People without heart disease may lower their risk of having a heart attack or stroke by taking a daily aspirin, but they also increase their risk of experiencing severe and potentially fatal internal bleeding, according to a major new study published this week in the Journal of the American Medical Association (JAMA).
Aspirin, which thins the blood, is often prescribed to reduce cardiovascular risks for individuals who have previously had a heart attack or stroke. That’s because the drug’s benefits (preventing blood clots) are believed to outweigh its known risks (causing bleeding ulcers in the gastrointestinal tract or hemorrhaging in the brain).
Whether the benefits also outweigh the risks for people without a history of heart attack or stroke has been a matter of debate, however.
This new study is an attempt to get some evidence-based clarity on the issue.
Analyzing multiple studies
The study, conducted by scientists at King’s College London and Imperial College London, is a systematic review and meta-analysis of 13 randomized clinical trials (considered the gold standard of medical research). Each trial compared aspirin use with no aspirin (either a placebo or no treatment). The trials involved 164,225 participants aged 53 to 74 (mean age: 62) with no known history of heart disease.
The participants were followed for at least five years.
An analysis of all that data showed that the use of aspirin was associated with a 0.38 percent decrease in the absolute risk of heart attacks and ischemic strokes (ones caused by blood clots). As the study’s authors point out, that means that 265 individuals would need to take aspirin for five years to prevent one heart attack or stroke.
The analysis also revealed that aspirin was associated with a .47 percent increase in the absolute risk of severe internal bleeding. That means that for every 210 people treated with aspirin for five years, one would have a major bleeding episode.
Aspirin use was found to have no effect on new cancer diagnoses or cancer deaths. That finding is significant as there has been conflicting evidence about whether aspirin helps with the treatment of colorectal and other types of cancer.
“This study demonstrates that there is insufficient evidence to recommend routine aspirin use in the prevention of heart attacks, stroke and cardiovascular deaths in people without cardiovascular disease,” said Dr. Sean Zheng, the study’s lead author, in a released statement.
“There has been more uncertainty surrounding what should be done in patients who are at higher risk of cardiovascular disease and in patients with diabetes,” he added. “This study shows that while cardiovascular events may be reduced in these patients, these benefits are matched by an increased risk of major bleeding events.”
Limitations and implications
The study has several limitations. Most notably, although most of the clinical trials in the study used daily aspirin doses between 75 milligrams and 100 milligrams, some used doses as low as 50 milligrams or as high as 500 milligrams.
Doctors do not typically prescribed daily doses higher than 100 milligrams for the prevention of heart attack and stroke, primarily because of concerns about bleeding.
The researchers did, however, do a separate “sensitivity analysis” of the findings from only the trials that used doses of 100 milligrams or less. The results of that analysis turned out to be similar to those of the overall analysis, including the finding of an increased risk of major bleeding outcomes.
In Europe, including Great Britain, medical guidelines do not recommend daily aspirin for the primary prevention of heart attacks and strokes (in other words, for use among people without a history of those cardiovascular events). That is not the case in the United States. The U.S. Preventive Services Task Force recommends, for example, that people aged 50 to 59 take aspirin if they have a 10 percent or greater risk of having a heart attack or stroke over the next decade and if they don’t have a higher-than-average risk of bleeding.
No one should stop taking aspirin prescribed by their doctor on the basis of this one study. But its findings underscore that the decision to take aspirin needs to be a shared one between patient and doctor.
“Aspirin use requires discussion between the patient and their physician, with the knowledge that any small potential cardiovascular benefits are weighed up against the real risk of severe bleeding,” said Zheng.
FMI: You’ll find an abstract of the study on the JAMA website, but the full study is behind a paywall.