Iron is an essential trace mineral that is supplied only in the diet. It is a constituent of haemoglobin, the red pigment of blood; of myoglobin, the red pigment of muscles and other tissues; and a number of enzymes, notably the cytochromes. These are the functional forms of the mineral but as much as 30% of the body iron is found in storage forms such as ferritin and haemosiderin, which are concentrated mainly in the spleen, liver and bone marrow.
A small amount of iron is associated with the blood transport protein transferrin. An adult male has about 4 grams of iron in the body and an adult female about 2.5 grams.
Iron is widely distributed in foodstuffs and in a mixed diet. Meat, eggs, vegetables and cereals (especially if they are fortified) are the principal dietary sources.
With an intake of 10.7 mg for example, 31% of iron comes from meat, poultry and fish and 25% from foods to which the mineral has been added. Fruit, vegetables and juices represent another major source of dietary iron.
Haem iron, the most desirable form of the mineral, represents 7 to 10% of the dietary iron of girls and women and from 8 to 12% of the dietary iron of boys and men.
The signs of iron deficiency are generally associated with the anaemia that results from low blood levels of haemoglobin and hence reduced oxygen carrying capacity. In the early stages, symptoms include tiredness, fatigue and lack of stamina, indicated by:
- A pale complexion.
- The membrane inside the eyelids is pale rather than its normal pink colour.
- The usual red flare spreading from the half moons of the fingernails disappears.
Symptoms progress to:
- Breathlessness
- Giddiness
- Dim vision
- Headaches
- Insomnia
- Palpitations
- Fast pulse rate
- Heart murmurs
- Loss of appetite
- Indigestion
- Tingling in the fingers and toes
All of these are associated with decreased supplies of oxygen to the tissues and organs.
Generalised itching (pruritis), particularly in later life, may occur around the arms, the legs, the genitals and the abdomen. It appears to be related to low blood plasma levels of iron since anaemia is not always present. Increasing iron intake will often relieve the problem.
In young children, iron deficiency causes retarded growth and impaired mental performance, as well as anaemia.
Dietary deficiency of iron can be caused by insufficient intake of iron-rich foods and high intakes of foods containing phytic acid with little, if any, iron from meat, fish, poultry and dairy products.
Deficiency may also be a feature of:
- Chronic parasitic infections, usually in the Third World
- Heavy menstrual periods
- Pregnancy and lactation because of the demands of the foetus and the production of breast milk
- Chronic bleeding as from gastric and duodenal ulcers; haemorrhoids; gastro-intestinal cancer; prolonged use of aspirin and other drugs; and acute bleeding as in haemorrhage.
- Lack of stomach acid, which is needed to solubilise iron
- Excessive alcohol intake
- Low intakes of vitamin C and the mineral copper, both of which are needed to ensure efficient absorption and assimilation of iron.
On the positive side, vitamin C enhances the absorption of all types of dietary supplementary iron except haem iron.
Traces of copper are needed for the assimilation of iron into haemoglobin.
In vitamin A deficiency, less iron is incorporated into haemoglobin.
Excessive intakes of zinc can lower body iron levels.