Cholesterol-lowering drugs can benefit even apparently healthy people with no previous history of heart disease, a study has found.
The findings suggest everyone over a certain age should qualify for statin therapy, say experts.
Many doctors already take the pills, which lower levels of cholesterol in the blood.
But NHS prescriptions of the drugs are restricted to patients judged to have at least a 20 per cent risk of a "major vascular event" in the next 10 years.
A major vascular event can include a non-fatal heart attack, stroke, or surgery to bypass or unblock damaged arteries.
The authors of the new research say the findings suggest international treatment guidelines for statins should be reconsidered.
To conduct the "meta-analysis" study, they pooled together data on 175,000 patients who took part in 27 separate randomised trials.
Participants were grouped into one of five categories of five-year major vascular event risk.
Statins were found to reduce the risk of serious vascular events by more than a fifth (21 per cent) for each unit reduction in levels of harmful cholesterol.
The pattern was repeated in each of the five groups studied, including those people at lowest risk.
In individuals where the five-year chance of a major event was less than 10 per cent, the already small risk was significantly lowered, even in people with no history of vascular disease.
This was mainly due to reduced numbers of heart attacks and surgical operations.
The findings appear in the latest online edition of The Lancet medical journal.
Researchers measured millimoles per litre (mmol/L) reductions of "bad" low density lipoprotein (LDL) cholesterol in the blood.
They found that every one mmol/L lowering of LDL cholesterol reduced the risk of major vascular events by 21 per cent "irrespective of age, sex, baseline LDL cholesterol or previous vascular disease, and of vascular and all-cause mortality".
In people with a five-year risk of major vascular events lower than 10 per cent, each unit lowering of LDL cholesterol reduced event incidence by about 11 per 1,000 individuals over five years.
The authors, led by Professor Colin Baigent, from Oxford University, wrote: "This benefit greatly exceeds any known hazards of statin therapy.
"Under present guidelines, such individuals would not typically be regarded as suitable for LDL-lowering statin therapy. The present report suggests, therefore, that these guidelines might need to be reconsidered."
The research found no evidence that statins increased cancer incidence or deaths from non-vascular causes.
In an accompanying article, two UK experts said more affordable ways of identifying patients suitable for statins were needed.
Professor Shah Ebrahim and Dr Juan Casas, both from the London School of Hygiene and Tropical Medicine, wrote: "Because most people older than 50 years are likely to be at a greater than 10 per cent 10-year risk of CVD (cardio-vascular disease), it would be more pragmatic to use age as the only indicator of statin prescription.
"This approach would avoid the costs, ranging from £7 to more than £700 per patient screened, of vascular screening checks recently implemented in the UK."
June Davison, senior cardiac nurse at the British Heart Foundation, which part-funded the study, said: "Those who already have heart disease, or are at high risk, are offered statins because it's well established they help to lower cholesterol and reduce the risk of heart disease.
"This large-scale research found even people at low risk of heart disease could benefit from statin therapy. The findings will help to inform policy and treatment guidelines in the future."
Other research published in The Lancet challenges the widely-held view that raising levels of "good" cholesterol can reduce the risk of heart attacks.
Scientists looked at heart attack rates in people with naturally higher levels of high-density lipoprotein (HDL) cholesterol.
Analysis of data from 20 studies involving more than 100,000 people found no evidence that elevated HDL reduced the chances of having a heart attack.
Lead author Dr Sekar Kathiresan, from Harvard Medical School in the US, said: "If an intervention such as a drug raises HDL cholesterol, we cannot automatically assume that risk of myocardial infarction (heart attack) will be reduced."
A Department of Health spokesman said: "We keep all new research under consideration. Nice (National Institute for health and Clinical Excellence, which assesses the cost effectiveness of NHS treatments) regularly reviews its published guidance in order to take account of new evidence."