Magnesium L-threonate (Magtein) is a proprietary magnesium compound bound to threonic acid, developed through research at MIT and marketed as a food supplement. Preclinical studies suggest it may cross the blood-brain barrier, though robust human evidence remains limited. Magnesium is essential for over 300 enzymatic reactions, including neurotransmitter synthesis and nerve transmission. In the UK, magnesium L-threonate is not licensed as a medicine by the MHRA and is not subject to pharmaceutical regulatory standards. It should not replace a varied diet or prescribed treatment. This article examines the evidence, safety profile, and clinical considerations for this supplement.

What Is Magnesium L-Threonate (Magtein)?

Magnesium L-threonate is a compound in which magnesium is bound to threonic acid, a metabolite of vitamin C. Magtein is a proprietary brand of this compound, developed through research at the Massachusetts Institute of Technology (MIT) and marketed as a food supplement. In preclinical studies, magnesium L-threonate has shown potential to cross the blood-brain barrier, though robust human evidence confirming this property and its clinical significance remains limited.

Magnesium itself is an essential mineral involved in over 300 enzymatic reactions in the body, including neurotransmitter synthesis, nerve transmission, and synaptic plasticity. Adequate magnesium status is crucial for normal neurological function, muscle contraction, cardiovascular health, and bone metabolism. The UK Reference Nutrient Intake (RNI) for magnesium is 300 mg daily for men and 270 mg daily for women, with UK dietary surveys suggesting many adults may not achieve these targets.

Magnesium L-threonate supplements typically contain 1,000–2,000 mg per serving, providing approximately 72–144 mg of elemental magnesium, though this varies by brand. It is important to note that magnesium L-threonate is not licensed as a medicine by the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK. As a food supplement, it is not subject to the same rigorous regulatory standards as pharmaceutical products and should not be used as a substitute for a varied, balanced diet or prescribed medical treatment. Under GB Nutrition and Health Claims regulations, no cognitive enhancement or disease prevention claims are authorised for magnesium supplements.

Potential Benefits and Clinical Evidence

The primary interest in magnesium L-threonate centres on cognitive function and neuroprotection, particularly regarding memory, learning, and age-related cognitive decline. Preclinical studies in animal models have suggested that magnesium L-threonate supplementation may increase brain magnesium levels and enhance synaptic density and plasticity, mechanisms theoretically linked to cognitive function.

Human clinical evidence, however, remains limited and preliminary. A small randomised controlled trial published in 2016 (Liu et al., Journal of Alzheimer's Disease) involving 44 adults aged 50–70 years with cognitive complaints suggested that 12 weeks of magnesium L-threonate supplementation was associated with improvements in certain cognitive measures, including executive function and working memory. However, this study had significant methodological limitations, including small sample size, lack of independent replication, and industry funding, which warrant cautious interpretation.

There is currently no official endorsement from NICE, the NHS, or other UK clinical bodies recommending magnesium L-threonate for cognitive enhancement or dementia prevention. While magnesium deficiency may affect cognitive function, there is insufficient evidence that supplementation beyond correcting deficiency provides additional cognitive benefits in healthy individuals.

Patients with cognitive concerns should be encouraged to discuss this with their GP, particularly if they have underlying health conditions or are taking other medications. Cognitive complaints may warrant formal assessment to exclude treatable causes such as depression, thyroid dysfunction, vitamin B12 deficiency, or early dementia. Per NICE guidance, GPs may refer to a local memory assessment service when appropriate. Urgent medical attention is needed for sudden confusion, focal neurological symptoms, rapidly progressive decline, or cognitive changes following head injury.

Dosage, Safety and Side Effects

The typical recommended dosage of magnesium L-threonate is 1,000–2,000 mg daily, usually divided into two or three doses. This provides approximately 72–144 mg of elemental magnesium, which is below the UK Safe Upper Level for magnesium supplementation (400 mg elemental magnesium per day from supplements, as advised by the Expert Group on Vitamins and Minerals). It is generally recommended to take magnesium supplements with food to enhance absorption and reduce gastrointestinal discomfort.

Magnesium L-threonate appears to be generally well tolerated in the limited clinical studies available. Potential side effects may include:

• Gastrointestinal symptoms: nausea, loose stools, or mild diarrhoea

• Headache: reported occasionally in early supplementation

• Drowsiness: reported anecdotally by some users

These effects are typically transient and may resolve with continued use or dose adjustment. Lower elemental magnesium doses may be better tolerated than higher doses, though individual response varies.

Contraindications and precautions include:

• Renal impairment: patients with chronic kidney disease should avoid magnesium supplementation without medical supervision, as impaired renal excretion can lead to hypermagnesaemia

• Cardiac conduction disorders: high magnesium levels may affect heart rhythm

• Drug interactions: magnesium can reduce absorption of certain medications:

• Quinolone antibiotics: take magnesium 2 hours before or 4–6 hours after
• Tetracycline antibiotics: separate by at least 2–3 hours
• Bisphosphonates: take bisphosphonates when fasting; avoid minerals for at least 30 minutes after (follow PIL)
• Levothyroxine: separate by at least 4 hours

Patients should contact their GP if they experience persistent side effects or if symptoms they are attempting to self-treat worsen or fail to improve. Seek immediate medical attention for signs of hypermagnesaemia such as severe muscle weakness, profound drowsiness, breathing difficulties, or marked hypotension. Pregnant or breastfeeding women should seek medical advice before using any magnesium supplement beyond standard prenatal vitamins. Suspected adverse reactions can be reported via the MHRA Yellow Card Scheme.

Comparing Magnesium L-Threonate to Other Magnesium Supplements

Magnesium supplements are available in numerous forms, each with different bioavailability, tolerability, and clinical applications. Understanding these differences helps clinicians and patients make informed choices based on individual needs.

Magnesium oxide is one of the most common and inexpensive forms, containing a high percentage of elemental magnesium by weight. However, it has relatively poor bioavailability and commonly causes gastrointestinal side effects, particularly diarrhoea. It is often used as a laxative rather than for systemic magnesium repletion.

Magnesium citrate offers better absorption than oxide and is frequently recommended for correcting magnesium deficiency. It has a mild laxative effect, which may be beneficial for patients with constipation but problematic for others. It is widely available and relatively cost-effective.

Magnesium glycinate (magnesium bound to the amino acid glycine) is often well tolerated with minimal gastrointestinal effects. It is sometimes suggested for sleep support and anxiety, though robust clinical evidence for these specific indications is limited.

Magnesium L-threonate (Magtein) is distinguished by its potential to increase brain magnesium levels based primarily on preclinical research suggesting enhanced penetration of the blood-brain barrier. However, it provides less elemental magnesium per dose than other forms and is considerably more expensive. The clinical significance of increased brain magnesium in humans remains uncertain, and there is no established evidence of superior cognitive outcomes compared to other magnesium forms in human studies.

For general magnesium supplementation to address deficiency or support overall health, magnesium citrate or glycinate are typically more commonly chosen due to their tolerability and availability. Patients should be reminded that no supplement can replace a balanced diet rich in magnesium-containing foods such as green leafy vegetables, nuts, seeds, whole grains, and legumes.

Frequently Asked Questions