An analysis of data from two long-term epidemiologic studies has found that regular use of aspirin significantly reduces the overall risk of cancer, an effect that primarily reflects a lower risk of colorectal cancer and other tumors of the gastrointestinal tract.

The findings, published in JAMA Oncology, suggest that the use of aspirin may complement, but not replace, the preventive benefits of colonoscopy and other methods of cancer screening, according to the study authors.

“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 author Andrew Chan, a Harvard Medical School associate professor and chief of the Clinical and Translational Epidemiology Unit in the Division of Gastroenterology at Massachusetts General Hospital.

Aspirin’s impact on colorectal cancer

“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.”

A large number of studies have linked regular aspirin use to a lower risk of colorectal cancer, but without clarifying aspirin’s effects on overall cancer risk. To investigate that question, the researchers analyzed 32 years’ worth of data from almost 136,000 participants in the Nurses’ Health Study and the Health Professionals Follow-up Study. They found that participants who reported regular aspirin use — defined as a standard or a low-dose aspirin tablet at least twice a week — had a 3 percent absolute lower risk of any type of cancer than did those not reporting regular aspirin use. Regular aspirin use reduced the risk of colorectal cancer by 19 percent and the risk of any gastrointestinal cancer by 15 percent. No effect was seen in the risk of breast, prostate, or lung cancer.

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The protective benefit appeared after five years of continuous use at dosages ranging from 0.5 to 1.5 standard tablets a week or one low-dose tablet a day. The researchers estimate that regular aspirin use could prevent close to 30,000 gastrointestinal tract tumors in the United States each year.

“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,” said Chan. “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.”