Should we be taking aspirin daily to prevent heart attacks and strokes?
Aspirin is a medication we have been using for over one hundred years. At a low dose, which averages between 40-100 mg a day, aspirin has been used in the last two to three decades primarily for the prevention of heart attacks and strokes.
We know that heart attacks and strokes can occur when cholesterol plaque in one of our major heart or brain arteries first develops, then matures (which can take decades!), and -- without warning -- becomes unstable and cracks. When it reaches this point, the blood flow over the unstable plaque recognizes the situation as “bleeding” or a “hole” in the artery. It tries to repair the situation by flowing very quickly to where it believes the problem is happening, and in the process can form a clot over the unstable plaque in less than one minute. So here we have a situation where a cholesterol plaque may only obstruct 10-20% of the opening (lumen) of a heart or brain artery. When this plaque becomes unstable, the blood forms a clot over it and within a minute there is a 100% obstruction of the blood flow. Because there is no blood flow through the artery, the cells start dying in a matter of 3 minutes for the brain and 30 minutes for the heart. This is how most heart attacks and strokes can occur.
A low dose of aspirin works by inhibiting the sticky cells in the blood, called platelets, from sticking together and forming a clot. However, at a high dose, aspirin also inhibits various enzymes and good cells. While a low dose would protect the arteries from clotting, a higher dose would not. This is why we have been using a low dose for the prevention of heart attacks and strokes. If too much aspirin is taken, it can cause bleeding, which has the reverse effect and can encourage clotting of the arteries.
Those who have had a heart attack or stroke are instructed to continue taking a low dose of aspirin every day for the rest of their lives. However, we must remember that science has no “last word”: it’s all based on the function of time and the evaluation of the available evidence.
So let’s say that the evidence from twenty years ago overwhelmingly supported using aspirin for the prevention of heart attacks and strokes -- not only for secondary prevention (meaning you’ve already had a heart attack or stroke and you’re taking it as a way to prevent this from happening again), but for primary prevention, which means you never had a heart attack or stroke, but you were deemed to be at a higher risk for suffering from one. This includes people with diabetes, smokers, those with high LDL or high blood pressure, a family history of heart disease, etc. For all of these people, we thought it made sense to give a low dose every day for the rest of their lives to prevent heart attacks or strokes from ever occurring in the first place.
A few months ago, science came forward and said that this is not correct. We have reevaluated the evidence, and in the modern era of medicine-- with better use of “statins” (Lipitor, Crestor, etc), medications that lower the LDL (bad cholesterol), and improved treatment of high blood pressure-- we don’t think the benefits of taking aspirin for primary prevention outweigh the risks. This is big news for patients and doctors!
Randomized trials and observations from the American College of Cardiology and the American Heart Association, which included tens of thousands of patients for years, have concluded that the use of aspirin is no longer appropriate for primary prevention of heart attacks and strokes -- except for those at very high risk (meaning those who have at least a 10% risk of developing heart attacks or strokes over the next ten years). The studies indicated that patients who have already had a heart attack or stroke should absolutely continue taking aspirin for secondary prevention. But for using aspirin for primary prevention, we have to really dive into the risk factors of the patient (age, family history, lifestyle, blood pressure level, cholesterol level) and determine if this is appropriate. Only if we evaluate these factors as being high, and the risk of bleeding from aspirin is low, then it is ok to use aspirin for primary prevention.
As with any kind of medication or regimen, please speak with your doctor before determining whether you should start or stop taking aspirin.
To your health!
Dr. Anthony