An estimated 50-68% of Americans don't meet the RDA for magnesium. Modern agriculture, processed food, and depleted soils have made dietary deficiency the default. You're probably deficient. The question isn't whether to supplement — it's which form to use.
Why Magnesium Matters
Magnesium is a cofactor in over 600 enzymatic reactions. It's required for:
- ATP synthesis (energy production)
- DNA and RNA synthesis
- Muscle contraction and relaxation
- Nervous system regulation
- Blood pressure regulation
- Insulin sensitivity and glucose metabolism
- Bone formation (60% of body magnesium is in bone)
Deficiency symptoms are frustratingly nonspecific: fatigue, muscle cramps, poor sleep, anxiety, heart palpitations, headaches. Most people attribute these to stress or aging. Often it's just magnesium.
The Forms — Ranked by Use Case
Magnesium Glycinate (Best for: Sleep, Anxiety, General Use)
Magnesium bound to glycine, an inhibitory amino acid. Double benefit: magnesium itself calms the nervous system, and glycine independently promotes sleep quality by lowering core body temperature and modulating NMDA receptors.
Bioavailability: High (absorbs well, minimal GI issues)
Dose: 200-400mg elemental magnesium before bed
Best for: Sleep quality, anxiety, general deficiency correction, nighttime recovery
My pick for most people.
Magnesium L-Threonate (Best for: Cognitive Function)
The only form shown to cross the blood-brain barrier and increase brain magnesium concentrations. Developed at MIT, studied specifically for cognitive applications.
Bioavailability: Moderate (lower elemental magnesium per dose)
Dose: 1-2g of magnesium L-threonate (yields ~144mg elemental)
Best for: Memory, learning, cognitive performance, age-related cognitive decline
Downside: Expensive. Low elemental magnesium means you may need another form alongside it for body-wide needs.
Magnesium Citrate (Best for: Constipation, Quick Correction)
Highly bioavailable and the osmotic effect draws water into the intestines. Effective for both deficiency correction and regularity.
Bioavailability: High
Dose: 200-400mg elemental
Best for: Constipation, rapid deficiency correction
Caveat: The laxative effect can be too strong for some. Not ideal as a nightly sleep aid.
Magnesium Taurate (Best for: Cardiovascular Health)
Magnesium bound to taurine, which independently supports heart function, blood pressure regulation, and bile acid conjugation.
Bioavailability: Good
Dose: 200-400mg elemental
Best for: Blood pressure, heart arrhythmias, cardiovascular support
Magnesium Malate (Best for: Energy, Muscle Pain)
Bound to malic acid, a Krebs cycle intermediate. Some evidence for reduced muscle soreness and improved energy production.
Bioavailability: Good
Dose: 200-400mg elemental
Best for: Fibromyalgia, chronic fatigue, athletes who get muscle soreness
Magnesium Oxide (Avoid for Most Purposes)
The most common form in cheap supplements. Only 4% bioavailability. You're essentially paying for magnesium that passes straight through you.
Bioavailability: Very low (~4%)
Best for: Literally only as a laxative. Not for correcting deficiency.
Avoid: This is the form in most one-a-day multivitamins. It's there because it's cheap, not because it works.
Other Forms Worth Knowing
- Magnesium Chloride: Good topically (Epsom salt baths) and orally. Decent bioavailability.
- Magnesium Orotate: Some cardiovascular data, popular in Europe. Expensive.
- Magnesium Sulfate: Epsom salts. Best used topically. IV use is medical-grade.
The Multi-Form Strategy
Most optimization-focused protocols use 2-3 forms targeting different systems:
Example stack:
- Morning: Magnesium malate 200mg (energy, muscle function)
- Evening: Magnesium glycinate 300mg (sleep, relaxation)
- If cognitive focus is priority: Add magnesium L-threonate 1g midday
Total elemental magnesium: 500-700mg/day, which is appropriate for most active adults (RDA is 400-420mg for men, 310-320mg for women, but athletes and stressed individuals need more).
Testing Your Levels
Standard serum magnesium is nearly useless — only 1% of body magnesium is in blood, and your body will cannibalize bone and tissue stores to maintain serum levels. You can be severely deficient with "normal" serum magnesium.
Better tests:
- RBC (red blood cell) magnesium — measures intracellular levels
- Aim for: >5.5 mg/dL (optimal range: 5.5-6.5 mg/dL)
If your doctor runs standard serum magnesium and says you're fine, you might not be. Request RBC magnesium specifically.
Drug Interactions
Magnesium can reduce absorption of:
- Antibiotics (tetracyclines, fluoroquinolones) — take 2+ hours apart
- Bisphosphonates (osteoporosis drugs) — take 2+ hours apart
- Levothyroxine (thyroid medication) — take 4+ hours apart
- Some blood pressure medications
Always separate magnesium from medications by at least 2 hours.
Bottom Line
You need magnesium. You probably don't get enough from food. Glycinate is the safest all-around pick. Avoid oxide. Consider a multi-form strategy if you're optimizing seriously. Test with RBC magnesium, not serum.
This is one of the highest-impact, lowest-cost supplements you can add. There's no reason not to.