Magnesium Glycinate vs. Other OTC Magnesium Supplements
Magnesium glycinate is an organic magnesium salt with superior bioavailability compared to inorganic forms like magnesium oxide, though clinical differences between various organic forms (glycinate vs. citrate) remain poorly established, making the choice dependent primarily on your clinical goal rather than absorption differences. 1
Key Differences in Bioavailability
Organic vs. Inorganic Forms:
- Organic magnesium salts (glycinate, citrate, aspartate, lactate) have significantly higher bioavailability than inorganic forms (oxide, hydroxide). 1
- Magnesium oxide contains more elemental magnesium per dose but absorbs poorly compared to organic forms. 2
- Research confirms organic formulations demonstrate superior absorption, though the percentage is dose-dependent. 3
Between Organic Forms:
- The bioavailability differences between magnesium glycinate and citrate are not well-established in clinical trials. 1
- One comparative study showed magnesium bisglycinate (glycinate) had better intestinal permeability and sustained effects over 3 hours compared to other forms. 4
- However, another study found no significant increase in plasma magnesium levels with bisglycinate, while other forms showed measurable increases. 5
Clinical Decision Algorithm
For Constipation Management:
- Choose magnesium citrate over glycinate due to its stronger osmotic effect that draws water into the intestines. 1
- Magnesium oxide is also effective for constipation at 500-1000 mg daily, though it has lower bioavailability. 1, 2
- Magnesium citrate is specifically recommended as a second-line agent for persistent constipation. 1
For General Supplementation (without constipation):
- Either magnesium citrate or glycinate is acceptable, with preference for organic forms over inorganic. 1
- Magnesium glycinate may cause less gastrointestinal distress (bloating, diarrhea) compared to citrate, though effects are typically mild to moderate. 1
- Spread doses throughout the day rather than taking a single large dose for better tolerance. 1
For Chemotherapy-Induced Hypomagnesemia:
- Magnesium glycinate is specifically recommended for maintenance therapy after IV correction or for mild deficiency in oncology patients. 1
- Monitor calcium levels as patients are at increased risk of hypocalcemia after magnesium glycinate treatment. 1
For Patients with Diarrhea-Prone Conditions:
- Magnesium oxide capsules taken at bedtime are the best oral option, as they dissolve slowly and allow more absorption time before reaching the colon. 6
- All magnesium forms can cause loose stools through osmotic effects. 6
Critical Safety Precautions
Renal Impairment:
- Avoid ALL magnesium supplements if creatinine clearance is <20 mL/min due to hypermagnesemia risk. 1, 2, 6
Cardiac Conditions:
- Contraindicated in congestive heart failure patients. 1
- Use caution in elderly patients and those with heart failure or electrolyte disturbances. 1
Electrolyte Monitoring:
- Monitor calcium levels when using magnesium glycinate due to hypocalcemia risk. 1
- In patients ≥65 years, magnesium citrate carries a small increased risk of hyponatremia (0.05% absolute risk increase). 1
Common Pitfalls to Avoid
- Don't assume higher elemental magnesium content equals better absorption—magnesium oxide has high elemental content but poor bioavailability. 2
- Don't split high doses expecting better absorption—research shows dividing 405 mg doses into two 202.5 mg doses did not sufficiently increase tissue magnesium levels. 7
- Don't overlook hydration status—water and sodium depletion causes secondary hyperaldosteronism, which increases urinary magnesium losses and undermines supplementation efforts. 6
Practical Dosing Recommendations
- For general supplementation: Start with 300-500 mg daily of organic forms, increasing if necessary. 2
- For constipation: Magnesium citrate or oxide 500-1000 mg daily. 1
- Take magnesium oxide at night when intestinal transit is slower for better absorption. 2
- Ensure adequate fluid intake with all forms. 1