Jan. 12, 2012 -- Many people who have never had a heart attack or stroke take an aspirin every day to lower their risk for these events.

While some may benefit, for many others the benefits appear to be outweighed by an increased risk for potentially serious and even life-threatening bleeding, a new study shows.

Researchers analyzed data from nine large studies, including three published since 2007, which followed participants for an average of six years.

Aspirin therapy was not associated with a reduction in deaths due to heart attack and stroke, but it was associated with a significant increase in risk for bleeding, says researcher Kausik K. Ray, MD.

“The benefits of aspirin therapy are clear for patients who have a history of heart attack or stroke,” Ray says. “This is not the case, however, for patients who may have risk factors for [heart disease and stroke] but have no such history.”

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The analysis included more than 100,000 people who had never had a heart attack or stroke and participated in trials in the United States, Europe, and Japan.

About half the participants took either low-dose (75-100 milligrams) or full-strength (300-500 milligrams) aspirin daily or every other day. Everyone else took placebos.

Over an average follow-up of six years, about 1,500 nonfatal and 500 fatal heart attacks and about 1,500 fatal and nonfatal strokes were recorded.

Aspirin therapy was associated with a 10% decrease in heart attacks and strokes, which was largely explained by a reduction in nonfatal heart attacks, Ray says.

But patients on the aspirin regimens were also 31% more likely to experience significant bleeding.

Aspirin therapy has been shown in several previous studies to be associated with a reduced risk of death from cancer, but the association was not seen in the new analysis, which was published in the Archives of Internal Medicine.

Ray and colleagues from the Cardiac and Vascular Sciences Research Center at St. George’s University of London conclude that for many patients with no history of heart attack or stroke, aspirin adds little to strategies proven to reduce heart disease and stroke risk.

These strategies include drug treatments that regulate blood pressure and cholesterol, and lifestyle changes such as smoking cessation, weight loss, and regular exercise.
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The researchers add that more study is needed to identify patients who have not had heart attacks or strokes for whom the benefits of aspirin therapy outweigh the risks.

“In the absence of such information, a reappraisal of current guidelines appears to be warranted, particularly in countries where a large number of otherwise healthy adults are prescribed aspirin,” the researchers write.

Cardiologist Samia Mora, MD, of the Brigham and Women’s Hospital and Harvard Medical School, says patients need to discuss their individual risk for heart attack and stroke with their doctor before embarking on an aspirin therapy regimen.

In an editorial published with the paper, Mora writes that for low-risk patients the data “argue against the routine use of aspirin for primary prevention of [heart disease and stroke].”

“Right now, we really need to assess risk on a case-by-case basis,” she says. “For someone with a strong family history of heart attack or stroke, for example, a daily aspirin may be warranted even in the absence of other risk factors.”

New York University cardiologist Nieca Goldberg agrees that patients should always discuss their individual risks with their doctor before starting aspirin therapy.