Regular aspirin use may help lower risk of colorectal cancer, study finds, especially for those with unhealthy lifestyles

(CNN) — Regular aspirin use may keep the oncologist away, at least when it comes to colorectal cancer, according to a new study, and people with unhealthy lifestyles seemed to see the greatest benefit.

Colorectal cancer is the second most common cause of cancer death worldwide, predicted to cause more than 52,500 deaths in the US alone in 2023. About 153,020 people in the US were diagnosed with the condition in 2023, and it’s become much more prevalent among people under 55, with numbers more than doubling in this group from a decade ago, studies show.

The causes of colorectal cancer can be genetic, but certain lifestyle factors also seem to raise risk, including eating an unhealthy diet, not getting enough exercise, drinking alcohol, smoking and having a high body mass index.

In addition to adopting healthier lifestyles, doctors have often recommended low-dose aspirin to reduce the risk of colon cancer. The US Preventive Services Task Force made the aspirin recommendation in 2016 but reversed course in 2022 because of concerns that it might cause bleeding. Aspirin can also cause gastrointestinal trouble.

With the change in recommendations, the authors of the new study decided to look at whether there were any groups that would benefit more from the practice and for whom aspirin would be worth the risk.

For the study, published Thursday in the journal JAMA Oncology, the authors examined data from more than 107,655 people who were a part of large datasets of medical professionals called the Nurses’ Health Study and the Health Professionals Follow-Up Study. Most of the participants were White, so the authors suggest that their research should be replicated with more diverse populations to see if the conclusion would be the same.

Study participants were tracked for at least a decade, and in addition to being monitored for colorectal cancer, they were given surveys to determine the healthiness of their lifestyles. The surveys assessed their BMI, alcohol intake and diet, whether they smoked and how much they exercised. The use of two or more regular-strength aspirin or six or more low-dose aspirin per week was considered regular aspirin use for the purpose of this research.

Those regular users were found to have an 18% lower risk of developing colorectal cancer than non-users. Participants who were determined to have a less-healthy lifestyle had more benefit, particularly if they smoked or if their BMI was higher than 25. A BMI of 25 to 29.9 is considered overweight.

“Our results show that aspirin can proportionally lower the markedly elevated risk in those with multiple risk factors for colorectal cancer,” Dr. Daniel Sikavi, the lead author of the paper and a gastroenterologist at Mass General Brigham, said in an email. “In contrast, those with a healthier lifestyle have a lower baseline risk of colorectal cancer, and, therefore, their benefit from aspirin was still evident, albeit less pronounced.”

The study cannot determine why regular aspirin use seemed to be so helpful, but previous research has suggested that aspirin may inhibit pro-inflammatory signals that can lead to cancer.

Although other studies have shown the benefits of aspirin in the prevention of colorectal cancer among certain populations, the results have been inconsistent, according to the authors of the new research. They argue that doctors should weigh different lifestyle risk factors when they determine whether someone should take regular aspirin to prevent colorectal cancer.

Dr. Christina Annunziata, senior vice president of extramural discovery science with the American Cancer Society, noted that the research saw the greatest effect of aspirin in people with the most risk factors for colon cancer.

It’s important to keep in mind that the study is not a gold-standard randomized clinical trial that compared people who got aspirin with those who didn’t, meaning there are limitations to keep in mind and more research will be needed, she said. But the study serves as a good reminder that cancer is not inevitable and that people can take steps to lower their risk.

“There are things you can change about your lifestyle that will decrease your risk,” said Annunziata, who wasn’t involved with the new research. Those include maintaining a healthy weight, eating a diet rich in vegetables, fruits and whole grains, and drinking less.

Dr. Raymond DuBois, a past president of the American Association for Cancer Research, said that while keeping up with the changing aspirin recommendations over more than two decades, he has always wondered why some studies show a benefit and others don’t. He thinks this research may help solve that mystery.

The evidence in the study, DuBois said, demonstrates “quite convincingly” the beneficial effect of aspirin for the unhealthiest group of participants.

“We try as hard as we can to get people in a healthier state, but in some people, it’s just very difficult to lose weight or quit smoking. This could be a simple option that could help, especially for those who are at highest risk,” said DuBois, director of the Hollings Cancer Center in Charleston at the Medical University of South Carolina, who wasn’t involved with the new study.

Because it took only two regular aspirin per week to show a benefit, it might alleviate some concerns about the risk of bleeding, he said, particularly if people took the two over the course of the week.

Dr. Jennifer Davids, chief of colon and rectal surgery at Boston Medical Center, said she very much wants people to avoid ending up in her practice, but she cautions that everyone shouldn’t just start taking a regular aspirin.

“It’s inexpensive, it’s accessible, but it’s not without risk,” said Davids, who wasn’t involved in the new research.

She said that the study is a major step in the right direction in trying to understand who has the potential to benefit most from aspirin but that people should talk to their doctors first to determine whether regular aspirin is right for them.

Davids adds that “this is not permission to give up on healthful eating, exercise, avoidance of smoking and minimizing alcohol use.”

“By no means does that mean that an aspirin will compensate for all of the other factors, which are necessary for a healthy lifestyle and cancer risk reduction across the board,” she said.

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