What does bioavailability mean with magnesium?
Bioavailability describes how well a nutrient can be absorbed after intake and made available to the body. In food supplements, magnesium is not present as a free element but is bound to a partner – for example to citrate, glycinate or oxide.3
Several factors play a role in magnesium absorption: the solubility of the magnesium compound, the amount taken, the dosage form and individual conditions in the gastrointestinal tract. Well-soluble forms tend to be absorbed more completely than poorly soluble ones.3 That is why a single blanket percentage for bioavailability is often less meaningful than a comparison under the same conditions.
Magnesium is not simply magnesium: which forms are there?
Magnesium compounds can be divided, in simplified terms, into organic and inorganic forms. Organic compounds such as citrate, bisglycinate and malate are bound to organic acids or amino acids. Inorganic compounds such as oxide or carbonate have a different chemical structure and differ, among other things, in solubility and share of elemental magnesium.3
Which form makes sense should therefore not be decided solely on the basis of advertising statements about muscles, teeth, sleep or energy. For the choice, tolerability, actual magnesium content and the desired form of intake are above all relevant.
Magnesium bisglycinate or magnesium glycinate
In magnesium bisglycinate, magnesium is bound to the amino acid glycine. The term magnesium glycinate is sometimes used in a simplified way in trade – often magnesium bisglycinate is meant by it. Magnesium bisglycinate is regarded as well bioavailable and well tolerated.
Anyone comparing magnesium capsules or magnesium powder with bisglycinate should nevertheless pay attention to the amount of elemental magnesium. A large amount of the compound on the front of a pack does not automatically equate to the same amount of magnesium.
Magnesium citrate
Magnesium citrate is an organic magnesium compound in which magnesium is bound to citric acid. Magnesium citrate is highly water-soluble, is absorbed rapidly and has a high bioavailability.3
In sensitive people, magnesium citrate can have a stool-loosening or laxative effect at higher single doses.3,4 This is above all an aspect of tolerability and not a general recommendation to use magnesium citrate to treat constipation.
Magnesium malate
Magnesium malate combines magnesium with malic acid and is among the well-absorbable organic magnesium compounds.3
Malate is a component of various metabolic processes. From this, however, it cannot be derived that magnesium malate treats tiredness or automatically provides more energy.
Magnesium taurate, magnesium gluconate and magnesium L-threonate
Besides citrate, bisglycinate and malate, there are further magnesium forms. Magnesium taurate is bound to taurine, magnesium gluconate to gluconic acid and magnesium L-threonate to threonic acid.
Magnesium L-threonate is marketed as being able to cross the blood–brain barrier. From this, however, no blanket health advantage over other magnesium forms and no general effect on concentration, sleep or mental performance can be derived.
Magnesium oxide and magnesium carbonate
Magnesium oxide is an inorganic compound and contains up to 60 per cent elemental magnesium. At the same time, the compound is more slowly soluble and has a lower to medium bioavailability.3
elemental magnesium is contained in magnesium oxide – more than many organic forms. At the same time it is less soluble and described as low to medium in bioavailability.3
Magnesium that is not absorbed can bind water in the gut. As a result, gastrointestinal complaints or diarrhoea can occur at higher amounts.3,4
Magnesium carbonate is likewise an inorganic compound and reacts with stomach acid in the stomach.3 From this chemical property, however, no therapeutic recommendation for heartburn or other conditions can be derived.
Are magnesium combinations better?
Some magnesium supplements combine several magnesium compounds, for example citrate, bisglycinate and malate.3 Such a combination can be practical, but is not automatically better than a product with only one magnesium compound.
When comparing, it should therefore not only be the number of magnesium forms contained that counts. More important are the actual amount of elemental magnesium, the dosage per capsule or tablet, tolerability and a transparent declaration of the composition.
Combinations with further micronutrients such as vitamin B6, too, do not automatically make a product a test winner. What is decisive is whether the composition suits personal requirements.
