Studies in Iron Absorption V. Effect of Gastrointestinal Factors on Iron Absorption

1. Since previous studies could not demonstrate that any of several general plasma factors played a major role in intestinal iron absorption, local intestinal factors were examined in 240 iron absorption studies on 150 healthy subjects.

2. When the iron dose was increased 40 times, from 0.25 to 10 mg. the percentage absorption was halved.

3. Trebling the quantity of food (bread) in the intestine did not significantly decrease absorption.

4. Ascorbic acid in the intestinal lumen trebled the absorption even of ferrous iron. A stable pharmaceutical combination of iron and ascorbic acid was tested.

5. Sifted flour did not seem to inhibit the absorption of ferrous iron, but coarse ground flour did. When fat was added, no further decrease in absorption was found although iron soaps may be formed.

6. A further decrease in absorption was found after a complete meal.

7. When fine grain reduced iron was used to enrich flour—this is done in all Swedish flour—absorption was 50 per cent lower, and when a coarser grain reduced iron was used 85 per cent lower, than when ferrous sulfate was used for enrichment.

8. When oral iron treatment was given to persons with high iron absorption, absorption was decreased to normal.