Comparison of magnesium compounds: citrate, bisglycinate, oxide, etc.

Why are there different magnesium compounds?

Magnesium is a mineral. It is present in the body, in foods and in dietary supplements not as an element, but as a magnesium ion. This ion can be bound to a component of magnesium salts or to other molecules. 

Magnesium is found in various types of bonds in food. In green plants, for example, magnesium is a key component of the green plant dye chlorophyll.

Food supplements use specific forms of magnesium – often magnesium citrate, magnesium oxide, magnesium carbonate or magnesium bisglycinate. A distinction is made between inorganic and organic compounds.

In the digestive tract, magnesium is released from all these compounds and is usually absorbed as a magnesium ion (Mg²⁺).

What is the difference between inorganic and organic compounds?

Magnesium salts can be divided into organic and inorganic compounds. The name refers to the substance to which the magnesium is bound.

Organic magnesium compounds contain magnesium in combination with an organic constituent, for example an organic acid or an amino acid. In the case of magnesium citrate, magnesium is bound to citrate, the salt of citric acid, and in the case of magnesium bisglycinate to the amino acid glycine. Further examples of organic compounds are magnesium threonate, magnesium taurate and magnesium orotate. 

Organic magnesium compounds have a lower proportion of elemental magnesium than inorganic ones. This means that the actual amount of magnesium is small in relation to the total compound given the very large organic remainder and the very small magnesium ion. The magnesium content varies markedly in some cases: While magnesium citrate contains around 15% magnesium and magnesium bisglycinate contains a maximum of 11% magnesium, the proportion of magnesium in the inorganic compounds magnesium oxide and magnesium carbonate is much higher, at 60% and 29% respectively. In order to obtain the same amount of magnesium, a significantly greater amount of an organic magnesium compound is therefore required than of an inorganic compound.

Another difference is solubility – including in the digestive tract. Organic forms of magnesium are usually readily soluble over a broader pH range, whereas inorganic forms dissolve much better in an acidic environment. This can play a role if the stomach produces less acid – for example, when certain medications are taken.

Typical inorganic magnesium compounds are magnesium oxide and magnesium carbonate.

Overview of commonly used magnesium compounds:

• Magnesium citrate

Magnesium citrate is an organic magnesium compound in which magnesium is bound to citrate, the salt of citric acid. The compound is characterised by good solubility and is well absorbed by the body.

Magnesium citrate is therefore often used in dietary supplements. It is tasteless and thus well suited for magnesium products that are taken directly (e.g. sachets).

• Magnesium bisglycinate / Magnesium glycinate

Magnesium bisglycinate is an organic magnesium compound in which magnesium is bound to the amino acid glycine. The compound is considered to be well tolerated and is also well absorbed by the body.

Since the proportion of elemental magnesium is small at a maximum of 11%, dietary supplements that only contain magnesium bisglycinate do not usually contain a particularly high dosage, or the capsules/tablets are very large and difficult to swallow. Depending on the desired dosage, it may therefore be useful to combine magnesium bisglycinate with compounds that are richer in magnesium. Due to its unpleasant taste, magnesium bisglycinate is particularly suitable for taking in tablet or capsule form. 
 

• Magnesium oxide

Magnesium oxide is an inorganic magnesium compound with a high proportion of elemental magnesium.

As a result, comparatively little magnesium oxide is required in order to provide a certain amount of magnesium. This is particularly beneficial for higher-dose dietary supplements.

In addition, magnesium oxide is a well-researched magnesium compound and is tasteless.
 

• Magnesium carbonate

Magnesium carbonate is also an inorganic magnesium compound. It has a comparatively high proportion of elemental magnesium. Magnesium carbonate is tasteless and neutralises acid, e.g. stomach acid, directly, forming water and CO2.
 

• Magnesium orotate

Magnesium orotate is an organic magnesium compound. Magnesium is bound to orotate, the salt of orotic acid.

Compared to magnesium oxide, magnesium orotate contains only a very small proportion of elemental magnesium. Therefore, a larger amount of the compound is required to provide a certain amount of magnesium.

Magnesium orotate may only be used in medicinal products in Switzerland and the EU.

How do the absorption and bioavailability of magnesium compounds differ?

Absorption is the process by which a substance is taken from the digestive tract into the body. In simplified terms, bioavailability describes what proportion of an ingested substance is actually available to the body.

In the case of magnesium, various factors play a role. In addition to the chemical compound, other important factors include solubility, the amount taken, whether it has been taken with or without food, the composition of the food with which magnesium is taken and the individual magnesium status. Someone with a good level of magnesium in their body will absorb less than a person with a low magnesium status.

Magnesium absorption is estimated to be about 30–40% of the ingested amount under usual conditions, with organic magnesium compounds tending to be slightly better absorbed than inorganic compounds (a difference of about 5–10%).

Therefore, when assessing and selecting a magnesium product, it is not only the compound used that should be considered. The amount of elemental magnesium per daily dose, the intended dosage and the form of administration, for example tablet, capsule or powder, are also important.

Why can magnesium have a laxative effect?

What is the magnesium content of the individual compounds?

The proportion of elemental magnesium varies depending on the compound. Magnesium oxide, for example, has a high content, whereas this is lower in the case of magnesium citrate and magnesium bisglycinate.

In the case of dietary supplements, the amount of magnesium declared on the label indicates how much elemental magnesium is actually contained in a daily serving.

References

Schuchardt JP, Hahn A. Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update. Curr Nutr Food Sci. 2017 Nov;13(4):260-278

Coudray C, Rambeau M, Feillet-Coudray C, Gueux E, Tressol JC, Mazur A, Rayssiguier Y. Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach. Magnes Res. 2005 Dec;18(4):215-23. PMID: 16548135