The rule to remember:<\/strong> before comparing forms, look at how much magnesium you’re taking per dose. And when you see a percentage on a supplement page, ask one question: measured in whom?<\/div>\nWhat really sets the types of magnesium apart<\/h2>\n
Magnesium never comes alone in a supplement. It’s always attached to a partner: citrate, malate, oxygen for oxide, two glycine molecules for bisglycinate. That partner affects two things: the amount of magnesium actually present<\/strong> (known as elemental magnesium)<\/em> and how easily the product dissolves<\/strong>.<\/p>\nAmount first. Oxide is 60% magnesium, pure bisglycinate 14% at most. In other words, 1,000 mg of pure bisglycinate provides about 140 mg of magnesium. If a product claims more, there’s something else in it.<\/p>\n
Then dissolving, and this is where oxide has its first problem. It barely dissolves in water and needs your stomach acid to be released. In the lab, 100 ml of a liquid mimicking this acid dissolves only 175 mg of oxide. Beyond that, the acid is used up and the rest moves on into the gut, where it dissolves even less. It isn’t slow by nature: in a large acid bath, a tablet dissolves in ten minutes. It’s your stomach that doesn’t have enough acid to handle it all.<\/p>\n
How magnesium gets into your blood<\/h2>\n
To reach the blood, magnesium has to cross the gut wall, and it has two routes.<\/p>\n
\n- Through the cells<\/strong> (the transcellular route)<\/em>, via the TRPM6 and TRPM7 channels. Think of them as Tube ticket barriers: the first sits mainly at the end of the intestine, the second all along it. When there’s little magnesium, they do much of the work. When there’s a lot, they hit their limit.<\/li>\n
- Between the cells<\/strong> (the paracellular route)<\/em>, through the tiny joints that link them, like water through tile grout. This route is passive. In rats, the only direct measurement gives it three-quarters of the work when magnesium is plentiful.<\/li>\n<\/ul>\n
Once dissolved, most of the magnesium ends up as an ion, the same one for every form. Neither the barriers nor the joints can see where it came from. In the lab, when all the salts are dissolved in advance, oxide actually crosses gut cells as well as the others.<\/p>\n
The real difference isn’t made at the door. It’s made beforehand: how much magnesium dissolves, and whether it dissolves early enough. Cyril acknowledges this: he used to explain that each form takes its own route, and the studies behind that idea remain weak.<\/p>\n
The main types of magnesium<\/h2>\n
Here are the forms you’ll come across most often, with the number of clinical trials that have tested them in humans. The forms sold to you as premium are also the least studied.<\/p>\n
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Compare magnesium forms<\/div>\n
What studies say about the forms you will find on labels. This is not a ranking: no form does significantly better than the others over time.<\/p>\n\n
\n
Form<\/div>\n
Human trials<\/div>\n
Digestive tolerance<\/div>\n
In brief<\/div>\n\n
Oxide<\/span><\/div>\n 79<\/span><\/div>\n Variable: well tolerated over 6 months in one study, bothersome in large doses<\/span><\/div>\n The most studied. Dissolves poorly, less absorbed in a single dose, the gap narrows over time.<\/div>\n\n
Citrate<\/span>In our formula<\/span><\/div>\n 53<\/span><\/div>\n Fair, stirs up the gut more in some people<\/span><\/div>\n Dissolves well, one of the forms that passes best in a single dose.<\/div>\n\n
Bisglycinate<\/span>In our formula<\/span><\/div>\n 6<\/span><\/div>\n Among the best tolerated, without being neutral<\/span><\/div>\n No better absorption demonstrated in humans. Intact passage not proven.<\/div>\n\n
Threonate<\/span><\/div>\n 3<\/span><\/div>\n Little data<\/span><\/div>\n Marketed for the brain, no measurement in humans.<\/div>\n\n
Malate<\/span>In our formula<\/span><\/div>\n 1<\/span><\/div>\n Little data<\/span><\/div>\n The least studied of the three. Rare absorption data.<\/div>\n\n
Marine magnesium<\/span><\/div>\n Not counted<\/span><\/div>\n Variable depending on the mix<\/span><\/div>\n Mix of salts, often rich in oxide and hydroxide.<\/div>\n <\/div>\n
Oxide: the most studied, and not so useless<\/h3>\n
Leaving aside infusions and laxative use, it’s the form most tested by mouth, with 79 trials against 53 for citrate. The reason is simple: it’s cheap and a small tablet is enough, which suits researchers.<\/p>\n
