Magnesium Glycinate vs Threonate: What Each Was Studied For
Key takeaways
- Magnesium bisglycinate is the mineral chelated to two glycine molecules. Magnesium L-threonate is the mineral bound to L-threonic acid, a breakdown product of vitamin C.
- A 2024 crossover study in 40 healthy adults found plasma magnesium rose after microencapsulated magnesium, oxide, and citrate, but not after bisglycinate. The study was funded by the company that sells the microencapsulated ingredient.
- An older crossover study in 12 patients with ileal resection found similar overall absorption for magnesium diglycinate and oxide (23.5% vs 22.8%), with the chelate ahead in the four patients who absorbed oxide worst.
- Threonate has human trial data on cognition. A 12 week trial in 44 older adults with cognitive impairment reported improved overall cognitive scores, and the authors were employees of the ingredient's developer.
- The tolerable upper intake level for supplemental magnesium in adults is 350 mg a day, and it does not include magnesium from food.
What each compound is
Magnesium bisglycinate is magnesium ion bound to two molecules of glycine, the simplest amino acid. That bond makes a chelate, a neutral ring structure able to move through amino acid transporters in the intestinal wall instead of competing at the general mineral channels. Magnesium L-threonate is magnesium bound to L-threonic acid, a metabolite of ascorbic acid, better known as vitamin C. L-threonic acid occurs naturally in cerebrospinal fluid, and the compound was developed specifically to target magnesium levels in the brain rather than in blood.
Elemental content differs a lot between the two. Magnesium L-threonate is mostly threonate by weight, so a 2 g dose supplies roughly 144 mg of elemental magnesium. Labels often print compound weight rather than mineral weight.
What the absorption studies show
Start with the broad pattern. Organic magnesium salts dissolve more readily than inorganic ones, and human trials have found citrate raises serum and urinary magnesium more than oxide, both after a single dose and over longer supplementation.
Glycinate's supposed advantage comes from the chelate. A 1994 crossover study in the Journal of Parenteral and Enteral Nutrition tested that in 12 patients with ileal resections. Each took 100 mg of magnesium labeled with the stable isotope 26Mg, as either the diglycinate chelate or oxide. Across the whole group, absorption was 23.5% with the chelate and 22.8% with oxide, which isn't a difference worth acting on. In the four patients who absorbed oxide worst, the gap opened up, 23.5% against 11.8%. The chelate also peaked earlier, by a mean of 3.2 hours.
A 2024 crossover in Nutrients ran the comparison in 40 healthy men and women.
Participants ate a low magnesium diet for a week, then took each product after an eight hour fast, with plasma magnesium measured at baseline and at one, four, and six hours. The microencapsulated product raised plasma magnesium at every point. Oxide raised it at one hour only, citrate at four hours only, and bisglycinate produced no statistically significant rise at all.
Two crossover studies, opposite results on glycinate, and one of them funded by the company selling the product being tested. That's where the absorption evidence stands.
Tolerance
Glycinate's reputation rests on chemistry as much as on trials. Unabsorbed magnesium pulls water into the bowel, which is why oxide and citrate at higher doses produce loose stools. A form absorbed higher in the gut leaves less behind.
In the 1994 ileal resection study, patients tolerated the chelate better than the oxide. That comes from 12 people with a specific surgical history, so it doesn't travel far. The 2024 trial reported less intestinal motility and less gastric heaviness with the microencapsulated form, and again, the funder markets that ingredient.
Threonate's profile in trials looks similar to other organic salts. The 2016 trial reported mild adverse events, more often in the placebo group, mostly gastrointestinal upset.
