Patient education: Aspirin in the primary prevention of cardiovascular disease and cancer (Beyond the Basics)

INTRODUCTION — 

In people who have had a heart attack or stroke, the reduction in risk of another heart attack or stroke are large enough that taking low-dose aspirin is the right choice for almost all patients. Researchers have also explored the possible benefits and harms of aspirin in people who have no known cardiovascular disease. They have discovered that aspirin protects against certain cardiovascular events but may also protect against some forms of cancer.

When medical treatments are used to prevent diseases or their complications (before they occur), it is called "primary prevention." This topic will discuss the research on the use of aspirin in the primary prevention of cardiovascular disease and cancer, address the potential risks of aspirin use, and summarize the findings of the pros and cons of aspirin use for primary prevention.

The use of aspirin in the prevention of the complications or recurrence of an established condition (called "secondary prevention") is discussed elsewhere. (See "Patient education: Heart attack (Beyond the Basics)" and "Patient education: Ischemic stroke treatment (Beyond the Basics)".)

HOW ASPIRIN PREVENTS DISEASE — 

The most common forms of cardiovascular disease start when fatty deposits called plaques form on the walls of the arteries throughout the body. A cardiovascular "event," such as a heart attack or stroke, happens when one of these plaques ruptures and causes a blood clot to form. The blood clot then blocks the flow of blood through that artery. As a result, the tissue downstream of the blockage does not get enough blood or oxygen and is damaged or dies.

If a clot forms inside one of the arteries that supply the heart muscle with blood (called the coronary arteries), a heart attack can occur (figure 1). Likewise, if a clot forms inside one of the arteries that supply the brain with blood, a stroke can occur. Aspirin can prevent cardiovascular events because it reduces the chance that blood clots will form inside any diseased arteries. That's why people who have already had a heart attack or stroke often take daily aspirin, and why people at risk for heart attack may also benefit from aspirin to prevent clots (and a first heart attack).

It is less clear how aspirin might help protect against cancer. Researchers suspect aspirin might prompt cancer cells to self-destruct. They also believe aspirin might be important in cancer prevention because it reduces inflammation, which seems to promote cancer.

PRIMARY PREVENTION OF CARDIOVASCULAR DISEASE — 

Large, well-performed studies have found that, in people without established cardiovascular disease, aspirin had the following effects:

●Aspirin reduced the risk of heart attack, but the effect was very small (depending on your cardiovascular risk profile, from 5 to 23 fewer heart attacks in 1000 people over 10 years of taking aspirin).

●Aspirin increased the risk of bleeding (most commonly in the stomach), but the effect was very small (from 4 to 11 more in 1000 people over 10 years of taking aspirin, depending on your bleeding risk).

●Aspirin had no significant impact on the risk of stroke.

PRIMARY PREVENTION OF CANCER — 

A number of studies suggest that aspirin may prevent both the development and spread of colorectal cancer (cancer of the colon and/or rectum) and that it lowers the risk of dying from colorectal cancer.

Colorectal cancer — The studies examining whether aspirin protects against colorectal cancer have had mixed results, and uncertainty exists regarding their findings. One analysis that looked at the data from more than 14,000 people who were followed long term (up to 18 years) found that:

●Aspirin reduced the risk of developing colon cancer, but that benefit was not apparent in the group overall until after 8 to 10 years of follow-up.

●The longer people took aspirin, the more protective it was.

●Aspirin may reduce the risk of dying from colon cancer, but this protective effect is seen only in those who take aspirin for at least five years.

Other cancers — It is unclear whether aspirin prevents the development of other cancers. Data from multiple studies suggest that aspirin does not meaningfully decrease the risk of death from cancer.

PRIMARY PREVENTION OF DEATH — 

Some data suggest that aspirin may have a very small effect on overall mortality. Data from a compilation of studies including over 100,000 people suggest that aspirin may lead to two fewer total deaths per 1000 people treated for 10 years. However, this is an uncertain estimate; the estimated range of possible benefit may be anywhere from six fewer to two more deaths.

RISKS AND SIDE EFFECTS OF ASPIRIN

Bleeding — The main problem that aspirin can cause is internal bleeding. Most often, it causes bleeding in the gastrointestinal tract (primarily the stomach and small intestines) that is not usually fatal. But bleeding can also occur at other sites, with bleeding in the brain being the most serious.

The risk of bleeding while taking aspirin is not the same for everyone. Some people, such as those with peptic ulcers (ulcers in the stomach or small intestine), are more prone to bleeding than others. (See "Patient education: Peptic ulcer disease (Beyond the Basics)".)

Factors that increase a person's risk of having a gastrointestinal bleed while on aspirin include:

●Having a history of peptic ulcers

●Being 65 years old or older

●Being on high doses of medications called nonsteroidal anti-inflammatory drugs, such as naproxen (sample brand name: Aleve) or ibuprofen (sample brand names: Advil, Motrin), often used to treat arthritis and other causes of chronic pain

●Using medications called corticosteroids in pill or injected form (but not if they are only applied to the skin)

●Taking medications called anticoagulants (often called blood thinners), such as warfarin (brand name: Jantoven), dabigatran (brand name: Pradaxa), apixaban (brand name: Eliquis), rivaroxaban (brand name: Xarelto), or edoxaban (Lixiana).