In a single dose, it’s less well absorbed. In 2017, a German study of 20 men showed an advantage for citrate, with a statistically significant difference. Converted into milligrams, that’s 13.7 mg of magnesium over 24 hours. Researchers at the University of Hanover judged it insignificant for the body, and the study was funded by the maker of the citrate tested.<\/p>\n
Over time, the gap narrows. The longest of these studies, run in the Netherlands in 2022, followed 164 people for six months on 450 mg a day. By the end, blood magnesium had risen similarly with citrate, oxide and sulfate. In urine, oxide reached about three-quarters of citrate’s level, and it caused less bowel disturbance than citrate. This study was funded by a magnesium producer. In rats, over several weeks, oxide and organic forms end up level, a result that doesn’t transfer well, because rats absorb far more magnesium than you do.<\/p>\n
Magnesium bisglycinate: well tolerated, not an absorption champion<\/h3>\n
Magnesium bisglycinate is magnesium held by two molecules of glycine, an amino acid. It’s described as chelated, from a Greek word meaning claw. The idea its fans promote: the claw holds firm and part of the product enters intact through a third door, the PEPT1 transporter.<\/p>\n
This idea comes mainly from the manufacturer’s work and a single human study from 1994, in twelve patients who’d had bowel surgery. Across the whole group, 23.5% was absorbed with bisglycinate against 22.8% with oxide, which is no difference. Since then, no intact bisglycinate has been found in the blood, in humans or in animals. And chemistry explains why: in stomach acid, glycine picks up a proton and lets go of the magnesium. According to a calculation based on published constants, fewer than one claw in a hundred would stay closed.<\/p>\n
In humans, in 2024, among 40 volunteers, bisglycinate, citrate and oxide didn’t differ over six hours. In rats, in two recent studies, glycinate did no better than the other forms. The door isn’t completely shut, because the claw could partly close again further down the gut, where it’s less acidic. But nobody has run the study that would settle it.<\/p>\n
What does hold up is tolerance. It’s one of the best-tolerated forms in humans, without being neutral: in the 2024 study, at 375 mg, 40% of volunteers reported a feeling of heaviness in the stomach. On sleep, the most robust trial, run in Germany in 2025, shows a small effect, with one big limitation: the capsules also provided 1.5 g of glycine a day, and no trial has compared two forms on sleep.<\/p>\n
Citrate: the most studied organic form<\/h3>\n
Magnesium citrate dissolves well and, in single-dose comparisons, it’s one of the best-absorbed forms. Its downside is that it can stir up the gut a little more in some people, especially at high doses. In the six-month Dutch study, 5 out of 46 people had mild diarrhoea on citrate, against 1 out of 46 on oxide.<\/p>\n
Malate: the least studied of the three<\/h3>\n
Malate binds magnesium to malic acid. Only one human clinical trial mentions it. In the few comparisons available, in rats and in an unpublished human study, it does better than oxide in a single dose, and about the same as other organic forms. It’s often presented as the energy form, but nothing proves that. Magnesium contributes to normal energy-yielding metabolism and to the reduction of tiredness and fatigue<\/strong> (claims authorised in the EU and in Great Britain)<\/em>, but these claims apply to magnesium, not to malate in particular.<\/p>\nThreonate and orotate: the trendy forms<\/h3>\n
Threonate is sold for the brain, but your brain is very well protected. Even with a hospital drip that doubles or triples blood magnesium, the level in the fluid around the brain barely rises. In rats, in 2010, threonate was the only form tested that raised this fluid, by about 7 to 15%, at a dose four times higher than capsules, in a study led by the co-founder of the company that developed it. In humans, nobody has yet measured brain magnesium after threonate. Positive trials are funded by companies selling it, and the only large publicly funded trial found nothing. Orotate, sold for the heart, isn’t authorised in supplements in the EU.<\/p>\n
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