Is Daily Aspirin Right For You?
By: David A Fein, MD
You may have already heard that aspirin can lower your risk of heart attacks and some types of strokes. Now, the news headlines are trumpeting new research that shows that aspirin can prevent cancer, too. Actually, the research isn’t that new. Several studies have been published in recent years showing that the risk of certain types of cancer may be lower in people taking daily aspirin. There have also been studies that failed to show a benefit. The latest attention comes from three articles published this week by the medical journal The Lancet showing that daily aspirin offered substantial protection from cancer and helped to stop it from spreading. So, is it time for you to start taking a daily aspirin?
It’s important to remember that aspirin, even though it is widely available without a prescription, is a powerful drug with multiple effects in the body. Taking a couple of aspirin to treat the occasional headache or fever is generally a safe thing to do. Taking it on a daily basis can be a very different matter that can lead to serious side effects. Balancing the benefits and the risks is critical. There is not much sense in a treatment that might be more dangerous than the disease.
Two potential side effects are of greatest concern:
Aspirin appears to interfere with the ability of the stomach and intestinal tract to handle contact with stomach acid and other digestive fluids. Although the estimates vary, daily aspirin may be associated with as much as a 1% per year risk of developing gastrointestinal ulcers and bleeding. Since aspirin also interferes with the blood’s ability to clot, bleeding from an aspirin-induced ulcer can be severe and even life-threatening.
Aspirin’s effects on blood clotting can help to reduce the risk of ischemic strokes. This type of stroke can be cause by a small blood clot obstructing an artery in the brain. On the other hand, aspirin can increase the risk of hemorrhagic strokes. This type of stroke is due to bleeding directly into the brain. In some studies this has occurred in 0.1% of patients.
While these risks are relatively small, they can be severe. So, taking a daily aspirin only makes sense if the reduction in your risk of heart attacks or cancer is likely to be significantly bigger than the risks of serious intestinal bleeding or hemorrhagic strokes.
Preventing Heart Attacks:
Researchers have long known that aspirin lowers the risk of heart attacks. This appears to be related to aspirin’s effects on blooding clotting. Most heart attacks happen when a rupture occurs on the surface of an atherosclerotic plaque in a coronary artery. This exposes the inside of the plaque to the blood stream. The substances inside the plaque cause a blood clot to form at the site of the plaque rupture. Within a few minutes that clot can become large enough to block all blood flow through the artery, causing a portion of the heart muscle to begin to die from lack of blood flow.
Aspirin inhibits the ability of the blood to form a clot. When aspirin limits clot formation, the clot that results from plaque rupture clot may be small enough to allow some blood to continue to get through the artery. Eventually, the body dissolves the clot and restores normal blood flow. If enough blood can get through without interruption, a heart attack is averted.
Various studies have found differing levels of protection from aspirin. Overall, it appears that a daily aspirin can reduce heart attack risk by about 20-25%. While that sounds like a significant benefit, it is important to first establish your odds of having a heart attack to determine if the benefit of treatment exceeds the risks.
The most effective tool for establishing cardiac risk is a CT Scan to measure the Coronary Calcium Score. Calcification of an artery is an indicator of the presence of plaque in the artery. People with no evidence of calcification in their coronary arteries have a heart attack risk of about 0.1% per year. Even if taking a daily aspirin will lower that risk by 25%, the likelihood of preventing a heart attack will be much smaller than the risk of side effects and we would not recommend aspirin therapy.
In people with Calcium Scores that indicate a heart attack risk of 2% per year or higher, the benefits of daily aspirin are very likely to outweigh the risks.
The papers published this week were not based on new research. Instead, the authors combined the findings of multiple prior studies. Overall, the authors found that the risk of developing cancer was reduced by almost 25% after 3 years of taking daily aspirin compared with a control group that did not take aspirin. After 5 years, the risk of dying from cancer was reduced by 37% for those who took aspirin. The effect was mainly seen for a particular type of cancer called adenocarcinoma. This type is often seen in colon, lung, breast, esophageal and prostate cancers.
The researchers also found that daily aspirin may have a significant effect in reducing the risk of an existing cancer spreading to other sites. Over a follow up period of 6.5 years there was a 36% reduction in the metastasis of cancers with aspirin. For colon cancer there was a 74% reduction in the risk of metastasis.
Overall, the death rate from cancer was significantly lower in those who took daily aspirin.
So, does this mean you should reach for the aspirin bottle right now? Well, that depends on your risk of getting a specific cancer in the first place.
If your risk of a particular cancer is more than 1-2% per year then taking a daily aspirin may result in a bigger benefit than the risks associated with taking the aspirin. But unless you have some pretty strong risk factors, such as family history of a particular cancer or are a smoker, it is unlikely that your risk of getting a particular cancer is anywhere close to that high.
Take the two of the most common cancers as examples:
Lung cancer accounts for approximately 25% of all cancer deaths in the USA. Roughly 90% of these are related to smoking and most of the rest are related to radon or other environmental exposures. So, while aspirin can cut your risk of lung cancer, you can reduce your risk of lung cancer by almost 99% without any risk of side effects by not smoking and checking your home for radon if you live in a high risk area.
Colorectal cancer accounts for about 12-15% of cancer deaths. Lifestyle factors may account for many of those cases. Following a healthy diet and lifestyle is likely to have a bigger effect than aspirin in reducing your risk. Colon cancer is also unique in that we can identify a precursor lesion. More than 80% of colon cancers arise from polyps. Periodic screening with colonoscopy to remove those polyps before they become cancers has been shown to be effective in reducing colon cancer deaths. Even without those steps, unless you have a family history or other risk factors for colon cancer, your likelihood of developing colorectal cancer in any given year is only a fraction of one percent.
Most other types of cancer are even less common than colorectal cancer. If the risk-to-benefit ratio does not work well for colorectal cancer, it is very likely that the risk of side effects will outweigh the benefit for cancers that are less common.
At this point, we remain hesitant to recommend daily aspirin therapy for the general population. If you have documented coronary artery disease with a risk level greater than 2% per year then daily aspirin to lower your cardiac risk is warranted. If you are very high risk for a particular type of cancer based on family history or genetic factors, then daily aspirin may be advisable to help lower that risk. For most of the population, the safest course remains following a healthy lifestyle including maintaining an ideal weight, staying physically active and eating a well-rounded and healthy diet.