Intestine, human, iron uptake

Tandy S., Williams, M., Leggett, A., Lopez-Jimenez, M., Dedes, M., Ramesh, B., Srai, S. K., and Sharp, P. (2000). Nramp2 expression is associated with pH-dependent iron uptake across the apical membrane of human intestinal Caco-2 cells. /. Biol. Chem. 275, 1023-1029. 

The uptake of iron by the human intestine is governed not only by its dietary form and companion consituents, but also by the iron condition of the individual. Iron-depleted subjects absorb all forms of iron with greater avidity than do iron-replete individuals. In human dietetics, therefore, the ascorbic content of a diet can be included in the equation for describing the bioavailability of iron from a mixed diet (35). The interaction of iron nutrition and graded intakes of ascorbic acid (< 25 mg > 25 but < 75 mg and > 75 mg) as a prediction of iron availability from a mixed North American diet is plotted in Figure 1. 

High levels of administered zinc limits copper uptake in humans and certain animals, and provides protection against toxicosis produced by copper in pigs and sheep. Excessive zinc in humans interferes with copper absorption from the intestine, resulting in copper deficiency, and eventually to cardiovascular diseases hi zinc intakes also decrease iron bioavailability, leading to a reduction of erythrocyte life span by 67%. Copper deficiency induced by excess dietary zinc is associated with lameness in horses, donkeys, and mules. 

---