Title: The Influence of Other Dietary Components on the Bio-Availability of Trace Metals
Key words: trace metals, iron, zinc, copper, calcium, selenium, antioxidant, bioavailability, enzyme systems, Phytates, unrefined cereals, ligands, absorption, antiphytates, animal protein, vitamin C, milk, haem, phenols, competitive inhibition, tea, omnivores
Date: Sept 2006
Author: Morgan, G.
The Influence of Other Dietary Components on the Bio-Availability of Trace Metals
Trace metals form an essential part of the diet, helping to service essential and metabolic functions of the body. Of these metals, four – iron, zinc, copper and selenium – have special nutritional importance. All four function in important enzyme systems controlling, for example, oxidation, electron transfer, protein and nucleic acid synthesis. They are vital in maintaining cell membrane function, acting as anti-oxidants and in helping to control the bio-availability of essential nutrients. Iron also plays a key role in oxygen transport in the form of haemoglobin.
Bio-availability of these trace elements depends on absorption and utilization within the gut. Intake and losses of these elements may be significant factors in the overall equation as in the iron deficiency anaemia of menorrhagia or in dietary selenium deficiency due to soil depletion. In most instances, however, diminished absorption due to binding of these elements within the lumen of the gut is of equal importance. In this respect the following points can be made:
The above factors illustrate the complexity of trace metal absorption and utilization. Many interactions are not fully understood but it is known that the effects can be marked. Iron absorption, for example, can vary by a factor of ten depending on the type of meal eaten (Hallberg 2000). Zinc absorption amongst omnivores is 20-40%, yet drops to 15% in people living on a diet high in unrefined cereals.
For common clinical problems such as iron deficiency anaemia, advice regarding high phytate foods, tea consumption and supplements, for example, is of obvious practical value.
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