Aspirin, a common over-the-counter medication, is widely used for its ability to relieve pain, reduce fever, and ease inflammation. You may already be taking aspirin regularly for other reasons.
Did you know that aspirin may also protect you from developing colorectal (bowel) cancer? Studies suggest that the regular intake of aspirin may have a protective effect against colorectal cancer, particularly when started before the age of 70.
The evidence points to aspirin’s ability to interfere with mechanisms linked to cancer development, such as inflammation and platelet aggregation. These anti-inflammatory benefits are thought to be a key factor in aspirin’s potential to stop the progression of cancerous cells in the colon and rectum.
While all this sounds promising, epidemiological studies suggest that aspirin may reduce your risk of bowel cancer, randomized trials provide conflicting evidence. If you’ve had bowel cancer in the past, intervention trials have so far shown no benefit of using aspirin to prevent a recurrence of bowel cancer.Â
Let’s take a deep dive into the evidence and who will benefit from taking aspirin:
What is aspirin?
Aspirin, chemically known as acetylsalicylic acid (ASA), is a widely used medication recognized for its ability to relieve pain, reduce fever, and ease inflammation.
How does aspirin work?
When you consume an aspirin tablet, the acetylsalicylic acid inhibits the production of specific enzymes that play a key role in the synthesis of prostaglandins—substances in your body responsible for promoting inflammation, pain, and fever.
This is why aspirin is effective for pain relief, as an anti-inflammatory drug to reduce inflammation in conditions like arthritis, lowers body temperature during a fever, and even helps prevent blood clots, reducing the risk of heart attacks and strokes.
Role of aspirin in cancer prevention
Aspirin’s benefits, however, extend beyond pain relief. Aspirin’s anti-inflammatory properties work by inhibiting the enzymes known as cyclooxygenase (COX); COX-1 and COX-2. These enzymes contribute to the production of prostaglandins and thromboxanes, compounds that have roles in inflammation, blood clotting, and transformation of normal cells to cancer (tumorigenesis).
- COX-1 Inhibition: By inhibiting COX-1, aspirin reduces the production of thromboxane A2, a substance that promotes platelet aggregation and vasoconstriction. These effects provide aspirin with its well-known antithrombotic properties.
- COX-2 Inhibition: Inhibition of COX-2 is particularly relevant to cancer prevention. This enzyme is often overexpressed in various types of tumors, including those in the colon. Aspirin’s suppression of COX-2 leads to a reduction in inflammatory prostaglandins, which are believed to promote tumor growth and progression.
By regularly taking aspirin, you may lower your risk of developing colorectal cancer. Clinical studies suggest that the cancer-protective effects of aspirin are associated with long-term use at low doses.
Who benefits from taking aspirin
Whether it’s for its cardiovascular protective properties or its role in reducing the risk of certain cancers, understanding who can benefit from taking aspirin is crucial for both patients and healthcare providers alike.
- People Aged Under 70: If you began taking aspirin before turning 70, there may be a preventative effect against colorectal cancer.
- Individuals with Cardiovascular Concerns: Aspirin is often prescribed for its cardiovascular benefits. Those who are already taking low-dose aspirin to reduce the risk of heart disease may also gain protective benefits against colorectal cancer.
However, that starting aspirin at the age of 70 or older has not demonstrated the same protective effect.
The relationship between aspirin dosage and optimal effectiveness is currently under research, with some studies suggesting that low-dose aspirin could be impactful.
A notable point for those with a higher risk for colon cancer, such as a family history of the disease, is that your potential to benefit from aspirin may be greater.
Before you run out to get a pack of aspirin, wait! Let’s take a closer look at some of the published data first.
Epidemiological studies
Data from epidemiological studies and cohort studies provide some evidence supporting the role of aspirin in reducing the incidence of bowel cancer. Many studies found that regular aspirin users have a lower incidence of colorectal adenomas, which are precursors to cancer.
However, epidemiological studies are like detective work for understanding health issues within groups of people. Imagine scientists as detectives trying to figure out what factors might cause certain illnesses, how they spread, and what we can do to prevent them. These studies look at patterns, causes, and effects of health and disease conditions in specific populations.
Epidemiological studies can be subject to various biases and confounding factors. Consequently, while results are promising, they should be interpreted cautiously.
Let’s look at some clinical trials instead:
Aspirin for primary prevention of bowel cancer
It all started with a study published as far back as 1988. The researchers were exploring numerous medications and their links with colorectal cancer and found that there was an association between the use of aspirin and a reduced risk of bowel cancer.
A large number of studies were then done by various groups to confirm this association, many of which showed some benefit and some showing none.
Rather than going through the individual trials ourselves, we’re better off focusing on the systematic reviews and meta-analyses. These thorough reviews take relevant studies into account, appraises their quality and summarizes the evidence.
