I blame Marco Polo for importing fireworks from the Far East.

The Chinese invented fireworks by filling bamboo shoots with gunpowder and exploding them in the New Year to ward off evil spirits.

Judging by the number of fireworks let off this year, we should be rid of quite a few!

Marco Polo is less well known for reporting the first incidence of selenium toxicity.

The famous traveller and merchant was only 17 years old when he left Venice for China in 1271.

He rode across the deserts and mountains of Asia with his father and uncle, finally reaching the palace of Kublai Khan in Shangdu three years later.

As Polo was fluent in several languages, the Emperor sent him on official tours all over China.

But his European pack animals became gravely ill on these travels and it seems they were poisoned by plants grown in soil containing high levels of selenium.

Local horses had no such problems they had learned which plants to avoid.

Selenium is abundantly but unevenly distributed in the earth's crust as a result of ancient volcanic eruptions.

Although an essential trace mineral for humans and other mammals, it is poisonous in overdose.

Selenium toxicity is extremely rare but includes loss of hair, nails and teeth, dermatitis, gastroenteritis and mild nerve damage.

Nowadays, we are far more likely to be lacking in selenium but require only small amounts to remain healthy.

Deficiencies may occur where wind and rain have removed selenium from the soil into the sea.

This is particularly the case in underdeveloped countries where the diet is limited to local foods and there is little access to seafood, which contains selenium.

In the Keshan district of China, for instance, the levels of selenium in bedrock, soil and water are very low.

A heart muscle disorder afflicting women and children was first identified there in the Thirties and a large number of cases have since been recorded in an area which geographically forms a low selenium belt.

Now that the cause has been established, the disease is being successfully prevented and treated with selenium therapy.

As an antioxidant and part of an enzyme involved in protecting the body from free radical damage, selenium has important applications in fighting infection and inflammation.

Studies indicate the numbers of breast, ovarian, lung and bladder cancers are reduced in areas with a higher selenium content.

The mineral is vital for the normal function of the thyroid gland and may help those with low thyroid function.

It also guards against prostate problems and the toxic effects of cadmium and mercury.

Selenium is found in meat, fish, shellfish, dairy, citrus, avocados and whole grains.

Brazil nuts and walnuts are excellent sources. If supplementing, remember the old saying that "more is not necessarily better".

Do not exceed 200 micrograms of selenium per day and always combine it with other antioxidants such as the vitamins A, C and E.