Elemental magnesium: why the big number on the front can mislead
Nutriens editors
Magnesium can’t be put in a capsule on its own. It always comes bound to something else: glycine, citrate, oxide, chloride. That partner has weight. So a bottle can print a big number that describes the whole compound, while the magnesium you actually get is a fraction of it.
That fraction is called elemental magnesium, and it’s the number that matters for how much you’re taking. Here’s how to find it, how to check it, and how to keep your daily total sensible.
Compound weight vs elemental magnesium
Take our own label as the example. Magnesium Foundation’s Supplement Facts panel reads:
- Magnesium 275 mg, 65% DV
- from 2,500 mg magnesium glycinate
The 2,500 mg is the compound. The 275 mg is the magnesium in it. On this label, magnesium is about 11% of the compound’s weight; the rest is mostly glycine, an amino acid. That’s why the dose takes 3 capsules: 2,500 mg of powder doesn’t fit in fewer.
Different compounds carry very different fractions. Magnesium oxide is about 60% magnesium by weight, simply because oxygen is light. Glycinate and citrate carry much less magnesium per gram, because their partners are heavier molecules.
Where the confusion comes from
On the Supplement Facts panel, the line for a mineral states the amount of the mineral itself, with the source named in parentheses or underneath, for example “Magnesium (as magnesium oxide) 50 mg” on our Daily Foundation label. The front of a bottle is marketing space, though, and some brands put the compound weight there in large type. “Magnesium Glycinate 1,000 mg” on the front may mean only around 100–150 mg of magnesium inside.
Neither number is false. They just answer different questions, and only one tells you your dose.
Check the math with %DV
The Daily Value for magnesium is 420 mg. The %DV printed on the panel is always based on the magnesium itself, so you can use it as a check:
- Find the magnesium line on the Supplement Facts panel, not the front.
- Note the milligrams and the %DV.
- Multiply 420 mg by the %DV. 420 × 0.65 = 273 mg, which matches 275 mg after rounding. 420 × 0.12 = 50 mg, which matches Daily Foundation’s 50 mg.
- If the numbers don’t line up, the large number elsewhere on the bottle is probably the compound weight.
Does the form matter beyond the arithmetic?
Somewhat. The NIH Office of Dietary Supplements notes that forms of magnesium that dissolve well in liquid tend to be absorbed more completely, and that small studies found the aspartate, citrate, lactate and chloride forms more bioavailable than oxide and sulfate. So a high-percentage form like oxide isn’t automatically the better buy.
Glycinate binds magnesium to glycine. It’s the form printed on our label, not oxide, and many people choose it for everyday use. For more on that choice, read magnesium glycinate explained. We don’t claim it absorbs better than every other form; the research comparing forms is limited.
How much is enough, and how much is too much
Adults need 310–420 mg of magnesium a day from all sources, depending on age and sex. Food comes first: beans, nuts, seeds, whole grains and leafy greens.
For supplements there’s a ceiling. The upper limit for magnesium from supplements and medicines is 350 mg a day for adults. Food doesn’t count toward it. The most common sign of too much supplemental magnesium is loose stools or an upset stomach.
That’s where elemental milligrams earn their keep. Add the magnesium lines of every product you take, not the compound weights:
- Magnesium Foundation: 275 mg
- Daily Foundation: 50 mg
- Rest Balance: 13 mg. It also contains 10 mg of melatonin, St. John’s wort and 5-HTP, so ask your doctor before taking it, especially if you take medication or are pregnant, and skip other melatonin products.
If you take more than one product with magnesium, ask your doctor about your total. Ask first, too, if you have a kidney condition, take medication (some antibiotics and osteoporosis medicines need to be spaced from magnesium), or are pregnant or nursing.
Magnesium Foundation in one line
3 capsules once a day, 275 mg of magnesium (65% DV) from 2,500 mg of magnesium glycinate, nothing else active, no melatonin, no allergens listed, 90 capsules for 30 days. The label doesn’t set a time; we suggest the evening. The label says it “supports muscle function, eases tension & restores evening calm.*” It isn’t a sleep formula; that’s Rest Balance.
Keep reading
Why magnesium matters day to day: tense evenings and magnesium and 7 habits that leave you short. How to take it: Magnesium Foundation in the evening and the FAQ. To read any label the same way, see how to read a supplement label. Not sure where to start? Find your formula.
References
- NIH Office of Dietary Supplements. “Magnesium: Fact Sheet for Health Professionals.”
- Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. National Academies Press, 1997.
- U.S. FDA. Dietary Supplement Labeling Guide (Nutrition Labeling section).
- Magnesium Foundation and Daily Foundation Supplement Facts panels (the product labels).
