INFLUENCE OF DIETARY CALCIUM INTAKE ON CA47 ABSORPTION IN MAN

The absorption of calcium, using Ca47 as the tracer, was determined in twenty-one patients under controlled dietary conditions during both low and high calcium intake; each patient served as his own control. The absorption of Ca47, determined from the fecal Ca47 excretion and as judged by the Ca47 plasma levels, varied greatly in different persons on the same constant low calcium intake and also during a period of constant high calcium intake. The Ca47 absorption differed significantly during low and high calcium intake in the same patients. The average per cent absorption of Ca47 in the twenty-one patients was 63.6 per cent during low calcium intake and 30.5 per cent during high calcium intake. The Ca47 plasma curves were similar during low and high calcium intake, the highest level being attained at four hours after the ingestion of the dose under these study conditions. The Ca47 plasma level in all patients was significantly lower during high than during low calcium intake, the lower Ca47 plasma levels corresponding to the higher fecal Ca47 excretion in the high calcium study. The studies emphasize three observations: (1) the importance of calcium intake in estimating calcium absorption from radiocalcium data in man, (2) the great variability in calcium absorption of persons on the same calcium intake (low or high), and (3) the need for stool collections over a period sufficiently long to permit estimations of radiocalcium absorption from fecal radiocalcium excretion. © 1969.