You're standing in front of the supplement shelf, between magnesium citrate, bisglycinate, and oxide. They all talk about magnesium, and they all sound somehow equally important. The reason for the variety among the different forms of magnesium is simple: in capsules, magnesium is always bound to another substance, and it's exactly this partner that determines how much magnesium is inside and how well you absorb it.
Two tubs with "magnesium" on the label may deliver the same mineral, but they can still feel completely different: sometimes there's simply more magnesium inside, sometimes it's absorbed better, sometimes it agrees with you less.
In this article, we look at the most important forms of magnesium, with what studies actually show about their absorption and what each of them is suited for in everyday life.
Important: This article does not replace medical advice. If you have kidney disease, take medication, or are pregnant or breastfeeding, you should clarify taking magnesium supplements with your doctor or pharmacy beforehand. Special recommendations apply to children, so talk to a doctor beforehand here as well.
Table of Contents
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What does the body need magnesium for?
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What does bioavailability mean?
- An overview of the forms of magnesium
- Which magnesium is right for you?
- Taking magnesium correctly: timing and combinations
- What to look out for when buying
- My personal assessment
- Conclusion
- Frequently asked questions
- Sources
What does the body need magnesium for?
Magnesium is involved in a whole range of bodily functions, as the number of health claims the EU has authorized for this mineral already shows:
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Tiredness: Magnesium contributes to the reduction of tiredness and fatigue.
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Muscles: Magnesium contributes to normal muscle function.
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Nervous system: Magnesium contributes to normal functioning of the nervous system.
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Mind: Magnesium contributes to normal psychological function.
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Energy metabolism: Magnesium contributes to normal energy-yielding metabolism.
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Electrolyte balance: Magnesium contributes to electrolyte balance.
- Bones and teeth: Magnesium contributes to the maintenance of normal bones and teeth.
This list does not imply that any particular form of magnesium fulfills these functions better or faster than another. What determines how much magnesium is actually available to the body is how well the respective compound is absorbed.
What does bioavailability mean?
Bioavailability describes what share of an ingested substance is actually available to the body. This matters for magnesium because in food supplements the mineral is never present in pure form, but is always coupled to a binding partner. Three groups of binding partners are the most common:
- Organic acids: for example citric acid (citrate) or malic acid (malate).
- Amino acids: for example glycine (bisglycinate) or taurine (taurate).
- Inorganic salts: for example oxide or carbonate.
Depending on which partner magnesium is bound to, there's more or less of it in the capsule, and the compound dissolves to different degrees in the digestive tract. In a randomized crossover study with 20 healthy adult men, magnesium citrate showed higher excretion via the kidneys and significantly higher magnesium levels in blood serum than magnesium oxide after the body's own magnesium stores had been saturated. (1) This suggests that organic compounds are absorbed better than this inorganic form under certain conditions, but it can't be generalized from a single study with a small, homogeneous group.
How much magnesium actually arrives in the end also doesn't depend on the form alone. The dose and how well supplied with magnesium you already are also play a role. If you're already well supplied, you tend to absorb a smaller share of the magnesium you take in than someone with lower stores.
An overview of the forms of magnesium
The common magnesium compounds differ mainly in two things: how much elemental magnesium they contain and how well your gastrointestinal tract copes with them. We'll now go through the most important forms based on exactly these two criteria.
Magnesium bisglycinate and magnesium glycinate
In this form, magnesium is bound to the amino acid glycine; this compound is also called a chelate. So far there are few direct comparative studies on the absorption of this form in people with healthy digestion, so no general statement about its bioavailability can be made. Bisglycinate is often described as gentle on the stomach, but robust comparative studies on this are lacking. If you have a sensitive stomach, bisglycinate is one form worth considering.
Magnesium citrate
Magnesium citrate is magnesium bound to citric acid, an organic acid. Among the forms discussed here, it is one of the best studied1. In higher amounts, citrate, like other forms of magnesium, can have a laxative effect, which is why splitting the daily amount into several portions makes sense.
