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Aspirin for prevention: Know your risk of heart attack or stroke

In this installment of "Aspirin for prevention," physician-researcher Randall Stafford provides tips to calculate the risk of heart disease or stroke, to inform decisions about taking aspirin preventatively.

Editor's note: In March 2019, new guidelines were released that recommend more limited use of aspirin for prevention of cardiovascular disease. This is the second installment of a revised blog series.

In the first post of this series, I discussed the possible benefits and harms of taking low-dose aspirin. While aspirin can prevent heart attacks, strokes and some cancers, it can cause stomach and brain bleeding. If someone has a history of a heart attack or stroke, then he or she should definitely take aspirin to prevent a recurrence.

But how does someone like Fred, the slightly overweight 58-year-old we met last time, who is wondering whether he should take aspirin, determine his or her risk?

There are three alternatives:

  • If you have known disease of your arteries (see below), then you are automatically at high risk.
  • If you're a woman under 60 or a man under 50, then you are likely to be low risk unless you smoke or have diabetes.
  • Otherwise you need to use an online risk estimator to determine your risk.

Known artery disease (atherosclerosis)

People known to have problems with cholesterol in their arteries (atherosclerosis) should take aspirin or an alternative anti-blood clotting medication. If you have had a history of heart attack, angina, bypass surgery or a stent, this indicates problems with the arteries providing blood to the heart muscle. If you have had a stroke or a mini-stroke (transient ischemic attack), this means that your brain arteries (cerebral arteries) are damaged. These problems or damage to other arteries in the body indicate that you should also take aspirin or an alternative.

No known artery disease

Except for smokers and those with diabetes, younger women (under 60) and men (under 50) are unlikely to benefit from aspirin.

If you're older, aspirin may or may not be beneficial. It depends on your future risk of having a heart attack or stroke. You can determine the chances of having problems in the next ten years using an online risk calculator (of the many available, I like this one from the American College of Cardiology). In addition to finding out whether aspirin is right for you, knowing this risk can be useful in treating high blood pressure and high cholesterol.

Let's use this calculator to figure out Fred's risk. To prepare for a doctor's visit to discuss aspirin, he had some blood tests performed. These showed a fasting blood glucose of 98, total cholesterol of 214, and high-density lipoprotein (HDL) of 44. His average home blood pressures are 135/82. He's on a blood pressure medication. And since his fasting blood sugar is under 126, he doesn't have diabetes. He continues to smoke cigarettes.

Based on this information, we get back the number 20% from the calculator.

What does this mean? It indicates that in the next ten years, there's a 1 in 5 (20%) chance that Fred will have a stroke or heart attack. While this number may not seem large, it should cause concern. By comparison, if Fred were 10 years younger, were a woman and didn't smoke, then the risk would be only 2.7% (or 1 in 37).

Taking action based on the calculated risk

What do you do with the risk information?  A simple rule of thumb is that a risk above 10 percent indicates that:

  • You're at higher risk for cardiovascular disease and should discuss the potential harms and benefits of starting aspirin with your doctor
  • You should be treated with a moderate to high-intensity dose of a statin medication for cholesterol
  • Your blood pressure should be treated through drugs or health behavior changes to less than 130/80.

In the next piece, we will talk about some additional necessary steps before you start aspirin, including things to discuss with your health care provider. Calculating your risk is an important first step in taking care of your health. What's yours?

This is the second in a revised series of three blog posts on aspirin for prevention. 

Randall Stafford, MD, PhD, a professor of medicine and director of the Program on Prevention Outcomes and Practices, is a primary care internal medicine physician at Stanford. He is developing practical strategies to improve how physicians and consumers approach chronic disease treatment and prevention. Additional information about the preventive use of aspirin is available at

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