Key points:
– Large-scale review found daily low-dose aspirin probably does not reduce colorectal cancer risk in the first 15 years of use.
– Daily aspirin may increase risk of bleeding, including bleeding in and around the brain.
– Lifestyle measures — plant-forward diet, less red/processed meat, limited alcohol, no smoking, regular exercise, healthy weight, and screening — are recommended to lower colorectal cancer risk.
A new analysis of randomized trials concluded that daily low-dose aspirin (typically 75–100 mg) probably produces little to no reduction in colorectal cancer risk over 5–15 years and may only show a small benefit after 15 years, although confidence in long-term effects is low. The review pooled data from 10 randomized controlled trials with more than 120,000 participants, mostly from North America and Europe. Three trials evaluated higher aspirin doses.
The investigators reported mixed, time-dependent findings: aspirin might slightly reduce colorectal cancer incidence after 15 years but likely does little during the first 5–15 years. They also observed possible increases in colorectal cancer mortality between 5 and 10 years of use, little to no difference in mortality between 10 and 15 years, and a potential reduction in mortality after 15 years — conclusions the authors say are uncertain.
On harms, the review found that aspirin probably increases the risk of hemorrhagic stroke and increases the risk of serious extracranial bleeding. Overall serious adverse events appeared similar, but the bleeding risks are a clear concern.
Clinical experts emphasize caution. Ketan Thanki, MD, a colorectal surgeon, said the study shows limited (if any) protective benefit from aspirin for colorectal cancer in the general population and warned against taking daily aspirin solely to reduce colorectal cancer risk given known complications of long-term use. He recommended considering daily aspirin for cancer prevention only in select high-risk groups — for example, people with Lynch syndrome or those who have had adenomatous polyps removed — and only after discussion with a physician.
The reviewers recommend individualized assessment and shared decision-making, weighing any delayed or uncertain preventive benefit against a definite bleeding risk. They also noted that aspirin’s role in prevention depends on a patient’s broader cardiovascular risk profile and bleeding risk.
Conflicting evidence and policy shifts
Research on aspirin and cancer prevention has been inconsistent. Some prior studies reported reduced colorectal cancer risk with regular aspirin use, particularly in certain subgroups, while others found no benefit or even increased cancer-related mortality in older adults. Because of mixed evidence, some guideline bodies have revised recommendations; for example, a major task force withdrew a prior recommendation for aspirin for colorectal cancer prevention in 2022, citing insufficient evidence of benefit.
Experts underscore that age and timing of aspirin initiation may matter. Katherine Van Loon, MD, a gastrointestinal cancer specialist, noted that younger patients may derive more benefit and that clinicians generally should not start aspirin in older adults solely for cancer prevention.
What helps prevent colorectal cancer
Physicians continue to recommend proven lifestyle and screening strategies to reduce colorectal cancer risk:
– Eat more plant-based foods and reduce intake of red and processed meats.
– Limit alcohol consumption.
– Avoid tobacco use.
– Maintain a healthy weight.
– Exercise regularly.
– Participate in age-appropriate colorectal cancer screening (colonoscopy is the most effective for prevention; noninvasive tests such as stool-based screening are alternatives).
“Diet and exercise are the best and easiest ways you can decrease your cancer risk,” one expert said, adding that getting screening tests on schedule is critical for prevention and early detection.
Bottom line
Current randomized trial evidence does not support routine daily low-dose aspirin for primary prevention of colorectal cancer in the general population, because any delayed benefit is uncertain and must be balanced against clear bleeding risks. Aspirin may still be appropriate for certain high-risk groups (for example, people with Lynch syndrome or prior adenomas) after individualized discussion with a clinician. For most people, focusing on healthy lifestyle habits and regular screening is the recommended approach to lower colorectal cancer risk.