Magnesium malate
Magnesium malate is bound to malic acid. Direct comparative studies on the absorption of this form in humans are still largely lacking, and we're deliberately saying so openly here. There is also hardly any data of its own on tolerability. A link to more energy or performance can't be derived from the available data.
Magnesium L-threonate
This comparatively new compound is being researched specifically in connection with magnesium in the brain. The human studies so far are small, short, and in some cases involve financial participation by the manufacturer that sells the patented raw material. A reliable assessment is therefore not yet possible; further independent research would be helpful here. No statement about an effect on memory or concentration can be derived from the data so far.
Magnesium taurate
Magnesium taurate is a compound of magnesium and the amino acid taurine. So far there are hardly any studies on this form as a compound in its own right; statements about the heart or nervous system are mostly based on the separately studied effect of taurine and not on studies of the compound itself.
Magnesium oxide and magnesium carbonate
Oxide and carbonate are inorganic salts with a high share of elemental magnesium per gram. For oxide, the comparative data described above show lower absorption than for citrate1, which may help explain the laxative effect observed at higher doses. For carbonate, as a closely related inorganic compound, we don't have any comparative absorption data of its own. That doesn't make either form worthless: oxide and carbonate have been in use for a long time and are usually cheaper to produce than organic compounds.
Other forms in short
You'll also find a few less common compounds on the market:
- Magnesium chloride: is used more often in products applied externally, for example as a bath additive.
- Magnesium sulfate: known as Epsom salt, also mainly used externally.
- Magnesium gluconate: tends to be found in liquid preparations.
Comparative studies on these three forms are considerably rarer than on citrate or oxide.
| Form | Magnesium content | Absorption according to studies | Tolerability | Evidence |
|---|---|---|---|---|
| Bisglycinate / glycinate | medium | hardly any direct comparative data | considered gentle on the stomach | limited |
| Citrate | medium | higher serum levels than oxide shown | may be laxative in higher amounts | well studied |
| Malate | medium | hardly any human data | hardly documented | hardly studied |
| L-threonate | low | small, short human studies | hardly documented | limited |
| Taurate | medium | hardly any studies on the compound itself | hardly documented | hardly studied |
| Oxide | high | lower than citrate shown | less well tolerated by some | well studied |
| Carbonate | high | no comparative data of its own available | less well tolerated by some | hardly studied |
Which magnesium is right for you?
When choosing, it's worth looking above all at your daily routine and your tolerance. If you have a sensitive stomach, forms that are gentle on the stomach, such as bisglycinate, are an option. If a particularly broad evidence base is important to you, citrate is the best studied of the forms discussed here.
Whether you take magnesium in the evening or in the morning depends mainly on when you can fit it into your day and when it agrees with you. All the forms presented here can basically be taken at any time of day.
If you eat a vegan diet, it's worth checking the capsule shell: some manufacturers use plant-based capsules made of hydroxypropyl methylcellulose instead of gelatin; on the label you'll usually find this noted as "plant-based capsule shell" or with a vegan seal. If you're generally interested in nutrient needs on a plant-based diet, this article might be interesting for you: Food supplements for vegans.
If you're a beginner trying magnesium for the first time, two things matter most: a transparent statement of the form of magnesium on the label and an amount that fits into your daily routine. Many people are also interested in magnesium in connection with sleep, sport, or stress. Whether a particular form has advantages over another here is not sufficiently supported by science.
If you want to know more about the functions of magnesium in the body and the signs of a deficiency, this article might be interesting for you: Magnesium – deficiency, function & sources.
Taking magnesium correctly: timing and combinations
Whether taking it with a meal improves tolerability is not consistently supported. Leaving a time gap from iron, zinc, or calcium can make sense, but no fixed number of hours can be derived from this in general.
With certain medications, a gap is more relevant: magnesium can reduce the absorption of certain antibiotics from the tetracycline and quinolone groups, as well as of oral osteoporosis medications such as bisphosphonates, in the gut.(2) In this case, talk to your doctor or pharmacy beforehand about how best to time your intake.
