Aspirin is an old standby, yet it continues to surprise. This common, inexpensive drug helps protect survivors of heart attack and stroke from subsequent heart attacks and death, and even helps reduce the number of deaths that occur within the first hours following a heart attack. Although aspirin is best known as an antiplatelet drug, it may also subdue the inflammation that is central to coronary artery disease.
Randomized trials have provided clear evidence of aspirin's value in both preventing heart attacks in men and treating coronary artery disease in both sexes. Over all, dozens of studies, involving tens of thousands of people, have shown that low-dose aspirin reduces the risk for heart disease and stroke by about 25%. A standard dose of aspirin to prevent heart attack is 81 mg per day, about what you'd find in a baby aspirin.
Guidelines from nearly every major medical group urge people with heart disease or at high risk for it to take aspirin. Although a major study reported in 2005 concluded that the advice is not as clear-cut for how to prevent first heart attacks in women (see "Advice for women," below), the prevailing consensus remains that in general, unless you are allergic to aspirin or it causes you problems, you should take it if you
- have had a heart attack
- have had an ischemic (clot-caused) stroke or a mini-stroke (transient ischemic attack)
- have angina (chest pain)
- have had a coronary artery bypass or angioplasty
- have diabetes
- are at high risk for heart disease.
Despite aspirin's benefits, it also has some drawbacks. The evidence that its benefits exceed its risks is much stronger in men than in women, at least in terms of primary prevention (avoiding a first cardiovascular event). It can increase the risk for stroke and significant gastrointestinal bleeding. Even people who take aspirin occasionally with no problems could experience bleeding complications with regular use over prolonged periods. In particular, it may not be a good choice for people with uncontrolled hypertension (a major cause of hemorrhage into the brain). In such people, aspirin could more likely cause dangerous bleeding than prevent a heart attack. In addition, aspirin occasionally irritates the stomach lining without causing bleeding. However, these side effects can be reduced with the use of coated aspirin, which minimizes stomach irritation.
Advice for women. The first large-scale randomized study to specifically examine aspirin's effectiveness in preventing first heart attacks in healthy women, reported in the New England Journal of Medicine in 2005, showed that the risk/benefit analysis for aspirin is not as straightforward in women as it is in men. The study involved almost 40,000 healthy women ages 45 and older, who took 100 mg of aspirin or a placebo every other day. To their surprise, the researchers found that aspirin did not affect the risk for a first heart attack one way or the other in the group as a whole, although it did reduce the risk for stroke by 17%. Yet when the researchers did subgroup analyses, they discovered that aspirin significantly reduced the risk for first heart attack, stroke, and other cardiovascular events in women who were 65 and older. This benefit has to be weighed, however, against an increased risk for gastrointestinal bleeding.
So what do you do? If you're a woman who has already had a heart attack, stroke, or some other cardiovascular event, the advice remains the same: Take aspirin to reduce the risk for a second event. (A large study that looked at such secondary prevention concluded that aspirin benefits both men and women.) But if you're considering taking aspirin to prevent a first event, the advice is less clear-cut. Talk with your physician to determine whether — in your case — the benefits outweigh the risks.
Aspirin resistance. Some people are resistant to aspirin's anticlotting effects. So far the research indicates that aspirin fails to affect platelets' tendency to clump, or does so only partially, in 5%–40% of people who take it. These people therefore don't have the same reduction in heart attack and stroke risk that other people gain from aspirin use.
There are probably several reasons why aspirin resistance occurs. The body's response to aspirin may change over time. Some people have trouble absorbing aspirin from the digestive tract. Smoking blunts the effect of aspirin on platelets, as do being overweight and having high cholesterol or high blood pressure. A variety of genes influence how the body responds to aspirin. Finally, a few studies have indicated that a common nonsteroidal anti-inflammatory drug (NSAID), ibuprofen, may block aspirin's protective effects. The occasional dose of ibuprofen isn't likely to do this, but daily use could.
Although two laboratory tests are available to measure how well aspirin may be working for you, the idea of aspirin resistance is so new that many doctors either aren't aware of it or are waiting for more evidence that it's real before ordering these tests. So what do you do in the meantime? First, talk with your doctor about being tested for aspirin responsiveness. Second, if you need to take an NSAID for arthritis or some other condition, pick one that doesn't interfere with aspirin, such as naproxen (Aleve, Naprosyn) or diclofenac (Cataflam, Voltaren). Third, don't stop taking aspirin — regardless of whether you can get tested or what the results are. Aspirin probably works in several ways to prevent heart attacks. If do you find you are aspirin resistant, talk with your doctor about other antiplatelet medications.
Several other options are available to inhibit platelets, but these tend to be more expensive than aspirin and are not as well studied.
(This article was first printed in the Special Health Report from Harvard Medical School "The Healthy Heart: Preventing, Detecting, and Treating Coronary Artery Disease". )