Effects of magnesium ions on calcium and phosphorus metabolism

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Abstract
The effects of supplemental but nontoxic amounts of orally administered Mg ions on Ca and phosphate metabolism of adult male rats fed diets containing varied amounts of Ca and P were studied. A 12-day balance period was investigated after the animals were habituated to their respective diets for 5 days. If the diets contained adequate amounts of Ca, supplemental Mg decreased fecal Ca (increased absorption) and increased urinary Ca irrespective of the dietary level of Ca. The net effect of supplemental Mg was to increase Ca balance. The mechanism for the increased absorption of Ca from the intestinal tract or the hypercalciuria is not known. Supplemental Mg had no effect on P absorption when dietary P was suboptimal; it increased it when the dietary Ca-to-P ratio was low. The effects of Mg on phosphate absorption appear to be the result of a Mg-Ca interaction. Urinary P decreased with increasing Mg intake. In general, Mg increased P balance primarily as a result of renal conservation of P.