Evidence is lacking to support widespread use of cholesterol-lowering drugs among the "worried well", a study has found.

Statins are highly effective at reducing blood cholesterol levels and are routinely given to heart patients.

But some GPs also advocate their wider use for at-risk patients, and a number of healthy doctors take the pills themselves on a precautionary basis.

Low dose statins are also available over-the-counter at pharmacies without prescription.

The new findings from a review of 14 statin trials found that the drugs did reduce death rates and helped prevent heart attacks and strokes.

However the authors, who sifted through data on more than 34,000 patients, concluded there was insufficient evidence to justify widespread use of statins in people with no previous history of heart disease.

They stressed the need for caution when balancing the risks and benefits of statins - and questioned the validity of drug company-sponsored trials.

Lead researcher Dr Fiona Taylor, from the Cochrane Heart Group at the London School of Hygiene and Tropical Medicine, said: "It is not as simple as just extrapolating the effects from studies in people who have a history of heart disease.

"This review highlights important shortcomings in our knowledge about the effects of statins in people who have no previous history of CVD (cardiovascular disease). The decision to prescribe statins in this group should not be taken lightly."

The findings are published today in the Cochrane Library, which produces comprehensive reviews of drug trial evidence.

The researchers pointed out that all but one of the studies they looked at were industry-sponsored.

Dr Taylor added: "We know that industry-sponsored trials are more likely to report favourable results for drugs versus placebos (inactive dummy drugs), so we have to be cautious about interpreting these results.

"The numbers eligible for treatment with statins are potentially great so there might be motivations, for instance, to stop trials earlier if interim results support their use."

One large trial called Jupiter, studying the drug rosuvastatin, was halted after just two years because the "endpoint" results it had obtained in that time were considered sufficient.

"Early stopping of trials is of particular concern because, in this and other situations, early stopping may lead to an over-estimation of treatment effects, particularly when the number of events is small," the Cochrane researchers wrote.

Selective reporting and the inclusion of people with heart disease in many trials made the evidence "impossible to disentangle", they said.

Statins generally have mild side-effects but in rare cases can lead to a serious muscle-wasting condition.

The researchers said that for people at high risk of heart disease it was likely the benefits of statins outweighed any harm they might cause. But they pointed out that the long-term effects of the drugs, spanning decades, remained unknown.

Amy Thompson, senior cardiac nurse at the British Heart Foundation, said: "This systematic review echoes what we already know - that statins have huge benefits for people with heart and circulatory disease, or those who are high risk, as they help to reduce the risk of heart disease including heart attacks.

"It is still unclear whether statins provide any real benefits for people without heart and circulatory disease and who are at low risk of developing it. There is little to suggest that statins should be prescribed routinely for these people. However, it is good practice for health professionals to consider each person individually.

"As well as lowering your cholesterol, there are a number of ways that you can help reduce your risk of heart disease. Making healthier lifestyle choices, such as eating well and getting regular exercise, will help to keep your heart healthy.

"If you are over 40, the best way of finding out your own risk of heart disease is to ask for a 'health check' at your GP surgery."