The Effect of Level of Intake on Calcium and Phosphorus Metabolism in College Women ,

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Calcium and phosphorus metabolism were studied on 17 college women from two states. Five subjects, two in Ohio and three in Minnesota, were maintained for a period of 8 weeks on a basal diet which supplied approximately 300 mg of calcium and 800 mg of phosphorus daily. A second group of 6 subjects, three in Ohio and three in Minnesota, were maintained on the basal diet for 4 weeks. This was followed immediately by a 4-week period during which the basal diet was supplemented by 1,200 mg calcium, making the total calcium intake 1,500 mg daily. A third group of 6 subjects, following the 4-week period on the basal diet, received supplements of calcium and phosphorus, making the total intake 1,500 mg of calcium and 1,400 mg of phosphorus. One week was shown statistically to be an adequate period for adjustment to the calcium and phosphorus levels in the basal diet. Negative calcium balances were observed on the basal diet, whereas more positive than negative phosphorus balances were noted. Increasing the calcium intake from 300 mg to 1,500 mg without altering the phosphorus intake resulted in a statistically significant increase in calcium retention. Urinary calcium excretion also increased significantly. Phosphorus retention, however, was unchanged, but there was a decrease in the urinary excretion of this element. When supplements of both calcium and phosphorus were added to the basal diet, calcium retention was somewhat greater than on the unsupplemented basal diet but was very much less than when the basal diet was supplemented with calcium alone. Phosphorus retention, on the other hand, was not influenced by these changes in calcium and phosphorus intake. Within the limits of the calcium and phosphorus intake levels employed in this investigation, the amount of phosphorus in the diet would appear to be a factor of considerable importance in determining calcium utilization in adult subjects.