At a Glance
| Property | Value |
|---|---|
| Evidence Level | Glycinate: Moderate-Strong. Threonate: Emerging (1 human RCT; strong preclinical) |
| Primary Use | Glycinate: sleep, anxiety, muscle relaxation. Threonate: cognition, neuroprotection |
| Key Difference | Glycinate enhances peripheral and GABAergic function. Threonate crosses BBB and elevates brain Mg²⁺ |
Magnesium Glycinate vs. L-Threonate: The Honest Comparison
This has become one of the most searched supplement comparison queries, largely driven by podcast hosts discussing magnesium for sleep and brain health. The recommendations often lack precision — “take magnesium” without specifying which form, at what dose, for what purpose.
The form matters enormously. Different magnesium chelates have different absorption profiles, different tissue distribution, and different co-factor effects. Glycinate and threonate are not interchangeable, and choosing between them requires understanding what you are trying to achieve.
Here is what the research actually says.
The Bioavailability Question
All oral magnesium supplements face the same fundamental challenge: getting magnesium ions across the intestinal wall and into target tissues. Elemental magnesium has poor intestinal absorption (~30-40%), which is why the chelating agent matters.
Magnesium Glycinate
Magnesium glycinate (also called magnesium bisglycinate) is magnesium chelated to two molecules of the amino acid glycine. The glycine chelate protects the magnesium from forming insoluble complexes in the gut and facilitates absorption via amino acid transport pathways rather than mineral channels.
- Bioavailability: High (~80% relative to magnesium citrate). Among the best-absorbed oral forms.
- Elemental magnesium per gram: ~14% (you need ~2,800 mg of the compound to get 400 mg elemental magnesium)
- GI tolerance: Excellent. Glycine is a calming amino acid; the compound does not have the osmotic laxative effect of magnesium citrate or oxide.
Magnesium L-Threonate (Magtein)
Magnesium L-threonate is a patented form (brand name Magtein) developed at MIT. L-threonate is a metabolite of vitamin C that was selected because of its unique ability to transport magnesium across the blood-brain barrier.
- Bioavailability (systemic): Moderate — comparable to citrate for raising serum magnesium.
- Bioavailability (brain): Significantly superior. Slutsky et al. demonstrated that magnesium L-threonate increased cerebrospinal fluid (CSF) magnesium levels by 15% in animal models, while other forms (including citrate and chloride) did not meaningfully change brain magnesium levels (1).
- Elemental magnesium per gram: ~8% (very low — you need ~3,750 mg of compound for 300 mg elemental magnesium)
- GI tolerance: Good, though large capsule volume can be a practical issue.
The Critical Insight
Most magnesium forms raise serum and intracellular magnesium levels adequately. What makes threonate unique is its ability to raise brain magnesium levels. If your goal is peripheral — muscle relaxation, sleep via GABA modulation, general magnesium repletion — glycinate is superior on a cost-per-benefit basis. If your goal is central — cognitive function, memory, neuroprotection — threonate has a mechanistic advantage that other forms lack.
The Evidence: Head to Head
Magnesium Glycinate Evidence
For sleep: Magnesium supplementation improves sleep quality in multiple RCTs, particularly in older adults with insomnia. Abbasi et al. showed 500 mg elemental magnesium over 8 weeks increased sleep time, sleep efficiency, and melatonin while decreasing cortisol (2). The glycine component adds independent value — glycine at 3g before bed lowers core body temperature and improves sleep onset (see my deep sleep supplement guide).
For anxiety: Magnesium acts as a natural NMDA receptor antagonist, dampening excitatory neurotransmission. Boyle et al. conducted a systematic review finding that magnesium supplementation reduced subjective anxiety measures, particularly in magnesium-deficient individuals (though the studies were heterogeneous in quality).
For general health: Decades of clinical use. Well-established safety profile. Addresses the widespread magnesium deficit (an estimated 50-80% of the Western population fails to meet the RDA).
Magnesium L-Threonate Evidence
For cognition (preclinical): Slutsky et al. at MIT demonstrated that magnesium L-threonate enhanced synaptic plasticity in hippocampal neurons, increased synapse density, and improved spatial and associative memory in both young and aged rats (1). The magnitude of the cognitive improvement was significant — aged rats supplemented with MgT performed comparably to young adult rats on memory tasks.
For cognition (human): Liu et al. conducted the only published human RCT to date: 44 adults aged 50-70 received magnesium L-threonate (1.5-2g/day, providing ~144 mg elemental magnesium) for 12 weeks. The treatment group showed significant improvements in executive function and working memory compared to placebo, with the treatment group’s cognitive age estimated as 9 years younger post-supplementation (3).
Important context: This is one small RCT. It is promising. It is not definitive. The preclinical data is strong, and the mechanism (BBB penetration) is well-supported. But anyone claiming that magnesium threonate has “proven” cognitive benefits is overstating a single 44-person trial.
