Magnesium glycinate and bisglycinate: is there actually a difference?

Two tins stand next to each other. One says magnesium glycinate. The other says magnesium bisglycinate. Price difference: nine euros. And you wonder whether you are holding the worse version in your hand.

I know this scene. It repeats itself in my consulting room with remarkable regularity, usually with a phone photo taken in front of the shelf.

The reassuring news comes first. In the vast majority of cases, both tins contain the same raw material. Bisglycinate is the chemically more precise name, glycinate the short form. That is not a grey area, that is nomenclature.

The less comfortable news comes after. There really is a difference that decides the quality of a magnesium supplement. It just sits somewhere other than where the front of the tin suggests. And once you know where, you will never stand clueless in front of that shelf again.

The short answer sits in the chemistry, not in the marketing

Let us start with the word, because the word already holds everything.

Glycine is an amino acid. The smallest one we know. When a mineral is bound to it, the salt or the complex is named after it: glycinate. And because with magnesium it is not one glycine that docks on but two, chemical nomenclature puts the prefix bis in front. Bis means two. Just like in bicarbonate or biceps.

So magnesium bisglycinate is nothing other than magnesium glycinate, pronounced precisely.

That is not a trick and not a seal of quality. It is a question of whether a manufacturer names the raw material the way a chemist would name it, or the way the industry names it in everyday life. Both spellings appear in scientific papers. In a randomised cross-over study from Spain with 40 healthy adults, the test substance is simply called Mg bisglycinate. In a cell study from Italy, the same type of substance is called buffered chelate bisglycinate.

So why is it still worth reading on? Because there really are different things to buy under the same name. Just not where most people look for them.

And now you know why I do not tick this question off in one sentence, even though the first sentence already held the answer.

What a chelate is, and why exactly two glycine arms

Picture a magnesium ion. It carries two positive charges and is therefore about as clingy as a magnet in a drawer full of paper clips. In the gut that is a problem. Free mineral ions bind to whatever they meet: to phytates from whole grain, to oxalates from spinach, to fibre.

A chelate is the attempt to send this ion through the gut with company. The word comes from the Greek chele, the crab claw. Two glycine molecules reach around the magnesium like two claw arms and bind it at two points each, once through the amino group and once through the acid group. The result is a ring that appears electrically balanced from the outside.

The idea behind it: a mineral that behaves inconspicuously in chemical terms may be intercepted less in the gut and may take a different route through the gut wall than a free ion.

What remains is the question of whether the crab claw really delivers in humans what it promises in theory. We will get to that in a moment, and the answer is more mixed than the price suggests.

But first the number that decides almost everything.

And now you know why a chelate is always heavy, and why that does not speak against it but explains why the capsules are so big.

The number everything turns on: elemental magnesium

When the pack says 1,000 mg of magnesium bisglycinate, that is not 1,000 mg of magnesium. It is 1,000 mg of the whole compound. The magnesium inside it is the smaller part.

This is not a question of studies, this is arithmetic. One magnesium ion weighs about 24.3 units, the two glycine residues together about 148. That makes around 172 for the whole molecule. The magnesium share therefore sits at around 14 percent.

I deliberately calculate with 250 mg here. That is the tolerable upper level European authorities name for magnesium added on top from supplements. What fits you personally belongs in a medical conversation, not in an arithmetic formula.

And exactly here a conflict of aims arises that the front of a tin rarely explains. People want few capsules, high numbers and a low price. Pure bisglycinate can meet none of these three expectations.

So there is a way around it. And it has a name.

And now you know why capsule size gives you a more honest answer on this topic than any advertising promise.

Buffered material: when magnesium oxide rides along in the glycinate

The technical term is buffered magnesium bisglycinate. It sounds technical and harmless, and it is not illegal either. It means that magnesium oxide has been blended into the chelate.

The effect is purely arithmetic. Oxide contains around 60 percent elemental magnesium, the chelate around 14 percent. Mixing the two lifts the elemental share of the final product and lowers the raw material cost. The number on the tin then goes up. Whether a manufacturer does that for cost reasons, because of capsule size, or for both, I cannot judge from the outside. It is declared if it appears in the ingredient list.

The word buffered is not an invention of critics. It appears in the specialist literature as a product category of its own. An Italian group studied exactly such a buffered chelate form on human gut cells.

