Why the chelation form matters
Magnesium needs a carrier molecule to absorb across the gut wall. The choice of carrier dramatically affects both bioavailability and side-effect profile:
- Magnesium oxide: ~4% bioavailable. Cheap and dominant in drugstore multivitamins. Causes diarrhea before it raises serum levels meaningfully.
- Magnesium citrate: 25-30% bioavailable. Good absorption but laxative-dose limited. Best used for constipation relief.
- Magnesium glycinate (bisglycinate): ~80% bioavailable. Glycine chelation survives stomach acid intact. Minimal GI effect. Glycine itself is a mild calming neurotransmitter — pairs synergistically for sleep + anxiety indications.
- Magnesium threonate: ~75% bioavailable. Uniquely crosses the blood-brain barrier (Slutsky 2010) — good for cognitive support. 3-5x more expensive per dose.
- Magnesium malate: ~70% bioavailable. Fatigue / muscle pain indications.
The sleep evidence
Abbasi et al. 2012 (Journal of Research in Medical Sciences) — RCT in 46 elderly adults with insomnia — showed 500mg/day magnesium oxide over 8 weeks significantly improved sleep efficiency, sleep time, and reduced sleep-onset latency vs placebo. Most subsequent sleep trials use glycinate form for better tolerance at the elderly population dose. The mechanism: magnesium acts as a GABA receptor cofactor (the brain's primary calming neurotransmitter system), supports muscle relaxation, and regulates melatonin synthesis.
Dose + timing protocol
Standard sleep-support dose: 200-400mg magnesium glycinate, taken 30-60 minutes before bed with a small amount of fat (improves absorption). Start at 200mg and increase by 100mg/week as tolerance builds. The NIH Tolerable Upper Intake Level for supplemental magnesium is 350mg/day (not a toxicity threshold — just where GI side effects become common). The Abbasi 2012 study used 500mg/day under medical supervision with no serious adverse events.
Functional deficiency is hard to test for
Standard serum magnesium tests miss most functional deficiency — DiNicolantonio et al. 2018 (Open Heart) noted only 1% of body magnesium is in blood, so serum levels can be normal while cellular stores are depleted. The more sensitive RBC magnesium test exists but isn't routinely ordered. Practical screening: muscle cramps, twitching, restless legs, anxiety with no obvious trigger, constipation, migraine history, high alcohol or caffeine intake, GI conditions (Crohn's, celiac), diuretic use, low intake of leafy greens/nuts/whole grains. If 3+ apply, supplementation is likely beneficial.
Primary sources: Abbasi B et al. 2012 (J Res Med Sci) — PubMed; DiNicolantonio JJ et al. 2018 (Open Heart); Slutsky I et al. 2010 (Neuron) — threonate brain delivery.