Magnesium Supplements: How to Read the Form and Elemental Amount on the Label

Magnesium labels look simple, but two lines cause most of the confusion: the form (oxide, citrate, glycinate, malate and so on) and the amount. Is “200 mg” the magnesium itself or the whole compound? This guide shows how to read both, using two products we carry: Thorne Magnesium Bisglycinate, a powdered dietary supplement, and LMNT Zero Sugar Electrolytes, Citrus Salt, a drink mix labeled as a food. For the basics of any supplement panel, start with how to read a supplement label.

How we wrote this: every fact comes from the FDA labeling rules in the Code of Federal Regulations, the National Academies report that set the upper limit for magnesium, the brands’ own pages, the NIH Dietary Supplement Label Database (DSLD) and PubChem, all linked where they are used. We describe what the labels and rules say. We have not tested either product, and this is not diet or medical advice.

Elemental magnesium: the number on a US label

Magnesium in a supplement is always bound to something else, such as glycine, citrate or oxygen. “Elemental magnesium” means the amount of magnesium inside that compound, not the weight of the whole compound.

On a Supplement Facts panel, the FDA rule settles which one you see. 21 CFR 101.36(b)(2)(ii) says the amount by weight must be the weight of the dietary ingredient rather than the weight of its source, and gives the example of calcium rather than calcium carbonate. Applied to magnesium, a line that reads “Magnesium 200 mg” means 200 mg of magnesium itself. You do not need to convert it. Calcium panels work the same way; our calcium citrate vs calcium carbonate labels guide reads three of them.

Worked example: Thorne Magnesium Bisglycinate

Here is the Supplement Facts panel for the 187 g powder, as shown on the Thorne product page and in NIH DSLD record 298074:

• Serving size: 1 scoop (3.11 g).
• Servings per container: 60.
• Amount per serving: Magnesium 200 mg.
• Form: “(as Magnesium Bisglycinate)”.
• % Daily Value: 48%, for adults and children 4 years and older.

Three things are worth reading closely.

The 200 mg is magnesium, not bisglycinate. Under the FDA rule above, the label lists the weight of the magnesium. The bisglycinate compound in each scoop weighs more than 200 mg. The same word turns up on iron capsules; our iron supplement label guide reads one.

The scoop weight is not the magnesium weight. A 3.11 g scoop also holds the other ingredients. The Thorne page lists citric acid and monk fruit concentrate, and the label in DSLD 298074 names the monk fruit as Tate & Lyle’s Purefruit Select. So you cannot work out the magnesium share from the scoop weight. Read the amount line instead.

The form sits in parentheses. The line reads “Magnesium (as Magnesium Bisglycinate)”: the nutrient first, then its source. 21 CFR 101.36(d) allows the source to be shown this way, after the word “as” or “from”, and when it is, the source does not have to be repeated in the ingredient list. That is why the other ingredients line on this label lists only citric acid and monk fruit.

Reading the % Daily Value

The FDA sets the Daily Value for magnesium at 420 mg for adults and children 4 years and older, according to the reference table in 21 CFR 101.9(c)(8)(iv). The same table lists 400 mg for pregnant and lactating women, 80 mg for children 1 to 3 years and 75 mg for infants.

Both labels in this guide use the 420 mg figure. Thorne’s 200 mg works out to 48%, and LMNT’s 60 mg works out to 15%. The percentage is a reference point for comparing products. It is not a target or a limit.

The upper limit for supplemental magnesium

The National Academies (Institute of Medicine) 1997 report on Dietary Reference Intakes set the Tolerable Upper Intake Level (UL) for magnesium at 350 mg a day for adolescents and adults. The report applies this limit to magnesium from nonfood sources, such as supplements and medications, and says a UL cannot be set for magnesium found naturally in food. It names diarrhea as the first sign of too much magnesium from nonfood sources.

That is why the elemental amount matters when you add things up. The 420 mg Daily Value counts all magnesium, food included. The 350 mg UL counts only magnesium from supplements and similar sources. If you take more than one product that contains magnesium, add up the “Magnesium” lines from each label and talk to your doctor about what makes sense for you.

Supplement Facts vs Nutrition Facts: the LMNT example

Not every product with added magnesium is sold as a dietary supplement. LMNT Citrus Salt carries a Nutrition Facts panel, the label used for foods, as the panel image on LMNT’s site shows. It is not in the NIH DSLD, which lists supplement labels.

The two panel types follow different FDA rules. Dietary supplements use Supplement Facts under 21 CFR 101.36, which can name the form right beside the amount. Foods and drink mixes use Nutrition Facts under 21 CFR 101.9, where the magnesium line shows only the nutrient and its amount. The form, if any, appears only in the ingredient list.

Per the LMNT Citrus Salt panel, one stick pack (6 g) contains:

• Magnesium: 60 mg, 15% DV.
• Sodium: 1000 mg, 43% DV.
• Potassium: 200 mg, 4% DV.
• Other lines: 5 calories, 1 g total carbohydrate, 0 g total sugars.

