Magnesium is the fourth most abundant mineral in the human body and a cofactor in over 300 enzymatic reactions. It is involved in ATP production, protein synthesis, muscle contraction, nerve transmission, and GABA receptor function. Despite its ubiquity, approximately 50-60% of adults consume less magnesium than recommended, and many supplements use forms with extremely poor absorption that provide false confidence of adequacy.
Forms Compared: Absorption and Target Systems
| Form | Elemental Mg % | Bioavailability | Best for | GI tolerance | Cost |
|---|---|---|---|---|---|
| Magnesium Oxide | 60% | Very low (4%) | Not recommended | Poor — laxative effect | Very low |
| Magnesium Glycinate | 14% | High (~80%) | Sleep, anxiety, deficiency correction | Excellent — no laxative effect | Moderate |
| Magnesium L-Threonate (Magtein®) | 7.2% | High for CNS specifically | Cognitive function, memory, brain Mg elevation | Excellent | High |
| Magnesium Citrate | 16% | Moderate (60-70%) | General supplementation | Good — mild laxative at high dose | Low |
| Magnesium Malate | 11% | Moderate-high | Energy metabolism, muscle soreness | Good | Low-moderate |
| Magnesium Taurate | 8.9% | Moderate | Cardiovascular support (theoretical) | Good | Moderate |
| Magnesium Chloride (topical) | 12% | Moderate (transdermal) | Muscle cramps (topical application) | N/A (topical) | Low |
Why Magnesium Oxide Is a Poor Choice
Magnesium oxide is the most common form in cheap supplements and multivitamins. It has the highest percentage of elemental magnesium by weight (60%) — making it look impressive on labels — but a 1998 study by Firoz & Graber found only 4% bioavailability in humans. At 400mg elemental magnesium from oxide, your body absorbs approximately 16mg. A 200mg glycinate dose absorbs 160mg. This is a 10× difference in actual magnesium delivered.
Magnesium Glycinate — The Sleep and Anxiety Workhorse
Magnesium glycinate is the chelate of magnesium with the amino acid glycine. Both magnesium and glycine have independent calming effects on the nervous system. Magnesium activates GABA receptors and inhibits NMDA receptor overactivation; glycine is itself a calming inhibitory neurotransmitter. The combination produces reliable improvements in sleep latency, anxiety scores, and muscle relaxation at 200-400mg elemental magnesium doses.
Target dose: 200-400mg elemental magnesium from glycinate daily, taken before bed for sleep application. This is achieved with approximately 1,400-2,800mg of magnesium bisglycinate (which contains ~14% elemental magnesium).
Magnesium L-Threonate — The Brain Magnesium
Magnesium L-threonate (Magtein®) is the only magnesium form with published human evidence for raising central nervous system magnesium concentrations via blood-brain barrier penetration. Standard magnesium (glycinate, citrate, oxide) raises serum and muscle magnesium but cannot meaningfully penetrate the BBB. Magtein® uses L-threonate as a carrier that accesses the L-type amino acid transporter pathway across the BBB.
The cognitive research at 2,000mg Magtein (144mg elemental Mg) daily shows improvements in memory, cognitive flexibility, and anxiety reduction in human RCTs. The limitation: Magtein costs 4-5× more per day than glycinate. It is the right choice if cognitive enhancement is the primary goal; glycinate remains the correct choice for sleep and general deficiency.
Which Form to Choose
- For sleep quality and anxiety: Magnesium Glycinate (200-400mg elemental Mg, before bed)
- For cognitive function and memory: Magtein® L-Threonate (2,000mg/day = 144mg elemental Mg)
- For general deficiency correction: Magnesium Glycinate or Citrate (easier to find, lower cost)
- For muscle cramps or acute cramping: Magnesium Citrate (faster absorption) or topical Magnesium Chloride
- To avoid entirely: Magnesium Oxide (4% bioavailability — essentially worthless for supplementation)