Citrate, glycinate, oxide, malate, threonate - the choice of forms of magnesium is huge, and the difference in price can be tenfold. The editors compared the main forms according to the content of elemental magnesium, absorption and tolerability and offers a simple selection algorithm.
What are the different forms of magnesium?
Any magnesium supplement is a compound of magnesium ion with an inorganic anion (oxide, chloride, sulfate) or an organic acid or amino acid (citrate, lactate, malate, glycinate, threonate). Three things depend on this "partner": the proportion of elemental magnesium, solubility and tolerability from the intestines.
A paradox worth remembering: the form with the highest magnesium content — oxide — is absorbed the worst. It dissolves poorly, especially with reduced stomach acidity. Organic salts contain less magnesium per gram, but are soluble and better absorbed.
However, the difference between organic forms is much smaller than the marketing claims. Most comparative studies are small, short-term, and assess absorption by urine or blood magnesium rather than clinical outcomes.
Therefore, the editors suggest approaching the choice pragmatically: absorption, tolerability, the number of tablets per day and the price for 100 mg of elemental magnesium.
Inorganic forms: oxide, chloride, sulfate
Magnesium oxide is the cheapest and most common form, especially in multivitamins and antacids. In a 2001 study by Firoz and Graber, uptake of oxide was found to be significantly lower than that of chloride, lactate, and aspartate. Lindberg and co-authors in 1990 showed that citrate dissolves and is absorbed better than oxide. Oxide is fine as a laxative or antacid, but as a primary supplement it is a worse choice.
Magnesium chloride dissolves well and has good absorption. It is produced in tablets, solutions and in the form of so-called "magnesium oil" for the skin. It should be noted that there is no convincing data on significant transdermal absorption of magnesium.
Magnesium sulfate (Epsom salt) is primarily a laxative and an intravenous drug in medicine. For daily oral intake as a supplement, it is inconvenient due to its pronounced laxative effect. Baths with Epsom salts are pleasant, but as a way to replenish magnesium, they are not proven.
Magnesium chloride is one reasonably absorbed inorganic option. Oxide and sulfate also have medical and supplemental uses, but solubility, laxative effects and the intended purpose matter; the form alone does not determine whether a product is appropriate.
Organic forms: citrate, glycinate, malate, lactate, threonate
| Form | Absorption | Tolerability | For whom |
|---|---|---|---|
| Citrate | Good, the best studied organic form | May loosen stool | Common option; may help where a laxative effect is desired |
| Glycinate (bisglycinate) | Good | Often well tolerated; direct comparisons are limited | An option for a sensitive stomach |
| Malate | Limited comparative data | Good | Citrate alternative |
| Lactate | Good | Good | Alternative for poor tolerance of other forms |
| L-threonate | Limited human evidence | Good | Expensive niche form |
Magnesium citrate is the best studied organic form. In a 2003 randomized study by Walker et al., citrate provided higher bioavailability than amino acid chelate and oxide. The disadvantage is a moderate laxative effect at higher doses.
Glycinate is linked to the amino acid glycine and is often well tolerated by the gut. It is often recommended for people who do not tolerate citrate well. There are few direct comparisons of glycinate with citrate in humans, but from a practical point of view it is a good alternative.
Malate and lactate are soluble organic salts with good absorption and tolerance. The claim that malate is "especially good for energy" because of malic acid has no convincing clinical support.
L-threonate rose to prominence after a 2010 study in rats by Slutsky et al., where this form increased magnesium levels in the brain and improved memory performance. However, human data are limited, the proportion of magnesium in the compound is small, and the price is high.
How to choose a form in practice
The editors offer a simple algorithm for most healthy adults:
- Basic Choice: Magnesium Citrate - Well researched and affordable.
- Sensitive intestine: glycinate or malate, taken with food.
- Tendency to constipation: Citrate (its mild laxative effect will be an advantage).
- Budget is limited: chloride or citrate; oxide — only realizing worse absorption.
- “For the brain”: threonate—with the understanding that the human evidence base is limited.
Compare the price per 100 mg of elemental magnesium, not per package. The expensive, low-magnesium form may require three to four capsules per day to get the same amount as a single citrate tablet.
Pay attention to the composition: some products contain a mixture of forms, and the cheapest one prevails on the label. If it says "magnesium glycinate", but in the fine print of the composition the oxide is the first, this should be taken into account.
And finally - ZMA and "magnesium with B6". Vitamin B6 is added for marketing purposes or to improve intracellular absorption, but with a normal diet, its additional benefit is small, and with long-term intake of high doses of B6, peripheral neuropathy is possible.
Editorial conclusions
The form of magnesium affects absorption and tolerability: organic salts and chloride are absorbed better than oxide, and glycinate is often well tolerated, though robust head-to-head evidence is limited. However, the difference between good forms is smaller than the advertising promises.
For most people, citrate or glycinate at a dose based on elemental magnesium is the optimal choice. Expensive niche forms have a limited evidence base in humans.
Any form does not compensate for a poor diet, and in case of kidney diseases, the choice of form and dose should be made by the doctor.
We also advise you to read "How to take Magnesium: dosage, time of administration, duration", "Side effects of Magnesium" and "Zinc: formulations and which one to choose".
References
- Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnes Res. 2003;16(3):183–191.
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257–262.
- Lindberg JS, Zobitz MM, Poindexter JR, Pak CY. Magnesium bioavailability from magnesium citrate and magnesium oxide. J Am Coll Nutr. 1990;9(1):48–55.
- Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165–177.
- de Baaij JHF, Hoenderop JGJ, Bindels RJM. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1–46.
- National Institutes of Health, Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
