In the new systematic review from King's College London and Imperial College London, researchers examined data on 164,225 participants without diagnosed heart disease and found the use of aspirin was associated with an 11 percent lower risk of cardiovascular events counterbalanced by increased risks of major internal bleeding. The findings were published in the Journal of the American Medical Association.
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According to a 2014 edition of the Harvard Heart Letter, while aspirin can lower the blood's ability to clot, it "also inhibits helpful substances that protect the stomach's delicate lining," which can lead to bleeding in the stomach and intestines. Serious gastrointestinal bleeding can destabilize a patient's vital signs.
Compared to those who didn’t take aspirin, aspirin use was associated with a 43 percent increase of major bleeding events. In other words, researchers wrote, approximately one in 200 people treated with aspirin would experience significant bleeding.
To prevent a single heart attack, stroke or cardiovascular death, approximately 250 patients needed to be treated with the drug for five years. Additionally, the study found “no overall association between aspirin use and incident cancer or cancer mortality.”
"While aspirin is known to reduce risks for those who have previously suffered strokes and heart attacks, the evidence of the role of aspirin in the initial prevention of cardiovascular events, is uncertain," researchers wrote in a university news release.
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"This study demonstrates that there is insufficient evidence to recommend routine aspirin use in the prevention of heart attacks, strokes and cardiovascular deaths in people without cardiovascular disease," lead author Dr. Sean Zheng said in a statement.
Even when it comes to patients at heightened risk of heart disease or diabetes, there's still too much uncertainty, according to Zheng. "While cardiovascular events may be reduced in these patients, these benefits are matched by an increased risk of major bleeding events," he said.
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In Britain, aspirin is not recommended for prevention of heart disease. But the United States Preventive Services Task Force recommends low-dose aspirin use "for the primary prevention of cardiovascular disease (CVD) and colorectal cancer in adults aged 50 to 59 years who have a 10 percent or greater 10-year CVD risk, are not at increased risk for bleeding, have a life expectancy of at least 10 years."
Whether the potential benefits of aspirin use are worth it against the “real risk of severe bleeding” should be part of an important discussion between patients and their doctors, Zheng said.
Read the full study at jamanetwork.com.