One or two baby aspirins a day -- not the standard dose of regular strength adult aspirin -- are enough to lower the risk of heart attack or stroke for those at high risk.
The study also found that aspirin can help a wider range of people with potential heart trouble.
Aspirin is the cornerstone of blood thinning treatment for people who have had a heart attack or stroke but is not normally used for those who suffer ailments that put them at risk for those conditions, such as diabetes, chest pain, irregular heart beat and diseased leg arteries.
The latest research found that aspirin reduced the risk of heart attack or stroke, or death from those events, by 25 percent -- even when the patients had not had a heart attack or stroke previously.
The findings come from an analysis that combines evidence accumulated over the years on the effectiveness of aspirin and its alternatives in staving off heart trouble. Coordinated by scientists at Oxford University in England, it encompassed 287 studies involving more than 200,000 people.
Most doctors and heart specialists use a dose of 325 milligrams of aspirin per day when applying it as a blood thinner. That's the dose in a regular strength adult aspirin tablet.
The latest analysis shows that 75 to 150 milligrams works just as well, with less chance of internal bleeding.
In the United States, baby aspirin, also available as low-dose adult aspirin, contains 81 milligrams. In Europe aspirin comes in doses of 75 milligrams and 300 milligrams.
The study concluded that most healthy people, who have less than a 1 percent chance of having a heart attack or stroke, should not regularly take aspirin to prevent heart trouble.
Low doses of aspirin cut the risk of heart attack and stroke among people at high risk.
Although patients are getting aspirin if they have had a heart attack or previous stroke, there is a vast range of patients out there who haven't yet had such an event but who can be identified as high-risk.
Research has long attributed such benefits to antiplatelet drugs like aspirin, which prevent blood platelets from sticking together and forming clots. Blood clots can block blood flow to the heart and trigger a heart attack, or obstruct arteries to the brain and potentially cause an ischemic stroke -- the most common type of stroke.
In the new study, UK researchers reviewed 287 trials of treating high-risk individuals with antiplatelets such as aspirin. The 135,000 patients involved either had cardiovascular disease or conditions that predisposed them to heart attack and stroke, such as diabetes and peripheral artery disease, which is characterized by blockages in arteries supplying the legs and feet.
The investigators, all part of a team known as the Antithrombotic Trialists' Collaboration (ATC), looked at whether the antiplatelets cut patients' risk of heart attack, stroke and death from a cardiovascular cause.
They found that overall, any antiplatelet therapy led to a one-third drop in heart attack risk, while the risk of non-fatal stroke fell by a quarter and cardiovascular death risk declined by one sixth.
Aspirin was the most widely studied antiplatelet. Based on this review, the evidence "supports daily doses of aspirin in the range of 75-150 mg for the long-term prevention of serious vascular events in high risk patients.
British Medical Journal January 12, 2002;324: 59-60
British Medical Journal January 12, 2002;324:71-86