As for the amount: stick to the recommended intake on the respective product and don't exceed it. The German Federal Institute for Risk Assessment (BfR) recommends not taking in more than 250 mg of magnesium per day from food supplements and spreading this amount over at least two portions during the day, as this probably improves tolerability. (3)
What to look out for when buying
The most common point of confusion on the label is the difference between elemental magnesium and the weight of the entire compound. If the package says "1000 mg magnesium citrate", that doesn't mean it contains 1000 mg of pure magnesium, because part of the weight is accounted for by the binding partner. What's meaningful is the statement of how much elemental magnesium a daily portion actually provides, usually supplemented by the percentage of the nutrient reference value (NRV).
If you want to avoid animal ingredients altogether, it's worth checking the capsule shell: plant-based capsules are usually indicated on the label. It also makes sense to look for a manageable list of additives and to make sure the form of magnesium used is clearly named and doesn't just appear as a "magnesium complex".
In any case, stick to the recommended intake stated on the packaging, regardless of which form or which brand you choose.
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My personal assessment
Studies usually compare individual forms under laboratory conditions, but your daily life looks different. A capsule that doesn't agree with you will end up in a drawer at some point, no matter how well it performs in the lab.
That's why, when choosing, I mainly pay attention to whether taking it fits easily into my day, and less to which form happens to be trending.
Conclusion
Forms of magnesium differ mainly in two things: how much elemental magnesium they contain and how well your gastrointestinal tract copes with them. According to the current evidence, there is no form that solves both points optimally for everyone at the same time, which is why we're deliberately not crowning a "best" form here. Rather than searching for the optimal form, it makes more sense to choose a compound that agrees with you and that you build into your daily routine regularly, because only magnesium that is actually taken can play any role at all.
If you have health complaints, take medication, or are unsure which form or amount is right for you, talking to your doctor or pharmacy is the right way to go.
Frequently asked questions
Is bisglycinate the same as glycinate?
In practice, both terms are mostly used synonymously and describe magnesium bound to the amino acid glycine. "Bisglycinate" is chemically correct, because two glycine molecules are bound to one magnesium ion, but labels often also use the shortened name "glycinate" for the same compound.
Can you combine different forms of magnesium?
Several forms of magnesium can generally be combined; some preparations deliberately mix two or three compounds anyway. What matters is not the number of forms, but the total amount of elemental magnesium taken in, which should not exceed the recommended daily dose.
When will I notice anything from magnesium?
There's no universal time frame for this; it depends, among other things, on how well supplied you were beforehand. If you're already adequately supplied with magnesium, you often won't notice any perceptible change at all, and that's normal, not a sign that the product isn't working.
Can you take too much magnesium?
Too high an intake from food supplements can lead to diarrhea, among other things, which usually subsides within a few days. Particular caution is needed with kidney disease, so stick to the dosage stated on the product and, if in doubt, talk to your doctor or pharmacy.
Which form is vegan?
As a mineral, magnesium itself is of mineral origin regardless of the binding form; whether a product is vegan or not usually comes down to the capsule shell and any additives. Look for a plant-based capsule shell, for example made of hydroxypropyl methylcellulose, as well as a vegan seal or corresponding labeling on the packaging.
Related reading: Magnesium – deficiency, function & sources, Food supplements for vegans
Sources
- Kappeler C, et al. Higher bioavailability of magnesium citrate as compared to magnesium oxide shown by evaluation of urinary excretion and serum levels after single-dose administration in a randomized cross-over study. BMC Nutrition. 2017;3:7. doi: 10.1186/s40795-016-0121-3.
- NIH Office of Dietary Supplements. Magnesium – Fact Sheet for Health Professionals. National Institutes of Health, continuously updated.
- Bundesinstitut für Risikobewertung (BfR). Stellungnahme Nr. 034/2017: Bewertung der empfohlenen Tageshöchstmenge für die Aufnahme von Magnesium über Nahrungsergänzungsmittel. 2017.
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