Why Magnesium Form Matters
Magnesium is involved in over 300 enzymatic reactions in the body, yet an estimated 50% of Americans don't meet the recommended daily intake. When you decide to supplement, you're immediately confronted with a confusing array of forms: glycinate, citrate, oxide, threonate, taurate, malate, orotate, chloride, sulfate, and more. The form you choose matters enormously because it determines three things: bioavailability (how much magnesium actually gets absorbed), target tissue (some forms preferentially accumulate in certain tissues), and additional benefits from the compound magnesium is bound to. For example, magnesium glycinate provides both magnesium and glycine (a calming amino acid), while magnesium threonate is specifically designed to cross the blood-brain barrier for cognitive benefits.
Key Takeaways
- 50% of Americans don't meet the RDA for magnesium
- Form determines bioavailability, target tissue, and secondary benefits
- Absorption ranges from 4% (oxide) to 80%+ (glycinate)
- The compound magnesium is bound to provides additional benefits
- Different forms are optimal for different health goals
Magnesium Glycinate: Best for Sleep & Anxiety
Magnesium glycinate (or bisglycinate) is magnesium bound to two molecules of the amino acid glycine. It has excellent bioavailability (approximately 80%) and is the gentlest form on the digestive system — it rarely causes the laxative effect associated with other forms. Glycine itself is an inhibitory neurotransmitter with calming properties. It activates NMDA receptors in the brain that promote sleep, and studies show that 3g of glycine before bed improves sleep quality and reduces daytime sleepiness. When you take magnesium glycinate, you get the benefits of both magnesium (muscle relaxation, stress reduction) and glycine (calming, sleep-promoting). This makes it the top choice for people supplementing for sleep, anxiety, or general relaxation. The typical dose is 200–400mg of elemental magnesium from glycinate, taken in the evening.
Key Takeaways
- ~80% bioavailability — one of the highest
- Gentlest on the stomach — rarely causes laxative effect
- Glycine provides additional calming and sleep benefits
- Best choice for sleep, anxiety, and stress relief
- Typical dose: 200–400mg elemental magnesium in the evening
Magnesium L-Threonate: Best for Brain Health
Magnesium L-threonate (sold as Magtein) is a patented form specifically designed to cross the blood-brain barrier and increase brain magnesium levels. Standard magnesium supplements raise blood and muscle magnesium but have limited ability to increase brain concentrations. A study published in Neuron found that magnesium threonate increased brain magnesium levels by 15% and improved learning, working memory, and both short-term and long-term memory in animal models. Human studies have shown improvements in cognitive function, particularly in older adults with age-related cognitive decline. The downside is that magnesium threonate contains relatively little elemental magnesium per capsule (about 48mg per 2g dose), so it's often combined with another form for overall magnesium repletion.
Key Takeaways
- Only form proven to significantly increase brain magnesium levels
- Improved learning and memory in published studies
- Best choice for cognitive function and brain health
- Low elemental magnesium content — may need to combine with another form
- Typical dose: 2g magnesium threonate (144mg elemental Mg)
Magnesium Oxide: The Form to Avoid
Magnesium oxide is the most common form found in cheap supplements and multivitamins because it's inexpensive and contains the highest percentage of elemental magnesium by weight (60%). However, it has an absorption rate of only 4% — meaning that of a 500mg magnesium oxide capsule (containing 300mg elemental magnesium), your body only absorbs about 12mg. The rest passes through your digestive system, often causing a laxative effect. This makes magnesium oxide essentially a very expensive laxative when used as a supplement. If you see magnesium oxide on a supplement label, it's often an indicator of a lower-quality product that prioritizes cost over efficacy. The only legitimate use for magnesium oxide is as an osmotic laxative for constipation relief.
Key Takeaways
- Only 4% absorption rate — the worst of all forms
- Most common in cheap supplements due to low cost
- Contains 60% elemental Mg by weight but almost none is absorbed
- Primarily acts as a laxative, not a magnesium supplement
- Its presence on a label often indicates a lower-quality product
Quick Reference: All 10 Forms Compared
Here's a comprehensive comparison of all major magnesium forms. Magnesium Glycinate: 80% absorption, best for sleep and anxiety, gentle on stomach. Magnesium Citrate: 25-30% absorption, good general-purpose form, mild laxative effect. Magnesium L-Threonate: crosses blood-brain barrier, best for cognitive function, low elemental Mg. Magnesium Taurate: good absorption, best for heart health, taurine supports cardiovascular function. Magnesium Malate: good absorption, best for energy and muscle pain, malic acid supports ATP production. Magnesium Orotate: good absorption, best for heart health and athletic performance, orotic acid supports mitochondria. Magnesium Chloride: good topical absorption, available as oil/spray for muscle cramps. Magnesium Sulfate: Epsom salt, primarily for baths and topical use. Magnesium Oxide: 4% absorption, avoid for supplementation, only useful as laxative. Magnesium Carbonate: moderate absorption, antacid properties, converts to chloride in stomach acid.
Key Takeaways
- Glycinate: Sleep & anxiety (80% absorption)
- Threonate: Brain health (crosses blood-brain barrier)
- Citrate: General purpose (25-30% absorption, mild laxative)
- Taurate: Heart health (taurine supports cardiovascular function)
- Malate: Energy & muscle pain (malic acid supports ATP)
- Oxide: AVOID for supplementation (4% absorption)