Aspirin has one of the best benefit-to-risk ratios of any therapy for reducing risk of cardiovascular events. The drug has been shown to prevent heart attacks and ischemic stroke, which is caused by an artery-blocking clot, as well as reduce the incidence of colorectal cancer (CRC) with long-term use. However, aspirin use is not without its own set of potential risks such as gastrointestinal bleeding (GIB) and hemorrhagic stroke.
The United States Preventive Services Task Force (USPSTF), an independent volunteer panel of national experts in prevention and evidence-based medicine, has updated its recommendations from 2009 and 2007 based on five additional studies on primary prevention of cardiovascular disease (CVD) and additional data on CRC follow-up. The recommendations are “initiating low-dose aspirin use for the primary prevention of CVD and CRC in adults aged 50-59 who have a 10 percent or greater 10-year CVD risk, are not at increased risk for bleeding, have a life expectancy of at least 10 years, and are willing to take low-dose aspirin daily for at least 10 years.” The panel designated this with a B recommendation – that there's some certainty that the overall benefit is moderate to substantial.
It gave a "C" grade to individuals who are between 60 and 69 years of age – which means that there should be selective offering of aspirin on an individual basis – those who value benefits over potential harms. There is insufficient data to support daily aspirin use in individuals younger than 50 years of age as well as those aged 70 years and older.
The reason why this news is a big deal is because of the magnitude of the problem, according to the authors. One of every two deaths in 2011 were attributable to heart disease, cancer or stroke.
To calculate percentages of risk, individual data can be entered into a risk calculator based on equations from pooled cohort data from the American College of Cardiology (ACC)/American Heart Association. Similarly, there is also a risk calculator for bleeding in individuals who ought to be placed on aspirin therapy. GIB and hemorrhagic stroke risks are not uniform in a population and are affected by risk factors such as older age and male sex, which are considered to be the most important. In addition, other risk factors include upper GI tract pain, GI ulcers, concomitant use of other blood thinners or NSAIDs, and uncontrolled hypertension.
The optimal aspirin dose is unknown but the most commonly prescribed dose of aspirin in the U.S. is 81 milligrams per day. It is advisable according to USPSTF, to reassess CVD and bleeding risk periodically from 50 years of age onward.
Other than the USPSTF, no other organization recommends daily aspirin usage for the primary prevention of CRC. The exact mechanism of how this aspirin inhibits a colon polyp’s transition to CRC is poorly understood and it is assumed that it has to do with aspirin’s anti-inflammatory properties.
These recommendations are based on population data, and any aspirin recommendations should always be based on the clinician and the individual patient.