Magnesium Glycinate vs Threonate: Which Magnesium Form is Best?

Magnesium Glycinate

Magnesium glycinate is a chelated form where magnesium is bound to two glycine molecules. The chelation protects magnesium from forming insoluble salts in the GI tract and allows absorption via amino acid transporters rather than the magnesium-specific TRPM7 channels, which can become saturated. This dual absorption pathway gives glycinate superior GI tolerance compared to oxide, citrate, or chloride forms. Typical absorption rates are 35–50% for glycinate versus 10–20% for oxide. Serum magnesium levels respond well to glycinate supplementation.

Magnesium L-Threonate

Magnesium L-threonate was developed specifically to cross the blood-brain barrier (BBB), where standard magnesium forms have limited penetration. Research by Slutsky et al. at MIT (2010) showed that threonate uniquely raised cerebrospinal fluid magnesium levels and synaptic magnesium concentrations in rodents, improving synaptic plasticity and memory. The threonate molecule facilitates transport across brain endothelial cells. The clinical relevance of brain-specific magnesium elevation in humans is the key question separating threonate from glycinate.

Magnesium Glycinate

Magnesium glycinate is widely used and reported (with reasonable supporting evidence) to improve sleep quality. Magnesium activates GABA receptors and is a NMDA receptor antagonist, reducing neuronal excitability and supporting sleep onset. The glycine component adds additional sleep-promoting effects (as discussed in the collagen/glycine comparison). Multiple small RCTs and observational studies show improved sleep onset and maintenance with magnesium supplementation in deficient individuals. Effect sizes are larger in those with pre-existing deficiency.

Magnesium L-Threonate

Magtein (the branded magnesium threonate form) is marketed partly for sleep improvement, and some users report improved sleep. Magnesium's sleep-promoting mechanisms apply to threonate as with other forms, but the brain-specific elevation may provide additional benefit via enhanced GABAergic inhibition in sleep-related brain circuits. Clinical sleep data specific to threonate versus other magnesium forms are limited — the difference in sleep outcomes between forms in well-designed head-to-head trials has not been established.

Magnesium Glycinate

For general cognitive health, correcting magnesium deficiency (which glycinate reliably achieves) may be sufficient for the majority of benefits. Magnesium plays roles in BDNF signalling, synaptic plasticity, and neuroprotection, and deficiency is associated with cognitive decline. However, if the brain is the target tissue, the question is whether standard systemic magnesium repletion adequately raises brain magnesium levels — the data suggest it does to some degree, but not as specifically as threonate.

Magnesium L-Threonate

The cognitive case for threonate is built on the MIT rodent studies showing improved memory and learning with threonate-driven increases in synaptic magnesium. A small but well-designed 2016 human study by Liu et al. (n=44) found Magtein significantly improved cognitive function in older adults over 12 weeks, including working memory and attention. These results are promising but require larger replication. Magtein is the most studied threonate brand and has the most supporting evidence.

Magnesium Glycinate

Magnesium is essential for muscle contraction and relaxation, and glycinate effectively corrects the deficiency states underlying muscle cramping, restless legs, and hypertension. Multiple meta-analyses confirm that magnesium supplementation modestly reduces blood pressure (by ~3–4 mmHg systolic) in hypertensive individuals. Glycinate's systemic distribution makes it the better choice for metabolic, cardiovascular, and musculoskeletal magnesium-dependent functions.

Magnesium L-Threonate

Threonate's systemic magnesium distribution is lower than glycinate at equivalent doses because threonate is specifically formulated for brain penetration rather than general magnesium repletion. This means threonate is a poor choice as a primary magnesium supplement for individuals with systemic magnesium deficiency and its associated metabolic or cardiovascular consequences. Using threonate alone without addressing overall magnesium status is a common misuse of the supplement.

Magnesium Glycinate

Magnesium glycinate is widely available and affordable — $10–20/month for 300–400 mg elemental magnesium per day. The form is well-tolerated at typical doses, with diarrhoea only occurring at very high doses (>600 mg elemental magnesium). Multiple commodity suppliers offer clean products, and basic quality verification (elemental magnesium content on label) is straightforward.

Magnesium L-Threonate

Magnesium threonate (Magtein) is significantly more expensive — $30–60/month — due to the proprietary threonate molecule and patent protection. The typical dose provides a lower amount of elemental magnesium than glycinate at the same cost, reflecting the premium for the brain-specific delivery. For budget-conscious consumers or those without specific cognitive goals, the cost premium of threonate over glycinate is difficult to justify given the limited head-to-head comparison data.