Iron: Functions, Food sources, Absorption and excretion
Iron is a trace element present in the body to the extent of 3-5g. Most of it is found in the blood (about 75 per cent). All cells and tissues especially the muscle tissues contain a little iron (about 5 per cent) and the rest of the iron i.e. about 20 per cent is stored in the body organs such as the liver, spleen, kidney and bone marrow collectively.
The study of iron and its functions is fascinating. After many years of research, there are still many puzzling aspects about the role of iron, especially about
those related to brain functioning. Let us now study some of the known and well established functions of iron.
- Oxygen transport: lron is a major constituent of a red-coloured compound called haemoglobin present in the blood. Iron is present in the haem part of haemoglobin.
What is the role of haemoglobin?
Haemoglobin is necessary for transport of oxygen to various parts of the body. Haemoglobin carries oxygen from the lungs to the tissues and in turn helps in carrying carbon dioxide from the tissues to the lungs as indicated in Figure. From the lungs carbon dioxide is then exhaled out. Carbon dioxide, in fact, is a waste product formed in all cells as a result of metabolism and it needs to be removed from the body.
Haemoglobin as a carrier for oxygen and carbon dioxide
Provision of oxygen for muscle contraction: Iron is also present in the muscle in the form of myoglobin. Myoglobin has the capacity to store oxygen. This oxygen is used for muscle contraction and for other immediate needs of the muscle cells.
Promotion of oxidation within cells: lron facilitates the complete oxidation of carbohydrates, fats and proteins within the cell. This of course, would essential to release of the energy locked up in these molecules. The role of iron in oxygen transport and release of energy is now clear to you. You know that energy is required for the various physical activities we perform everyday This is the reason why iron is crucial in helping us to perform physical work.
Iron plays an impoiant role in maintenance of specific brain functions like immediate memory, capacity to learn and attention span.
Iron forms a vital component of certain enzymes and substances that aid in metabolism.
Iron has protective functions as well. Like vitamin A, iron too helps in preventing infections.
Liver is an excellent source of iron. Other organ meats like kidney, spleen also contain substantial amounts of iron. Among the plant foods the list of iron sources includes green leafy vegetables (like amaranth leaves, mustard leaves, colocasia leaves, mint leaves), cereals (like whole wheat flour, rice flakes, bajra, ragi, jowar) and pulses (especially the whole ones). Soyabean is an example of a pulse containing good amounts of iron. Jaggery is another food that contains fair amounts of iron. We have mentioned several foods which contain substantial amounts of iron. However, we have a paradoxical situation here. There is so much of iron present in food and yet very little gets into the body. Why is this so? You would find the answer to this question in the subsequent section.
Absorption and excretion
What happens to iron once it enters the body?
The ingested iron gets absorbed from the upper part of the intestine. The extent of iron absorption from different foodstuffs varies. In general, its absorption from animal foods is high. But the amounts of iron absorbed from many of the plant sources is very low. This is because certain substances present in plant foods bind iron and hinder its absorption. These substances are called inhibitors. You would remember that some plant foods such as green leafy vegetables and cereals contain fairly substantial amounts of iron. Unfortunately they also contain inhibitors which prevent much of the iron from being absorbed. On the other hand, there are substances like protein and vitamin C present in foods that aid in the absorption of iron. These substances can be called enhancers as indicated in figure.
Nutrients that increase iron absorption
It is, therefore, suggested that protein-rich foods like milk and vitamin C-rich foods like oranges, lime, amla and guava should be included in the diet so as to promote the absorption of iron. The inclusion of animal foods, if possible, in the diet greatly enhances iron absorption.
After absorption, iron is transported by the blood to the body cells where it performs its varied functions. Some amount of iron is also transferred to the storage sites in the body such as the liver, spleen, kidney and the bone marrow. Very small amounts of iron are lost through sweat and urine. In the case of women, iron losses include the above but in addition fairly substantial amounts are lost in the menstrual flow.
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