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Inhibition of haem-iron absorption in man by calcium
L Hallberg1, L Rossander-Hulthén, M Brune
1Department of Internal Medicine II, University of Göteborg, Sahlgren Hospital, Sweden.
Insights
Calcium (Ca) inhibits both heme and non-heme iron absorption directly. This suggests Ca interferes with a common late-stage iron transport process in mucosal cells.
Area of Science:
- Nutritional Science
- Human Physiology
- Mineral Metabolism
Background:
- Calcium's inhibitory effect on non-heme iron absorption is established.
- Meat enhances heme iron absorption, but Ca's effect on this interaction was unclear.
Purpose of the Study:
- To investigate if calcium (Ca) inhibits heme iron absorption.
- To determine if Ca interferes with meat's enhancing effect on heme iron absorption.
- To elucidate the mechanism of Ca-mediated inhibition of iron absorption.
Main Methods:
- Administered radio-iron labeled hemoglobin in meals with and without meat and calcium chloride (CaCl2).
- Compared heme iron absorption ratios with and without added Ca.
- Conducted control studies to ensure heme iron integrity.
Main Results:
- Calcium inhibited heme iron absorption similarly to non-heme iron absorption.
- The presence of meat did not alter the inhibitory effect of Ca on heme iron absorption.
- Heme iron absorption ratio with added Ca was 0.59 (hamburger) and 0.52 (wheat roll), not significantly different.
Conclusions:
- Calcium directly inhibits heme iron absorption, independent of meat's enhancing effect.
- The findings suggest Ca interferes with a common late-stage transport mechanism for both heme and non-heme iron in the intestinal mucosal cell.
Abstract:
The inhibiting effect of Ca on non-haem-Fe absorption is well established. Present studies showed that Ca inhibited haem-Fe absorption to the same extent when the same amount of Ca (165 mg Ca as CaCl2) was added to a meal. Attempts were made to examine the mechanism for this inhibition in the present studies. Meat is the only known dietary factor influencing haem-Fe absorption. The present studies were designed to examine whether Ca interfered with the enhancing effect of meat on haem-Fe absorption. We found that the inhibition was the same whether biosynthetically radio-Fe-labelled haemoglobin was given in meals with or without meat. The haem-Fe absorption ratio with:without added Ca was 0.59 (SE 0.07) when Ca was added to a hamburger meal, and 0.52 (SE 0.03) when added to a wheat roll. These values were not significantly different (t 0.95; P = 0.35). The inhibition of haem-Fe absorption by Ca is, thus, a direct effect on the absorption of haem-Fe and not an indirect counteracting effect of the well-known enhancing effect of meat on haem-Fe absorption. Control studies were conducted to ensure that haem-Fe had not been degraded to non-haem-Fe during preparation of the foods. Since Ca inhibits the absorption of haem- and non-haem-Fe to the same extent, the present results strongly suggest that Ca interferes with the transport of Fe through the mucosal cell, and at a late stage, is common for haem- and non-haem-Fe transport.(ABSTRACT TRUNCATED AT 250 WORDS)