Magnesium bioavailability from magnesium citrate and magnesium oxide.

Abstract

This study compared magnesium oxide and magnesium citrate with respect to in vitro solubility and in vivo gastrointestinal absorbability. The solubility of 25 mmol magnesium citrate and magnesium oxide was examined in vitro in solutions containing varying amounts of hydrochloric acid (0-24.2 mEq) in 300 ml distilled water intended to mimic achlorhydric to peak acid secretory states. Magnesium oxide was virtually insoluble in water and only 43% soluble in simulated peak acid secretion (24.2 mEq hydrochloric acid/300 ml). Magnesium citrate had high solubility even in water (55%) and was substantially more soluble than magnesium oxide in all states of acid secretion. Reprecipitation of magnesium citrate and magnesium oxide did not occur when the filtrates from the solubility studies were titrated to pH 6 and 7 to stimulate pancreatic bicarbonate secretion. Approximately 65% of magnesium citrate was complexed as soluble magnesium citrate, whereas magnesium complexation was not present in the magnesium oxide system. Magnesium absorption from the two magnesium salts was measured in vivo in normal volunteers by assessing the rise in urinary magnesium following oral magnesium load. The increment in urinary magnesium following magnesium citrate load (25 mmol) was significantly higher than that obtained from magnesium oxide load (during 4 hours post-load, 0.22 vs 0.006 mg/mg creatinine, p less than 0.05; during second 2 hours post-load, 0.035 vs 0.008 mg/mg creatinine, p less than 0.05). Thus, magnesium citrate was more soluble and bioavailable than magnesium oxide.

Mechanism of Urinary Calcium Regulation by Urinary Magnesium and pH

“…Our results suggest that high urinary magnesium can increase calciuria and potentially increase stone risk. Some have espoused the notion that magnesium is efficacious in preventing stone formation by binding or complexing oxalate in the bowel and urine, 26,27,40,41 by inhibiting calcium oxalate crystal formation, 26,42,43 and by increasing urinary citrate when given as alkali salt. 44 In vitro studies have shown that magnesium is an inhibitor of calcium oxalate crystal growth in artificial, rodent, and human urine but at supraphysiologic concentrations.…”

“…In the remaining 11 trials, only the test potassium or magnesium salts were given. 27,31 Forty-seven individuals participated in the four trials (four to 21 per trial). In group 2, KHCO 3 was given in one trial, 33 and K 3 Citrate was given in seven trials.…”

Bioavailability of Minerals and Trace Elements

“…Mg oxide has a lower bioavailability than citrate (Lindberg et al 1990) or Mg-L-aspartate-HC1 (Muhlbauer et al 1991). There are no significant differences between Mg lactate, citrate and hydroxide (Bohmer et al 1990) but Mg orotate has a higher bioavailability than Mg hydroxycarbonate (Schlebusch et al 1992).…”

Magnesium bioavailability from mineral waters with different mineralization levels in comparison to bread and a supplement

“…The Mg/creatinine ratio reveals to possible bias due to incomplete urine collection. Furthermore, a normal urinary Mg/creatinine ratio indicates normal urinary Mg excretion and adequate Mg intake [28,29]. Our finding of normal Mg/creatinine ratios implies that there was complete urine collection and adequate Mg intake for all subjects.…”