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Taking aspirin can reduce the risk of a second heart attack or stroke, but worldwide, many people aren't taking it.
CNN  — 

For adults who have survived a heart attack or stroke, taking aspirin regularly may reduce the risk of another cardiovascular event. But a new study suggests that less than half of these cardiovascular disease patients around the world are using aspirin to prevent a new event.

Among people with a history of cardiovascular disease who were surveyed in the new study, only about 40% reported taking aspirin to prevent another heart attack, stroke or cardiovascular event.

The proportion of patients using aspirin to reduce the risk of a secondary event varied by country, however, ranging from 16.6% in low-income countries such as Afghanistan, Benin and Ethiopia to 65% in high-income countries such as Czechia, the UK and the US, according to the study, published Tuesday in the medical journal JAMA.

“We had hoped that the rates of aspirin use for secondary prevention would be much higher. Particularly I think, overall, globally, there has been an emphasis on improving cardiovascular health, and one of the efforts is to improve use of some of these evidence-based medications,” said Dr. Sang Gune Yoo, an author of the study and a cardiovascular disease fellow in the cardiovascular division at Washington University School of Medicine in St. Louis.

Secondary prevention refers to using aspirin to reduce the risk of a second or additional heart attack or stroke. It’s different from primary prevention — using aspirin to reduce the risk of a first heart attack or stroke.

Unlike with primary prevention, where the risk-benefit ratio of aspirin is not as clear, available research on secondary prevention shows that the benefits of taking aspirin far outweigh the risks for people who have had a heart attack or stroke.

The World Health Organization has a target for at least 50% of those eligible people to receive some type of drug therapy and counseling to prevent heart attacks and strokes.

Cardiovascular diseases are the leading cause of death worldwide, claiming about 18 million lives each year, according to WHO. It’s estimated that more than 4 in 5 cardiovascular disease deaths are due to heart attacks and strokes. Because aspirin helps thin the blood, that can help reduce the risk of blockages in the arteries that may cause a heart attack or stroke.

“What our study is highlighting is that despite efforts being put in to improve cardiovascular health globally, aspirin continues to be underused in secondary preventions,” Yoo said. “Given that it continues to be the number one cause of mortality, it’s very important that health systems and countries strategize ways to improve uptake of aspirin use as well as other cardiovascular medicines.”

Where aspirin is used

For the new study, Yoo and his colleagues from Washington University, the University of Michigan and other institutions around the world analyzed data from 51 countries where surveys were conducted between 2013 and 2020. Seven of the surveys were conducted in low-income countries, 23 in lower-middle-income countries, 14 in upper-middle-income countries and seven in high-income countries.

The surveys included responses from more than 124,500 adults ages 40 to 69 who reported their history of cardiovascular disease and aspirin use. More than 10,500 of them reported having cardiovascular disease.

When the researchers examined aspirin use among people with a history of cardiovascular problems, they found that in low-income countries, 16.6% were taking aspirin to prevent another event; in lower-middle-income countries, it was 24.5%; in upper-middle-income countries, it was 51.1%; and in high-income countries, it was 65%.

“To our knowledge, the current study provides the most extensive and updated estimates of the worldwide use of aspirin for secondary prevention of CVD,” the researchers wrote, using the abbreviation for cardiovascular disease.

“Our findings revealed marked inequities worldwide, as illustrated by 4-fold greater aspirin use for secondary CVD prevention in high-income compared with low-income countries,” they wrote. “None of the 30 low-income or lower-middle-income countries in our sample achieved the WHO target that at least 50% of eligible individuals with a history of CVD take aspirin. Only about half of upper-middle-income and high-income countries included in our analysis achieved this target.”

Yoo said that the study did not analyze why there were such differences in the low use of aspirin, and he said more research is needed to determine whether it is related to access, to providers not recommending aspirin or other factors.

Among people with a history of cardiovascular disease, there was more aspirin use in those who were older, who were male, who had higher levels of education and who lived in urban areas, the researchers found.

The researchers say their findings suggest that aspirin is underused as an inexpensive tool for the secondary prevention of cardiovascular disease events globally. In the United States, low-dose aspirin is available over-the-counter and can cost as little as $5 to $10.

Who should take aspirin?

“We live in a time where we have incredible, well-established therapies that are effective at reducing the risk of cardiovascular events, and despite the plethora of evidence supporting its use, we suboptimally use many lifesaving medicines. And this is just one example,” said Dr. Jeffrey Berger, director of the Center for the Prevention of Cardiovascular Disease at NYU Langone Heart in New York, who was not involved in the new study.

He added that many people with cardiovascular disease who could benefit from regular exercise and a healthy diet also do not adhere to those practices, just as they may not take aspirin for secondary prevention.

“Aspirin has been around for more than a century. It has been shown to be effective at lowering the risk of a cardiovascular event by close to 40 years, over four decades or so. I think people forget about the overwhelming data supporting its use,” said Berger, who is also an associate professor at the NYU Grossman School of Medicine.

“Unfortunately, there is sometimes a misunderstanding of patients and health care providers,” he said. “I think there is a lot of uncertainty over who should be on aspirin for the prevention of a first heart attack or stroke.”

The US Preventive Services Task Force recommends against adults 60 and older starting on low-dose aspirin for the primary prevention of cardiovascular disease, and for people ages 40 to 59 who have a 10% or greater risk of cardiovascular disease over 10 years, it leaves the decision up to doctors and patients. But that’s much different from someone who has a history of cardiovascular disease taking aspirin to prevent a second heart attack or stroke.

“Aspirin is a double edge sword,” Dr. Erin Michos, associate director of preventive cardiology at Johns Hopkins Medicine in Baltimore, wrote in an email.

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“It can reduce the risk of thrombosis but this comes at the expense of increased risk of bleeding, so it has a narrower therapeutic window. A delicate balance between thrombosis risk and bleeding risk,” said Michos, who was not involved in the new study.

“People who have already had a cardiovascular event such as a heart attack, coronary revascularization or stroke are at greater risk for a recurrent vascular event, so they are at higher vascular risk and thus derive a greater net benefit from aspirin,” she said.

For someone who doesn’t have cardiovascular disease, the absolute risks of vascular events like heart attack or stroke are lower, but the risks of bleeding are still comparable.

So for most healthy adults who would take aspirin for primary prevention, “aspirin might cause more harm than benefit,” Michos said. “However it seems from the current article that worldwide, aspirin is still sorely underutilized in secondary prevention, particularly in low-income countries.”