About 2.5% of women and 12% of men would likely benefit from daily aspirin during a five-year period, based on an analysis of more than 245,000 heart-healthy New Zealand residents.
"In our study, we were able to predict for each individual, by taking into account their personal characteristics, their propensity to benefit from or be harmed by aspirin," said lead researcher Vanessa Selak, an epidemiologist with the University of Auckland in New Zealand.
"Using this personalized approach enabled us to identify specific individuals who were likely to benefit from aspirin after weighing up aspirin's effects on both cardiovascular events and serious bleeding," Selak continued.
That would seem to contradict new guidelines issued earlier this year by the American Heart Association (AHA) and the American College of Cardiology (ACC).
The two groups concluded that for older adults with healthy hearts, the risk of bleeding that comes with aspirin therapy outweighs any heart benefit.
"We used to say aspirin generally yes, occasionally no. Now we say aspirin generally no, occasionally yes," said Dr. Amit Khera, who served on the ACC/AHA committee that wrote the guidelines.
However, Khera feels this new study actually supports the new guidelines.
"This modeling exercise confirmed it's a very small group of the population that potentially could be eligible for aspirin," said Khera, a professor of cardiology with UT Southwestern Medical Center in Dallas.
These guidelines are not for people who've had an emergency regarding their heart health. Those people do derive overall benefit from aspirin, he said.
"If you've had a heart attack or stroke, continue to take your aspirin," Khera said.
But clinical trial data that emerged in 2018 showed that daily aspirin taken by people in good heart health only reduces their risk of heart attack and stroke by 11%, but increases their risk of dangerous bleeding by 43%, he added.
"I want to be clear that I'm not talking about nosebleeds," Khera said. "I'm talking about needing a transfusion, being hospitalized, bleeding in the brain. Big stuff."
To take a closer look at the potential benefits of aspirin, Selak and her colleagues studied hundreds of thousands of New Zealanders without heart disease who had their heart health risk calculated between 2012 and 2016.
The net effect of aspirin was calculated for each person by subtracting the number of heart emergencies the person was likely to have over five years from the number of major bleeds aspirin could cause.
After personalizing the risk-versus-benefit calculation, the researchers found that a select group of people would have a net benefit from aspirin if one heart health emergency that led to hospitalization or death was considered equal to one major bleed that led to hospitalization or death.
The percentages increased to 21% of women and 41% of men if a heart health emergency was considered equal to two major bleeds, the findings showed.
"This research suggests that decisions regarding the use of aspirin among people who have not already had a cardiovascular event should be made after undertaking a personalized prediction of cardiovascular benefits and bleeding harms from aspirin," Selak said.
That's already standard procedure under the U.S. guidelines, Khera said.
"No one is saying aspirin doesn't help. It just doesn't help as much as we used to think, and you have to appreciate the bleeding penalty," Khera said. "Some people are more concerned about heart attack risk and are willing to pay the bleeding penalty, especially if they've never had any bleeding problems. It's still OK for them to consider it."
Both Selak and Khera recommended that people talk with their doctor about the risks and benefits before starting to take daily aspirin. Calculators are available that help physicians weigh your risk of heart attack and stroke against the risk of bleeding.
"In many ways, people think of aspirin as this benign thing because it's been around for centuries. Anybody can get it over the counter," Khera said. "But if you're going to take it every day for the next couple of decades, there are definite penalties to it."
The new study was published online Sept. 17 in the Annals of Internal Medicine.