What threonate was studied for
Threonate was built around a brain hypothesis, and the animal work came first. A 2010 study in Neuron gave magnesium L-threonate to rats and found higher brain magnesium, more synapses in the hippocampus, more NR2B-containing NMDA receptors, and better performance on learning and memory tasks in both young and aged animals. That's rat data, and plenty of compounds that work in rats do nothing in people. The first human trial appeared in 2016 in the Journal of Alzheimer's Disease. It enrolled 51 adults aged 50 to 70 reporting cognitive decline, and 44 finished. Participants took MMFS-01, which is magnesium L-threonate, at roughly 25 mg/kg/day, or placebo, for 12 weeks. The overall cognitive composite improved significantly against placebo, at p = 0.003 with a Cohen's d of 0.91. Executive function, measured with Trail Making Test part B, improved enough to bring the group near age-matched norms.
Read the affiliation. The authors worked for Neurocentria, the company that developed MMFS-01. The trial was run by the ingredient's developer, and no independent group has replicated it at that dose and duration.
A 2022 trial in Nutrients tested a different product in 109 healthy Chinese adults aged 18 to 65.
The formula combined magnesium L-threonate with phosphatidylserine plus vitamins C and D, dosed at 2 g a day for 30 days. Scores improved across all five subcategories of the Clinical Memory Test and on overall memory quotient, with larger gains in older participants. Three other active ingredients were in the capsule, so the finding can't be pinned on magnesium L-threonate alone.
What glycinate has been studied for
Much less, and that's the honest answer. Magnesium glycinate turns up as a comparator or inside a general magnesium trial far more often than as the isolated subject of a cognition study. Its tolerance reputation comes from the chelate chemistry and from comparisons against oxide, not from trials measuring thinking.
Glycine is an inhibitory neurotransmitter in the spinal cord and brainstem, and marketing leans on that fact constantly. It doesn't tell you whether a magnesium glycinate capsule changes anything measurable in a person's brain.
Where the evidence is thin
Two gaps are worth naming.
Plasma magnesium is a poor proxy for body stores.
NIH's Office of Dietary Supplements notes that under 1% of the body's magnesium sits in blood serum, held in a narrow range. A six hour curve after one dose says little about tissue status.
Neither form has long-term trials against clinical outcomes. The cognition trials ran 30 days to 12 weeks, in 44 to 109 people, and they measured test scores.
Frequently asked questions
Which form raises brain magnesium more?
Only threonate has been tested for that question, and the human evidence is thin. The 2010 Neuron study showed brain magnesium rising in rats, while the 2016 human trial measured cognitive test scores.
Is glycinate gentler on the stomach?
That's the common claim, and the mechanism makes sense. Unabsorbed magnesium pulls water into the bowel, so a form absorbed higher in the gut leaves less to cause loose stools. Head-to-head tolerability data in general populations are thin.
How much magnesium do adults need?
The Recommended Dietary Allowance runs 400 to 420 mg a day for men and 310 to 320 mg for women, depending on age. The tolerable upper intake level of 350 mg a day covers supplements and medications only, not food.
Can magnesium cause problems?
High supplemental doses commonly cause diarrhea and cramping. Impaired kidney function raises the risk of magnesium building up, and several medicine classes interact with it.
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This article is for general information only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration and are not intended to diagnose, treat, cure, or prevent any disease. Talk with your health care provider before using magnesium, especially if you have kidney disease or take prescription medication.
Sources
- NIH Office of Dietary Supplements. Magnesium Fact Sheet for Health Professionals.
- Schuette SA, Lashner BA, Janghorbani M. Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN J Parenter Enteral Nutr. 1994;18(5):430-435.
- Pajuelo D, Meissner JM, Negra T, Connolly A, Mullor JL. Comparative clinical study on magnesium absorption and side effects after oral intake of microencapsulated magnesium versus other magnesium sources. Nutrients. 2024;16(24):4367.
- Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-177.
- Liu G, Weinger JG, Lu ZL, Xue F, Sadeghpour S. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. J Alzheimers Dis. 2016;49(4):971-990.
- Zhang C, Hu Q, Li S, et al. A Magtein, magnesium L-threonate, based formula improves brain cognitive functions in healthy Chinese adults. Nutrients. 2022;14(24):5235.