275 mg From 2,500 mg: How to Read a Magnesium Label

Pick up two mineral bottles. One says 500 mg. One says 1,800 mg. The 1,800 mg bottle can easily hold less of the mineral.

That is not a typo, and it is not only a magnesium problem. The same gap sits on zinc, on iron, on calcium and on potassium. One division on the back of the panel closes it permanently, and learning it takes about ninety seconds.

This site is named after that division. A tare is the weight of the empty container — the figure you subtract to find out what is actually in it. A mineral compound is a container too: the mineral, plus the carrier molecule it is bound to. Subtract the carrier and what is left is the only number that describes what you are taking.

Why is the milligram number on the front different from the one in the panel?

Because the two numbers measure different things. The front of a container is generally free to print compound weight — the mineral plus the carrier it is bound to. The Supplement Facts panel has to declare elemental weight, which is the mineral on its own. Both numbers can be true at the same time. Only the second one is the mineral.

That is not a house convention. The NIH Office of Dietary Supplements sets the rule out plainly for magnesium: the Supplement Facts panel declares the elemental amount, not the weight of the whole compound. The front of a container is where a brand chooses what to show. The back is where it has to answer.

Which is why the argument the front of a bottle starts is always settled on the back of it.

The bottle says 2,500 mg — so why is the magnesium only 275 mg?

Because 2,500 mg is the weight of the compound and 275 mg is the weight of the magnesium inside it. Our own panel prints both, in that order: 275 mg of elemental magnesium from 2,500 mg of magnesium glycinate, three capsules, 30 servings to a bottle. Divide, and 275 ÷ 2,500 is 11%. Eighty-nine per cent of the weight of those three capsules is not magnesium.

Nothing has been padded out to get there. Magnesium is a light atom, and glycine — the amino acid it is bound to in a bisglycinate — is not. The carrier is most of the weight because the carrier is most of the molecule.

It also answers the question a buyer asks next, and the answer looks bad right up until the arithmetic is in front of you: the serving is three capsules rather than one because 275 mg of elemental magnesium needs roughly 2,500 mg of compound to carry it. A single capsule cannot physically hold that much powder. Where a container offers the same elemental figure in one capsule, the arithmetic says it has used a form with a far higher elemental fraction — and which forms those are, and what the higher fraction costs elsewhere, is the rest of this page.

Why the difference is worth ninety seconds

Because on the mineral this question gets asked about most, there is a real gap underneath it.

NIH Office of Dietary Supplements — magnesium is a cofactor in more than 300 enzyme systems, including protein synthesis, muscle and nerve function, and energy production. Not 600, not 800, and not "processes": that is the Office's number and the Office's wording, and it is the one line in this category that gets inflated every time it is repeated.

The recommended dietary allowance is 400 mg a day for men aged 19 to 30 and 420 mg for men 31 to 50. Set against that, the intake figure everyone quotes deserves its date printed beside it: Am J Clin Nutr, 2011, on national survey data — American men who do not supplement averaged 268 mg of magnesium a day from food. Fifteen years is a long time for a dietary survey, and a population average is not a finding about any one person.

Then the figure nobody holds at all. National surveys have not measured serum magnesium since 1974, and it is not on a standard electrolyte panel. No brand, ours included, is in any position to say where an individual sits. A gap in the average diet is a reason to read a label carefully. It is not a diagnosis, and this page is about the label.

Which is what makes the arithmetic worth ninety seconds. There is a real gap, and a large share of what is sold to close it is priced on a number that is not the mineral.

How do I convert a compound weight to an elemental one myself?

The atomic masses are the standard published ones and they do not vary between brands: magnesium 24.305, zinc 65.38, iron 55.845, calcium 40.078, potassium 39.098, carbon 12.011, hydrogen 1.008, nitrogen 14.007, oxygen 15.999, sulphur 32.06, chlorine 35.45. Every figure in the next section is those numbers and a division. Nothing else went into any of them.

Does this apply to anything other than magnesium?

The first warning is that these are ceilings for a pure, dry compound, and a raw material is rarely either. Water of crystallisation is the usual reason, and it is not a trick: the water is part of the salt. Magnesium citrate is 16% magnesium anhydrous and about 12% as the nonahydrate, because nine water molecules add 162 to the formula mass and no magnesium whatsoever. Ferrous sulphate is 37% iron anhydrous, 33% as the monohydrate and 20% as the heptahydrate — one salt, three honest labels, nearly a factor of two between them. That is the reason the elemental figure has to be printed by the maker rather than worked out by the reader from a form name.

The second warning is larger, and it applies to every table of this kind including ours. No human study publishes per-form elemental percentages. The versions that circulate in this category are usually traced back, when anyone bothers, to a mouse study or a cell-culture experiment that never reported such a figure at all. The rows above are arithmetic and nothing else: they state the weight ratio of a named compound, and they say nothing about how much of the mineral crosses a gut wall. A table like this one is a tool for reading a label. It is not evidence, ours is not presented as evidence, and anyone offering you one as a finding is quoting nothing.

