Millions of people who have hypertension, high blood cholesterol, diabetes, or a family history of premature heart disease—or who have already had a heart attack—have been advised by their doctors to take low-dose aspirin. Just one-quarter adult tablet (81 milligrams, sometimes called a "baby" aspirin) daily reduces the tendency of the blood to clot, thus helping to ward off heart attack and stroke. Some people take half a tablet (162 milligrams) every other day or daily. Aspirin therapy has probably saved thousands of lives. If you are on it, you may have noticed recent headlines and TV news reports claiming that for some people, aspirin doesn’t work. What’s going on here?
As aspirin therapy has become commonplace, scientists have learned more about it. While low-dose aspirin reduces the risk of a first heart attack in middle-aged men by 44%, for example, it is not a cure-all. Some people on aspirin therapy have a heart attack anyway. No one is sure why—but one factor may be that anywhere from 5% to as many as 40% of us do not respond to aspirin as expected. This range is huge, in large part, because it’s difficult to test for aspirin resistance. Various chemicals found in blood or urine may tip off researchers to aspirin resistance, but levels vary confusingly. There’s no evidence that having diabetes or pre-existing kidney or liver disease adversely affects a person’s response to aspirin. Being a woman and being older may increase the risk of aspirin resistance. Smoking may also counteract the anti-clotting effects of aspirin. Nobody on aspirin therapy should be smoking, anyway.
Here are some guesses about why aspirin may fail:
• People may not take their aspirin regularly and faithfully.
• Perhaps, for some people, the low dose is too low. Also, different people may absorb aspirin differently.
• Emotional stress and—it’s hard to believe—exercise may counter aspirin’s beneficial effects in some people. (That doesn’t mean you should stop exercising, though.)
• Other drugs, such as ibuprofen and naproxen, can interfere with aspirin’s anti-clotting effect. (Advil is one brand of ibuprofen; Aleve is a brand of naproxen.)
• People may become resistant over time, or be genetically predisposed not to respond to aspirin.
• The benefits of aspirin, under certain conditions, may not last until the next dose.
What about a test for aspirin resistance?
Any such test would have to be cheap, quick, painless, and easy to interpret. There are some promising tests under study, but so far doctors are not even sure what "normal values" would be. It is known that aspirin-resistant people are at higher risk for heart attacks than others. No one is quite sure why this is true. Doctors are not certain just how useful a test would be—you would probably be advised to continue taking aspirin anyway, perhaps higher doses. There are, of course, other anti-clotting drugs (all far more costly than aspirin) that might be useful if aspirin resis-tance could be reliably identified.
Where this leaves you
• Aspirin does reduce the risk of heart attack and stroke in the great majority of people. There’s solid clinical evidence for this—it is not a theory. Most studies, however, have looked only at men.
• On the other hand, you should not simply begin aspirin therapy on your own. Aspirin can cause serious side effects, such as gastrointestinal bleeding or ulcers. Be sure to talk with a doctor before going on aspirin therapy.
• If you are on aspirin therapy, stick with the program. Take it every day or every other day, as prescribed by your physician. Because it can interfere with aspirin, don’t take ibuprofen or naproxen frequently, or during the few hours before the aspirin. Acetaminophen (such as Tylenol) is okay.
• Even if you could be shown to be aspirin-resistant, your doctor would probably advise you to keep taking it.
• Remember that cardiovascular disease is complex. You need to work in many ways to prevent heart attack and stroke. Aspirin alone will never be enough. Even if you take aspirin, you still need a heart-healthy diet and regular exercise. Don’t smoke. If you are at risk for diabetes, do all that you can to prevent it; if you have diabetes, work with your doctor to keep it under control.
UC Berkeley Wellness Letter, December 2004
As aspirin therapy has become commonplace, scientists have learned more about it. While low-dose aspirin reduces the risk of a first heart attack in middle-aged men by 44%, for example, it is not a cure-all. Some people on aspirin therapy have a heart attack anyway. No one is sure why—but one factor may be that anywhere from 5% to as many as 40% of us do not respond to aspirin as expected. This range is huge, in large part, because it’s difficult to test for aspirin resistance. Various chemicals found in blood or urine may tip off researchers to aspirin resistance, but levels vary confusingly. There’s no evidence that having diabetes or pre-existing kidney or liver disease adversely affects a person’s response to aspirin. Being a woman and being older may increase the risk of aspirin resistance. Smoking may also counteract the anti-clotting effects of aspirin. Nobody on aspirin therapy should be smoking, anyway.
Here are some guesses about why aspirin may fail:
• People may not take their aspirin regularly and faithfully.
• Perhaps, for some people, the low dose is too low. Also, different people may absorb aspirin differently.
• Emotional stress and—it’s hard to believe—exercise may counter aspirin’s beneficial effects in some people. (That doesn’t mean you should stop exercising, though.)
• Other drugs, such as ibuprofen and naproxen, can interfere with aspirin’s anti-clotting effect. (Advil is one brand of ibuprofen; Aleve is a brand of naproxen.)
• People may become resistant over time, or be genetically predisposed not to respond to aspirin.
• The benefits of aspirin, under certain conditions, may not last until the next dose.
What about a test for aspirin resistance?
Any such test would have to be cheap, quick, painless, and easy to interpret. There are some promising tests under study, but so far doctors are not even sure what "normal values" would be. It is known that aspirin-resistant people are at higher risk for heart attacks than others. No one is quite sure why this is true. Doctors are not certain just how useful a test would be—you would probably be advised to continue taking aspirin anyway, perhaps higher doses. There are, of course, other anti-clotting drugs (all far more costly than aspirin) that might be useful if aspirin resis-tance could be reliably identified.
Where this leaves you
• Aspirin does reduce the risk of heart attack and stroke in the great majority of people. There’s solid clinical evidence for this—it is not a theory. Most studies, however, have looked only at men.
• On the other hand, you should not simply begin aspirin therapy on your own. Aspirin can cause serious side effects, such as gastrointestinal bleeding or ulcers. Be sure to talk with a doctor before going on aspirin therapy.
• If you are on aspirin therapy, stick with the program. Take it every day or every other day, as prescribed by your physician. Because it can interfere with aspirin, don’t take ibuprofen or naproxen frequently, or during the few hours before the aspirin. Acetaminophen (such as Tylenol) is okay.
• Even if you could be shown to be aspirin-resistant, your doctor would probably advise you to keep taking it.
• Remember that cardiovascular disease is complex. You need to work in many ways to prevent heart attack and stroke. Aspirin alone will never be enough. Even if you take aspirin, you still need a heart-healthy diet and regular exercise. Don’t smoke. If you are at risk for diabetes, do all that you can to prevent it; if you have diabetes, work with your doctor to keep it under control.
UC Berkeley Wellness Letter, December 2004
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