CHOLESTEROL-lowering drugs taken by thousands of Britons can directly increase the risk of diabetes because of the way they function, research has shown.

Statins have previously been associated with higher rates of type 2 diabetes, but it was not clear whether the drugs were responsible or some other coincidental factor.

Now a study involving experts from Glasgow University has produced strong evidence that the drugs' basic mechanism can lead to weight gain and a modest increase in diabetes risk.

However, experts said the benefits of taking statins still greatly outweigh the risks and advice on taking the drugs should not be changed.

Scientists analysed genetic data from up to 220,000 people and results from almost 130,000 patients who took part in earlier statin trials. They found patients taking statins experienced a modest 12 per cent increased risk of developing type 2 diabetes over a four-year period, and gained around half a pound in weight on average.

Statins work by reducing the efficiency of a liver enzyme, causing liver cells to trap more low-density lipoprotein (LDL) - the harmful form of cholesterol - from the bloodstream.

The cholesterol is converted to bile salts and eliminated naturally from the body.

Lead researcher Dr Daniel Swerdlow, from University College London's Institute of Cardiovascular Science, said: "Commonly occurring variants in the gene encoding the same liver enzyme are associated with a lower LDL cholesterol.

"Incorporating information from up to 220,000 individuals, we found that these genetic variants were also associated with a higher weight and marginally higher type 2 diabetes risk.

"The effects were very much smaller than from statin treatment, but the genetic findings indicate that the weight gain and diabetes risk observed in the analysis from trials are related to the known mechanism of action of statins rather than some other unintended effect."

The findings are published in the latest online edition of The Lancet medical journal. Co-senior author Professor Naveed Sattar, of the University of Glasgow Institute of Cardiovascular and Medical Sciences, said: "Previous analyses have indicated that the cardiovascular benefits of statin treatment greatly outweigh the risk of new-onset type 2 diabetes.

"Nevertheless, many patients eligible for statin treatment would also benefit from lifestyle changes including increased physical activity, eating more healthily and stopping smoking."