COMPARISON OF STABLE ISOTOPES AND RADIOISOTOPES IN THE MEASUREMENT OFIRON-ABSORPTION IN HEALTHY WOMEN

1. Stable isotope methods are being used to investigate the absorption of dietary iron. In order to be certain that this new methodology is accurate, we have compared results obtained using stable isotopes and inductively coupled plasma mass spectrometry with those determined usi ng a radioisotope and whole body counting. 2. The stable isotope Fe-54 (2.8mg) was given to 10 healthy non-pregnant women. Six women receive d the isotope in aqueous form, and four took it with a meat meal. The Fe-54 served as a carrier for 10ng of the radioisotope Fe-59. An ampou le (200 mu g) of the isotope Fe-57 or Fe-58 was then given intravenous ly, and in serum samples taken over the next 10 h the ratios of the st able iron isotopes were measured by inductively coupled plasma mass sp ectrometry and the oral iron absorption was calculated. This was then compared with the results obtained by using a whole body counter to me asure (on day 0 and day 14) the gamma-activity emitted by the radioiso tope. 3. The mean iron absorption measured by both methods ranged from 8% to 45%. Measurement of the post-absorptive serum enrichment of the stable isotopes provided estimates of absorption from both aqueous an d food iron which were similar to that yielded by whole body counting, the mean difference being -1.5% (95% confidence interval -5.2 to 2.1% ). Absorption estimated by stable isotopes exhibited the same inverse relationship with the serum ferritin level (body iron stores) to that known to exist with whole body counting. Similar estimates of food iro n absorption were obtained irrespective of the type of isotope used as an extrinsic label, implying that stable isotopes are as valid as rad ioisotopes in reflecting intrinsic food iron absorption. 4. This study validates the use of stable isotopes and post-absorption curves as a new and accurate technique in the measurement of iron absorption.