The box holds 30 stick packs. To find the form, go to the ingredient list. On the panel image and the LMNT ingredients page, Citrus Salt lists salt (sodium chloride), citric acid, magnesium malate, potassium chloride, natural lemon and lime flavors, and stevia leaf extract. So the magnesium here comes from magnesium malate.

LMNT also gives a clear example of the gap between compound and elemental weight. LMNT says it takes about 390 mg of magnesium malate, or 265 mg of di-magnesium malate, to supply 60 mg of magnesium. By our calculation from the formula in PubChem, 390 mg of magnesium malate holds about 61 mg of magnesium, which matches. The panel shows the 60 mg, not the 390 mg. For the sodium, potassium and sugar lines on the same panel, see our guide on how to read an electrolyte drink mix label.

How much of each form is magnesium?

Different compounds carry different shares of magnesium by weight. By our calculation from the chemical formulas in PubChem (using 24.305 as the atomic weight of magnesium):

• Magnesium oxide (MgO): about 60% magnesium, per the PubChem oxide entry.
• Magnesium citrate (trimagnesium dicitrate): about 16%, per the PubChem citrate entry.
• Magnesium malate: about 16%, per the PubChem malate entry.
• Magnesium glycinate or bisglycinate: about 14%, per the PubChem glycinate entry.

Two cautions on these numbers. Real ingredients can be hydrates or blends, so the share in a given product can be lower than the pure formula suggests. And you never need them to read a US Supplement Facts panel, because the label already states the elemental amount. Use them only to make sense of a brand that quotes compound weights, as in the LMNT example. These percentages say nothing about how one form compares with another in the body.

Directions and cautions on the label

Directions and warnings tell you how the brand expects a product to be used. Here is what each source says for the two products.

• Directions (Thorne label): the label in DSLD 298074 says to mix 1 scoop with at least 8 ounces of water daily, or as recommended by your health-care practitioner.
• Pregnancy (Thorne label): the Thorne label says that if you are pregnant, consult your health-care practitioner before using it.
• Digestive warning (Thorne product page): Thorne notes that gas, bloating or diarrhea may occur in some people taking magnesium supplements, at amounts that vary by person, and that it resolves when the amount is reduced.
• Allergies (Thorne product page): Thorne lists the product as contraindicated for anyone with a history of hypersensitivity to any of its ingredients. The label in DSLD 298074 also marks it gluten free.
• Storage (Thorne label): per DSLD 298074, use only if the bottle is sealed and store it tightly sealed in a cool, dry place.
• LMNT: we found no printed directions or cautions on the LMNT panel image or the product page. Note the 1000 mg of sodium per stick if you watch your salt intake.

The Thorne powder is also listed in NSF Certified for Sport. Read more about what that seal covers in our supplements buying guide.

Whatever the label says, talk to your doctor before starting a new supplement, especially if you are pregnant, nursing, take medication or have a health condition.

A quick magnesium label checklist

1. Panel type: is it Supplement Facts or Nutrition Facts?
2. Serving size: one scoop, capsule or stick pack, and how much it weighs?
3. Amount: how many mg of magnesium per serving? On a US panel, this is elemental magnesium.
4. Form: is it in parentheses after the amount, or only in the ingredient list?
5. % Daily Value: figured against 420 mg for adults.
6. Total from all products: add the magnesium lines from every supplement you take.
7. Cautions: what does the container say, and what does the brand page add?

FAQ

What does “elemental magnesium” mean?

It is the weight of the magnesium itself inside a compound such as magnesium glycinate. Under 21 CFR 101.36, a US Supplement Facts panel lists this amount, not the weight of the compound.

Does “200 mg magnesium bisglycinate” mean 200 mg of magnesium?

On Thorne’s panel the line reads “Magnesium (as Magnesium Bisglycinate) 200 mg”, which means 200 mg of magnesium supplied by the bisglycinate. If a product page quotes a compound weight instead, the magnesium amount will be lower.

Why is the form in parentheses?

The FDA rule lets a supplement name the source after the nutrient with “as” or “from”. When it does, the source does not need to be repeated in the ingredient list.

Why doesn’t LMNT show the form next to the magnesium?

LMNT is labeled as a food with a Nutrition Facts panel, which lists nutrients without their source. The form, magnesium malate, is in the ingredient list.

What Daily Value does the label use?

420 mg for adults and children 4 years and older, set by the FDA in 21 CFR 101.9.

Is there an upper limit for magnesium?

The National Academies set a UL of 350 mg a day for adolescents and adults, for magnesium from supplements and medications only, not from food.

Where to go next

Read the full product pages for Thorne Magnesium Bisglycinate and LMNT Citrus Salt, go back to the basics in how to read a supplement label, or compare more products in our supplements buying guide. Browse the vitamins and supplements collection to see everything we carry.

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.