[Enteral absorption of high calcium doses determined by means of stable isotopes (author's transl)].

The calcium absorption was determined in 8 healthy test persons (average age 25.6 years) after oral administration of 500 mg and 1000 mg of this element. A double isotope method with enriched stable calcium isotopes was used which can be applied without any restriction as, unlike in radiotracer techniques, any exposure to ionizing radiation is avoided. The calcium administered orally was labelled with 48Ca, the CaCl2 injected intravenously with 46Ca. The determination of both isotopes in serum and urine samples was carried out by means of neutron activation analysis. Independent of the calcium dose given, an absorption of 30% was found. From the 46Ca content in the serum samples a mean value of 6.4 +/- 1.0 g calcium or 98.8 +/- 15.4 mg Ca/kg body weight was calculated for the 24 hr-exchangeable calcium body pool.