Anemia — In persons ages 65 and older, low-dose aspirin (75 to 100 milligrams a day) may increase the risk of small amounts of bleeding and anemia (low red blood cell count) caused by a lack of iron.

Aspirin sensitivity — A very small minority of people cannot take aspirin because of a hypersensitivity to the drug. This usually manifests as respiratory symptoms, such as nasal irritation or asthma, but can also manifest as hives or swelling.

DOSING — 

We suggest that people using aspirin for primary prevention take 75 to 100 milligrams a day. Experts believe that the protective benefits of aspirin for cardiovascular disease occur at doses of 75 to 100 milligrams a day. (A standard bottle of aspirin that you might buy at a drug store to treat pain has pills that each contain 325 milligrams. "Low-dose" aspirin that you might buy at a drug store usually has pills that each contain 81 milligrams.) While 75 to 100 milligrams doses seem to offer all the benefit possible for cardiovascular disease, it's not as clear which dose would be best for colorectal cancer prevention.

WHO SHOULD TAKE ASPIRIN FOR PRIMARY PREVENTION? — 

To summarize, in people who do not have cardiovascular disease or cancer, daily, low-dose aspirin reduces the risk of heart attack and increases the risk of major bleeding. These effects are very small. Aspirin may also reduce the risk of colorectal cancer in people, but this is less certain.

The decision about whether to take aspirin for primary prevention is one you should make with your doctor or nurse after learning about all the potential benefits and risks.

Remember, if you have already had a heart attack, your clinician is likely to recommend that you take aspirin because your risk of having another heart attack or stroke is high. (This is called "secondary prevention.")

●People who should not take aspirin – Most experts agree that the following people should not take aspirin for primary prevention:

•People younger than age 40

•People aged 70 and older

•People who are between the ages of 40 and 70 who are at low risk of developing cardiovascular disease and cancer

In these people, the harms of aspirin, such as bleeding, are likely to outweigh the benefits.

●People who may consider taking aspirin – People between the ages of 40 and 69 who have a high risk of developing cardiovascular disease or colorectal cancer are most likely to benefit from taking daily low-dose aspirin for primary prevention, especially if their risk of bleeding is low. For people between the ages of 40 and 69 who have a moderate risk of cardiovascular disease and/or colorectal cancer, the benefits and harms of daily low-dose aspirin are closely balanced.

•Estimating your risk – If you are between the ages of 40 and 69, you can ask your doctor or nurse these questions:

-Given my age, risk factors, and overall health, should I be particularly concerned about my risk of developing either cardiovascular disease or colorectal cancer?

-Are there any reasons why I might have an increased risk of bleeding if I take aspirin?

It's important to know the answers to these questions because if you have a high risk of cardiovascular disease or colorectal cancer, that may tip the scales in favor of you taking daily aspirin. Likewise, if you are at high risk of bleeding, that could tip the scales against you taking aspirin.

•Understanding your preferences – Your preferences and priorities are also important to consider and discuss with your clinician. The most important factor in the decision may be how worried you are about heart attack (high worry, maybe you would want to use aspirin) or bleeding (high worry, stay away from aspirin). Your feelings about taking a pill every day for a very small benefit may also affect your decision.

Consider your responses to the following questions:

-How do you feel about taking a pill every day for years?

-How worried are you about the possibility that you might develop cardiovascular disease or colorectal cancer?

-How worried are you about the possibility that you might develop bleeding while on aspirin?

After you have thought about how the risks and benefits apply to your individual situation, work with your doctor or nurse to make the decision that's right for you.

WHERE TO GET MORE INFORMATION — 

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient education: Medicines after an ischemic stroke (The Basics)
Patient education: Medicines after a heart attack (The Basics)
Patient education: Coronary artery disease (The Basics)
Patient education: Heart attack – Discharge instructions (The Basics)
Patient education: Lowering the risk of having a stroke (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

Patient education: Stroke symptoms and diagnosis (Beyond the Basics)
Patient education: Heart attack (Beyond the Basics)
Patient education: Heart attack recovery (Beyond the Basics)
Patient education: Recovery after coronary artery bypass graft surgery (CABG) (Beyond the Basics)
Patient education: Stenting for the heart (Beyond the Basics)
Patient education: Ischemic stroke treatment (Beyond the Basics)
Patient education: Transient ischemic attack (Beyond the Basics)
Patient education: Peripheral artery disease and claudication (Beyond the Basics)
Patient education: Peptic ulcer disease (Beyond the Basics)
Patient education: Helicobacter pylori infection and treatment (Beyond the Basics)
Patient education: Warfarin (Beyond the Basics)

Professional level information — Professional level articles are designed to keep doctors and other health professionals up to date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

Aspirin in the primary prevention of cardiovascular disease and cancer
Overview of primary prevention of cardiovascular disease in adults
Prevention of cardiovascular disease events in those with established disease (secondary prevention)

The following organizations also provide reliable health information.

●National Library of Medicine

(www.medlineplus.gov/healthtopics.html)

●National Heart, Lung, and Blood Institute

(www.nhlbi.nih.gov/)

●American Heart Association

(www.heart.org)

●The National Coalition for Women with Heart Disease

(www.womenheart.org/)

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