Aspirin may offset increased colorectal cancer risk from unhealthy lifestyle choices

• Colorectal cancer is considered to be the third most common cancer worldwide.
• Certain unhealthy lifestyle factors such as smoking and following a poor diet can increase a person’s colorectal cancer risk.
• Researchers from Massachusetts General Hospital and Harvard Medical School have found that taking aspirin may help reduce colorectal cancer risk in people following unhealthy lifestyle choices.

Colorectal cancer is considered to be the third most common cancer around the globe, with over 1.9 million people worldwide newly diagnosed with colorectal cancer in 2020 alone.

Although colorectal cancer — also called colon cancer or rectal cancer — normally affects adults over age 50, recent studies show cases are increasing at an alarming rate in children, teens, and young adults .

Previous studies show that following unhealthy lifestyle choices such as smoking , excessive alcohol use , not exercising , and unhealthy eating can increase a person’s risk for colorectal cancer.

Now researchers from Massachusetts General Hospital and Harvard Medical School have found that taking aspirin may help reduce colorectal cancer risk in people following unhealthy lifestyle choices.

The study was recently published in the journal JAMA Oncology .

Why aspirin?

For this study, researchers recruited almost 108,000 adults with an average age of 49. Participants were evaluated for five lifestyle factors associated with colorectal cancer: BMI , smoking, alcohol intake, physical activity, and diet, and were given a healthy lifestyle score from zero to five.

Scientists also recorded study participants’ regular aspirin use, which was defined as two or more standard-sized tablets per week.

Past studies have linked aspirin use to lowering colorectal cancer risk. A study published in August 2021 reported that aspirin use was correlated to a reduction in overall risk of recurrence and mortality of colorectal cancer. And research published in April 2024 found long-term aspirin use was linked to a 10% reduction in the odds of certain cancers including colon and rectum cancer.

“Our group has contributed to the now-convincing body of literature that aspirin is effective in reducing the risk of colorectal cancer because there remains a critical unmet need for low cost, effective options for cancer prevention beyond screening, which is resource intensive and underutilized,” Andrew T. Chan, MD, MPH , professor of medicine at Harvard Medical School, chief of the Clinical and Translational Epidemiology Unit at Massachusetts General Hospital, director of epidemiology at the MGH Cancer Center, and co-corresponding author of this study, told Medical News Today .

“We are now focused on identifying who is most likely to benefit from regular aspirin use recognizing that aspirin also comes with side effects, such as gastrointestinal bleeding ,” he said.

Aspirin lowers risk in unhealthiest lifestyle factors

Participants of this study were followed for 30 years.

At the study’s conclusion, researchers found that the 10-year cumulative incidence of colorectal cancer was 1.98% among participants who regularly took aspirin compared to 2.95% incidence in those who did not.

When looking at absolute risk reduction, scientists discovered that the largest reduction was seen in participants who took aspirin and had the unhealthiest lifestyle scores. The greatest differences in colorectal cancer risk reduction were in participants who took aspirin and had BMI and smoking-related lifestyle risk factors.

“We observed that participants in our study with the least healthy lifestyle, as assessed by higher body mass index, more smoking, greater alcohol use, less physical activity, and poorer diet quality, had the greatest absolute benefit from aspirin use,” Long H. Nguyen, MD, MS, physician investigator and core faculty at the Clinical and Translational Epidemiology Unit, assistant professor of medicine and gastroenterology at the Massachusetts General Hospital and Harvard Medical School, and co-corresponding author of this study explained to MNT .

“These participants had multiple risk factors that increased their overall risk of developing colorectal cancer, and our results show that aspirin can proportionally lower this comparably elevated risk. In contrast, those with a healthier lifestyle had a lower baseline risk of colorectal cancer, and therefore, their benefit from aspirin was still evident, but less pronounced. This fits with our pre-study hypothesis.”
— Long H. Nguyen, MD, MS

How does aspirin lower colorectal cancer risk?

Chan said that aspirin likely prevents colorectal cancer through a variety of mechanisms.

“One major pathway is the reduction in inflammation, including the production of specific proinflammatory proteins known as prostaglandins that can promote the development of cancer,” he explained.

“Aspirin also appears to block signaling pathways within cells that cause them to grow and spread. Finally, aspirin may additionally influence the immune response against cancer cells and block the development of blood vessels that supply nutrients to growing cancer cells.”
— Andrew T. Chan, MD, MPH

“Given the current emphasis on targeted therapies and precision cancer prevention, more studies like this one are needed to move beyond one-size-fits-all universal strategies that do not adequately account for other personal risk factors,” Chan continued.

“We plan additional studies to further refine our understanding of the specific patient subgroups most likely to benefit from aspirin prevention and also large-scale international studies to identify additional lifestyle and pharmacologic strategies for cancer prevention,” Nguyen added.

Be cautious of potential aspirin side effects

After reviewing this research, Anton Bilchik, MD, PhD , surgical oncologist, chief of medicine and Director of the Gastrointestinal and Hepatobiliary Program at Providence Saint John’s Cancer Institute in Santa Monica, CA, told MNT it is a very important study because it covers a long period of time.

“There’s been a lot of discussion about the preventative role of aspirin in colorectal cancer, since it’s well known that aspirin has been shown to reduce the incidence of colorectal cancer,” Bilchik continued. “But at the same time, there has also been concern about the potential side effects of aspirin in particular gastritis and bleeding from the stomach. So trying to better understand which patients to treat with aspirin and which patients not to treat is very important information.”

As there are potentially serious side effects to taking aspirin, Bilchik advised readers to focus on other ways they can help lower their colorectal cancer risk.

“There are lifestyle modification factors that are likely to be even more relevant and more important than aspirin, such as weight reduction, exercise, prevention of smoking, as well as dietary modifications — eating healthy , reducing the intake of processed food — so many other factors to take into account.”
— Anton Bilchik, MD, PhD