Posted by Larry Hoover on March 27, 2005, at 12:21:14
In reply to Re: Magnesium survey, posted by banga on March 27, 2005, at 9:02:33
> I have heard magnesium oxide is not well absorbed. It is cheap and that is why many companies use it. Someone said you may as well chew on cement!
> I have heard the salts are much better....The first abstract shows nearly 40 times higher magnesium concentration in urine following citrate, compared to oxide. Oxide was poorly soluble, even in pure stomach acid.
The second abstract give mag oxide a bioavailability of 4% of total dose. Unfortunately, it doesn't put a number on the other preparations, for comparative purposes.
Lar
Magnesium bioavailability from magnesium citrate and magnesium oxide.
Lindberg JS, Zobitz MM, Poindexter JR, Pak CY.
Center for Mineral Metabolism and Clinical Research, University of Texas,Southwestern Medical Center, Dallas 75235.
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.
Magnes Res 2001 Dec;14(4):257-62
Bioavailability of US commercial magnesium preparations.
Firoz M, Graber M.
Department of Veterans Affairs Medical Center, Northport, NY 11768, USA.
Magnesium deficiency is seen with some frequency in the outpatient setting and requires oral repletion or maintenance therapy. The purpose of this study was to measure the bioavailability of four commercially-available preparations of magnesium, and to test the claim that organic salts are more easily absorbed. Bioavailability was measured as the increment of urinary maginesium excretion in normal volunteers given approximately 21 mEq/day of the test preparations. Results indicated relatively poor bioavailability of magnesium oxide (fractional absorption 4 per cent) but significantly higher and equivalent bioavailability of magnesium chloride, magnesium lactate and magnesium aspartate. We conclude that there is relatively poor bioavailability of magnesium oxide, but greater and equivalent bioavailability of magnesium chloride, lactate, and aspartate. Inorganic magnesium salts, depending on the preparation, may have bioavailability equivalent to organic magnesium salts.
poster:Larry Hoover
thread:476058
URL: http://www.dr-bob.org/babble/alter/20050323/msgs/476224.html