Availability of Magnesium: Balance Studies in Rats with Various Inorganic Magnesium Salts

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Abstract
This study was conducted to determine the relative availability of magnesium from six inorganic magnesium salts. Magnesium balance was determined in weanling rats fed diets containing either 200 or 400 mg added magnesium per kilogram as the carbonate, chloride, oxide, phosphate, sulfate or silicate. Coprophagy was prevented by tail cups. Magnesium carbonate was the most available form in this study based on percentage absorption, percentage retention and femur magnesium concentration. Availability of magnesium as the chloride was nearly equivalent to that of magnesium carbonate. Although absorption and retention of magnesium provided as the oxide, phosphate, sulfate and silicate salts were slightly lower than that of carbonate or chloride, all of the salts were nearly equivalent in their ability to support growth, plasma magnesium levels and kidney magnesium concentrations. Neither the salt form nor the dietary level of magnesium had any significant effect on calcium absorption or retention, or on calcium concentration in plasma or kidney.