Magnesium: which form to buy and how they really differ
There is no single form of magnesium that is best for everyone. Oxide delivers a lot of magnesium per capsule but is poorly absorbed; citrate and bisglycinate deliver less per capsule but are better tolerated and absorbed. What should decide your purchase is how much elemental magnesium you actually get, not how many milligrams of salt the front of the bottle shows.
The mistake almost everyone makes
A bottle says "Magnesium citrate 500 mg". It sounds like a lot. But those 500 mg are of citrate salt, not magnesium. Magnesium is only part of that molecule, and the proportion varies enormously depending on the salt.
That proportion is called elemental magnesium, and it's the only number that matters:
| Form | Elemental magnesium | In 500 mg of salt |
|---|---|---|
| Oxide | 60 % | 300 mg |
| Carbonate | 45 % | 225 mg |
| Hydroxide | 42 % | 210 mg |
| Citrate | 16 % | 80 mg |
| Chloride | 12 % | 60 mg |
| Lactate | 12 % | 60 mg |
| Sulfate | 10 % | 50 mg |
| Gluconate | 5 % | 25 mg |
Bisglycinate (or glycinate) sits at the lower end of that scale, well below oxide: the glycine molecule attached to it is heavy. That's why a bisglycinate product needs more capsules, or larger ones, to reach the same figure.
So why not always buy oxide?
Because the elemental percentage only tells half the story. The other half is how much of that magnesium actually reaches your bloodstream. Magnesium oxide is notoriously poorly soluble and hard to absorb; much of what you take stays in the gut, where it draws in water. Hence its classic use as a laxative.
Organic forms —citrate, bisglycinate, malate— are more soluble and easier on digestion. They deliver less magnesium per milligram of salt, but make better use of what they deliver.
The practical takeaway, without the mystique: an honest label tells you the milligrams of elemental magnesium per daily dose. If a product only lists milligrams of salt, you're comparing blind.
What can be claimed about magnesium
Magnesium is one of the nutrients with the most authorized health claims in the European Union. These are all ten, worded as authorized:
"Magnesium contributes to a reduction of tiredness and fatigue."
Regulation (EU) 432/2012
"Magnesium contributes to electrolyte balance."
"Magnesium contributes to normal energy-yielding metabolism."
"Magnesium contributes to normal functioning of the nervous system."
"Magnesium contributes to normal muscle function."
"Magnesium contributes to normal protein synthesis."
"Magnesium contributes to normal psychological function."
"Magnesium contributes to the maintenance of normal bones."
"Magnesium contributes to the maintenance of normal teeth."
"Magnesium has a role in the process of cell division."
What's not on that list: sleep. There is no authorized claim linking magnesium to sleep. It's true that many sleep formulas include it, and that magnesium contributes to normal muscle and nervous system function, but saying "magnesium helps you sleep" goes beyond what European regulations allow.
How much magnesium per day
The nutrient reference value used on European labels is 375 mg per day. It's the figure used to calculate the %NRV you see on the nutrition panel, and it's a population reference, not a personal recommendation.
Keep in mind that much of your magnesium already comes from your diet: nuts, legumes, whole grains, leafy greens and cocoa. A supplement covers a gap, not the total.
Too much magnesium from supplements, especially in the less absorbed forms, has a fairly obvious laxative effect. It's the body's natural warning that you've overdone the dose.
When to take it
There's no magic time. Splitting the dose into two improves digestive tolerance if you take larger amounts. And if it sits heavy on an empty stomach, take it with food.
How to compare two bottles in thirty seconds
- Look for the milligrams of elemental magnesium per daily dose, not those of the salt.
- Check how many capsules make one dose. Three capsules per serving in a bottle of 90 is 30 days, not 90.
- Check the form. If it's oxide and the price is low, now you know why.
- Work out the cost per day from those two figures. That settles almost every debate.
Frequently asked questions
Which form of magnesium is best?
It depends on what you're after. Oxide packs a lot of magnesium per capsule but is poorly absorbed; citrate and bisglycinate are easier on the stomach. Always compare the milligrams of elemental magnesium per daily dose.
Does magnesium help you sleep?
No EU-authorized claim links magnesium to sleep. What is authorized is that it contributes to normal functioning of the nervous system and muscles, and to the reduction of tiredness and fatigue.
How much elemental magnesium is in magnesium glycinate?
Around 10-14% of its weight, depending on the product. For example, 2,500 mg of magnesium glycinate provides about 275 mg of elemental magnesium.
What time of day should you take magnesium?
There's no proven best time. If you take a high amount, splitting it into two doses and taking it with food makes it easier on the stomach.
Ivalro magnesium
Our magnesium glycinate shows the milligrams of elemental magnesium per dose and how many capsules make it up on its product page. If you're after a more complete nighttime routine formula, take a look at Sleep Support, and the rest of our minerals in vitamins and minerals.
Magnesium Glycinate275 mg of elemental magnesium per dose.View product →
Sleep SupportMagnesium citrate and B6 for your nighttime routine.View product →
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Food supplement. Not a substitute for a varied, balanced diet and a healthy lifestyle. Do not exceed the recommended daily dose.
Ivalro editorial team. Written from EU regulations and published scientific sources, linked below. Last reviewed: October 2026. For information only: not a substitute for advice from a healthcare professional.