The Cooper Institute

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH


Risks and Benefits of Daily Low-Dose Aspirin for Prevention of Cardiovascular Disease and Colon Cancer

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Live well

Thursday, Mar 22, 2018

Most fans of The Cooper Institute are already aware that cardiovascular disease (CVD) and cancer are the #1 and #2 causes of death in the U.S., respectively. Despite the fact that a substantial portion of CVD and cancers are caused by unhealthy lifestyle, most of the nearly $3 trillion spent on health care annually is for diagnosis and treatment of these and other health conditions. Only a tiny fraction of health care expenditures are geared towards disease prevention. So, what can at-risk people do in their day-to-day lives in order to decrease their risk of these two serious health conditions? Quite a bit, actually! Let’s take a look at daily low-dose aspirin therapy as an example.

A full-strength aspirin tablet is 325 mg. A ‘baby aspirin’ contains 81 mg, which is ¼ of the amount present in full-strength aspirin. Baby aspirin is considered low-dose therapy. Medical professionals have known for many years that low-dose daily aspirin therapy is of great benefit if you have had a heart attack or ischemic stroke* in the past, as it will help to prevent another heart attack or ischemic stroke. This is known as ‘secondary prevention.’ Whether or not low-dose daily aspirin therapy will help to prevent a first heart attack or stroke has been a bit controversial for many years; this concept is known as ‘primary prevention.’ As you might guess, much of this controversy stems from the ‘risk versus benefit’ issue. The major risk of aspirin therapy is gastrointestinal and intracranial (brain) bleeding, which can be quite severe in some cases.

Next to lung cancer, colon cancer is the second leading cancer killer among U.S. men and the third leading cancer killer for U.S. women. Each year, approximately 50,000 Americans and 600,000 people worldwide die as a result of colon cancer. 

Diets high in red and processed meats, sedentary lifestyle, obesity, smoking, heavy alcohol intake, increasing age, presence of type 2 diabetes, and genetics are some of the most important risk factors for colon cancer. Many of these are also important risk factors for heart attack and stroke. So, it should be easy to see that lifestyle habits play an important role in determining your risk of developing CVD and colon cancer! While conducting clinical trials regarding the effectiveness of daily low-dose aspirin therapy on CVD events, researchers noticed a substantial reduction in the risk of developing and dying from colon cancer. More specifically, the results of 5 large studies were combined in a study published in The Lancet a few years back. Researchers found that aspirin taken for at least 5 years at doses of greater than or equal to 75 mg daily resulted in a 24% reduced risk of developing colon cancer over a 20-year period, and a 35% reduced risk of dying from colon cancer over the same period when compared to groups who received a placebo. 

A valuable tool to determine the likelihood of having a heart attack or stroke in the next 10 years is called the Atherosclerotic Cardiovascular Disease (ASCVD) risk calculator. This easy-to-use tool takes into account your age, gender, race, resting blood pressure and blood cholesterol level, along with your smoking and diabetes status to determine your risk. The result is given as a percentage. For example, if your ASCVD risk result is 2.0%, it means that you have a 2.0% chance of having a heart attack or stroke in the next 10 years. To put that into perspective, this is a very low risk value.

In 2016, the U.S. Preventive Services Task Force (USPSTF) issued the latest guidelines regarding daily low-dose aspirin use for primary prevention of CVD and colorectal cancer. A summary of the guidelines is found in Table 1 below. Notice that the important cutoff value is an ASCVD risk of >10%; this is considered a ‘moderate risk’ value.       

Population Adults aged 50-59 years with a >10% 10-year ASCVD risk Adults aged 60-69 years with a >10% 10-year ASCVD risk Adults younger than 50 years Adults 70 years of age and older
Recommendation Initiate low-dose aspirin use (81 mg/day). The benefits of aspirin use outweigh the increased risk of bleeding by a moderate amount. The decision to initiate low-dose aspirin use is an individual one. The benefits of aspirin use outweigh the increased risk of bleeding by a small amount. No recommendation because the balance of benefits and harms cannot be determined. No recommendation because the balance of benefits and harms cannot be determined.

Let’s walk through a couple of examples: For the goal of primary prevention of CVD and colon cancer in a 35 year old healthy person, there is no recommendation for primary prevention because there is insufficient evidence at this time. However, for a 55 year old person with a 12% ASCVD risk, the benefits of low-dose daily aspirin therapy for primary prevention outweigh the risks of bleeding by a moderate amount.  
So, what’s the bottom line? Low-dose daily aspirin therapy has benefits as well as risks.

No one should begin daily aspirin therapy without first discussing the risks and benefits with their primary health care provider.  
*about 88% of all strokes are ischemic strokes; which are caused by blood clots.

Aspirin Use to Prevent Cardiovascular Disease and Colorectal Cancer: Recommendation Statement. (2016). American Family Physician, 94(8):online

Rothwell, P. M., Wilson, M., Elwin, C., Norrving, B., Algra, A., Warlow, C. P., Meade, T. W. (2010). Long-term effect of aspirin on colorectal cancer incidence and mortality: 20-year follow-up of five randomized trials. The Lancet, 376:1741-50. DOI:10 1016/S0140-6736(10)61543-7

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