Which magnesium is the best? The direct comparison
| Magnesium form | Type | Classification | What to look out for |
|---|---|---|---|
| Magnesium bisglycinate | organic, chelate | well bioavailable and well tolerated | elemental magnesium amount per portion |
| Magnesium citrate | organic, salt | highly water-soluble, high bioavailability3 | can loosen stool at higher single doses3,4 |
| Magnesium malate | organic, salt | well absorbable3 | do not derive blanket effect claims |
| Magnesium taurate | organic, chelate | organic compound | do not choose on the basis of use claims alone |
| Magnesium gluconate | organic, salt | organic compound | compare tolerability and dosage |
| Magnesium L-threonate | organic | marketed as crossing the blood–brain barrier | do not derive blanket superiority |
| Magnesium oxide | inorganic | up to 60% elemental magnesium, lower to medium bioavailability3 | solubility and gastrointestinal tolerability |
| Magnesium carbonate | inorganic | reacts with stomach acid3 | do not derive therapeutic effect |
The table shows the most important differences of the magnesium forms at a glance. There is no general test winner.
What should you look out for when buying magnesium?
When buying magnesium, the name of the magnesium compound is only part of the decision. A good product should transparently show how much elemental magnesium is actually contained per daily portion.
- Magnesium compound: which form is contained and how is it declared?
- Elemental magnesium: how much magnesium does a capsule or tablet actually provide?
- Dosage: how many capsules or magnesium tablets are intended per daily portion?
- Composition: are further micronutrients or vitamin B6 added?
- Additives: which further ingredients does the product contain?
- Tolerability: how does your own gastrointestinal tract react to the chosen form?
- Dosage form: capsules, tablets or powder should suit your personal everyday life.
Anyone comparing different magnesium products should therefore not choose solely by buzzwords such as “highly bioavailable” or “test winner”. A sensible comparison takes into account the whole composition and the actual magnesium dosage.
Which dosage form makes sense?
Magnesium is available as powder, magnesium capsules and magnesium tablets. The dosage form does not automatically change the fundamental properties of the magnesium compound contained.
Capsules can be practical when a clearly portioned intake is desired. Tablets differ depending on composition and additives. Powders allow flexible portioning – the actual dosage must be observed particularly carefully here.
What should be considered with the magnesium dosage?
Which magnesium form is chosen and how much magnesium is taken are two different questions. The magnesium requirement describes the total daily intake from food and, where applicable, food supplements. The magnesium dosage of a supplement, by contrast, describes the additional amount from capsules, tablets or powder.
The DGE states an estimated value of 300 mg of magnesium per day for adult women and 350 mg per day for adult men. The EFSA, too, uses corresponding Adequate Intake values of 300 and 350 mg per day for adult women and men respectively.1,2 These values refer to the total daily magnesium intake and not to the dosage of a single magnesium supplement.
are the estimated values of the DGE and EFSA for the total daily magnesium intake in adults (women 300 mg, men 350 mg) – not the dosage of a single supplement.1,2
A higher dosage does not automatically mean a better effect or magnesium absorption. With food supplements, higher amounts can, depending on the compound, lead to gastrointestinal complaints and diarrhoea.4 How much magnesium per day is generally sensible we cover separately from the question of the best form in the article How much magnesium per day?.
With a suspected magnesium deficiency, too, intake should not be decided on the basis of individual complaints alone – the question of how a magnesium deficiency makes itself felt is covered in a separate article. Anyone taking medicines or several micronutrients at the same time should also consider possible intervals and interactions: What should not be taken together with magnesium?
What role does magnesium play independently of the magnesium form?
On the question of the best form, one point must not be forgotten: the different magnesium compounds do differ in properties such as solubility, elemental magnesium content or absorption – the fundamental functions of magnesium in the body, however, relate to the mineral itself.
Magnesium is involved, among other things, in processes in nerve and muscle cells as well as in numerous enzymatic processes.1,2 The choice between magnesium citrate, magnesium bisglycinate, magnesium oxide or another compound does not change this fundamental role of magnesium.
Magnesium from food or supplement?
Magnesium does not have to be taken in exclusively via food supplements. Many foods provide the mineral as well. Which foods contain particularly high amounts we answer separately in the article Where is the most magnesium found?.
If you are interested in the interplay of different minerals, you will find additional information in our article Magnesium and potassium: why do we need them?.
What applies during pregnancy?
In pregnancy and breastfeeding, magnesium supplements should not be chosen or dosed solely on the basis of general product recommendations. The question Why no magnesium during pregnancy? is therefore covered separately and with a view to the particular circumstances of this phase of life.
What does magnesium stearate have to do with magnesium supplements?
In the ingredient list, the term magnesium stearate can also appear. Magnesium stearate is, however, not the same as magnesium in the form of a food supplement – it is a different substance that can be used, among other things, as a technological aid. More on this in the article Magnesium stearate: a bad reputation without cause?.
