Cholesterol-lowering drugs slightly reduce the risk of heart attack and stroke in people with no history of the disease but their overall risk of death does not fall, a Canadian-led review concludes.

Statins are a bestselling family of drugs that lower levels of artery-clogging "bad" cholesterol, called LDL or low-density lipoprotein. The medications are thought to help ward off heart attacks and strokes.

In Monday's issue of the Archives of Internal Medicine, Dr. Paaladinesh Thavendiranathan of the University of Toronto and colleagues analyzed the results of seven previously published clinical trials on the benefits of statins.

The team concluded statins help lower the risk of heart attacks and strokes in people at risk from heart disease or high cholesterol. But for otherwise healthy adults, the benefits are limited.

On average, an adult has a nearly six per cent chance of having a heart attack or stroke over a 4.3-year period. Statins reduced that risk to four per cent, the researchers said.

"Therefore, 60 patients would need to be treated for an average of 4.3 years to prevent one major coronary event," Thavendiranathan and colleagues wrote.

To prevent one stroke, 268 people would need to take statins, and to prevent one nonfatal heart attack, 61 would need to take the pills.

Rates of death from cardiovascular disease and other causes were about the same in the statin and control groups.

Statins are expensive and other therapies may work to reduce the risk, the researchers said in calling for more research to clarify the cost-effectiveness of statin therapy for people at intermediate risk.

Drug-free ways such as improving your diet and exercising more also lower blood cholesterol levels, studies show.