Iron is an important trace mineral required for the synthesis of the haemoglobin molecule in red blood cells and also acts as a cofactor in a number of enzymatic reactions in human metabolism. In this regard dietary sources of iron are essential. Iron is present in red meat as haemoglobin and myoglobin and this form of iron is readily absorbed and utilised by humans. Consumption of red meat a few times per week can supply all the iron required by a normal healthy individual. Iron is also available as non-haem iron from plant sources, but the binding and storing of iron in plant tissues inhibits its absorption in humans and this means that plant sources of iron are not as bioavailable as animal sources. Iron deficient anaemia is the most common mineral deficiency in developing nations and this relates to the reliance on plant sources of iron. However, iron deficiency is also the most common (known) mineral deficiency in Western nations, and this is puzzling considering the high intakes of red meat.
Legumes are good sources of iron, but the absorption of iron is poor (here). Soybeans in particular have very low iron bioavailability even when the beans are processed into powdered formula. Vitamin C has been tested for its ability to increase the iron absorption from iron1. The vitamin C was added to a soy based infant formula at various concentrations to assess its ability to increase iron absorption in 64 adult female Indian subjects. The iron absorption was assessed by addition of a radioactive tracer to the molecules of iron in the infant formula. As had been shown elsewhere, the iron absorption from the soy formula was low (only 1.8 %). When ascorbic acid was added to the formula at a concentration of 80 mg per 100 gram there was a significant increase in absorption (to 6.9 %). However, addition of ascorbic acid at a concentration of 40 mg per 100 gram did not improve the iron absorption compared to the control. A doubling of the vitamin C content to 160 mg per 100 grams did not increase absorption above the 80 mg per 100 gram concentration.
This study therefore highlights the capacity of vitamin C to improve the absorption of iron from soy. This ability is thought to centre on the ability of vitamin C to retain the iron its reduced state (Fe2+) which increases its passage through the brush border membrane and increases its association with transporters required for receptor mediated transport to the circulation. Protein has also been shown to improve iron absorption and this may be why the iron from meat it more readily absorbed. The ability of protein to enhance iron absorption may also relate to the reduction of the iron molecules through the action of cysteine peptides which can keep the iron in its Fe2+ state. In addition, the proteins in animal tissue may form low molecular weight iron-protein complexes that increase the association of the iron with the brush border membrane of the enterocytes. This effect was demonstrated in the same study when the iron absorption from a milk formula was shown to be superior to that from the soy formula.
RdB
