Why the Type of Magnesium Matters
Not all magnesium supplements are created equal. The mineral must be bound to a carrier molecule (called a chelate or salt) for stability, and that carrier dramatically affects how well the magnesium is absorbed, what benefits it provides, and what side effects it produces. Choosing the wrong form means you may absorb as little as 4% of the magnesium you paid for.
Approximately 50% of Americans consume less than the estimated average requirement for magnesium, making it one of the most widespread nutrient deficiencies. Choosing a highly bioavailable form is essential for actually correcting this shortfall.
The 8 Major Magnesium Forms
Magnesium Glycinate (Bisglycinate)
Bioavailability: ~80% (among the highest of all forms)
Best for: General supplementation, sleep, anxiety, muscle relaxation
Magnesium glycinate is magnesium bound to the amino acid glycine. This chelated form is highly bioavailable and uniquely well-tolerated — it is the least likely form to cause GI distress. The glycine component provides independent calming benefits, activating NMDA receptors in the brain that promote relaxation and sleep.
Dose: 200-400mg elemental magnesium, ideally taken in the evening
Side effects: Very rare at standard doses. Occasional mild drowsiness, which is a feature for evening use.
Magnesium L-Threonate (Magtein)
Bioavailability: Moderate systemically, but uniquely high brain bioavailability
Best for: Cognitive function, memory, brain health, neuroprotection
Magnesium L-threonate is the only form demonstrated to significantly increase magnesium concentrations in the brain by crossing the blood-brain barrier. A 2010 study in Neuron by Bhatt et al. found that magnesium threonate enhanced learning and memory in both young and aged rats, with increases in synaptic density in the hippocampus.
Dose: 1,500-2,000mg magnesium L-threonate (providing ~140mg elemental magnesium)
Note: The elemental magnesium content is low per capsule, so this form is best used specifically for cognitive benefits rather than correcting whole-body magnesium deficiency.
Magnesium Citrate
Bioavailability: ~30-40%
Best for: Constipation relief, general supplementation (if you tolerate it)
Magnesium citrate has decent bioavailability and is widely available at low cost. Its primary distinguishing feature is its osmotic laxative effect — it draws water into the intestines, making it effective for constipation but problematic for people prone to loose stools.
Dose: 200-400mg elemental magnesium
Side effects: Loose stools and diarrhea are common, especially above 300mg.
Magnesium Taurate
Bioavailability: ~25-30%
Best for: Heart health, blood pressure, cardiovascular support
Magnesium taurate combines magnesium with the amino acid taurine, which has independent cardiovascular benefits including blood pressure regulation, antiarrhythmic effects, and endothelial protection. This makes magnesium taurate the preferred form for people with cardiovascular concerns.
Dose: 200-400mg elemental magnesium
Side effects: Well-tolerated; minimal GI effects.
Magnesium Malate
Bioavailability: ~25-30%
Best for: Energy production, fibromyalgia, muscle pain
Magnesium malate combines magnesium with malic acid, a key molecule in the Krebs cycle (cellular energy production). Some preliminary evidence suggests benefits for fibromyalgia-related pain and fatigue, though large-scale trials are lacking.
Dose: 200-400mg elemental magnesium
Side effects: Generally well-tolerated; less laxative than citrate.
Magnesium Oxide
Bioavailability: ~4% (extremely poor)
Best for: Laxative use only (not recommended for supplementation)
Despite being the most commonly sold form (due to low cost and high elemental magnesium per capsule), magnesium oxide is almost worthless for correcting magnesium deficiency. A 500mg magnesium oxide capsule delivers only about 20mg of absorbable magnesium. It is useful only as an osmotic laxative.
Dose: Not recommended for supplementation
Magnesium Chloride
Bioavailability: ~20-25%
Best for: Topical application (magnesium oil, bath flakes), general supplementation
Magnesium chloride is commonly used in topical magnesium products (oils, lotions, bath salts). Oral bioavailability is moderate. Topical absorption is debated — some studies suggest meaningful transdermal absorption, while others question whether enough crosses the skin barrier to affect serum levels.
Dose: Oral: 200-400mg elemental magnesium. Topical: as directed.
Magnesium Sulfate (Epsom Salt)
Bioavailability: Low orally; primarily used topically or intravenously
Best for: Bath soaks for muscle relaxation; clinical IV use for eclampsia, severe asthma
Epsom salt baths are popular for muscle soreness, though evidence for meaningful transdermal magnesium absorption is limited. Oral magnesium sulfate is a potent laxative and is not suitable for routine supplementation.
Comparison Table
| Form | Bioavailability | Best For | GI Side Effects | Cost |
|---|---|---|---|---|
| Glycinate | ~80% | General use, sleep, anxiety | Very low | $$ |
| L-Threonate | Moderate (high in brain) | Brain health, memory | Low | $$$ |
| Citrate | ~30-40% | Constipation, general use | Moderate (laxative) | $ |
| Taurate | ~25-30% | Heart health, blood pressure | Low | $$ |
| Malate | ~25-30% | Energy, fibromyalgia | Low | $$ |
| Oxide | ~4% | Laxative only | High (laxative) | $ |
| Chloride | ~20-25% | Topical, general use | Low-moderate | $ |
| Sulfate | Low | Bath soaks, IV clinical | High orally | $ |
How to Choose Your Form
For most people: Magnesium glycinate is the clear winner. High absorption, minimal side effects, and calming benefits make it the ideal daily supplement.
For cognitive goals: Add magnesium L-threonate specifically for brain benefits. Because its elemental magnesium content is low, many people take threonate for the brain plus glycinate for general body magnesium needs.
For heart health: Magnesium taurate combines the benefits of magnesium with the cardiovascular support of taurine.
For constipation: Magnesium citrate or oxide can provide reliable laxative effects, but they are not ideal for correcting magnesium deficiency.
What to avoid: Magnesium oxide for anything except laxative use. Despite being the cheapest and most common form on store shelves, its 4% bioavailability makes it nearly useless for supplementation.