What are the differences between magnesium glycinate, magnesium citrate, and magnesium oxide supplements?

Comparison of Magnesium Glycinate, Citrate, and Oxide Supplements

Magnesium oxide is the only form that has been evaluated in randomized controlled trials for constipation, while organic forms like magnesium glycinate and citrate have better bioavailability but lack clinical efficacy data for specific conditions. 1

Bioavailability Differences

Magnesium supplements differ significantly in their absorption and bioavailability:

• Magnesium Oxide:

  • Lowest bioavailability (approximately 4% absorption) 2
  • Highest elemental magnesium content (60%)
  • Most commonly studied in clinical trials for constipation 1
  • Creates stronger osmotic effect in the intestines, making it more effective for constipation
  • Least expensive option

• Magnesium Citrate:

  • Higher bioavailability than oxide 3, 4
  • Increases muscle and brain magnesium levels in a dose-independent manner 3
  • Moderate osmotic effect, often used for constipation
  • Moderate elemental magnesium content (16%)
  • More palatable taste than oxide

• Magnesium Glycinate:

  • Higher bioavailability as an amino acid-bound compound 3, 4
  • Better tolerated with fewer gastrointestinal side effects
  • Lower elemental magnesium content (14%)
  • Less laxative effect, making it better for those seeking magnesium supplementation without bowel changes

Clinical Applications

For Constipation:

Magnesium oxide is recommended by clinical guidelines for chronic idiopathic constipation at doses of 1.5g/day in clinical trials, though lower doses of 500mg-1g/day are commonly used in practice 1. The osmotic effect creates a net secretion of water and electrolytes in the GI tract.

For General Magnesium Supplementation:

Organic magnesium salts (glycinate, citrate) are preferred for general supplementation due to better bioavailability 1, 3, 4.

For Specific Conditions:

• Bartter Syndrome: Guidelines recommend organic magnesium salts due to their better bioavailability 1
• Neurological Benefits: Magnesium acetyl taurate showed highest brain concentration in animal studies, followed by other organic forms 5

Important Considerations

• Renal Function: All magnesium supplements should be avoided in those with creatinine clearance <20 mg/dL due to risk of hypermagnesemia 1

• Dosing Strategy:

  • Spreading supplements throughout the day improves absorption 1
  • Dividing high doses may not necessarily increase tissue levels 3

• Absorption Mechanisms:

  • Passive paracellular absorption is the main mechanism
  • Organic forms have additional transport mechanisms that improve bioavailability 3, 4

Practical Selection Guide

1. For constipation: Choose magnesium oxide (strongest osmotic effect)
2. For better absorption with fewer GI side effects: Choose magnesium glycinate
3. For balanced approach (moderate absorption and moderate laxative effect): Choose magnesium citrate
4. For those with renal impairment: Avoid all magnesium supplements or use with extreme caution under medical supervision

The choice should be guided by the specific need for magnesium supplementation, considering that only magnesium oxide has been evaluated in randomized controlled trials for constipation, while organic forms may offer better bioavailability for general supplementation purposes.