Effects of calcium phosphate supplementation on calcium, phosphorus, and magnesium metabolism in the Wistar rat

Abstract

Calcium supplementation has been used in humans and in experimental animals to retard bone loss and lower blood pressure, but there are few data in regard to the metabolic effects of supplementation. This study evaluated the impact of supplementing the AIN-76 diet with various amounts of CaHPO 4 on food intake, growth, Ca, Mg and P balance and serum and bone concentrations of these nutrients. Four groups of nine 5-wk old normal male Wistar rats were fed ad libitum for 12 wks the AIN-76 semi-purified diet either unsupplemented (nominally 0.5% Ca), or supplemented to approximately 1.0%, 1.4% or 2.2% Ca with CaHPO 4. Another group of five rats was fed Rat Chow ®. Addition of CaHPO 4 did not alter intake of other nutrients. Dietary Ca level had no effect on whole blood or plasma ionized Ca, plasma total Ca or plasma P in fasted animals, whereas plasma Mg tended to decline with increased Ca supplementation. Increased Ca balance followed CaHPO 4 supplementation, whereas Mg balance declined. P balance was positive and similar in all study groups. Femur dry weight and length did not differ with diet nor did bone Ca content increase with supplementation. Bone Mg content decreased with CaHPO 4 supplementation. The results indicate that ingestion of CaHPO 4 in supplementary amounts does not increase bone Ca in the young normal rat but it is accompanied by other metabolic changes, particularly a striking decrease in net absorption of Mg.