Influence of Dietary Phosphate on Bone Resorption in Senescent Mice

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Abstract
The influence of dietary phosphate on bone resorption was investigated in adult mice fed a high calcium diet. Nine-month-old mice were fed a diet containing 1.2% Ca and either 0.6% or 1.2% P for 16 months. At 25 months of age the femurs of the animals fed the higher phosphorus diet exhibited a lower breaking strength and a reduced content of ash, calcium, and phosphorus. This accelerated rate of bone resorption was arrested by lowering the phosphorus content of the diet from 1.2% to 0.6% at 18 months of age. The exacerbating effect of the high phosphorus diet on the development of senile osteoporosis was confirmed by measurements of 45Ca exchange, which revealed a lower proportion of compact bone in the femurs and lumbar vertebrae. This study confirms the results of previous experiments in this series which indicate that high intakes of phosphorus increase net bone resorption in adult mice, rats and man. This effect has been attributed to a mild secondary hyperparathyroidism resulting from a depression of serum calcium concentration caused by the flux of excess phosphorus through the blood.