Magnesium bisglycinate, citrate or oxide: which one

There is no outright winner among bisglycinate, citrate and oxide. For most people who want a magnesium supplement, the form on the label matters less than the dose and the magnesium status of the person taking it. If you have to pick one, pick the one you can take consistently and whose label you can actually read. Oxide is the cheapest and the most studied in the lab, but it dissolves poorly; citrate dissolves better and shows up in many studies; bisglycinate is sold as the "gentlest" form, but there are no data comparing it directly with the other two.

That is the honest answer. The rest of this article explains why that is the case and what you should check before you spend money.

What each one is, without heroes or villains

All three are magnesium bound to another molecule. Oxide binds magnesium to oxygen; it is the most common form in cheap supplements and in some laxatives. Citrate binds magnesium to citric acid; you find it in tablets, powders and gummies too. Bisglycinate binds magnesium to the amino acid glycine; it is the form that appears most often in products sold for sleep and relaxation.

None of these names describes an effect. They describe a chemical bond. What your body does with it depends on factors the label does not show.

A recent review of magnesium absorption concluded that the type of salt appears less relevant than is often assumed. Some studies showed a slightly higher bioavailability of organic salts under standardised conditions; others showed no difference. Which bond produces the highest absorption remains unclear. This applies to all forms, including the three on this page.

What really changes between them

Solubility changes. A 1990 laboratory study compared citrate and oxide: oxide was practically insoluble in water and only 43% soluble under conditions simulating stomach acid at peak digestion; citrate was 55% soluble even in water. In the same study, the amount of magnesium in urine rose significantly more after citrate than after oxide. The authors concluded that citrate was more soluble and more bioavailable.

That is not a condemnation of oxide. It is a laboratory finding on solubility, with a small number of volunteers, and it does not automatically translate into what you feel at home. But it is the kind of evidence that exists, and it is more than exists for bisglycinate.

What also changes is the amount of elemental magnesium in each serving, which the label states. If you are comparing prices, compare the cost per milligram of elemental magnesium, not the cost of the pack.

Bear in mind too that the NHS notes high doses of magnesium, above 400 mg, taken for a short time can cause diarrhoea. This applies to magnesium in general, not to a specific form.

What does not change, despite what you are told

What does not change is the fact that magnesium is not stored in the body. The same recent review notes that, because magnesium is not stored, higher absorption is usually followed by higher excretion. In other words: absorbing more at a given moment does not guarantee retaining more.

What does not change is the importance of dose and of each person's magnesium status. The review is explicit: the dose and the individual's magnesium status count for more than the form. Bioavailability varies within a wide range depending on dose and food matrix.

What does not change is the evidence on sleep. There is very little research on magnesium for insomnia. A 2021 review of three studies and 151 participants suggested that magnesium may help older adults with insomnia fall asleep faster, but the studies were of low quality. Another review, of nine studies and 7,582 participants, published in 2022, showed contradictory results on sleep quality and sleep disturbances. This applies to magnesium in general. There are no data comparing different forms for this purpose.

The marketing of bisglycinate for sleep and relaxation goes beyond what is known. So does the marketing of citrate as "the most absorbed". The marketing of oxide as "the only one studied" is equally overstated: a 2019 study tested 15 commercial magnesium formulations and found very wide variation in how they dissolved and were absorbed in laboratory models. In 30 people, two formulations with contrasting predictions showed significant differences in magnesium absorption in the blood. Absorption can differ between products, not just between salts.

Do people use both? Yes, but that proves nothing

Some people combine citrate and bisglycinate on different days, or alternate them. It is a common practice. There is no evidence that the combination works better than either one alone, and there are no data to support a combined dose. If you choose to combine, add up the total elemental magnesium and do not exceed the upper limit of 350 mg per day for adults from supplements and medicines, unless a healthcare professional recommends otherwise. The NCCIH is clear: high doses can cause diarrhoea, nausea and abdominal cramps; extremely high doses can cause irregular heartbeat and cardiac arrest.

We do not give a combined dose because we cannot justify one. What we can say is that the sum of two forms is not magically safer than one.

Who gets on well with each one

Citrate is a reasonable choice for someone who wants a form with some evidence of greater solubility and has no digestive trouble with it. Oxide is a reasonable choice for someone who wants the lowest cost per milligram and tolerates it well. Bisglycinate is a reasonable choice for someone who prefers small tablets or gummies and finds a product whose label they can read.

None of these sentences is a medical recommendation. If you have a health condition, take medication, are pregnant or breastfeeding, speak to a healthcare professional before starting any supplement.

What to check on the label before buying

Check the amount of elemental magnesium, not the amount of salt. A label that says "360 mg magnesium citrate" is not saying you are taking 360 mg of magnesium. You need to look for the line "of which magnesium" or equivalent.

Check the dose per serving and the number of servings per day. Add them up. Compare with the upper limit of 350 mg per day for adults from supplements, unless a healthcare professional recommends otherwise.

Check whether the product states who it is for. TuttiBear's Magnesium Gummies, for example, state two gummies per day, preferably after a meal, for adults, and warn that you should not exceed the recommended daily dose. The label lists magnesium citrate 360 mg per two gummies, of which 50.4 mg magnesium (13% NRV), and vitamin B6 1.4 mg (100% NRV). Contains polyols; excessive consumption may produce laxative effects. This is label information, not a promise of effect.

Check whether the manufacturer says anything about quality control. A 2019 study showed that commercial formulations can differ widely in how they dissolve. The label rarely tells you this, but the manufacturer's reputation and the existence of testing may help you decide between two similar products.

Be wary of specific claims about sleep, relaxation or "liver function" without indication of the dose and the population studied. The evidence on magnesium and sleep is emerging and contradictory. There is no one form that resolves that.

What to do next

If your goal is to sleep better, magnesium is not the first place to invest. The evidence is weak and does not distinguish between forms. There are pages on this site about what to do before bed and about foods with melatonin and tryptophan that deal with that in more detail. Use this page to choose the form you can take consistently and whose label you can read, not to expect an effect that the studies do not demonstrate.

If your goal is to correct a deficiency, the NHS reminds us that magnesium is found in a wide variety of foods, such as spinach, nuts and wholemeal bread, and that a varied and balanced diet should provide all the magnesium you need. A supplement does not replace that. And if you are thinking about doses above the upper limit, speak to a healthcare professional before, not after.