A new study has suggested that taking low-dose aspirin every day is not a fast or dependable way to prevent bowel cancer for most people.
The new Cochrane review also indicates that those assigned to aspirin had a higher risk of cancer-related mortality and serious bleeding during the trial.
Aspirin is a common drug that can help relieve pain and fever. In addition, it may also have many other potential uses.
Bowel cancer, also called colorectal cancer, ranks among the most common cancers worldwide. Prevention usually focuses on healthy lifestyle choices and routine screening tests.
In recent years, scientists have investigated whether widely available medications, including nonsteroidal anti-inflammatory drugs (NSAIDs), might help lower the risk.
NSAIDs such as ibuprofen and aspirin are commonly used to treat pain, inflammation, and fever. But whether these drugs can prevent colorectal cancer before it develops remains unclear and widely debated.
To better understand the evidence, researchers at West China Hospital of Sichuan University in China reviewed 10 randomised controlled trials involving 124,837 participants.
They examined whether aspirin or other NSAIDs could reduce the risk of colorectal cancer or precancerous growths (adenomas) in people at average risk. No qualifying trials were found for non-aspirin NSAIDs, so the findings apply only to aspirin.
The review found that aspirin likely does not lower the risk of bowel cancer during the first 5 to 15 years of use. Some studies suggested there could be a protective effect after more than 10-15 years of follow-up, but confidence in that evidence is very low.
Those possible long-term benefits come from observational follow-up periods after the original trials ended. During that time, participants may have stopped taking aspirin, started using it on their own, or begun other treatments. These factors make the results more vulnerable to bias.
Lead author Dr. Zhaolun Cai declared that while the idea of aspirin preventing bowel cancer in the long run is intriguing, analysis shows that this benefit is not guaranteed and comes with immediate risks.
The researchers also found strong evidence that daily aspirin increases the risk of serious extracranial hemorrhage and likely raises the risk of hemorrhagic stroke.
Higher doses carry greater danger, but even low-dose aspirin increases the likelihood of bleeding. Older adults and people with a history of ulcers or bleeding disorders may face especially high risks.
Because of this, the authors declared that any possible long-term cancer benefit must be carefully weighed against the immediate and well-established bleeding risk.
Dr Bo Zhang, senior author, also added, “My biggest worry is that people might assume that taking an aspirin today will protect them from cancer tomorrow. In reality, any potential preventive effect takes over a decade to appear, if it appears at all, while the bleeding risk begins immediately.”
Earlier research has shown that aspirin may help certain high-risk groups, including people with inherited conditions such as Lynch syndrome that increase colorectal cancer risk. However, this review focused only on individuals at average risk, and for them, the long-term evidence was highly uncertain.
The authors advised against starting aspirin for cancer prevention without first discussing personal bleeding risks with a healthcare professional.