Choosing by Goal
| Your Primary Goal | Best Form | Dose | Rationale |
|---|---|---|---|
| Sleep quality | Glycinate | 400 mg elemental, before bed | GABA-A co-agonism + glycine temperature effect |
| Anxiety reduction | Glycinate | 400 mg elemental, evening | NMDA antagonism + GABA enhancement |
| Muscle cramps/tension | Glycinate | 300-400 mg elemental, divided | Direct muscle relaxation + high bioavailability |
| Cognitive function / memory | L-Threonate | 1,500-2,000 mg compound (~144 mg elemental), split AM/PM | BBB penetration, synaptic plasticity |
| Neuroprotection / dementia prevention | L-Threonate | 1,500-2,000 mg compound, split AM/PM | Brain Mg²⁺ elevation |
| General magnesium repletion | Glycinate | 300-400 mg elemental, with meals | Best absorbed, best tolerated |
| Both sleep AND cognition | Both | Glycinate 400 mg at night + Threonate 1,000 mg AM | Complementary targets |
The Combination Approach
In my clinical experience, many patients benefit from using both forms. This is not redundant — they serve different functions:
- Magnesium glycinate at bedtime (400 mg elemental): Targets peripheral relaxation, GABA modulation, and sleep architecture.
- Magnesium L-threonate in the morning (1,000-1,500 mg compound): Targets brain magnesium levels for cognitive function throughout the day.
The total elemental magnesium from this combination is approximately 500-540 mg — well within safe limits and appropriate for addressing the widespread subclinical magnesium deficiency. For more on whether you may be deficient, see my article on magnesium deficiency symptoms.
Cost Comparison
This matters practically:
| Form | Monthly Cost (quality brand) | Elemental Mg per $ |
|---|---|---|
| Magnesium glycinate | $12-20 | High |
| Magnesium L-threonate | $35-60 | Low |
| Magnesium oxide | $5-8 | Very low (poor absorption) |
| Magnesium citrate | $8-15 | Moderate |
Threonate costs 3-4x more than glycinate for less elemental magnesium. The premium is for the BBB penetration technology. Whether that premium is justified depends on whether cognitive health is your primary concern.
What About Other Forms?
Magnesium citrate: Good bioavailability, affordable. Mild laxative effect at higher doses. A reasonable budget option for general repletion but lacks the specific benefits of glycinate (GABA/sleep) or threonate (BBB penetration).
Magnesium oxide: 4% bioavailability. Essentially useless as a magnesium supplement. It is a laxative. If the label says “magnesium oxide,” put it back on the shelf.
Magnesium taurate: Some cardiologists prefer this form for cardiovascular applications (taurine has independent cardiac benefits). Limited comparative data for sleep or cognition.
Magnesium malate: Malic acid may support energy production via the Krebs cycle. Some practitioners recommend it for fibromyalgia and chronic fatigue. Limited head-to-head data against glycinate or threonate.
For optimal timing of any form, see my guide on when to take magnesium.
Safety and Considerations
Both forms are well-tolerated with a wide safety margin:
- Upper tolerable intake (elemental magnesium from supplements): 350 mg/day per Institute of Medicine guidelines. This is conservative — most adults can safely take 400-600 mg without adverse effects, particularly if divided.
- Kidney function: Magnesium is renally cleared. Reduce doses or avoid supplementation if eGFR is below 30 mL/min.
- Drug interactions: Magnesium can reduce absorption of certain antibiotics (tetracyclines, fluoroquinolones), bisphosphonates, and levothyroxine. Separate administration by 2 hours.
- Threonate-specific: The low elemental magnesium content means you would need impractical amounts to cause magnesium excess. The limiting factor is cost, not safety.
The Bottom Line
Magnesium glycinate is the best general-purpose magnesium supplement for sleep, anxiety, and magnesium repletion — well-absorbed, well-tolerated, affordable, and backed by decades of clinical use. Magnesium L-threonate has a unique and evidence-supported advantage for brain health through BBB penetration, but the human evidence is still early-stage and the cost is significantly higher. In my clinical experience, most patients should start with glycinate. Add threonate if cognitive health is a specific priority, and you have already optimized the fundamentals.
References
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Slutsky I, Abumaria N, Wu LJ, et al. Enhancement of learning and memory by elevating brain magnesium. Neuron. 2010;65(2):165-177. doi:10.1016/j.neuron.2009.12.026
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Abbasi B, Kimiagar M, Sadeghniiat K, et al. The effect of magnesium supplementation on primary insomnia in elderly: a double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. 2012;17(12):1161-1169. PMID:23853635
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Liu G, Weinger JG, Lu ZL, et al. Efficacy and safety of MMFS-01, a synapse density enhancer, for treating cognitive impairment in older adults: a randomized, double-blind, placebo-controlled trial. Journal of Alzheimer’s Disease. 2016;49(4):971-990. doi:10.3233/JAD-150538
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Boyle NB, Lawton C, Dye L. The effects of magnesium supplementation on subjective anxiety and stress: a systematic review. Nutrients. 2017;9(5):429. doi:10.3390/nu9050429
