Magnesium Oxid

Overview

Magnesium oxide is an inorganic magnesium salt with approximately 60% elemental magnesium content, the highest of all common supplement forms. However, its bioavailability is very poor due to limited water solubility. A 60-day randomized, double-blind, placebo-controlled trial (n=46, Walker et al. 2003) found that magnesium oxide at 300mg elemental Mg per day resulted in no significant differences in serum, urinary, or erythrocyte magnesium compared to placebo, while organic forms (citrate, amino-acid chelate) showed significantly greater absorption (P=0.033). Inorganic magnesium salts consistently show lower bioavailability than organic forms across multiple studies. Magnesium oxide is widely used in low-cost supplements because of its high elemental content per gram despite its poor absorption. At higher doses it acts as an osmotic laxative. The supplement upper limit is 350mg elemental magnesium per day from supplemental sources. People with kidney disease should not supplement without medical supervision.

Dosage

400 mg · With meal · Take with food

Scientific Sources

• RCT 60d n=46: MgO no difference vs placebo; citrate and chelate significantly better (P=0.033)
• 15 Mg formulations: inorganic salts poor bioavailability due to low solubility
• RDA 310-420mg/day, supplement UL 350mg/day, kidney disease caution
• PubChem Compound 14792

Frequently Asked Questions