Taking cholesterol-lowering statin drugs can raise the risk of developing Type 2 diabetes by 30 percent in some vulnerable people, say scientists from Albert Einstein School of Medicine.

The study was a follow-up to an earlier study which investigated whether or not modest weight loss or treatment with metformin — a diabetes medication that helps control blood sugar levels — could reduce the risk of Type 2 diabetes in people at high risk.

For the study, obese people were given standard advice on healthy eating and exercise, and were randomly assigned to either an intensive lifestyle program, treatment with metformin, or a dummy drug (placebo).

Their blood fats and blood pressure were measured annually. Blood glucose was measured twice a year, at which point new statin treatment was recorded.

The most commonly prescribed statins were simvastatin (40 percent) and atorvastatin (37 percent). The likelihood of being prescribed a statin drug rose substantially after a diagnosis of diabetes.

At the beginning of the trial fewer than 4 percent of volunteers were taking statin drugs, but usage gradually increased so that by the end of the 10-year study period, about a third of patients were taking them.

When treatment groups were combined, taking a statin was associated with a 36 per cent heightened risk of being diagnosed with Type 2 diabetes, compared to those who had not been prescribed these drugs.

This risk fell slightly to 30 percent after taking account of the clinical criteria used to determine the need for statins.

After analyzing all risk factors for developing diabetes, statin use was itself associated with an increased risk of being diagnosed with diabetes, regardless of which treatment group the participants had been in during the trial.

To find out if the strength of the statin had any bearing on the risk of developing diabetes, the researchers grouped the drugs into low (pravastatin, lovastatin, fluvastatin) or high potency (atorvastatin, simvastatin, rouvastatin, cerivastatin).

They found no link between the potency of the statin used and diabetes risk, nor between the reduction in low density lipoprotein or "bad" cholesterol.

The researchers theorize that statins contribute to the development of diabetes by impairing the production of insulin, the hormone that lowers blood glucose.

The study was published in the journal BMJ Open Diabetes Research & Care.