WASHINGTON (AFP) - New recommendations to expand the use of cholesterol-lowering medication to millions of adults to reduce heart attacks and strokes overestimated risks faced by that population, according to a new study.

An updated clinical guide released by the American College of Cardiology (ACC) and the American Heart Association (AHA) last week set new guidelines on who should take cholesterol-lowering drugs called statins.

The report said some 33 million Americans should be prescribed the medication.

But two researchers from Harvard University's medical school have concluded that the guidelines exaggerate the risks, recommending statins for too many people.

"It is possible that as many as 40-50 per cent of the 33 million middle-aged Americans targeted by the new ACC/AHA guidelines for statin therapy do not actually have risk thresholds" that exceed the threshold suggested for treatment, researchers Mr Paul Ridker and Ms Nancy Cook said in the British medical journal The Lancet.

Now, this kind of medicine is prescribed only to reduce high levels of so-called bad cholesterol, the main cause of arteriosclerosis, to bring it back down to an acceptable level.

Risk factors cited by the ACC include age, presence of diabetes, high blood pressure, high levels of bad cholesterol, smoking and ethnicity. Blacks are particularly vulnerable.

But by applying the calculation formula used by the ACC and AHA to five groups of people, the two Harvard researchers concluded that the formula overestimated observed risks by 75 to 150 per cent.