What types of magnesium are there, and how do they differ?

Magnesium in products is never on its own: it is always bound to another substance, and that partner gives each type its name, such as magnesium oxide, magnesium citrate, magnesium chloride, magnesium bisglycinate or magnesium carbonate. The types differ in what the magnesium is bound to and in how much of the compound's weight is magnesium. A 2020 chemistry review lists 60.3% for magnesium oxide, 25.5% for magnesium chloride and 11.3% for a magnesium citrate. The Thai Reference Daily Intake (Thai RDI) for magnesium is 310 mg a day.

In short:

• What differs: the partner (inorganic, organic acid or amino acid) and the share of magnesium in the weight
• Share of magnesium: from about 7% (orotate) to about 60% (oxide), depending on the weight of the partner
• Same name, different numbers: citrate, chloride and sulfate each exist in more than one form
• Daily amount: Thai RDI 310 mg

This article explains the types by their chemistry and composition only. For what magnesium does in the body and the full list of foods that contain it, see What does magnesium do, and which foods contain it?

What does "type of magnesium" mean?

Magnesium is a metal element. In food, water and products, it is found as part of a compound, joined to another molecule or ion.

Magnesium is always bound to a partner

The NIH Office of Dietary Supplements (ODS), part of the US National Institutes of Health, says magnesium supplements are available in a variety of forms, including magnesium oxide, citrate and chloride. Each name tells you the partner: oxygen in magnesium oxide, the citrate of citric acid in magnesium citrate, and chloride in magnesium chloride. The same naming works for zinc, which is explained in What types of zinc are there, and how do they differ?

Elemental magnesium and the weight of the compound

The amount of the magnesium element itself within a compound is called elemental magnesium. It is always less than the weight of the whole compound. A 2020 review in the journal Molecules, which surveys the chemistry of magnesium compounds, lists the molecular weight and the share of magnesium for common forms. Magnesium oxide, for example, has a molecular weight of 40.30 g/mol and is 60.3% magnesium.

Which magnesium compounds are there?

Magnesium compounds can be grouped by the partner. The formulas below come from PubChem, the chemistry database of the US National Library of Medicine. Where PubChem's main entry is a form with water attached, the table says so.

Magnesium with an inorganic partner: oxide, hydroxide, carbonate, chloride and sulfate

Magnesium oxide is magnesium joined to oxygen, with no other part. Magnesium hydroxide has two hydroxide groups, and magnesium carbonate has one carbonate group. Magnesium chloride and magnesium sulfate are salts that are often found with water molecules attached: the hexahydrate of magnesium chloride carries six, and the heptahydrate of magnesium sulfate carries seven, and that water counts towards the weight. Magnesium chloride is also used to set tofu, and in FoodData Central it appears in the names of tofu "prepared with calcium sulfate and magnesium chloride (nigari)".

Magnesium with an organic acid: citrate, lactate, malate and gluconate

Citric, lactic, malic and gluconic acids are organic acids. Citric acid is the acid found in citrus fruit. It has three acid groups, so it can bind magnesium in more than one ratio: PubChem's main entry for magnesium citrate is trimagnesium dicitrate, with three magnesium atoms shared between two citrate molecules, while magnesium citrate dibasic has one magnesium atom per citrate. Both are called "magnesium citrate" in everyday use.

Magnesium with an amino acid: bisglycinate, aspartate and taurate

"Bis" means two. In magnesium bisglycinate, one magnesium atom is bound to two molecules of glycine, the smallest amino acid; it is often called magnesium glycinate. The 2020 review in Molecules describes its structure: each glycine binds the magnesium through two points, forming a five-membered ring, and water molecules fill the remaining positions around the magnesium. Magnesium aspartate uses the amino acid aspartic acid, and magnesium taurate uses taurine.

Magnesium orotate

Orotic acid is a small organic acid that contains nitrogen. In magnesium orotate, one magnesium atom comes with two orotate molecules. The 2020 review notes that in this compound the orotate is held through the water molecules around the magnesium rather than bound directly to it.

How much of each compound is magnesium?

The share of magnesium depends on how heavy the partner is. Magnesium oxide has only a small oxygen atom as its partner, so most of its weight is magnesium. Orotic acid is a larger molecule, and two of them come with each magnesium atom, so only a small share of magnesium orotate is magnesium.

Values listed in a 2020 review

Source: Case, Zubieta, Doyle and Kostakis, Molecules 2020, table of common magnesium supplements. The review does not list a value for magnesium bisglycinate, lactate or gluconate, so they are not shown here.

Why do other sources give different numbers?

The molecular weights in the table show which compound each figure describes. The 95.21 g/mol for magnesium chloride and the 120.37 g/mol for magnesium sulfate match the forms without water in PubChem, while the hexahydrate of magnesium chloride has a molecular weight of 203.30 and the heptahydrate of magnesium sulfate 246.48. The 214.41 g/mol for magnesium citrate matches magnesium citrate dibasic, with one magnesium atom per citrate.

A 2019 review in the journal Medical Sciences gives a different set of figures, without stating which form of each compound it means:

The two reviews agree on oxide and hydroxide but give different figures for several other compounds. The 2019 review does not say which form it used.

The weight of a compound and the weight of its magnesium

The weight of a magnesium compound and the weight of the magnesium in it are two different numbers. The shares in the tables above describe how much of each compound's weight is magnesium.

How much magnesium do foods contain?

The ODS says magnesium is found naturally in many plant and animal foods and in some drinks, and that tap, mineral and bottled water can be sources too, with amounts that vary widely, from about 1 mg per litre to more than 120 mg per litre.

Magnesium in selected foods (per 100 g)

The figures below come from the US Department of Agriculture's FoodData Central database (SR Legacy), with each 100 g compared with the Thai RDI of 310 mg. Seeds, beans and rice are listed dry.

Brown rice and white rice in Thai markets

A 2013 study from the Chulabhorn Research Institute analysed 667 samples of rice, animal foods, eggs, vegetables, fruits, infant formula and drinking water bought in markets, supermarkets and grocery stores in Bangkok between 2005 and 2008. Non-polished rice had higher magnesium, calcium, manganese, iron and selenium than polished rice. The study covered foods sold in one city over three years, so it describes those samples rather than all Thai rice.

How much magnesium do you need a day, and how much is too much?

The Thai RDI for magnesium is 310 mg a day, for the general population aged 3 and over. Magnesium is a component of bones and teeth, and it contributes to the normal function of muscles and the nervous system and to normal energy-yielding metabolism. The UK's NHS says people should be able to get all the magnesium they need from a varied and balanced diet.

Upper limits

The ODS says too much magnesium from food does not pose a health risk in healthy people, because the kidneys eliminate the excess in urine. High doses from supplements or medicines can cause diarrhoea, sometimes with nausea and abdominal cramping.

Magnesium can come from more than one product

The ODS notes that some medicines sold without a prescription contain magnesium as an ingredient, often as magnesium hydroxide. Because the US upper limit counts supplements and medicines together, amounts from several products add up.

Who should talk to a doctor or pharmacist?

People who take regular medication

Some medicines can interact with magnesium, and some can increase the amount of magnesium lost in urine. If you take medication regularly, ask a doctor or pharmacist before adding magnesium.

Pregnant and breastfeeding women

If you are pregnant or breastfeeding, talk to a doctor or pharmacist before taking any dietary supplement, including magnesium.

Dietary supplements are not intended to prevent, treat or cure any disease.