Recommended Nutrient Intakes for Vitamin and Minerals

Iron

Functions

Over 60% of the body's iron is in the haemoglobin of the red blood cells, about 25% is storage form (especially the liver), and the remainder is found in myoglobin in muscles and in enzymes.

Iron is an essential nutrient that is vital to the process by which cells generate energy. In haemoglobin and myoglobin iron helps accept, carry, and release oxygen. Iron is also involved in enzymes for making amino acids, hormones, and neurotransmitters.

Recommended Intakes

Table: Recommended Intakes for Iron (mg/day)

Food Sources

There are forms of iron: haeme and non-haeme iron. Haeme iron is only present in the flesh of animals e.g. meat, poultry, and fish. Non-haeme iron is found in both plant-derived and animal-derived foods e.g. vegetables, fruits, grains, eggs, meat, fish, and poultry.

Haeme iron is absorbed at a rate of about 23% whereas non-haeme iron is absorbed at lower rates between 2-20%.

There are also factors which influence the absorption of non-haeme iron. Enhancers of non-haeme iron absorption include:

• Vitamin C
• Meat, fish, and poultry (MFP factor)
• Citric acid and lactic acid from foods and HCL in the stomach

Factors which reduce iron absorption include:

• Phytates and fibre
• EDTA  (in food additives)
• Calcium and phosphorous (in milk)
• Tannic acid e.g. in tea (and other polyphenols)

Deficiency

There are several stages to iron deficiency. Iron deficiency relates to a depletion of iron stores. Anaemia refers to severe depletion of iron stores that results in low haemoglobin concentrations. The red blood cells in those with iron-deficiency anaemia are pale and small. They are unable to carry sufficient oxygen from the lungs to the tissues, so metabolism in cells falters. The result is fatigue, weakness, headaches, apathy, pallor, and poor resistance to cold temperatures. Individuals may become pale, and the eye-lining which is normally pink may become pale.

Iron deficiency may alter behaviour. There can be a reduced physical work capacity and productivity because of reduced energy availability. This can reduce the ability to work, think and learn.

One bizarre behaviour seen in some iron-deficient individuals of low income is pica - an appetite for ice, clay, paste, and other non-food substances.

Toxicity

Usually the body will absorb less iron when its stores are full, but there are disorders of iron metabolism which lead to iron overload.

Iron overload is known as haemochromatosis and is usually caused by a gene that increases iron absorption. Other causes of iron overload include repeated blood transfusions, massive doses of dietary iron, and rare metabolic disorders. A condition known as haemosiderosis can result from prolonged over-consumption of iron. This condition is characterised by the deposition of the iron storage protein, haemosiderin, in the liver and other tissues.

Some signs of iron overload are similar to those of iron deficiency e.g. fatigue, headaches, irritability, lowered work performance, and anaemia.

Iron overload can cause tissue damage, especially in the liver. Other symptoms include enlarged liver, skin pigmentation, lethargy, joint disease, loss of hair, amenorrhoea, and impotence. Infections are more likely to develop as bacteria thrive on iron.