The research originally set out to test whether selenium supplements could prevent skin cancer and was conducted by Dr. Saverio Stranges of Warwick Medical School.

Some earlier research has suggested that the mineral might help prevent diabetes.

Dr. Stranges and colleagues looked at 1,202 people taking selenium for the skin cancer trial who did not have diabetes at the beginning of the study.

Half of the study group took a daily 200 microgram selenium supplement and half received a placebo pill for an average of 7.7 years.

The researchers found that 58 of 600 people taking selenium and 39 of 602 taking placebos developed type-2 diabetes over the 7.7 years; this equates to an increase in relative risk of about 50 percent.

The researchers say people taking selenium in the hope of preventing diabetes may actually increase their risk.

The trial showed that people who took selenium pills raised their risk of diabetes by more than half, compared to similar people taking placebos.

It is thought about 60 percent of Americans take multivitamin pills, many of which contain between 33 and 200 micrograms of selenium, in addition to the selenium taken in from food and the air.

Selenium is a naturally occurring trace mineral present in soil and foods; minute amounts are needed by the body to help the metabolism.

Selenium supplements are widely promoted on the Internet for a wide range of conditions from cold sores and shingles to arthritis and multiple sclerosis.

They are also promoted as preventing aging, enhancing fertility, preventing cancer and getting rid of toxic minerals such as mercury, lead and cadmium.

Dr. Stranges says he would not advise patients to take selenium supplements greater than those in multiple vitamins and says most people have adequate selenium in their diet.

Dr. Stranges says it's not clear as yet why selenium increases the risk of developing diabetes.

The research is published in the Annals of Internal Medicine.

Professor Lammert “ working together with his colleagues Dr. Frank Gr nhage, Maja Walier and Professor Dr. Thomas Wienker as well as scientists at the University Clinic of Cluj-Napoca in Romania “ has been searching for the specific genes involved. And he has succeeded, thanks to a study covering 178 women and men from 84 families. They all suffer from gallstones. In 21.4 per cent of cases the subjects were found to be carrying a particular gene variant. In healthy individuals studied as a control group, this variant also occurred, but only at a frequency of 8.6 per cent.

Cholesterol pump at full speed

"The mutation concerns what is known as the ABCG8-gene," Dr. Gr nhage explains. "It contains the instructions for building a pump responsible for transporting the blood lipid cholesterol from the liver into the bile ducts." Most of the gallstones consist to a high degree of crystallised cholesterol. The medical researcher concludes that, "The genetic alteration probably makes the pump run permanently at high speed."

The researchers now hope that their finding will have positive consequences for prevention and therapy. Professor Lammert thinks that, "It may be possible for certain patients to be helped with drug treatments in future, thus avoiding the need for an operation." However, the genetic contribution to the common problem of gallstones has not been fully explained by this study: "We believe there are at least three or four other gene variants that increase gallstone risk," says the medical scientist.

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