Impact of Low-Dose Aspirin on Lower Gastrointestinal Bleeding and Colorectal Neoplasms

Danish investigators conducted a cohort study to assess the impact of low-dose aspirin on lower gastrointestinal bleeding, colorectal bleeding, and colorectal polyps.

Aspirin may help to reduce the risk of colorectal cancer (CRC) by causing premalignant polyps to bleed, thereby expediting colonoscopy and polypectomy before CRC development, according to the results of a study published in BMJ Open Gastroenterology.

Long-term continuous use of low-dose aspirin has been found to be associated with a decreased risk of CRC; however, the underlying mechanisms for this are conflicting. Researchers investigated whether the use of low-dose aspirin, through initiation of lower gastrointestinal (GI) bleeding, may lead patients to undergo colonoscopy and polypectomy before manifest CRC by conducting a historical cohort study (2005-2013) of 412,202 Danish residents who initiated low-dose aspirin treatment without screening for CRC. Each new aspirin user was matched with 3 non-users (n=1,236,560). The researchers found that the absolute risks for lower GI bleeding, lower GI endoscopy, colorectal polyps, and CRC were higher for new users than non-users within the first 3 months of follow-up. Comparing new users with non-users, the relative risks were 2.79 for lower GI bleeding, 1.73 for lower GI, 1.56 for colorectal polyps, and 1.73 for CRC. The relative risks remained elevated for more than 12 months after the index date, with the exception of CRC, for which the relative risk was slightly decreased during 3 to 5 years and more than 5 years following the index date. 

The authors concluded that, “The potential of aspirin to increase the detection of premalignant polyps by triggering early gastrointestinal bleeding may have major public health importance, given the growing number of faecal blood test-based CRC screening programmes.” They added, “Future studies are needed to assess the impact of aspirin dosage, treatment duration and intensity and further elucidate whether the increased bleeding in aspirin users stem from premalignant polyps or other sources.”


Troelsen FS, Farkas DK, Erichsen R, Sorensen HT. Risk of lower gastrointestinal bleeding and colorectal neoplasms following initiation of low-dose aspirin: a Danish population-based cohort study. BMJ Open Gastro. 2020;7:e000453.