Studies in Iron Absorption IV. Effect of Humoral Factors on Iron Absorption

1. In a group of blood donors the mean serum iron concentration, and plasma clearance of iron did not differ significantly from normal means whereas the mean TIBC was increased. No statistically significant correlation existed between these values and the amount of blood donated in the year preceding the study.

2. The iron absorption was significantly correlated with the amount of blood donated during the year preceding the study, and the mean absorption value was significantly higher than in normal controls.

3. Compared to healthy men higher absorption values were likewise found in a group of healthy young women, without pathologic menstruations, and with essentially normal serum iron and TIBC values.

4. In order to discover how the intestine is instructed to increase iron absorption the correlations were studied between iron absorption and hemoglobin, serum iron, TIBC and plasma clearance of iron. No significant correlations were found. It is suggested that absorption is not primarily regulated by these factors. The finding of increased absorption in persons with essentially normal serum iron, TIBC and iron clearance supports this suggestion.

5. To determine whether the high absorption observed in women was a sign of iron deficiency, absorption was again studied after combined oral and parenteral iron treatment. It decreased in each case, except one where absorption remained unchanged.

6. Parenteral treatment alone, increased the serum iron but no statistically significant difference was found in TIBC, plasma clearance of iron, or iron absorption. Absorption after parenteral treatment was correlated mainly with pretreatment absorption.

7. After oral treatment on the other hand, absorption decreased significantly. No substantial changes were noted in serum iron or plasma clearance of iron, while TIBC unexpectedly increased. The findings support the view that no change in serum iron, TIBC or the plasma iron clearance is required to bring about a decrease in iron absorption.