Elemental Magnesium Content of Magnesium Glycinate
Magnesium glycinate contains approximately 14% elemental magnesium by weight, meaning that 100 mg of magnesium glycinate provides roughly 14 mg of elemental magnesium 1.
Chemical Composition and Molecular Weight
- Magnesium glycinate is a chelate complex in which one magnesium ion (Mg²⁺) binds to glycine molecules, forming an octahedral coordination structure 2, 3.
- The molecular formula varies depending on hydration state and whether it exists as mono-glycinate or bis-glycinate (diglycinate), with the metal-glycine complex moiety preserved in solution 4, 3.
- The low percentage of elemental magnesium reflects the molecular weight contribution of the glycine ligands and any coordinated water molecules in the complex 2, 3.
Practical Dosing Implications
- To achieve 400 mg of elemental magnesium (a common supplementation target), you would need approximately 2,857 mg (2.9 grams) of magnesium glycinate 1.
- For the recommended daily allowance of 320 mg elemental magnesium for women or 420 mg for men, you would require approximately 2,286 mg or 3,000 mg of magnesium glycinate, respectively 1.
- This substantially higher pill burden compared to magnesium oxide (which contains ~60% elemental magnesium) means patients typically need to take multiple capsules or tablets to achieve therapeutic doses 1.
Comparison with Other Magnesium Salts
- Magnesium oxide provides approximately 60% elemental magnesium (400 mg magnesium oxide = ~240 mg elemental magnesium), making it the most concentrated form by weight 1.
- Magnesium citrate provides approximately 16% elemental magnesium, similar to glycinate 5.
- Despite lower elemental magnesium content, organic salts like glycinate demonstrate superior bioavailability and cellular uptake compared to inorganic forms like magnesium oxide 2, 5, 6.
Bioavailability Considerations
- Magnesium glycinate exhibits improved cellular uptake in intestinal cell models (CaCo-2 cells) compared to commonly used magnesium supplements, partially offsetting its lower elemental content 2.
- The glycinate chelate is absorbed in part as an intact dipeptide in the proximal small intestine via dipeptide transport pathways, providing an absorption advantage over magnesium oxide 6.
- In patients with ileal resection and impaired magnesium absorption, magnesium diglycinate showed substantially greater absorption (23.5% vs 11.8%) compared to magnesium oxide in those with the most severe absorption impairment 6.
- Peak magnesium absorption occurs significantly earlier with glycinate (mean 3.2 hours faster) compared to magnesium oxide, and the area under the enrichment curve is greater 6.
Clinical Selection Guidance
- Choose magnesium glycinate when: the goal is magnesium repletion without laxative effects, the patient has gastrointestinal sensitivity, or the patient has malabsorption syndromes 1, 6.
- Choose magnesium oxide when: the indication is chronic constipation (where the osmotic laxative effect is desired), cost is a primary concern, or higher elemental magnesium per pill is needed 1.
- Magnesium glycinate causes significantly less gastrointestinal side effects (diarrhea, abdominal distension) compared to magnesium oxide due to better absorption and reduced osmotic load in the intestinal lumen 1, 6.
Common Pitfall
- Never assume equivalent dosing between magnesium salts—prescribing "magnesium 400 mg" without specifying whether this refers to elemental magnesium or the salt form leads to substantial under-dosing with glycinate formulations 1.