Eight laboratories conducted a test for the estimation of the bioavailability of iron from 4 sources, using depleted male albino rats. Ferrous sulfate was used as the reference standard. Ferric orthophosphate was found to have a relative biological value of 11 (range 6–22), an old sample of hydrogen-reduced iron 27 (range 15–41), and ferric citrate 96 (range 75–125). Good results were obtained with a simplified basal diet prepared without ingredients that had previously contributed variable quantities of iron. There was no apparent advantage in using the change in hemoglobin during the repletion period instead of the final homoglobin value as the criterion of response to iron supplements. Several statistical treatments of the data yielded similar conclusions regarding relative biological values of the iron sources.
The high incidence of iron deficiency anemia in the United States and elsewhere is caused by insufficient iron intake, plus poor utilization of many dietary sources of iron. There is need to select assimilable sources of iron for fortification of foods; animal studies show that many of the iron compounds used for cereal enrichment are poorly utilized. A method to measure availability of iron is proposed and is currently being studied collaboratively. Preliminary data indicate that in vitro solubility tests are not satisfactory to evaluate availability of iron supplements.
A collaborative study of the hemoglobin repletion test was conducted with male weanling rats. The rats were depleted for 4 weeks on a low-iron casein based diet. They were then divided into 13 comparable groups of at least 8 animals each. One group continued on the basal diet. Three groups were given different levels of each of 4 samples. Sample 1 was FeS04.7H20, used as the reference standard. Samples 2 and 3 were from the same lot of electrolytically reduced iron separated into fractions of different particle size by nitrogen elutriation, and were 7—10 and 27—40 /tm, respectively. Sample 4 was a mixture of several lots of food grade ferric orthophosphate. After 2 weeks on the test diets, individual blood samples were drawn for hemoglobin determinations. The data were analyzed by the parallel lines technique, and relative biological values, vs. FeS04 = 100, together with 95% confidence limits were calculated. The relative biological values were as follows: reduced iron, 7—10 /mi = 63.5 ± 10.9; reduced iron, 27— 40 /im = 3 7 . 9 ± 1 2 . 2 ; ferric orthophosphate = 44.5±4.8. This revised method for measuring bioavailability of iron has been adopted as official first action to replace the original method, 39.A15-39.A17.
The widespread incidence of iron deficiency anemia caused by insufficient iron intake and poor utilization of dietary iron sources prompted the search for a method which would be a reliable measure of availability. A hemoglobin repletion method has been proposed and studied collaboratively with 8 participating laboratories. The collaborators reported chick or rat data on the availability of supplemental iron from 5 uniform sources. There was very good agreement between collaborators. Expressed as relative biological values, versus ferrous sulfate = 100, the results on the other 4 samples were as follows: Sample 2 = 12±0.9; Sample 3 = 13±7.7; Sample 4 = 46±17.9; and Sample 5 = 3±4.5. Increases in plasma iron in human volunteers, following test doses of these samples, ranked these 5 samples in the same order as did the chick and rat hemoglobin repletion test. It is recommended that the hemoglobin test for measuring availability of iron be adopted as official first action.
Study was continued on the animal hemoglobin repletion test for measuring bioavailability of iron. With most iron sources, similar results were obtained with chicks and with rats. An important exception was noted with reduced iron. Seventeen samples were tested for solubility in dilute HCl and for bioavailability when fed to chicks and rats. The chicks utilized all samples reasonably well, but the rats were not able to efficiently utilize samples with particle sizes greater than 325 mesh. The mean relative biological value (vs. FeSO4 = 100) for the 17 samples was 50.5 ±8.3 when tested with chicks and 32.3±17.7 when tested with rats. Some, but not all, of the differences could be explained on the basis of particle size distribution. Similar relative biological values were obtained when the sample of reduced iron was added directly to the test diet or when it was used to enrich flour which was subsequently baked into bread and the bread was then added to the test diet. Plasma iron responses in human volunteers following test doses of the reduced iron samples were more closely related to the rat data, and this suggested that rats were the preferred species to measure bioavailability for man. The rat data also measured bioavailability of iron for guinea pigs.
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