A new study claims that a regular dose of aspirin is more likely to do harm than benefit healthy people with no history of cardiovascular disease (CVD), due to the increased risk of internal bleeding.

Researchers at St George's University of London (SGUL; United Kingdom), Addenbrooke's Hospital (Cambridge, UK), and other institutions analyzed data from nine clinical trials covering over 100,000 healthy people. Only placebo-controlled trials with at least 1,000 participants each were included, reporting on CVD, nonvascular outcomes, or death. Three authors abstracted the data, and study-specific odds ratios (ORs) were combined using random-effects meta-analysis. Risks versus benefits were evaluated by comparing CVD risk reductions with increases in bleeding.

The results showed that during a mean follow-up of six years, aspirin treatment reduced total CVD events by 10%, driven primarily by reduction in nonfatal myocardial infarct (MI). There was no significant reduction in CVD death or cancer mortality, but there was increased risk of nontrivial bleeding events; overall, the results showed that while one CVD was prevented for every 120 people, one in 73 developed significant internal bleeding over the same period. Significant heterogeneity was observed for coronary heart disease (CAD) and bleeding outcomes, which could not be accounted for by major demographic or participant characteristics. The study was published online on January 9, 2012, in the Archives of Internal Medicine.

“Despite important reductions in nonfatal MI, aspirin prophylaxis in people without prior CVD does not lead to reductions in either cardiovascular death or cancer mortality,” concluded senior author Professor Kausik Ray, MD, of SGUL, and colleagues. “Because the benefits are further offset by clinically important bleeding events, routine use of aspirin for primary prevention is not warranted and treatment decisions need to be considered on a case-by-case basis.”

Acetylsalicylic acid has an antiplatelet effect by inhibiting the production of thromboxane, which under normal circumstances binds platelet molecules together to create a patch over damaged walls of blood vessels. Because the platelet patch can become too large and also block blood flow both locally and downstream, aspirin is also used for primary prevention to help prevent heart attacks, strokes, and blood clot formation in people at high risk. It has also been established that low doses of aspirin may be given for secondary prevention immediately after a heart attack to reduce the risk of another MI or of the death of cardiac tissue.

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