I do not want to demonise this. A mixed form can be exactly right for some people, for example when a mild effect on digestion is welcome. It only becomes a problem when someone deliberately reaches for the chelate because they do not tolerate the oxide, and then buys it along anyway.

And then there is the calculation that brings clarity fastest in front of the shelf: the price per 100 mg of elemental magnesium.

An example. A tin with 120 capsules at 80 mg of elemental magnesium each contains 9,600 mg in total. If it costs 24 euros, you pay 25 cents per 100 mg. A discount store tin with 200 tablets at 150 mg elemental each from oxide contains 30,000 mg and costs 10 euros, so a good 3 cents per 100 mg.

The price difference is real. It just says nothing about how much of it arrives in the tissue. That is the point where the arithmetic ends and the study data begins.

And now you know why I talk so much about labels and so little about brands when it comes to magnesium.

Glycine is not just the packaging

Now comes the part about this compound that interests me most. And it gets overlooked in almost every comparison article.

We just said: glycine is the car, magnesium the passenger. That is a helpful picture for the label arithmetic. Physiologically it is incomplete, because glycine does not only sit at the wheel. It is itself a player in the nervous system.

In the spinal cord and the brainstem, glycine is an inhibitory messenger. It binds to its own receptors and can dampen the passing on of excitation there. At the same time it is a co-agonist at the NMDA receptor, so at the very channel where magnesium sits as the bouncer. Two substances, one channel, two entirely different roles.

Out of this observation grew the hypothesis that part of the calming reputation of magnesium bisglycinate might not come from the magnesium at all, but from the glycine.

There is human data on this. It is small, but it exists.

Let us do the maths quickly so the order of magnitude is clear. In 1,000 mg of magnesium bisglycinate there are around 140 mg of magnesium and around 860 mg of glycine. Anyone taking 250 mg of elemental magnesium from pure chelate carries about 1.5 grams of glycine along with it. That is closer to the study dose than many people assume. It is still less, and in this combination it has never been tested.

And now you know why I do not sort this form into a ranking, but into a question about your goal.

What the human data on bisglycinate gives us, honestly sorted

I am going to make this uncomfortable, because I do not want to write you a text that only confirms what you would like to hear.

Magnesium bisglycinate is one of the more expensive everyday forms. Calculated per 100 mg of elemental magnesium it sits clearly above citrate and oxide, and mostly below L-threonate. Prices change, so this ranking does not replace your own calculation at the shelf. The data on its absorption is thinner than its reputation. And individual studies even come out against it.

A second comparison from Italy came to a similar picture. There too, bisglycinate performed more weakly on magnesium in the red blood cells than the comparison form tested, and that work also comes from the environment of a manufacturer.

You could close the case with that. I think that would be too quick, for two reasons.

First, there is an older and more independent piece of work in which an amino acid chelate did well. In a randomised, double blind study over 60 days with 46 healthy people, citrate and an amino acid chelate showed better uptake than oxide, measured through magnesium excretion in the urine. In that study, magnesium oxide did not differ from placebo. Fairness calls for the second half of the result: the authors themselves concluded that citrate came out best, better than the chelate as well. For our question what counts above all is that both organic forms beat the oxide.

Second, there is now a clinical trial that does not measure absorption, but the thing people actually care about.

That fits with a meta-analysis of three small studies with 151 older people, in which time to fall asleep under magnesium was on average about 17 minutes shorter than under placebo. The authors themselves rated the quality of the evidence as low to very low.

And it fits with what the largest review on the comparison of forms says. A systematic evaluation from Spain screened 433 studies and analysed 14 in which magnesium forms were compared directly. Inorganic compounds appear to be absorbed less well than organic ones, and the share taken up depends strongly on the dose.

The four lenses: why this compound brings two active parts

In clinical psychoneuroimmunology we look at a topic through four lenses. With magnesium bisglycinate that is particularly appealing, because two substances are in play at the same time.

Physiological background on magnesium in metabolism: de Baaij JHF et al. Physiol Rev. 2015. DOI: 10.1152/physrev.00012.2014

And now you know why with this form I speak of two building blocks rather than of a better magnesium.

Glycinate or citrate? And where the other forms stand

The second most common question I meet on this topic is not glycinate or bisglycinate. It is: glycinate or citrate?

