Posted by Jamal Spelling on September 20, 2007, at 3:14:50
In reply to Re: Question for Larry Hoover: calcium carbonate » DSCH, posted by Larry Hoover on November 3, 2003, at 15:17:17
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> > IIRC, magnesium has the capacity for strong mixed bonding as MgO is quite refractory. None of the refractory ceramics I can remember had calcium as the main cation (indeed Ca is something more likely to be in a flux IIRC). But I don't know if this is at all relevant to bioavailabity or not.
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> This is a little off topic, but what the heck....
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> The equivalent to MgO, CaO, is also known as quicklime, or caustic lime. It reacts with water (called slaking), to form Ca(OH)2, and releases copious heat in the process.
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> I don't know why MgO is different, but it is. It is virtually insoluble in water (0.00062g/100g water), and poorly soluble even in strongly acidic solutions.
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> J Am Coll Nutr. 1990 Feb;9(1):48-55.
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> Magnesium bioavailability from magnesium citrate and magnesium oxide.
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> Lindberg JS, Zobitz MM, Poindexter JR, Pak CY.
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> Center for Mineral Metabolism and Clinical Research, University of Texas, Southwestern Medical Center, Dallas 75235.
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> 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.
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>I would like to address the last two sentences in the above abstract. It claims that because magnesium citrate produces greater levels of urinary magnesium than does magnesium oxide, therefore magnesium citrate has greater bio-availability. Shouldn't it be the other way around? Surely the fact that magnesium oxide ingestion results in lower levels of urinary magnesium implies that magnesium oxide is better absorbed in the body, rather than being excreted in the urine?
Jamal
poster:Jamal Spelling
thread:272898
URL: http://www.dr-bob.org/babble/alter/20070816/msgs/784097.html