Magnesium Glycinate vs Citrate vs Oxide: Which Form and Why
Magnesium is never sold on its own. It is a reactive metal, so it always comes bound to something else, and that partner molecule is the entire reason one magnesium supplement behaves differently from another.
This is a comparison of the forms you will actually see on an Australian shelf, and what the chemistry and the absorption research say about each. If you are trying to choose a product rather than understand the forms, start with our magnesium buyer’s guide instead.
In this article
The two numbers that decide everything
Every comparison of magnesium forms comes down to two things, and they pull in opposite directions.
Elemental content is how much of the compound’s weight is actually magnesium. This is fixed chemistry, calculated from molecular weight, and it is not a matter of opinion or brand quality.
Bioavailability is how much of that magnesium you absorb. This has to be measured in people, usually by tracking magnesium in urine or blood after a dose.
Magnesium oxide
Oxide is the cheapest form and the one with the highest elemental content, at roughly 60 per cent magnesium by weight. On paper that looks like excellent value.
In practice it is the poorest performer on absorption. A study in the Journal of the American College of Nutrition compared magnesium citrate against magnesium oxide and found citrate produced a significantly greater rise in urinary magnesium, which is the standard proxy for how much was absorbed. A later randomised cross-over trial published in BMC Nutrition reached the same conclusion using both urinary excretion and serum levels. High elemental content does not help if it stays in the gut.
Magnesium citrate
Citrate is around 16 per cent magnesium by weight and considerably more soluble than oxide, which is the practical reason it is better absorbed.
Its drawback is the flip side of the same property. Magnesium citrate is used clinically as a bowel preparation at high doses, and at supplement doses some people still notice a laxative effect. If you have taken magnesium before and found it disagreed with you, there is a reasonable chance it was citrate, or oxide, or both.
Magnesium bisglycinate
Bisglycinate, often shortened to glycinate, is magnesium bound to two molecules of the amino acid glycine. It has the lowest elemental content of the three main forms at roughly 14 per cent, which means you need more compound to deliver the same magnesium.
What you get in exchange is tolerance. Because it is chelated to an amino acid it can be taken up through amino acid transport pathways as well as as a free mineral, so less of it is left sitting unabsorbed in the gut. That is the mechanism behind its reputation for being gentler.
It is also the form used in the most directly relevant recent sleep research. A randomised, double blind, placebo controlled trial in Nature and Science of Sleep gave 250 mg of magnesium bisglycinate to 155 adults reporting poor sleep, and concluded that it modestly improved insomnia severity. The authors were explicit that longer trials with objective sleep measurement are needed. The timing that trial used, and what the evidence does and does not support about it, is covered in when to take magnesium glycinate.
Threonate, malate and the rest
Magnesium L-threonate is the most heavily marketed of the newer forms, usually on the basis of claims about crossing into the brain. It has a low elemental content, is expensive per milligram of magnesium delivered, and has a much smaller human evidence base than citrate or bisglycinate. That does not make it useless, but it does mean you are paying a premium for a thinner set of studies.
Magnesium malate is reasonably absorbed and often marketed for fatigue. Magnesium chloride and magnesium lactate are both well absorbed and less common in Australian retail. Marine magnesium, extracted from seawater, is usually magnesium oxide or hydroxide with a better story attached.
A general rule that holds up well: the more novel the form and the more elaborate the marketing, the thinner the evidence tends to be.
The comparison, side by side
| Form | Elemental | Absorption | Tolerance |
|---|---|---|---|
| Oxide | ~60% | Poorest of the three | Most likely to cause loose stools |
| Citrate | ~16% | Better than oxide, shown in trials | Laxative effect for some |
| Bisglycinate | ~14% | Well absorbed | Generally the gentlest |
| L-threonate | Low | Smaller evidence base | Generally well tolerated, expensive |
The bottom line
For most people taking magnesium daily, bisglycinate and citrate are the two sensible choices, and the deciding factor is your stomach rather than a meaningful difference in effect. Bisglycinate if you want the gentlest option, citrate if it agrees with you and you want more magnesium per dollar.
Oxide is worth avoiding as the main source, not because it is harmful, but because the elemental content on the label overstates what you will actually absorb.
Whichever form you choose, check the elemental magnesium on the label rather than the compound weight. We have set out how to do that, along with dosing and the supplemental upper limit, in the magnesium buyer’s guide. Ritua uses bisglycinate in Magnesium Glycinate, for the tolerance reasons above. For the chemistry behind that number, start with what magnesium glycinate actually is, and for how the same maths plays out in gummies, see magnesium gummies vs capsules. There is also a 7 night trial pack if you would rather try a week before committing to a full pack.
This article is general information, not medical advice, and is not a substitute for guidance from your doctor, particularly if you are managing an existing health condition, are pregnant or breastfeeding, have reduced kidney function, or are taking medication.
Jasmine Meagher
BSc Food Science and Nutrition · Founder, Ritua
Jasmine founded Ritua to bring evidence-based, TGA-compliant supplements to Australian women. She writes about the research behind every ingredient Ritua sells.
Frequently asked questions
Is magnesium glycinate better than citrate?
Neither is clearly superior on absorption. Bisglycinate is generally better tolerated, citrate delivers slightly more magnesium per gram of compound. For daily use the choice usually comes down to how your stomach responds.
Why is magnesium oxide still sold if it is poorly absorbed?
It is cheap and it has the highest elemental content, so a label can show a large magnesium number at low cost. That number reflects what is in the capsule, not what you absorb.
What does bisglycinate mean?
It means one magnesium ion bound to two molecules of glycine, an amino acid. Some labels write it as glycinate and some as bisglycinate, and in practice they refer to the same chelate.
Is magnesium L-threonate worth the extra cost?
It has a considerably smaller human evidence base than citrate or bisglycinate, a low elemental content and a high price per milligram of magnesium delivered. That does not mean it does nothing, but you are paying a premium for less certainty.
Why do magnesium supplements cause loose stools?
Magnesium that is not absorbed stays in the gut and draws water into it. Poorly absorbed forms and larger doses make this more likely, which is why citrate is used as a bowel preparation at high doses.
Sources
- Magnesium bioavailability from magnesium citrate and magnesium oxide. Journal of the American College of Nutrition, 1990.
- Higher bioavailability of magnesium citrate as compared to magnesium oxide. BMC Nutrition, 2017.
- Magnesium Bisglycinate Supplementation in Healthy Adults Reporting Poor Sleep. Nature and Science of Sleep.
- Nutrient Reference Values for Australia and New Zealand: Magnesium. NHMRC.