That question makes far more sense, because these two forms really do differ. I do not sort them by better and worse, but by what they are meant for.

If you want to go deeper into the comparison of forms, with the studies on each single one, you will find that in the detailed form comparison: which magnesium is the best. This article here deliberately stays with the glycinate question.

And now you know why asking back about your goal is not an evasion, but the only route to a usable answer.

Topping up or therapy: why the dose makes the difference

At this point a step back is worth it, away from the label, towards a question that sits above all of it.

There are two completely different worlds that both use the word nutrient. They get confused constantly, and most disappointments grow out of that confusion.

The clearest example of this difference does not come from magnesium, but from vitamin D. For meeting requirements, the usual amounts sit in the low four-figure range of International Units. As a food supplement, the German Federal Institute for Risk Assessment recommends at most 20 micrograms per day, that is 800 International Units, and from 1,000 units per single dosage form vitamin D3, the active substance colecalciferol, is prescription only in Germany. That too is an authority value, not a personal recommendation.

In the so-called Coimbra protocol for autoimmune diseases, vitamin D3 is used at a multiple of what covers requirements. At that order of magnitude it is a prescription only medicine, and its use in autoimmune diseases lies outside the marketing authorisation, so it is off-label use.

Why a nutrient is never travelling alone

The second thought that sits above all label reading is called homeostasis. Your body regulates nutrients in feedback loops. Turn one screw and you move others with it.

Magnesium is a good example. In the gut it competes with other minerals for transport routes. High doses of other minerals can push magnesium uptake down, which the Hannover review states expressly. The other way round, a permanently high magnesium intake can interfere with calcium balance. And high dose vitamin D without an eye on magnesium and vitamin K2 can shift this balance in a direction nobody planned. Mechanistically that is plausible, large human studies on it are missing.

This is expressly not an argument against supplementation. It is a plea for precision.

Real food first, and why topping up is still more often justified today

The first choice for me stays the same: real food from good sources and good husbandry. Nuts, seeds, pulses, green leafy vegetables, whole grain, cocoa. Food delivers nutrients in a matrix of cofactors that no capsule rebuilds. No supplement replaces nutrition, sleep, movement, sun and good relationships.

And still I consider targeted topping up more often justified today than fifty years ago. Not because it is fashionable, but because the conditions have changed.

A third factor is medication. Diuretics can pull magnesium and potassium out through the kidney. Proton pump inhibitors have been linked with low magnesium in the blood. Chronic stress and environmental exposures could raise the need for micronutrients. That is mechanistically plausible and often assumed clinically, large human studies that put a clean figure on it are missing. None of this is a scandal. It is the sum of small shifts.

Measure instead of guess, and set an endpoint

From this follows my position, and it is unspectacular. Better to measure and know what you are doing. With magnesium that is unfortunately harder than it sounds, because over 99 percent sits in cells and bones, and less than one percent floats in the serum. The body holds this serum value tightly, if necessary by taking magnesium out of the bone. A normal serum value therefore does not reliably rule out a deficiency in the tissue.

The second part is just as important. A supplement is as a rule a time limited intervention with a goal and a follow-up appointment, not a lifelong subscription. There are well founded exceptions, for example vitamin B12 after stomach surgery or targeted substitution with a chronic absorption disorder. And that is exactly what they are: well founded exceptions.

And now you know why the question of glycinate or bisglycinate is rarely the first one in my consulting room.

Safety: kidneys, diarrhoea and three interactions that count

Now the part I leave out of no text, even though it is uncomfortable.

Magnesium counts as good natured, and with normal kidney function it mostly is. Surplus magnesium can as a rule be excreted through the kidney. Whether your kidney function is normal is something you only know after a measurement, though, not by feel. And exactly this good nature ends in four places.

That leaves the interactions. They all follow the same principle: magnesium is a doubly positively charged ion and can form poorly soluble complexes with certain drugs in the gut. What is bound does not get through the gut wall.

And now you know why with magnesium the question of timing is sometimes more important than the question of the form.

Three levers you can put in place today

No protocol, no weekly plans, no brands. Just three things that lie in your hands.

And now you know why the most honest answer to the question of glycinate or bisglycinate starts with a look at the back of the tin.

Frequent questions on magnesium glycinate and bisglycinate

How this topic connects with the others

The label question is only the entry point. If you want to think further, these paths lead into the depth.