Magnesium glycinate vs citrate: the difference that actually matters

What actually differs between the two forms

Both deliver elemental magnesium. What changes is the molecule magnesium is attached to, and that carrier decides how the dose behaves in the gut.

• Magnesium citrate pairs magnesium with citric acid. It is highly soluble and draws water into the bowel, which is why it is used at high doses as an osmotic laxative and in bowel preparation.
• Magnesium glycinate (bisglycinate) pairs magnesium with the amino acid glycine. It is generally reported as gentler on the gut at supplement doses.
• Elemental content differs by product, not just by form: a 500 mg capsule of magnesium citrate is not 500 mg of magnesium. Labels in the US list elemental magnesium under Supplement Facts, and that is the number to compare.
• Magnesium oxide, the cheapest common form, has high elemental content but poor absorption in comparison studies — which is why it is often the form behind a disappointing result.

What absorption studies show

The evidence base is smaller than the marketing suggests. A handful of small crossover studies do most of the work.

• In a 60-day randomized comparison, magnesium citrate raised salivary and urinary magnesium more than magnesium oxide, with an amino-acid chelate falling in between.
• Reviews of magnesium bioavailability consistently rank organic salts and chelates above oxide, while differences between citrate and chelates are small and inconsistent.
• No trial establishes that one form treats a symptom better than another at matched elemental doses; the reliable difference is tolerability, not potency.
• Absorption also falls as the single dose rises, so split doses generally deliver more than one large one.

Choosing between them in practice

For most people the decision comes down to what the gut does with it and what else is being taken.

• Constipation is a reason people choose citrate; loose stools are the most common reason people leave it.
• Glycinate is usually the form chosen when stool-softening is unwanted, including by people already taking other magnesium-containing products.
• The NIH sets a tolerable upper intake level of 350 mg per day for supplemental magnesium in adults — that applies to magnesium from supplements, not from food.
• Magnesium reduces absorption of several medicines, including levothyroxine, tetracycline and quinolone antibiotics, and bisphosphonates. Labels for those medicines specify separating the doses by hours, not minutes.
• Impaired kidney function changes the whole picture, because magnesium clearance drops and supplemental magnesium can accumulate.

References

• NIH Office of Dietary Supplements — Magnesium fact sheet for health professionals
• Walker AF, et al. Mg citrate found more bioavailable than other Mg preparations (Magnes Res 2003)
• Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium (2017)
• MedlinePlus — Magnesium in diet