Accurate measurement of stable isotopes 46Ca and 48Ca in human feces, plasma, and urine in relation to human nutrition of calcium.

A method based on Radiochemical Neutron Activation Analysis (RNAA) is described which allows simultaneous measurement of two stable isotopes of calcium, 46Ca and 48Ca, in human feces, plasma, and urine for the purpose of studying human nutrition and metabolism of calcium. It is shown that these measurements can be made with relative analytical precision of 1--5% depending on the particulars of a given experiment. The method has been applied in humans and data are given showing that kinetics of plasma appearance of 46 Ca administered orally with food can be readily investigated. This method allows investigation of a number of important nutritional and metabolic issues in all human population groups without regard to radioisotope safety considerations, and should prove especially helpful in relation to studies of calcium bioavailability from different foods in a variety of population groups for whom use of radiocalcium is not warranted.