Magnesium is one of the most popular supplements around, and it comes in a confusing number of forms. Two of the most common are magnesium glycinate and magnesium citrate. Here’s what the difference actually is, and what the evidence does and doesn’t say.
What magnesium does
Magnesium is a mineral your body uses in hundreds of processes, including muscle and nerve function, making energy from food, and building bone. The NIH’s Office of Dietary Supplements sets the recommended daily amount for adults at:
- Men: 400 mg (ages 19 to 30), 420 mg (31 and older)
- Women: 310 mg (ages 19 to 30), 320 mg (31 and older)
Food covers a lot of that. Leafy greens, nuts, seeds, beans and whole grains are all good sources.
What the form means
Magnesium in a supplement is always bound to another compound, and that partner gives the form its name:
- Magnesium citrate is magnesium bound to citric acid.
- Magnesium glycinate, often labeled bisglycinate, is magnesium bound to the amino acid glycine.
- Magnesium oxide is magnesium bound to oxygen. It’s cheap and compact, so it shows up in a lot of multivitamins.
The partner changes how well the supplement dissolves and how your gut handles it.
Absorption
According to the NIH, forms of magnesium that dissolve well in liquid are absorbed better than forms that don’t. Its fact sheet says the aspartate, citrate, lactate and chloride forms tend to be absorbed better than magnesium oxide and magnesium sulfate.
Glycinate isn’t part of that comparison. It’s widely marketed as better absorbed and easier on the stomach, but good head-to-head studies in people comparing it with citrate are limited. If someone tells you one is definitely better, ask which study they mean.
Side effects
Too much magnesium from supplements often causes diarrhea, sometimes with nausea and cramps. The NIH says the forms most commonly reported to cause diarrhea are magnesium carbonate, chloride, gluconate and oxide. Magnesium citrate is also sold in much larger doses as a laxative, which tells you what it can do in high amounts.
How much is too much
For adults, the NIH’s upper limit for magnesium from supplements and medications is 350 mg a day. That limit doesn’t count magnesium from food. Add up everything you take, because magnesium also turns up in multivitamins, antacids and some laxatives.
Check with a doctor or pharmacist first if
- You have kidney problems. Your kidneys remove extra magnesium, so the risk of getting too much rises when they aren’t working well.
- You take certain antibiotics. The NIH says tetracyclines and quinolones should be taken at least 2 hours before or 4 to 6 hours after a magnesium supplement.
- You take a bisphosphonate for your bones. Magnesium can reduce how well it’s absorbed, so the NIH suggests taking them at least 2 hours apart.
- You take diuretics, or you’ve taken acid-reflux medicines called proton pump inhibitors for a long time. Both can change your magnesium levels.
How to read the label
On a US Supplement Facts panel, the amount listed is the magnesium itself, not the whole compound. The form usually appears in brackets, like “Magnesium (as magnesium glycinate) 100 mg.” That makes it easy to compare products and add up your total for the day.
The short version
- Citrate is well absorbed and well studied, but higher doses can loosen your stools.
- Glycinate is popular and often described as gentle, but direct comparisons are thin.
- Oxide packs the most magnesium into a small pill but is absorbed less well.
- Whatever the form, stay at or under 350 mg a day from supplements unless your doctor tells you otherwise.
Sources
- NIH Office of Dietary Supplements, Magnesium: fact sheet for health professionals