Take a moment to look at your fingernails. Are they brittle and do they peel

easily? Are they so thin you are inclined to bite them?

Perhaps they grow very slowly, are opaquely white or splattered with white dots.

Any one of these symptoms could indicate a zinc deficiency. So if a nutritionist asks to hold your hand and peer at your nails, I can assure you their intentions are strictly honourable.

The ancient Egyptians knew a thing or two about the healing properties of zinc and used it to treat irritated skin. Now we find it in calamine lotion and skin creams.

Zinc was only recognised as essential in the Thirties but is surely one of the most important of all trace elements.

Involved in most biological functions in the human body, deficiencies affect not only our nails or hair. A common sign is a poor sense of taste and smell.

Other tell-tale signs include poor wound healing, acne, stretch marks, hair loss and infertility.

In childhood, severe deficiencies can result in retarded growth, sexual and mental development.

According to Dr Carl Pfeiffer, the scientist who helped to establish the importance of zinc for brain function, depression is a classic symptom. He said he had never seen evidence of post-natal depression in patients treated with zinc and vitamin B6.

During adolescence, too, adequate stores of zinc are essential.

For male teenagers, zinc is required for the entire reproductive system.

Growing boys may try to make up for a lack of zinc by eating voraciously.

Unfortunately, junk food and soft drinks do not contain zinc (whereas whole grains, eggs, meat, fish, milk, nuts, pulses and vegetables do).

Teenage girls on the other hand are likely to become increasingly deficient in the mineral if they go on starvation diets. Affected by a lack of appetite, taste and smell, it becomes all the more difficult for them to return to healthy eating habits.

We all appear to be at risk.

Like selenium, zinc occurs as a water-soluble salt and is leached from the soil by excessive rainfall.

When the land is overfarmed and overfertilised and zinc is not replaced, deficiencies occur.

In some areas of the world, zinc in the soil has been depleted to such an extent that learning disabilities in children are as high as 30 per cent.

Food refining is another problem 80 per cent of zinc is removed, for instance, from wheat flour in the milling process.

Food processing and preparation yield further losses.

Stress and viral infections deplete zinc, as does the consumption of sugar, coffee, alcohol and nicotine.

Corticosteroid drugs and oral contraceptives are enemies of zinc and digestive problems such as low stomach acid, particularly in the elderly, prevent its absorption.

Zinc supplements are available in a variety of forms but individual dosage should be discussed with a qualified nutrition practitioner because long-term use of high doses could cause a secondary deficiency of copper.

Excessively high doses, above 150mg, may suppress immunity, cause nausea and anaemia.