Elemental magnesium explained

What elemental magnesium means

Magnesium is never sold on its own. In a supplement it is always bound to something else, such as oxygen, citric acid, glycine or chloride, to make a stable compound that can go into a tablet, capsule or powder.

Elemental magnesium is the weight of the magnesium itself inside that compound. The rest of the weight is whatever the magnesium is bound to.

That gap is the single most useful thing to understand when reading a magnesium label. Two products can list very different numbers and deliver exactly the same amount of magnesium, or list the same number and deliver very different amounts.

Why the compound weighs more than the magnesium in it

Magnesium is a light element. Most of the molecules it is paired with in supplements are heavier, so the magnesium ends up as a small share of the total.

Magnesium oxide is the exception. Oxygen is lighter still, so magnesium makes up about 60% of the compound. At the other end, magnesium L-threonate pairs each magnesium atom with two threonate molecules, and magnesium makes up only about 8%.

Magnesium glycinate sits in between. Each magnesium ion is held by two glycine molecules, and magnesium is about 14% of the weight. Our guide to what magnesium glycinate is works through what the other 86% delivers.

How Australian labels show elemental magnesium

In Australia, labels for non-prescription medicines follow a standard set by the Therapeutic Goods Administration. Where a medicine contains a mineral for supplementation, the label must declare the amount of the mineral element, not just the compound.

In practice that produces two numbers on the label, written something like this:

Magnesium glycinate 1,000 mg, equivalent to magnesium 141 mg

The first number is the compound. The second is the elemental magnesium. The TGA's own example uses calcium carbonate, with the phrase "equivalent to calcium 500 mg", and the rule applies to all mineral supplements.

The equivalent figure is the one that matters for comparing products and for checking an intake against the recommended amounts. The compound figure is useful for knowing which form you are buying, but it says little about how much magnesium is in the dose.

Magnesium by weight across common forms

These percentages are calculated from the chemical formula of each compound using standard atomic weights. They show how much of each form is magnesium, and what 1,000 mg of the compound supplies.

Form	Magnesium by weight	Magnesium in 1,000 mg of compound
Magnesium oxide	About 60%	About 603 mg
Magnesium hydroxide	About 42%	About 417 mg
Magnesium carbonate	About 29%	About 288 mg
Magnesium chloride (anhydrous)	About 26%	About 255 mg
Magnesium citrate (anhydrous)	About 16%	About 162 mg
Magnesium malate	About 16%	About 155 mg
Magnesium glycinate	About 14%	About 141 mg
Magnesium chloride hexahydrate	About 12%	About 120 mg
Magnesium sulfate heptahydrate	About 10%	About 99 mg
Magnesium L-threonate	About 8%	About 83 mg
Magnesium orotate	About 7%	About 73 mg

Seen the other way round, supplying 300 mg of magnesium takes roughly 500 mg of magnesium oxide, roughly 1,850 mg of anhydrous magnesium citrate, and roughly 2,130 mg of magnesium glycinate. That is why products built on the lighter forms tend to come as larger capsules, several capsules per dose, or powders.

Why a table can only take you so far

Real ingredients are not always the neat compound in the table.

Water. Many magnesium salts hold water inside their crystal structure. Magnesium chloride and magnesium sulfate are the clearest examples in the table above: the hydrated forms carry roughly half the magnesium of the dry forms, gram for gram. Commercial magnesium citrate is also commonly sold in hydrated grades, which lowers its magnesium share below the anhydrous figure.

Blends. Some ingredients sold under one name are mixtures of more than one magnesium compound, which can shift the percentage in either direction.

Names. "Magnesium amino acid chelate" is used on some labels for magnesium glycinate, but the name on its own does not pin down an exact composition.

For all three reasons, the equivalent figure printed on an Australian label is more reliable than a percentage worked out from a table. The table is for understanding why the numbers differ. The label is for knowing what is in a particular product.

A worked example

Imagine two labels side by side. These are illustrative figures, not real products.

• Label A: magnesium oxide 500 mg, equivalent to magnesium 300 mg.
• Label B: magnesium glycinate 1,500 mg, equivalent to magnesium 211 mg.

Label B has three times the compound weight. Label A has more magnesium. Anyone comparing the first number on each label would get the answer backwards.

Comparing the equivalent figures gets the elemental amount right. It still does not settle which dose delivers more magnesium to the body, and that is a separate question.

Elemental magnesium is not the same as absorbed magnesium

The equivalent figure tells you how much magnesium is in the dose. It does not tell you how much of it is absorbed.

Magnesium oxide is the clearest example. It has the highest magnesium content of the common forms, and it is also consistently among the least well absorbed. In a randomised, double-blind trial of 46 healthy adults, each group took 300 mg of elemental magnesium a day for 60 days as magnesium amino acid chelate, magnesium citrate or magnesium oxide. By 60 days, the two organic forms showed greater absorption than the oxide, measured by magnesium in the urine. The oxide group showed no difference from placebo on that measure.

Two things are worth keeping in view alongside that result. First, that trial measured absorption indirectly, through urine, blood and saliva, which is the usual approach but not the most precise one. Second, a 2021 systematic review found that all magnesium supplements can maintain normal magnesium levels in healthy people who are not already short of it. Differences between forms matter more for older people, people who are unwell, and people whose levels are already low.

Absorption is also shaped by the dose itself and by what is eaten with it. Our guide to magnesium absorption and bioavailability covers why it is so hard to measure, and our comparison of magnesium glycinate and magnesium citrate looks at two of the better-absorbed forms in detail.

Checking a dose against Australian intake figures

The equivalent figure is also the one to check against recommended intakes, because those intakes are set in terms of magnesium itself.

Australian recommended dietary intakes for magnesium are 400 mg a day for men aged 19 to 30 and 420 mg for men 31 and over, and 310 mg a day for women aged 19 to 30 and 320 mg for women 31 and over. Those figures cover all sources, and food is the main one.

The upper level for magnesium is 350 mg a day, and it applies to magnesium from supplements and medicines only, not to magnesium from food. It is also stated in elemental magnesium. A label reading "magnesium glycinate 2,000 mg" is not a 2,000 mg dose for this purpose. It is roughly a 280 mg dose, and that is the number to compare with the 350 mg limit.

Several magnesium products may be taken at once without anyone noticing, such as a standalone magnesium, a multivitamin and an antacid. The equivalent figures across all of them are what add up.

When to talk to a doctor or pharmacist

Higher supplemental doses of magnesium can cause diarrhoea, nausea and abdominal cramping. People with reduced kidney function, people taking prescription medicines, and anyone who is pregnant or breastfeeding should get advice before starting a magnesium supplement. Our guide to side effects and interactions explains why.

A pharmacist can also read a label with you and add up the elemental magnesium across everything you take. Nothing on this page is a substitute for individual medical advice.