Regularly taking aspirin may help reduce the risk of cancer, according to a new study. Researchers from Massachusetts General Hospital (MGH) found this was particularly true for lowering the risk of colorectal cancer and other tumors in the gastrointestinal tract.

Taking a standard low-dose aspirin tablet at least twice a week for six years or longer was found to lower the risk. The results are based on two major long-running studies of health information from men and women.

"We now can recommend that many individuals consider taking aspirin to reduce their risk of colorectal cancer - particularly those with other reasons for regular use, such as heart disease prevention - but we are not at a point where we can make a general recommendation for overall cancer prevention," said senior study author Dr. Andrew Chan, chief of the Clinical and Translational Epidemiology Unit at the MGH Division of Gastroenterology. "Our findings imply that aspirin use would be expected to prevent a significant number of colorectal cancers above and beyond those that would be prevented by screening and may have even greater benefit in settings in which the resources to devote to cancer screening are lacking."

To determine how taking aspirin might lower cancer risk, researchers analyzed 32 years of data from close to 136,000 participants in the Nurses' Health Study and the Health Professionals Follow-up Study.

Findings showed that participants who regularly took aspirin had a 3 percent lower risk for any type of cancer than those who did not report regularly taking aspirin during the study period. Risk of colorectal cancer was also reduced by up to 19 percent, along with the risk of gastrointestinal cancer by 15 percent, in participants who reported regular aspirin use compared to those who did not.

The protective benefits of aspirin, a nonsteroidal anti-inflammatory drug (NSAID), appeared five years after taking continuous dosages ranging from 0.5 to 1.5 standard tablets a week or one low-dose tablet a day.

"At this point, it would be very reasonable for individuals to discuss with their physicians the advisability of taking aspirin to prevent gastrointestinal cancer, particularly if they have risk factors such as a family history," Chan said. "But this should be done with the caveat that patients be well informed about the potential side effects of regular aspirin treatment and continue their regular screening tests. Furthermore, aspirin should not be viewed as a substitute for colonoscopy or other cancer screening tests."

The study is published today in JAMA Oncology.