Selenium has long been linked to disease prevention, but scientists remain unconvinced that there is enough evidence to be certain of its benefits.

The Cancer Research Campaign is funding a pilot study in the UK, which will lead on to far larger trials involving five different countries.

If the trials show that selenium does have a beneficial effect, the UK Government may consider following Finland's example and add selenium to crop fertilisers to increase public consumption.

Selenium occurs naturally in soil and is taken into the body via certain foods like Brazil nuts, kidneys and liver. It is also sold as a dietary supplement.

Intake of the mineral in Britain has fallen since flour has been increasingly imported from Europe rather than America, which produces particularly selenium-rich wheat.

Three years ago, an American trial showed that it dramatically reduced the number of deaths from certain cancers, in a small group of people with a history of the disease.