If you’ve never had bowel cancer, there are a few meta-analyses to be aware of:
- A U.S Preventive Task Force review published in 2007 found that cohort studies showed regular aspirin use was associated with a relative risk reduction of 22% for colorectal cancer. However, randomized controlled trials (RCTs) of low-dose aspirin failed to show benefit. They concluded that aspirin appears to be effective at reducing the risk of bowel cancer, especially if used in high doses.
- A meta-analysis of four placebo-controlled trials published in 2009 found that the risk of recurrent bowel adenomas (which are potentially pre-cancerous) was reduced by 17% (relative risk), corresponding to an absolute risk reduction of 6.7%.
- A 2007 systematic review examined cohort and case-control studies, finding that non-steroidal anti-inflammatory drugs (NSAIDS) reduced the risk of bowel adenomas and bowel cancers. However, they also cautioned that these agents can cause harm.
- A 2003 randomized trial randomly assigned 1121 patients with a history of bowel adenomas to aspirin (81 mg or 325 mg daily) or placebo and found that the risk of recurrent adenomas was significantly lower in the 81 mg group than placebo (38 vs 47%). The 325 mg group did not show any benefit.
In other words, even though many of these trials offer some evidence of causality, they provide limited and conflicting data regarding the optimal dosing for bowel cancer prevention and even whether it prevents bowel cancer at all.
Aspirin for secondary prevention of bowel cancer
Even though aspirin use has been widely studied in patients with bowel adenomas and to reduce risk of bowel adenomas, small studies in people who have had bowel cancer in the past report conflicting evidence.
Most recently, you need to be aware of the ASCOLT trial, a well-run AGITG trial, randomizing patients with resected bowel cancer to aspirin 200 mg daily or placebo. The trial is now closed and the findings were presented a the ESMO Congress at the end of 2023. ASCOLT found no benefit from aspirin compared to placebo in reducing risk of bowel cancer recurrence at 5 years.
Does aspirin protect against other cancers?
So far, there is very little evidence that aspirin can help prevent cancers other than bowel cancer or help people live longer after a cancer diagnosis. Only a few studies suggest aspirin might help with cancer prevention but other larger studies didn’t find the same results, which makes me doubtful about aspirin’s benefits for cancers other than colorectal cancer.
A meta-analysis from 2012 looked at data from six separate trials and found that taking aspirin every day might reduce the chance of getting cancer by 12% after following up for 10 years. This benefit was seen after four years and didn’t depend on how old people were, their gender, or whether they smoked. If people took aspirin for five years or more, the study suggested the risk of getting cancer could drop by 30%. This number may sound high, but remember that it’s relative. For example, if your risk of getting any cancer in the first place is 1%, taking aspirin for at least 5 years lowers your cancer risk to 0.7%.
Another meta-analysis in 2019 that included more trials (16 trials with over 100,000 patients) didn’t find that aspirin had any effect on how often people got cancer. This study only followed people for an average of 5.5 years.
In the ASPREE trial, which looked at older adults, showed that taking low-dose aspirin every day didn’t really change the number of new cancer cases compared to a fake pill (placebo) after about 4.7 years. However, the group taking aspirin had a slightly higher chance of having cancer that had spread or was very advanced when it was found.
Potential risks of aspirin
Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) that carries its own risks, especially related to bleeding. Your doctor should always be consulted before starting aspirin to weigh the benefits against potential harm.
Major bleeding
Aspirin can cause serious bleeding problems. The worst kind of bleeding is when it happens inside your head, which is very rare but can be deadly. A 2019 meta-analysis found that low-dose aspirin use (≤100 mg daily) increased your risk of intracranial bleeding by 0.2% (an additional 2 bleeds per 1000 people). This doesn’t sound like much but there is a 50% chance you’ll die with a bleed in the brain.
Taking aspirin every day can also make you bleed more easily, especially from places like your stomach or your bowels. A 2016 meta-analysis showed aspirin increases your risk of a non-fatal extracranial (below your neck) major bleed by up to 50% over 10 years.
For young and healthy people, the risk of bleeding from aspirin is pretty low.
Some risk factors can make bleeding more likely if you’re taking aspirin, like being older, being a man, having diabetes, kidney problems, smoking, high blood pressure, and being overweight.
If you bleed a lot while taking aspirin to prevent health problems, you should talk to your doctor about whether the benefits of taking aspirin are worth the risks.
Aspirin can also cause minor bleeding problems and make you lose iron, which can lead to anemia, especially in older people.
A few people can’t take aspirin because they’re allergic to it. This can cause problems like a runny nose, asthma, or swelling. Some people who are allergic to aspirin might also react to other similar medicines.
For elderly or older adults, especially those with cardiovascular disease, aspirin may increase the tendency to bleed. The elderly are more susceptible to the side effects of NSAIDs, including an increased risk of bleeding even with minor injuries.
