The Relation of Calcium-to-Phosphorus Ratio to the Utilization of These Minerals by 18 Young College Women

Abstract

Eighteen normal healthy young women served as subjects in a calcium-phosphorus balance study designed to determine the effect of varying the ratio of calcium to phosphorus upon the balances of these two minerals. A basal diet, furnishing 344 mg of calcium and 766 mg of phosphorus, was supplemented by varying amounts of calcium or phosphorus, or both, to give ratios of calcium to phosphorus varying from 1:0.50 to 1:3.97. The calcium intake levels were 344, 944, and 1,544 mg; the phosphorus levels, 766, 1,066 and 1,366 mg. Sodium glycerophosphate, calcium carbonate, sodium phosphate and calcium phosphate were used as supplements to the basal diet. The mean calcium balances varied from —46 to +196 mg and the mean phosphorus balances from —64 to +86 mg. At each level of calcium intake, an increase in phosphorus intake was without significant effect on calcium retention. However, when phosphorus was kept constant, an increase in calcium intake resulted in a significant increase in calcium balance. With constant phosphorus intake phosphorus balances were not affected by an increase in calcium intake. An increase in phosphorus intake from the amount in the basal diet, 766 mg, to 1,366 mg resulted in a higher mean phosphorus balance only if the calcium level was as much as 944 mg. The indications were that the balances of both minerals were more closely related to intakes than to the ratios of calcium to phosphorus. Urinary calcium, calculated as a percentage of calcium intake in milligrams per kilogram, showed a consistent increase with increasing calcium-to-phosphorus ratio and constant calcium intake. The absolute amount of urinary calcium increased with increased intake but the percentage of intake found in the urine decreased with increased intake.