And why you want it measured, which is a different thing again. A printed elemental figure beats one calculated from a textbook, and a figure an outside laboratory found in the lot you are holding beats a printed one. Night Work has that row for the powder, not for the capsule: the document held for it measures 102.54 mg against a 91.6 mg specification in the laboratory's own 926 mg serving of a raw-material lot, and Testing & Certification prints it in that serving rather than running it forward to three capsules. That is the whole argument of this article, run on our own panel — and it still cuts against us until a finished-lot result exists.

Why the biggest number is the one brands print

Look at which form has the highest elemental fraction. Magnesium oxide, at roughly 60%, lets a manufacturer put a large magnesium number on a small, cheap capsule.

It is also the form with the weakest absorption profile. Poor solubility means a substantial share passes straight through, and its most reliable effect at higher doses is a laxative one.

That is the trap. The form that produces the most impressive label is the form least likely to be absorbed. A 500 mg oxide capsule and a 1,800 mg glycinate capsule can look similar on paper and behave nothing alike.

Chelated forms like glycinate carry the opposite trade: a lower elemental fraction, so the capsule has to be physically larger, in exchange for better tolerability. Glycine is a small, well-tolerated amino acid, and the resulting compound is markedly gentler on the gut than oxide at comparable elemental doses. You pay for that in capsule size. It is a trade worth making if you intend to take the thing every day for a year, which is the only way it does anything.

What 275 mg elemental is actually sized for

About 65% of the daily value, which is 420 mg on a supplement panel.

That number is deliberate, and the reason is a second published figure most brands never mention. There is a tolerable upper intake level of 350 mg per day for magnesium from supplements specifically. Food magnesium is not subject to it — the kidneys handle dietary magnesium comfortably — but supplemental magnesium is, and the ceiling is lower than a lot of bottles on the shelf.

275 mg sits under that ceiling with 75 mg to spare, and the spare seventy-five is the point rather than the slack, so here is our own arithmetic before anyone else’s.

Night Work is the only supplemental magnesium in the TARE range. Nothing else we make carries any. Run everything we sell and the supplemental total is 275 mg against a 350 mg ceiling, which leaves 75 mg for whatever else is in the cabinet. That seventy-five is not spare capacity. It is the room a multivitamin, a greens powder or an electrolyte mix will occupy without announcing it — count them against it rather than assuming it is free, because loose stools arrive before any label warns of it.

We are printing that here rather than letting you find it, because a brand that teaches you to add up your stack has to add up its own first. Plenty of products carry magnesium quietly. Ours does not get to be one of them.

Where the evidence sits, honestly

Magnesium supports normal muscle function.* That is the strongest thing about it and the honest basis for taking it.

*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.

Night Work sits at 22:00 in the Protocol because one fixed slot a day is the easiest dose to keep.

Consistency is the mechanism. Timing folklore isn't.

The ceiling the gut enforces

Take too much supplemental magnesium, particularly in poorly absorbed forms, and the result is gastrointestinal and unmistakable. Loose stools are the standard signal and it is dose-dependent.

Treat that as useful feedback rather than a failure. If a magnesium product is running straight through, the answer is less of it or a better-tolerated form, not more of it.

One practical note that matters: magnesium can interfere with the absorption of certain medications, including some antibiotics. If you take prescription medication of any kind, space your magnesium away from it and ask your doctor or pharmacist rather than guessing.

Reading any magnesium label in sixty seconds

1. Find the elemental figure. If the panel gives only a compound weight with no elemental number, the brand is either careless or counting on you not to ask. Either is disqualifying.
2. Divide. Elemental ÷ compound weight. Land near 60% and you are looking at oxide, whatever the front of the bottle says.
3. Check the serving size. A "600 mg" claim spread across three capsules is a 200 mg capsule. Price the daily serving, not the headline.
4. Read the form name exactly. "Magnesium glycinate" and "magnesium oxide blended with glycinate" are different products. Buffered blends are legitimate; they should be disclosed.
5. Add up your whole stack. Multivitamins, electrolyte powders, and greens products all carry magnesium quietly. The 350 mg supplemental ceiling applies to your total, not to one bottle.
6. Look for proprietary blends. If magnesium sits inside a blend with a single combined weight, you cannot calculate anything. Walk.

The bottom line

The number on the front of a magnesium bottle is compound weight. The number that decides what you are actually taking is elemental. They can differ by a factor of seven, and the direction of the difference is not the one most people assume.

Ours is 275 mg elemental from 2,500 mg of magnesium glycinate, three capsules, 30 servings to a bottle — both numbers printed because both numbers are true. Run the division on us first: 275 ÷ 2,500 is 11%, which is what a real chelate looks like. About 65% of the daily value, 75 mg under the supplemental upper limit, in the form built to be taken every day rather than to look impressive once.

Do the division. Then decide, on us or on anyone else. That is what The Monograph is for.

Also in the Journal: how to read a colostrum label, the same exercise on a different panel. Or run all three: The Standard.