Magnesium Supplementation: Forms, Absorption, and Which Type Actually Works
An evidence-based comparison of magnesium forms — glycinate, citrate, threonate, oxide, taurate — covering bioavailability data, clinical uses, dosing, and which form matches your goal.
Lead Science Writer · Peer-Reviewed Sources
Magnesium participates in over 300 enzymatic reactions in the human body. Despite this, an estimated 50% of Americans and Europeans consume less than the recommended daily amount. Subclinical deficiency — not severe enough for obvious symptoms but enough to impair metabolic function — is widespread.
The challenge with magnesium supplementation is that not all forms are equal. Bioavailability varies dramatically, and different forms have different clinical applications.
Why Magnesium Deficiency Is So Common
Soil depletion has reduced magnesium content in crops by an estimated 20-30% over the past century. Modern food processing removes additional magnesium. Meanwhile, stress, alcohol, caffeine, and certain medications (PPIs, diuretics) increase magnesium excretion.
The RDA is 400-420mg/day for adult men and 310-320mg/day for women. Most people get 250-300mg from diet.
The Forms: A Bioavailability Comparison
Magnesium Oxide
- Bioavailability: ~4% (lowest among common forms)
- Elemental magnesium: 60% (highest per pill)
- Clinical use: Primarily as a laxative; poor choice for correcting deficiency
- Evidence: A 2001 JACN study found magnesium oxide absorption was only 4.2% vs. citrate at 25.3%
Magnesium Citrate
- Bioavailability: ~25-30%
- Elemental magnesium: 16%
- Clinical use: General supplementation, constipation relief
- Evidence: Well-studied, good balance of absorption and cost. The standard benchmark form.
Magnesium Glycinate (Bisglycinate)
- Bioavailability: ~30-40% (among the highest)
- Elemental magnesium: 14%
- Clinical use: Sleep, anxiety, muscle relaxation. Least likely to cause GI distress.
- Evidence: The glycine amino acid chelate provides dual benefit — glycine itself is an inhibitory neurotransmitter that promotes sleep. A 2012 study in the Journal of Research in Medical Sciences found magnesium glycinate improved sleep quality in elderly subjects.
Magnesium L-Threonate
- Bioavailability: Moderate orally, but unique CNS penetration
- Elemental magnesium: 8% (lowest)
- Clinical use: Cognitive function, brain magnesium levels
- Evidence: Developed at MIT, a 2010 Neuron paper showed it was the only form that significantly increased brain magnesium levels in animal models. A 2016 human RCT (Journal of Alzheimer’s Disease) found improved cognitive function in older adults. However, evidence is still limited and primarily from the patent holders.
Magnesium Taurate
- Bioavailability: Good (~25-30%)
- Elemental magnesium: 9%
- Clinical use: Cardiovascular health, blood pressure
- Evidence: Taurine provides additional cardiovascular benefits. A 2018 review in Biological Trace Element Research suggested synergistic effects on blood pressure and arrhythmia prevention.
Magnesium Malate
- Bioavailability: Good (~25-30%)
- Elemental magnesium: 15%
- Clinical use: Energy production, fibromyalgia
- Evidence: Malic acid participates in the Krebs cycle. A small 1995 study found benefit in fibromyalgia patients, but evidence is limited.
Choosing by Goal
| Goal | Best Form | Dose (elemental Mg) |
|---|---|---|
| General deficiency correction | Citrate or Glycinate | 200-400mg/day |
| Sleep improvement | Glycinate | 200-400mg before bed |
| Cognitive function | L-Threonate | 144mg (as 2g MgT) |
| Cardiovascular support | Taurate | 200-400mg/day |
| Constipation relief | Citrate or Oxide | 200-400mg/day |
| Muscle cramps | Citrate or Glycinate | 200-400mg/day |
| Anxiety/stress | Glycinate | 200-400mg/day |
Dosing Principles
- Split doses: Absorption decreases with dose size. Two 200mg doses absorb better than one 400mg dose.
- Timing: Glycinate and threonate work best taken in the evening for sleep benefits. Malate is better in the morning for energy.
- With food: Most forms absorb better with food except citrate (fine either way).
- Upper limit: 350mg/day supplemental (in addition to dietary intake) per the IOM. GI tolerance is usually the limiting factor.
Testing Magnesium Status
Standard serum magnesium tests are nearly useless for detecting deficiency — only 1% of body magnesium is in blood. Better options:
- RBC magnesium: Measures intracellular levels. Target: 5.0-6.5 mg/dL
- Ionized magnesium: More accurate but less available
If in doubt, a therapeutic trial of 200-400mg glycinate or citrate for 4-6 weeks is often more practical than testing.
Interactions
- Antibiotics: Magnesium chelates fluoroquinolones and tetracyclines. Separate by 2+ hours.
- Bisphosphonates: Same chelation concern. Separate by 2+ hours.
- PPIs: Chronic PPI use depletes magnesium. Supplementation is especially important.
- Zinc: High-dose zinc (>142mg/day) can interfere with magnesium absorption.
The Bottom Line
Magnesium deficiency is common and worth addressing. The form matters as much as the dose. Glycinate for sleep and general use, citrate for a reliable all-rounder, threonate if cognitive function is the priority, and taurate for cardiovascular focus. Split your doses, take with food, and expect 2-4 weeks before noticing effects.