Elemental vs Compound Magnesium

Pick up any magnesium supplement and you're looking at two different numbers that both describe "magnesium."

The front panel usually gives you the compound weight — how much of the magnesium-containing substance is in a serving. The Supplement Facts panel on the back gives you the elemental weight — how much actual magnesium that substance contains.

They can differ by more than fourfold.

Magnesium is a metal. You can't put loose magnesium metal in a capsule; it has to be bound to something. What it's bound to determines two things at once: how the compound behaves in your body, and how much of the capsule's weight is the mineral you're actually after.

Same number on the front. Four times the difference in the dose.

This is not a trick anyone is playing — it's chemistry, and every one of those compounds is a legitimate ingredient. The problem is only that front panels are designed to be read and back panels are designed to be compliant.

1. Turn it over. Find the Supplement Facts panel.
2. Find the line that says Magnesium with a milligram figure and a % DV. US labeling practice is to declare minerals as the element, so that figure is elemental magnesium. That is the dose.
3. If the front panel gave you a bigger number, that's the compound. Divide the elemental figure by it to see what proportion of the compound is actually magnesium.
4. Check the serving size. A bottle can reach an impressive number by making a serving three capsules instead of one. Divide by capsules to compare bottles honestly.

* Adequate Intake, not an RDA — set where there isn't enough evidence to establish an RDA.

The upper level of 350 mg per day is lower than the recommended intake for most adults, which looks like a contradiction until you see that the two numbers measure different things. The recommendation counts magnesium from everything you eat and drink as well as supplements. The upper level applies to supplements and magnesium-containing medications only — healthy kidneys clear the magnesium you get from food without difficulty.

The Recommended Dietary Allowance for adults is roughly 400–420 mg per day for men and 310–320 mg for women, counting food and supplements together. Food contributes a substantial share for most people.

The tolerable upper intake level for supplemental magnesium in adults is 350 mg per day — a limit on supplements and medications only, not on magnesium from food, which healthy kidneys clear without difficulty.

All of those numbers are elemental. A "500 mg" bottle of magnesium bisglycinate is not close to the upper level; a "500 mg" bottle of magnesium oxide is most of the way there in one tablet. Same front-panel number, different position relative to the ceiling.

Which form is better. Elemental percentage tells you what's in the powder. It says nothing about how much reaches your bloodstream, and the comparative human data needed to rank the common forms honestly does not exist. We wrote about that at length on the magnesium bisglycinate page →.

That a lower percentage is a worse product. Bisglycinate has the lowest elemental percentage of the three above, because glycine is heavy. That's a property of the compound, not a defect.

That a higher dose is a better dose. More elemental magnesium is not automatically better, and the upper level exists for a reason.

200 mg of elemental magnesium per two-capsule serving — 48% of the Daily Value, and comfortably under the 350 mg upper level. The compound weight it comes from is roughly 1.4 g of fully reacted bisglycinate.

We put the elemental number on the front of our label, because it's the one that means something.