For years, we have been told that most adults should take a baby aspirin every day to help prevent heart attacks and strokes. Now we are told not to do that because it doesn’t work. What is going on? Why can’t science make up its mind? The recommendations are not exactly simple and straightforward; the details can be confusing. To better understand, let’s look at what the science says.
How Does Heart Disease Kill?
Heart disease is the leading cause of death in the United States. It is responsible for 696,962 deaths every year, compared to 602,350 for cancer. Strokes (another form of cardiovascular disease) cause an additional 160,264 deaths a year. We worry about deaths from the pandemic, but heart disease kills roughly twice as many people as COVID-19.
Heart attacks are more correctly called myocardial infarctions. The underlying problem is atherosclerosis, where plaques develop in the lining of arteries, with inflammation, cholesterol, and fibrous material. When a plaque ruptures, a clot forms that can obstruct the flow of blood. If the blood flow to a coronary artery is blocked, heart muscle cells can die. Time is of the essence; if a heart attack is suspected, the patient should immediately chew a regular 325 mg. aspirin tablet. In this emergency, other forms of aspirin won’t do. The dose in a baby aspirin is too low (81 mg.) to be effective, and swallowing a regular aspirin or taking an enteric-coated form takes longer to absorb. Chewing is the quickest way to get an effective dose into the bloodstream.
Note: It’s better to call it “low dose aspirin.” The term “baby aspirin” is no longer appropriate, because aspirin is associated with Reye’s syndrome, a rare but potentially fatal disease. Most experts in the United States recommend not giving aspirin to children under the age of nineteen. In the UK, the recommended cutoff is age sixteen. Safer alternatives are available: acetaminophen (Tylenol) and ibuprofen (ibuprofen is only approved for those over the age of six months).
Symptoms include chest pain that can be crushing and has been described as feeling like an elephant is sitting on the chest. Sometimes pain is felt in the shoulder, arm, back, neck, or jaw. Other symptoms include sweating, shortness of breath, nausea, faintness, and fatigue. It may feel like heartburn. Women are more likely to have pain other than chest pain. There may be no symptoms at all, especially in those over the age of seventy-five. EKGs and blood troponin tests can confirm the diagnosis.
Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet, and excessive alcohol intake.
The problem is the risk/benefit ratio. There are pros and cons. Aspirin is acetylsalicylic acid. It inhibits the activity of the enzyme cyclooxygenase (COX), which reduces the level of the prostaglandins that cause inflammation, swelling, pain, and fever. That’s why it works well to reduce inflammation, swelling, pain, and fever. But prostaglandins also protect the stomach mucosa from damage by hydrochloric acid, maintain kidney function, and aggregate platelets. This explains aspirin’s unwanted side effects of gastrointestinal irritation and bleeding.
In 2016, the USPSTF (US Preventive Services Task Force) prepared a decision analysis evaluating “Aspirin Use to Prevent Cardiovascular Disease and Colorectal Cancer.” It concluded:
“Benefits are predicted to exceed harms among persons aged 40-69 with non-elevated bleeding risk who take aspirin for primary prevention of CVD and CRC over their lifetimes. Net benefits from routine aspirin use over a 10- or 20-year horizon are expected to be substantially smaller, and in many cases, harms may exceed benefits. Findings do not differ markedly between men and women; however, deterministic and probabilistic sensitivity analyses reveal meaningful uncertainty about the magnitude of net benefit.”
Primary vs. Secondary Prevention
Primary prevention is intended to prevent disease in patients who have never had a cardiovascular event. Secondary prevention is intended to prevent recurrence when patients have already had a previous event. There appeared to be good evidence that secondary prevention was effective, but the evidence was not clear for primary prevention. And as more and more studies were done, doctors began to question whether the evidence was really so good for secondary prevention.
Aspirin is clearly effective for emergency treatment of patients who are having a heart attack, but do they need to take it for the rest of their life? Based on the evidence available at the time, it became standard practice to leave them on low dose aspirin forever. But new evidence continued to be published and was not as clear-cut. And questions were raised about the historical studies when the data was re-examined. A 2020 review article in Circulation questioned the practice. It concluded, “The totality of recent evidence supports further study of the universal need for lifelong aspirin in secondary prevention for all adults with CCS, particularly in stable older patients who are at highest risk for aspirin-induced bleeding.”
The 2016 Guidelines for Primary Prevention
“In 2016, the USPSTF recommended initiating low-dose aspirin use for the primary prevention of CVD and CRC in adults aged 50 to 59 years who have a 10% 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, and that the decision to initiate low-dose aspirin use in adults aged 60 to 69 years who have a 10% or greater 10-year CVD risk should be an individual one. The USPSTF previously found that the evidence was insufficient to assess the balance of benefits and harms of initiating aspirin use for the primary prevention of CVD and CRC in adults younger than 50 years or adults 70 years or older.”
The New Guidelines
“The US Preventive Services Task Force (USPSTF) concludes with moderate certainty that aspirin use for the primary prevention of CVD events in adults aged 40 to 59 years who have a 10% or greater 10-year CVD risk has a small net benefit. The USPSTF concludes with moderate certainty that initiating aspirin use for the primary prevention of CVD events in adults 60 years or older has no net benefit.”
What Has Changed?
The guidelines for aspirin for secondary prevention have not changed. The age at which starting primary prevention is not recommended has changed from over seventy years to over sixty years. The recommended age for starting primary prevention has changed from 50–59 years to 60–69 years for patients who have a 10 percent or greater ten-year risk.
One size does not fit all. Individuals vary in the kind of CVD risk factors and the risk of bleeding complications. If you are already taking low dose aspirin and think you should stop, or if you are thinking of starting, it would be a good idea to consult your doctor who can consider the entire picture and share in the decision-making process.
Why Recommendations Change
It can be frustrating and annoying when science changes its mind, but instead it should be cause for celebration. That’s the beauty of science. It follows the evidence and is always ready to change its mind when better evidence comes along. An apple a day may not keep the doctor away, and a baby aspirin a day may not be much better and could even cause harm. At least the apple can be part of a nutritious diet.
This article was originally published in Skeptical Inquirer.