Copper is a metallic trace mineral that is essential for all vertebrates and some lower animal species. It is distributed widely in the earth’s crust at a concentration of 70 mg per kg. Seawater contains between 1 and 2 mg per litre. Copper occurs naturally in many minerals but is also present as the native metal.
Adult body contents of copper vary between 75 and 150 mg. It is present in low concentration in the glands, bones and muscles but because of their large mass, the skeleton and muscles account for some 50% of body copper. The liver is a rich source with about 10% of total body copper. Other organs that contain significant amounts include the brain, heart and kidney.
From birth to adulthood, liver copper levels gradually decrease, while those in the brain gradually increase. Eventually there are equal concentrations in each site but the significance of this is not known.
In the developing foetus, half the copper content is concentrated in the liver. These reserves are believed to protect the full-term infant against copper deficiency during the first four months of life.
Adults in a well-nourished population retain remarkably steady tissue concentrations of copper, which suggests that man is able to regulate levels of the mineral, despite variable intakes.
Liver is the richest food source of copper but other organ meats also supply significant amounts.
Seafood, nuts and seeds provide reasonable quantities and pulses and dried fruits are useful sources.
Potatoes contain low concentrations of copper but, because they are eaten in high quantities, they can contribute meaningful amounts of copper to the diet.
The copper content of drinking water is highly variable and is greatly influenced by the interaction between the acidity of the water and the piping system, which is often made of copper. This is why soft water areas supply more copper than those with hard water.
Human milk provides four times as much copper as cow’s milk which may reflect higher human requirements. Copper is readily removed by food processing and refining techniques.
Babies with depleted copper reserves fail to thrive and show certain physical signs such as pale skin, de-pigmentation of the hair and skin, prominent dilated veins in the skin and diarrhoea.
Copper deficient adults develop anaemia, usually after prolonged intravenous feeding following extensive bowel surgery. They suffer from retarded growth and water retention with chronic or recurrent diarrhoea. They also show signs of nervous irritability and bones often become brittle as a result of osteoporosis. Hair is often de-pigmented although in the majority of people greying hair is not related to copper deficiency.
The white blood count may also be low, which leads to a reduction in the ability to resist infection. Copper deficiency may also lead to a loss of the sense of taste. These symptoms have been observed in individuals with conditions known to cause malabsorption of copper and do not necessarily suggest a specific deficiency of the mineral.
Deficiency in human beings has been noted in:
- Malnourished children on diets deficient in protein and calories.
- Children and adults with various malabsorption syndromes, who cannot absorb dietary copper.
- Premature babies with insufficient liver reserves.
- Children with a genetic defect that means they cannot absorb copper (Menk’s syndrome).
- Lack of copper in intravenous feeds, in dialysis fluids and in diets which contain a high proportion of processed and refined foods.
- Anyone with prolonged diarrhoea, leading to non-absorption of copper.
- Some cases of high blood cholesterol, impaired glucose tolerance and heart-related abnormalities.
- Those with high dietary intakes of zinc, cadmium, fluorine or molybdenum.
- Those with high dietary intake of phytic acid (from dietary fibre) that can immobilise copper as insoluble copper phytate.
A depressed level of serum iron can lead to copper deficiency.
High intakes of zinc can reduce body copper levels.
High dietary intakes of manganese can reduce body copper levels.
Vitamin C improves copper absorption.
Starch and glucose improve copper absorption, while fructose appears to reduce copper absorption.