Taking an aspirin a day appears to increase a person's risk of dangerous gastric bleeding as much as it decreases their risk of heart attack or stroke, researchers have found.
"We don't have good evidence that, for healthy people, the benefits of long-term aspirin exceed the risks by an appropriate margin," said lead researcher Colin Baigent, of the Clinical Trial Service Unit at Oxford University.
Health experts have been recommending for more than a decade that people considered at increased risk of cardiovascular disease (due to high blood pressure or cholesterol, obesity, advanced age or other risk factors) take one aspirin pill per day, as the medicine has been clinically shown to reduce the risk of serious vascular events in those people. This strategy -- treating people with no symptoms of heart disease -- is known as "primary prevention."
A serious vascular event is a heart attack, stroke or cardiovascular death.
Many health agencies have shied away from issuing official recommendations, however, such as the United Kingdom's National Institute for Health and Clinical Excellence.
"There is no definitive guidance," said Steve Field, chair of the Royal College of
General Practitioners, "and it makes it bewildering when you have a series of papers which then hint it would be beneficial to take aspirin."
According to Field, many patients are attracted to aspirin as a way to stave off heart attacks because the over-the-counter pills are very inexpensive.
But the findings of the newest study, published in The Lancet, suggest that the risks of aspirin match the benefits in cases of primary prevention. Only in patients who have already had a heart attack or stroke does the benefit appear to outweigh the risk.
"This important study does suggest people shouldn't take aspirin unless indicated by disease," Field said.
While primary prevention recommendations have been based on estimated risks and benefits of aspirin treatments, the current study actually analyzed the effects of the treatment in 22 studies involving more than 100,000 participants. Six of the studies involved 95,000 people with a low to average risk of heart attack or stroke -- the typical primary prevention population -- and the other 16 involved 17,000 people who had already experienced at least one heart attack or stroke.
In both groups, taking an aspirin a day decreased the risk of a serious vascular event by about 20 percent in both men and women. It also increased the risk of gastric bleeding by about 33 percent.
In the lower-risk group, this came out to five fewer serious vascular events each year per 10,000 people taking a daily aspirin. It also meant three extra cases of gastric bleeding, however, and one extra stroke caused by internal bleeding. This led the researchers to conclude that the risks and benefits of the treatment were equivalent.
The results might be explained by the fact that people at increased risk of cardiovascular disease also tend to be at higher risk of gastric bleeding.
Because people who had already experienced a heart attack or stroke had such a heightened risk of further vascular events, however, the benefits exceeded the risks in that group -- roughly 150 serious vascular events prevented per year for every 10,000 people treated, with the same three extra gastric bleeds and one stroke from bleeding.
"Aspirin is of clear benefit for people who already have cardiovascular disease, but the latest research does not seem to justify general guidelines advocating the routine use of aspirin in all healthy individuals above a moderate level of risk for coronary heart disease," the researchers concluded.
"It is better for doctors to weigh up the benefit and risk of prescribing aspirin on an individual basis, rather than develop a blanket guideline suggesting everyone at risk of heart disease is routinely given aspirin," said Ellen Mason of the British Heart Foundation.