep, given as 414 mg of magnesium oxide twice a day | 828 mg of magnesium oxide × 60.3 percent = about 499 mg of magnesium a day, matching the 500 mg elemental figure the trial reports (PMID: 33865376). |
| Magnesium citrate, 1,000 mg compound | A label that shows only the compound weight | 1,000 mg × 16.2 percent = about 162 mg of magnesium, or 39% DV, if the material is anhydrous trimagnesium citrate. A hydrated raw material gives less. |
| Zinc picolinate, 50 mg compound | A label that shows the compound weight | 50 mg × 21.1 percent = about 10.6 mg of zinc, or 96% DV. The same bottle labelled by elemental zinc would say 10.6 mg. |
| Zinc gluconate, 50 mg compound | A label that shows the compound weight | 50 mg × 14.4 percent = about 7.2 mg of zinc, or 65% DV. |
| Calcium carbonate, 1,250 mg compound | A common tablet strength | 1,250 mg × 40.0 percent = about 500 mg of calcium, or 38% DV. |
| Calcium citrate, 1,000 mg compound | A label that shows the compound weight | 1,000 mg × 24.1 percent = about 241 mg of calcium if anhydrous; the tetrahydrate form commonly used in tablets contains proportionally less. |
Research discussed here relates to individual ingredients and does not establish that the finished Veluna product has been clinically studied or will produce the same results.
%DV, RDA and UL: three different numbers
%DV is a labelling figure. FDA sets one Daily Value per nutrient for adults and children aged 4 and over, and the panel's percentage is the elemental amount divided by that value: 420 mg for magnesium, 11 mg for zinc and 1,300 mg for calcium (21 CFR 101.9). It is one number for everyone, so it is a comparison tool, not a personal target.
RDA is the Recommended Dietary Allowance set by the Food and Nutrition Board, and it varies by age, sex and pregnancy. For magnesium the adult RDAs are 400 mg to 420 mg a day for men and 310 mg to 320 mg a day for women, from all sources including food (NIH ODS).
UL is the Tolerable Upper Intake Level, the maximum daily intake unlikely to cause adverse health effects. For magnesium the UL applies only to magnesium from supplements and medications, not food, and is 350 mg a day for everyone aged 9 and over. ODS notes that this is why the magnesium UL appears to be lower than the RDA: the RDA counts food, the UL does not (NIH ODS).
All three are elemental amounts. A 2,500 mg compound figure cannot be compared with any of them until it is converted.
Why forms are not interchangeable even at equal elemental amounts
Two labels can both say 300 mg of magnesium and deliver different amounts to the body. ODS reports that forms which dissolve well in liquid are more completely absorbed, and that small studies found magnesium in the aspartate, citrate, lactate and chloride forms to be more completely absorbed and more bioavailable than magnesium oxide and magnesium sulfate (NIH ODS). Elemental amount is the first conversion; form is the second question. Our guides to chelated magnesium and to bisglycinate versus glycinate cover the forms, and our reference table of trial doses lists the elemental amounts used in the magnesium trials.
Where Veluna fits. The Veluna Magnesium Glycinate label is written in the format the regulation describes: Magnesium (from 2,500 mg magnesium glycinate) 275 mg per three-capsule serving, 65% DV. The 275 mg figure is the one to compare with a trial dose, an RDA or the 350 mg supplemental UL.
Common questions
Is 2,500 mg of magnesium glycinate the same as 2,500 mg of magnesium?
No. 2,500 mg is the weight of the compound. The magnesium inside it is a fraction of that weight, 14.1 percent for the pure anhydrous salt and often less for commercial raw materials. The Supplement Facts panel states the elemental amount, which on the Veluna label is 275 mg.
Which number should I compare against a dose in a trial?
The elemental figure. Trials report elemental magnesium: the systematic review of magnesium trials in older adults lists daily elemental intakes of 320 mg to 729 mg, with the compound (oxide or citrate) stated separately (PMID: 33865376). Compare 275 mg of magnesium with 320 mg of magnesium, not 2,500 mg of compound with 320 mg of element.
Why is the magnesium UL lower than the RDA?
Because they count different sources. The RDA includes magnesium from food, drinks, supplements and medications; the UL of 350 mg applies only to supplements and medications. ODS explains this directly on its fact sheet (NIH ODS).
Does elemental amount tell me how much is absorbed?
No. It tells you how much mineral is in the serving. How much is absorbed depends on the form, the dose and the person. ODS reports better absorption for more soluble forms such as citrate and chloride than for oxide (NIH ODS). A label cannot show absorption, only content.
References
- US Food and Drug Administration. 21 CFR 101.36, Nutrition labeling of dietary supplements (paragraphs (b)(2)(ii) and (d)). ecfr.gov
- US Food and Drug Administration. 21 CFR 101.9(c)(8)(iv), Reference Daily Intakes. ecfr.gov
- US Food and Drug Administration. Dietary Supplement Labeling Guide: Chapter IV. Nutrition Labeling. fda.gov
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals. ods.od.nih.gov
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther. 2021;21(1):125. PMID: 33865376
- National Center for Biotechnology Information. PubChem compound records for magnesium glycinate (CID 84645), magnesium citrate (CID 6099959), magnesium oxide (CID 14792), magnesium L-threonate (CID 45489777), zinc picolinate (CID 9904746), zinc gluconate (CID 443445), calcium citrate (CID 13136) and calcium carbonate (CID 10112). pubchem.ncbi.nlm.nih.gov
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for informational purposes only and does not constitute medical advice. Talk to a healthcare professional before starting any supplement, especially if you are pregnant, nursing, taking medication, or have a medical condition.
