Doctors have long recommended daily aspirin for years as a low-cost protection against cancers of the lower bowel.

New research suggests there might not be a dependable benefit for low-risk patients. However, the drug can increase the risk of dangerous bleeding by preventing clotting, according to a report published in the Cochrane Library Feb. 26.

Lead author Dr. Zhaolun Cai told SciTechDaily, “While the idea of aspirin preventing bowel cancer in the long run is intriguing, our analysis shows that this benefit is not guaranteed and comes with immediate risks.”

People with specific genetic markers may benefit from taking aspirin to reduce cancer risk, the National Cancer Society website states. Nonsteroidal anti-inflammatory drugs, including aspirin, are widely used to reduce pain, fever and swelling. Their anti-inflammatory properties led doctors to believe they could help reduce cancer risk, as inflammation is linked to tumor formation and growth.

Researchers from West China Hospital of Sichuan University in China examined 10 medical trials with 124,837 participants. These studies focused on people with an average colorectal cancer risk and tracked whether taking aspirin or other NSAIDs reduced cancer or precancerous polyps.

No qualifying trials for non-aspirin NSAIDs were found, so the reviewers said their conclusions apply only to aspirin.

For the first five to 15 years of use, they found no significant benefit, but some studies suggested a very low likelihood of protection, as seen in follow-up visits 10-15 years later.

On the other hand, the National Institutes of Health reports that the common practice of prescribing low-dose aspirin to prevent stroke does not provide significant protection either. Those findings also found a significant risk of bleeding in the brain or skull after head injuries, as well as a risk of intestinal ulcers.

“My biggest worry is that people might assume that taking an aspirin today will protect them from cancer tomorrow,” senior author Dr. Bo Zhang told SciTechDaily. “In reality, any potential preventive effect takes over a decade to appear, if it appears at all, while the bleeding risk begins immediately.”

For specific, high-risk groups, including those with inherited Lynch syndrome, the aspirin prescription may work. But the study authors cautioned that any decisions should be made with a physician’s help.

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